Friday, December 18, 2009

When two might mean nothing, or it might be the future of physics


Yesterday saw the culmination of weeks of building buzz surrounding the announcement of results from one (of many!) searches for dark matter in the laboratory.  The result: two "events" that look like dark matter, but there's a 23% chance that these are just background events.  In science, 23% chance of being wrong is too high, so most people are seeing this as, at best, an ambiguous result.  Read more about the announcement here, or take it straight from the team's mouth (in PDF format).

What was all the excitement about?  Let me explain.  No, there is too much.  Let me sum up. Buttercup is marry Humperdink in little more than half an hour. (Sorry).  The story begins in the 1930s, when astronomer Fritz Zwicky noticed that galaxies in galaxy clusters were moving faster than could be explained by the gravity of visible stars, so he proposed some sort of invisible matter was responsible.  Most people (wrongly!) dismissed this idea until the 1970s and 1980s, when astronomer Vera Rubin discovered that the outer parts of spiral galaxies were orbiting faster than could be explained by the visible stars and gas alone.  About the same time, X-ray telescopes confirmed that Zwicky's galaxy clusters were more massive than the visible material alone could explain.  Meanwhile, comparison of the Big Bang theory's predictions of the amounts of different elements produced during the Big Bang with the actual amounts we see in the Universe said that much of this dark matter could not be made of normal atoms.  Skipping over many equally-important observations, the summary is that astronomy needs some sort of matter in the Universe that is different from the atoms stars, planets, and people are made out of.

Thursday, December 17, 2009

Water world, water world


An artists conception of the red dwarf star GJ 1214 and its planet
Image Credit: David A. Aguilar, CfA



Yesterday, astronomers announced that they had found a new "super-earth" planet around another star.  The team also claims that the planet must be made of a substantial amount of water.  Perhaps as interesting as the discovery is the story of how it was made and the timing of the announcement.

Let's start with the discovery.

Wednesday, December 16, 2009

In the valley of the jolly (ho ho ho!) red giant


The changing size and shape of chi Cygni
Image Credit: Sylvestre Lacour, Observatoire de Paris


Looking and behaving like one right jolly old elf, red giant stars tend to shake like a bowlful of jelly.  In a press release yesterday from the Center for Astrophysics (and, more importantly, a paper published in last week's issue of the Astrophysical Journal), a team of astronomers announced that they had obtained images of this shaking in one star, chi Cygni.  The illustration above shows the images of the star derived from their work.

Stars like the sun spend most of their lives looking a lot like the sun -- fairly small, at least in astronomical terms, fairly hot, and creating energy by fusing hydrogen atoms into helium atoms.  After some amount of time (a measly 10 billion years in the case of the sun), the star will exhaust its supply of hydrogen.  When it does so, it swells up into a truly monstrous size, and its outer layers cool off, fading and cooling from the blinding yellowish white of a star like the sun to a ruddy red or reddish orange color.  During this "red giant" stage, the star can get as large as the orbit of the Earth, Mars, or even Jupiter, depending on how massive ("heavy") the original star was.

Monday, December 07, 2009

Last chances to celebrate the International Year of Astronomy



Image Credit: IYA2009 (International Homepage / USA Homepage)


It's December, meaning that this is the last month of the year-long celebration of astronomy, the International Year of Astronomy 2009 (IYA2009).   Have you participated yet?  Although the year may be winding down and many of us are so busy that the last thing we need is more stuff to do, there's no need to panic.  Many of the official IYA2009 activities will continue into 2010 and beyond, and of course  the science itself will continue to push our bounds of knowledge about the Universe.

I'll get to a list of some of the activities you can still participate in shortly.  First, just a little background about the IYA2009, in case you were unaware or had forgotten.  The IYA2009 is an effort sponsored by the United Nations, the International Council on Science, and the International Astronomical Union.   International Years are not new; for decades the UN has sponsored scientific projects intended to bring scientists from around the world together to study a particular branch of science.  The IYA2009 is slightly different; rather than focusing scientists on a specific problem, the IYA2009 is designed to bring the public into the science of astronomy.  The effort is truly international, with, at last count, 148 nations participating in the IYA2009 in some way, shape, or form.

This year was chosen because it marks the 400th anniversary of Galileo's first observations with a telescope and the 400th anniversary of Johannes Kepler's publication of Astronomia Nova, which contain Kepler's first two laws of planetary motions.  It is hard to overstate the importance of these two events, which were crucial parts of the birth of modern astronomical science.

The main goal of the IYA2009 is to get every human on the globe to think about astronomy or our place in the Universe at least once this year.  Spend a few minutes on the next clear night looking at the stars or pondering the wonders of nature, and you've helped fulfill that goal!  You can help further by talking to your family and friends about astronomy, or just showing them the stars.

But there is so much more you can do, and you don't have to do it all this month.  The following activities will be continued well into the future, and you can help with all of them!

  • 365 Days of Astronomy -- This daily podcast gives listeners a 5-10 minute daily dose of astronomy on a wide range of topics, from exciting new research to historical astronomy to personal anecdotes by professional and citizen astronomers.  This podcast was just renewed for another year, and it needs support in the form of listeners, donations ($30/day will get your name in front of 5-10 thousand listeners!), and contributed podcasts.  You can follow 365 Days of Astronomy from their website, through iTunes, and even on Twitter.
  • Citizen Sky -- The Citizen Sky project is an opportunity for everyone to contribute to a scientific research project.  The goal is to understand the mysterious star epsilon Aurigae, a star you can see with your plain eye on any clear winter night.  The star fades greatly for about two years every 27 years, and astronomers aren't sure why.  This year, the star began fading again right on cue, and your observations over the next year or more can help us professional astronomers!
  • Galileoscopes -- The Galileoscope is a small, inexpensive telescope similar in design (but far better quality!) than the telescope Galileo used for his groundbreaking observations of the Moon, Jupiter, and Venus (among other things) in 1609.  You can buy your own for $20 plus shipping (be patient, they take a while to ship because orders are filled by volunteers and sometimes you'll have to wait on the manufacturer), or you can donate telescopes to classrooms around the world for $15.
There are undoubtedly more IYA2009 activities that will continue into the future.  This website has a listing of many of the Cornerstone projects of the IYA2009, and most of these projects will be continued into the future (including She is An Astronomer, the Galileo Teacher Training Program, Dark Skies Awareness, and Astronomy and World Heritage).

The end of the IYA2009 is just the beginning of many of the programs.  Astronomers are seeking to find the best uses for  new technology and media, as well as expand astronomy within developing countries.  We celebrate our past and look to the future.  And, like Janus, after December 31 we will be looking both backwards and ahead, celebrating the end of a successful program and the start of a daunting new task of building on that success.

It's not too late!  Come join us in the fun!

Friday, December 04, 2009

Astronomy holiday shopping guide

It's a cold December morning in Austin TX.  The forecast is calling for a light dusting of snow today, and people are freaking out.  Last night the store was nearly sold out of milk and bread, and this morning, there are several wrecks on the road attributed to "winter conditions" even though the roads are dry and the temps are well above freezing.  My inner Hoosier is laughing at Texans.

Anyway, the weather makes me realize that the holidays are not only coming soon, but virtually here.  Since previous attempts at stopping the holidays from coming have failed miserably, I'm just going to give in and write my annual admonition about astronomy gift buying.

Sunday, November 22, 2009

My visit to Montreal


The latter half of last week found me in Montréal, Canada.  I was invited by colleagues in the astrophysics group at the Université de Montréal to give a talk on my research.

Wednesday I boarded a plane for Montreal, arriving in the early evening.  I've never been to Montréal before, and the only other time I was in Canada was over 30 years ago, when I was too little to remember.   I don't speak French, but I know enough to be polite, and everyone speaks English better than I do.  So, with no hassle at all, I found my way to my hotel and met with my host, Patrick, for dinner.  

Wednesday, November 18, 2009

Get your shots!



Whooping Cranes
Image Credit: Patuxent Widlife Research Center, USGS


When I was a kid, I thought that whooping cough was a disease caused by whooping cranes (pictured above).  But, it isn't.  It's caused by bacteria.  Whooping cough, a.k.a. pertussis, is a highly contageous disease, it is very dangerous for infants, and it can be prevented most of the time by a vaccination.

Why am I talking about pertussis on an astronomy blog?  Because I learned this morning that my daughter has contracted whooping cough.  She's a teenager, and so with treatment she'll fully recover. As an infant, she did receive her pertussis vaccination, but its effectiveness decreases over time.  Pertussis boosters are available, but we were not aware of them until now, when it is too late.

Monday, November 16, 2009

It's the size of Earth with lots of oxygen, but not a nice place to be.





Image Credit: Sloan Digital Sky Survey

Some acquaintances of mine in the United Kingdom have discovered two white dwarf stars that have a lot of oxygen in their atmospheres.  One of them, with the typical boring star catalog name of SDSS J1102+2054, is the blue dot in the center of the image above.  Although white dwarfs are roughly the size of the Earth,  the star in the color picture looks blue like the Earth, and we all love oxygen, this would not be a nice place to vacation.

Friday, November 13, 2009

Planets come and planets go, but not in 2012



An asteroid impacts ruins the day for a flock of pterodactyls
Image Credit: NASA / Don Davis



Today, the movie 2012 opens in theaters.  The basic plot is that the Mayan calendar ends on the solstice in 2012, portending doom for all on this planet.  I'm not going to see the movie, as I'm not a fan of disaster movies (except, perhaps, the Samuel L. Bronkowitz classic "That's Armageddon").  If you want to see major cities around the world destroyed and humanity struggle to survive, then this is probably the film for you.

I mention the film because there is an ever-growing chorus of people who think that the world actually will end on December 21, 2012.  These people are wrong, their claims are made on bad (and often fabricated) science, and many of them are just out to make money off of gullible people.  Rather than go through a litany of the claims about 2012, let me point you to a few reputable websites that have the science and the cultural history correct:
I mention this whole 2012 business because of anecdotes I've been reading.  Young people have been asking if it is best to commit suicide than to try and survive 2012.  Some people are spending loads of money to buy prefabricated shelters that supposedly will protect them.   This is not simply about yet another doomsday prediction based on invented "science"; we are talking about hucksters willing to ruin the lives and livelihoods of innocent people to make a quick buck; we are talking about everyday people who are scared because they heard misinformation about a cataclysm that is not going to happen.  (In case anyone has forgotten, dates for end of the world have been coming and going for nearly 5000 years.  Check out the list.)

I've seen comments on other blogs by people who think NASA is wasting money by trying to debunk the 2012 doomsday predictions.  First, the website doesn't cost that much money -- the web server already existed, and the salary cost for the appropriate research and page design is probably less than the cost of one bolt on the next shuttle launch's external tank.  If NASA's efforts can help people to realize that folks who claim 2012 will be the end of the world are full of it, then the investment is more than worthwhile.

If you know anyone who is worried about some looming disaster in 2012, please point them to reliable resources and try and dispel them of that mistaken notion.  Again, we are talking about our friends and neighbors who are being bilked and scared by a nonexistent threat.

 To those who will claim that I'm just part of a big conspiracy to hide the truth, you're sadly misinformed.  If I suspected that the world was going to end or an asteroid was going to hit or the Earth's rotation were going to stop or Mayan gods were going to descend and wreak havoc on the world, I would not be sitting in a dark little office in front of a computer screen writing this blog.  I'd be out enjoying life, exploring nature, and running up a huge tab because I'd know I'd never have to pay.  Even if "they" were to threaten to kill me, I still wouldn't be here.  If I'm going to die in the great catastrophe of 2012, then "they" would not be able to threaten me.



Water, water, everywhere.


Last month, after NASA's LCROSS spacecraft failed to make a noticeable splash when landing on the moon, I blogged about how it could take months for the data to be analyzed.  Well, it took only about five weeks.  Today, NASA announced that LCROSS did indeed detect water, and a fair amount of it.  Final results will still take months, but the data are clear that water was present.

Why didn't we see the show from Earth?  Part of the reason is that the probe crashed behind the big mountain visible in the bottom of this picture, so the mountain likely blocked our view of some or most of the plume.  It's also just difficult to predict what will happen when you crash one object into another.

Anyway, the LCROSS work is still just beginning, so be on the lookout for more results in future months!

Friday, November 06, 2009

Congratulations Steve!


Image Credit: Steven DeGennaro

Today, we astronomers are honored to welcome yet another newly-minted PhD into our midst: Steven DeGennaro.  Steve is a graduate student here at the University of Texas at Austin, and this afternoon he successfully defended his doctoral dissertation.  

Thursday, November 05, 2009

Begging for money


The past several weeks I've been working on funding proposals for the National Science Foundation.  This just means I'm asking the government for money to do research.  And, despite what you may think, the government is stingy.  There are a lot of astronomers, and limited resources for research.  We have to spell out our proposed research in only 15 pages, and in that small amount of space we have to make people excited about our research and convince them that it is important and will succeed.  We have to anticipate and answer questions the reviewers will have about our science and proposed methods. 


We also have to justify every penny we plan to spend.  It's not  easy.  How do you accurately estimate the costs of attending a conference that you know will happen somewhere in the world in either 2012 or 2013?  How many trips to which telescopes will we have to take?  Will we need new computers along the line?  What will our salary needs be over the next three or four years? This is hard, too.  My salary needs will be a lot less if I am offered a job as a professor somewhere, as that will pay my salary for at least 9 months of the year.  But will I get that job this year?  Or next year?  Or the year after that?  How many papers announcing our results will we need to write?  How many pages will each of these papers be?  How much money will I need for phone bills and photocopying in 2012?


We also have to discuss how our research will make an impact in the world outside of astronomy research.  This includes what sort of education and public outreach we will do if we get the money (such as this blogging or the teacher workshops I've helped with in the past).  The National Science Foundation takes this section of proposals very seriously.  If we want money, we cannot merely hide in our offices, write inscrutable scientific papers, and spend taxpayer money.  We have to show that we are sharing what we learn with the world outside of academia.


Anyway, that's a big reason I've been kinda quiet recently.  In 10 days, this will all be a bad dream, and I can get back to writing job applications.  And 2 or 3 months from now, that will be finished, and I can get around to writing proposals to use telescopes.  After that is done, I can get back to doing science.  Or it may be time to start applying for more funding.  We shall see.

Wednesday, November 04, 2009

A bitter retirement


Update: 12 January 2010

I've removed this post.  I'm not being censored, nor am I hiding what I've written.  The original post was a personal piece that helped me to work through difficult issues that a friend is facing, and it served that purpose. 

I've learned that some other people close to my friend were troubled by what I wrote, both because it was discussing personal issues in a public forum and because they are even closer to my friend and his troubles than I am.  I did not intend to cause anyone else grief, nor to humiliate a person of whom I think very highly.   I apologize to those anyone felt otherwise.

Wednesday, October 28, 2009

A prized lecture


Antoinette de Vaucouleurs
Image Credit: McDonald Observatory



Today we were treated to a lecture in memory of Antoinette de Vaucouleurs, who was an astronomer here at the University of Texas at Austin for 25 years.  She is well-known for extensive work on the photometry and radial velocities of galaxies, often collaborating with her husband, astronomer Gerard de Vaucouleurs.  She continued working until just ten weeks before her death of bone marrow cancer in 1987.  You can read more about her life and work here.


Every year, the Department of Astronomy invites an outstanding astronomer to receive a memorial medal, and to give public and research lectures in recognition of their lifetime of achievements. Past recipients read like a who's who of BIG astronomers, including Margaret Burbidge, Vera Rubin, Don Osterbrock, Sandy Faber, Frank Shu, and Nobel Laureate John Mather, among many other equally-distinguished astronomers. 

This year, we had the honor of hosting Dr. Rashid Sunyaev, director of the Max Planck Institute for Astrophysics in Garching, Germany, and Chief Scientist of the Russian Academy of Sciences Space Research Institute in Moscow.  Dr. Sunyaev is well-known for making many important predictions about the cosmic microwave background and X-ray radiation from black holes, many of which have been found to be true.  One of the things that I particularly like about much of his work is how he focuses on the observable signatures of the physical objects he is interested in.  It's one thing to hypothesize about some of the earliest structures in the Universe; it's another thing altogether to also tell us observers how we might be able to see these structures.

During today's research lecture, Dr. Sunyaev gave an overview of his most famous work on clusters of galaxies and cosmology, sprinkled with personal anecdotes about his advisor Dr. Yakov Zeldovich.  He also gave some advice to the graduate students, such as to publish results about "beautiful physics", even if the observations needed to test the prediction seem technically impossible, because we don't know how far technology may go in the next decades.  He also quipped that theorists have to be smart, but it's okay for them to be wrong, while observers don't have to be smart, but they'd better always be right.  Sunyaev was also very excited about some new results that will be coming out of the Planck satellite and telescopes at the South Pole, but he couldn't tell us details about the results yet because the findings are still being verified.

It is always a real morale booster to see talks by people who are so clearly passionate about their research and optimistic about the potential for new, exciting discoveries in the future.

Saturday, October 24, 2009

Clear Skies Abundant


Image Credit: McDonald Observatory

Crystal clear skies.  Maybe even clearer.  This is how I like my observing runs. 

I'm finishing the 10th night of a 13-night observing run dedicated to looking at my favorite white dwarf stars.  I haven't been out here all ten nights, as two of my colleagues kindly volunteered to cover the first nine nights of the run.  In those nine nights, the weather was ideal for seven nights.  Tonight has also been great, and it looks like at least two and maybe all three of the remaining nights will also be clear.  Given that two-thirds of my telescope time has been clouded out over the past 18 months, I'm grateful to finally be getting a lot of high-quality data.

This run has had me worried for a long time, and not because of triskaidekaphobia.  Two days before the run started, one of my volunteers had a family emergency, so I had a stressful 48 hours rearranging the observing schedule.  Then one of my cats got quite ill, and I wasn't sure how to make sure she was taken care of while I was gone.  (Thankfully she recovered enough that my pet sitter has been able to take care of her.)  Then one of my volunteer observers fell ill here at the mountain (she fully recovered).  About the same time, I got word from Arizona that one of my colleagues there was in the hospital and not doing very well (he's not recovered, but at least is stable and was able to go home).  Lastly, as I was preparing to leave Austin, I accidentally dinged the side of another car with my car door; the owner of that car got absolutely livid over the 1/8-inch long scratch (no dent, but I did flake the paint and primer off), so I spent an hour on the phone with insurance.

Still, the clear skies and good data are worth most of the stress.  The moon and Jupiter dominated the evening skies, and all morning I've seen a dribbling of bright, fast-moving meteors, the last dregs of this week's Orionid meteor shower.  Now the planets Venus and Saturn are rising, and the first hints of dawn are on the eastern horizon.  Time for bed!

Wednesday, October 21, 2009

Galilean Nights this weekend


Galilean Nights Teaser Poster
Image Credit: IYA2009 / James White



Galilean Nights, one of the cornerstone projects of the 2009 International Year of Astronomy, takes place around the world this weekend!  The goal of the weekend is to encourage those around us to look through a telescope at the same celestial objects that Galileo looked at 400 years ago, leading to a revolution in our understanding of the Universe and giving a new birth to the science of astronomy.  This weekend, the moon and Jupiter are both well-placed to see in the early evening sky. And, if you are a morning person, Venus and Saturn are both low in the pre-dawn sky, rising about 1 to 1 1/2 hours before the sun.  The Orionid meteors, bits of dust shed by Halley's Comet long ago, will also be an occasional visitor in the evening and morning skies. 


Do you want to participate?  You don't need any experience.  Many planetariums and observatories will be having festivities; contact them to find the place and time.  You can also find a nearby event from the Galilean Nights website: http://www.galileannights.org/find_event.html.  If you own a telescope, why not pull it out on a local sidewalk and show off the moon and Jupiter this weekend to friends, family and neighbors?


If you don't have a telescope and can't find a nearby event, you can also go out and look with your eye.  The moon will be obvious, and the planet Jupiter is the brightest object in the evening southern sky (if you live north of the equator).  400 years ago, Galileo alone knew that Jupiter had its own moons performing an intricate dance around it; now you, from the comfort of your own living room, can use a computer to see pictures of those moons taken by robots, pictures that give some hope that some other form of life may be swimming in oceans under dozens of miles of ice.  And think about how we now can find worlds like Jupiter around stars hundreds of light years away, and how very soon we will know about Earth-like planets around those same distant stars.

Sorry!

Sorry to a handful of commenters whose comments were awaiting moderation and just got rejected.  I was trying to reject an advertisement and accidentally clicked on the "Reject All" button.  My goof.


Just as a brief reminder on comment policy, any comments on posts over 7 days old have to be moderated to keep spammers away.  It can take me a few days to get around to it, depending on my schedule.  Thanks for your patience.  I accept most comments, but will reject anything that is obviously spam, that is way off topic, that is not family-friendly, or that is just a flame war.

Tuesday, October 20, 2009

Stop the world and let me off!

The past two weeks have been horribly busy with all kinds of things I hope to blog about over the weekend.  Yesterday and today I'm attending a postdoc-led symposium here at Texas.  (Here is my blog post from the last edition of this symposium two years ago).  Alas, it's keeping me even busier, but I'll summarize all the cool things I've learned in a few days.

Friday, October 16, 2009

I, for one, welcome our new grasshopper overlords




Image Credit: McDonald Observatory / MONET / D. Doss

What was that last night in the skies above McDonald Observatory?  An odd cloud?  An alien spacecraft arriving from the Orion Nebula?  Or (shudder) Melanoplus lakinus? We may never know.  By the time crack government agents arrived, it was gone.

Friday, October 09, 2009

Did NASA's Moon impact Fail?


Palomar Observatory's image of the LCROSS impact site
Image Credit: Palomar Observatory / Caltech


No. At least, not yet, and I don't think it will.

For a few months now, NASA has been hyping this morning's impact of the LCROSS spacecraft with a shadowed crater on the Moon.  Many websites (including this blog yesterday) passed on information on how people with 10-inch or larger telescopes could watch the event, yet professional observatories with 200-inch diameter telescopes didn't see anything obvious.  Because of this, many websites, bloggers, and news casts have painted the LCROSS mission as a fizzle and a failure.  This is as unfair and exaggerated as the predictions of spectacular fireworks were.

I do believe now that NASA overhyped the LCROSS impact, at least in terms of what we might be able to see from the Earth.  But I do not believe the mission has failed.  And that's because science is not about getting the answer we want, it's about getting the answer right.

Thursday, October 08, 2009

Two impacts that will happen, one that won't




NASA's LCROSS spacecraft and its Centaur booster rocket
Image Credit: NASA



Early tomorrow morning, the moon will be hit by two fast-moving bits of space debris.  In 2036, the Earth will almost certainly not be hit by a 250 yard-wide rock.  All three of these pieces of news make me happy.


First, the moon.  The two bits of "space debris" are NASA's LCROSS probe and its spent Centaur booster rocket.  The rocket, weighing in at about 2.5 tons, will hit first, impacting the crater Cabeus (near the moon's south pole) at 7:31 am (and 19 seconds) EDT tomorrow, while moving at a speed of 9000 kilometers per hour.  This hit should gouge a crater about 20 meters wide and 5 meters deep, and may toss as much as 385 tons of lunar soil and rock into the air.

NASA wants this plume of debris to be tossed up, because the LCROSS spacecraft is going to fly through the plume, taking pictures, analyzing the chemical makeup of the debris, and sending that information back to Earth before it collides with the moon itself 4 and a half minutes later.  That impact will create a second plume of debris.  Earth-based telescopes on the night-side of the Earth will be staring at and analyzing the impact site, too, assuming the weather is good.  (The weather at the observatories in Hawaii is looking chancy).

Wednesday, October 07, 2009

2009 Nobel Prize for Physics Part 2: Fiber Optics


Fiber optic cables used in McDonald Observatory's HETDEX project
Image Credit: HETDEX / McDonald Observatory



As I mentioned yesterday, this year's Nobel Prize in Physics was shared between scientists who developed digital imaging circuits known as Charge-Coupled Devices (CCDs) and a scientist, Dr. Charles Kao, who designed the first fiber optic cables that were useful for long-distance data communication.  Yesterday I blogged about the astronomy uses of CCDs, so today I'll talk about the astronomy uses of fiber optic cables.

At most telescopes, there are two primary kinds of instruments.  One kind is the imaging camera, which simply takes pictures of the sky.  That's easy enough to understand, and fairly straightforward to build.  (Don't get me wrong, building any astronomical instrument for a big telescope is very hard.)  The other type of instrument is a spectrograph, which splits light into its component colors.  These spectra are most often used for determining the chemical composition of things and for measuring how fast things are moving.

One problem with spectrographs in the past has that the number of stars or galaxies you can look at at one time is limited.  Some spectrographs only allow you to look at one star (which is fine if there's only one star in some area of the sky that you are interested in),  Some allow you to look at multiple stars or galaxies, but which ones you can look at are constrained by geometry -- you can't analyze spectra of individual objects if they criss-cross or lie on top of each other.  And if you are looking at a two-dimensional object, like a galaxy or nebula, traditional spectral only allow you to get a  spectrum of  a long thin slice of the object.  So, how can we get around these problems?

Tuesday, October 06, 2009

And the Nobel Prize for Physics Gadgets With Huge Astronomy Impact Goes To...


Many people will be blogging today about today's announcement of the 2009 Nobel Prize in Physics, what the awards are for, who did what, and who didn't get recognized that should have.  so I thought instead I'd focus on the astronomy aspects of today's awards, which are very important.  First, one paragraph on today's awards.


This morning, the winners of the 2009 Nobel Prize in Physics were announcedDr. Charles Kao won half of the prize for making some tremendous contributions in fiber optics that led to their usefulness for communication. (Contrary to some reports I've read, Dr. Kao did not invent fiber optics; he and his collaborators found a means to allow fiber optics to send messages over long distances, necessary if you want to make a phone call via fiber optic cable across a continent or ocean.)  Dr. Willard Boyle and Dr. George Smith jointly received the other half of the award for their work on charge-coupled devices (CCD), which are one of the major types of digital cameras.  Most cheaper digital cameras, including, most likely, any that you own, use a different type of digital imager called CMOS (read here to learn about the difference), but the CCD has traditionally provided better images and better sensitivity.


Both of these achievements have had crucial impacts on astronomy.  Today, below the jump, I'll talk about the CCDs, and tomorrow I'll talk about fiber optics.

Friday, October 02, 2009

Help astronomers support public education in science


When my daughter started school, I was shocked to learn how dismal the funding levels for public education truly are in much of the country.  Every year, teachers send home wish lists asking for donations of supplies for their classrooms; if these items are not donated, the teacher has to pay for them out of her already meager salary.  And we're not talking about "luxuries" like computers and other technology, we're talking absolute basics: pens, pencils, paper, even Kleenex.  What kind of country is this where we have to ask teachers to buy Kleenex for their students??  It makes me livid every time I think about it.  And, with the current bad economy, classrooms are being squeezed even more than normal.


Anyway, the folks over at the Cosmic Variance blog (another astronomy and physics-related blog run by some darn good scientists) are participating in a friendly fundraising competition run by DonorsChoose.  DonorsChoose allows people to donate money directly to individual classroom projects in public schools in the United States.  Basically a teacher proposes an activity, asks for the money she/he needs to do the activity, and you get to choose which activity you want to help fund.  Since they're all scientists, the Cosmic Variance folks have identified several science-related projects, and are trying to raise more money for these projects than other teams.


In short, you can directly further American science (and/or non-science-related) education by donating as little as $5, and also help a small band of astronomers win a friendly competition.  To donate money for the Cosmic Variance team effort, click here.  To read more about DonorsChoose, to start your own team, or to choose non-science related projects to donate to, look here.  And, lastly, encourage people you know to give what they can.

Monday, September 28, 2009

The sausage making of science


I have one last week of serious telescope proposal writing that will likely keep me from blogging very much.  In the meantime, here's an article by planetary scientist Dr. Mike Brown about some of the problems with doing science.  As I've said before, science is not devoid of emotion and egos, as much as we'd like to pretend it is.   I'm unfamiliar with the papers in Dr. Brown's article, so I don't know who's right scientifically.  All I can say is that these issues pop up much more often then I'd care to see.

Tuesday, September 22, 2009

Book Review: Backyard Guide to the Night Sky




National Geographic Backyard Guide to the Night Sky

I've been a subscriber to National Geographic magazine for many years, and I've always been impressed by the quality of that publication and other productions by the National Geographic Society.  So, when I was asked if I would write a review of their new book, Backyard Guide to the Night Sky, I was tickled pink and jumped at the opportunity.


The book I received (cover shot above) is a paperback, roughly eight inches tall and five inches wide.  It's easy to carry around, and the pages are a fairly heavy stock, similar to other high-quality field guides I have from the Audubon Society.  I wanted to test and see how the pages hold up to damp conditions like backyard astronomers might experience on a dewy night, but due to the ongoing massive drought here in Austin, I didn't have such a night for a test.  However, it did rain about a week ago, so I sat outside (under a porch) and read for about an hour with no noticeable effect on the book.  I did notice that my fingers would leave prints on some of the black pages in the book, but these prints disappeared within a few minutes.   The numerous prints, photographs, and illustrations were all sharp with vivid colors.  So, the overall impression I have is that this is both a beautiful and durable book.

Thursday, September 17, 2009

Data, Analysis, and Reality


As a scientist, I must always struggle to remember the difference between actual data and inferences based upon those data. This difference is often pretty clear. For example, if I take a picture of a star cluster, the actual data I've collected are counts of the number of photons arriving from different parts of the sky. I then infer that an excess of photons coming from a single point is a star, while an excess coming from an elongated smudge is likely a galaxy. My data are counts of photons, and my inferences are the nature of the object. Clear enough.

Sometimes the line is blurrier. For example, suppose I take a spectrum of the light from a star, where I split the light into its component colors. Typically, I see light from many colors of the rainbow, with perhaps a few specific colors missing (see some examples here). Those missing colors are due to individual elements, like hydrogen, helium, or oxygen, absorbing that light. Most often, that light is absorbed in the atmosphere of the star I'm looking at, and there are diagnostic tools that I can use that look at the lines and tell me the temperature of the star and how much of the given element exists in that star.

A few years ago, I wrote a paper on spectra of a group of white dwarf stars. I noticed that about one quarter of the white dwarf spectra showed the fingerprint of calcium. Calcium is an element that is very easy to see in stars, and it usually indicates the presence of many other elements, like iron and magnesium, that are not as easy to see. This is interesting, because the gravity of white dwarfs is so high that elements heavier than hydrogen and helium should sink out of sight below the stars' surfaces in a matter of years. Those white dwarfs with calcium and other heavier elements must therefore be swallowing this material from somewhere, and there's good reason to think that this material may be from asteroids or comets, the remains of solar systems around these dead stars. So, did 1/4 of my white dwarfs once have planets?

Monday, September 14, 2009

Looking for Planets Around White Dwarfs

An asteroid passing too close to a white dwarf gets shredded by gravity
Image Credit: NASA / JPL-Caltech
Our Solar System is such a nice, ordered place. Eight (or nine or thirteen) planets have been happily circling our sun for 4.6 billion years, and the whole system is stable enough to life to have formed on at least one planet. And the solar system looks like it will continue to be a nice, stable place to live, at least for another six billion years. At that time, the sun will run out of hydrogen fuel, swell up into a red giant star (swallowing Mercury, Venus, and maybe Earth in the process), expel about half of its mass as a planetary nebula, and then shrink into a white dwarf. When the sun loses mass, its gravitational pull will weaken a little. This will cause the remaining planets to move outwards in their orbits a little bit, but they should remain bound to the white dwarf sun, forever circling the ashes of our star.

Now that we astronomers are finding planets around all kinds of stars, we can estimate that at least ten percent of stars have planets of some sort. Many of these planets are very close to their parent star, much closer than Mercury is to our sun. But many are further away, like Jupiter. And, like Jupiter, these planets should survive the death throes of their parent star, and be circling white dwarfs.

Here at Texas, my colleagues have been looking for planets around white dwarf stars, with only one possible success so far. It's a long, hard, slow process that involves looking for the gentle tug of gravity that the planet exerts on its parent white dwarf.

Another of my colleagues, Dr. Mukremin Kilic of Harvard University, has been looking for white dwarf planets another way. He's trying to detect the infrared light given off by giant planets, a heat left over from the very creation of those planets. A newborn giant planet can be as hot as a few thousand degrees on its surface, and even Jupiter still glows at a more feeble one hundred degrees Kelvin (a modest -300 degrees Fahrenheit). With an infrared light telescope, it may be possible to detect these planets around white dwarf stars.

Today, Dr. Kilic released a study that he and his collaborators completed using the Spitzer Space Telescope to look for extra infrared light coming from 14 individual white dwarf stars. They specifically targeted white dwarfs that came from stars three to five times more massive than the sun. This is because astronomers have noticed that bigger stars tend to have bigger planets, and that bigger stars don't live very long. That means that any planets around these stars should be bigger and brighter (because planets cool over time). They found no evidence for any planets.

Does this mean that white dwarfs just don't have planets? Not necessarily. Even though Kilic looked at what should be fairly bright and young planets, he and his team were still limited to finding planets about five times the mass of Jupiter. Planet searches around living stars have found that these behemoth planets are rare; it's more common to find smaller planets than bigger ones. Also, more massive stars become larger red giant stars, and so they can swallow planets out to much larger distances. While the Earth may or may not survive a red giant sun, Jupiter might have trouble surviving around a star five times the mass of the sun.

And perhaps Kilic and his collaborators may just have gotten unlucky. Roughly 10% of stars have planets, and they looked at 14 stars, so they might have only expected 1 star to have planets. And, in the funny way that statistics work, expecting one and finding none doesn't prove very much. But, this isn't the first work on planets around white dwarfs that Kilic has published; he and his collaborators have now searched about 40 white dwarf stars for planets, so they might have expected to find four. If you expect to find four planets and find none, then you may be on to something.

There's another possibility. Many planetary systems we find tend to be chock full of planets. Our own Solar System has four giant planets. Remember how I said that when the sun loses mass, the planets will move a little further away? In that process of moving away, it is possible for the planetary orbits to become unstable, and one or more planets could be flung out of the system. So, maybe big planets won't be found around white dwarfs because of this. We don't know.

Astronomers today are finding planets everywhere, and we do expect to find them around white dwarfs, too. But studies like Kilic's are showing that these remnant solar systems, fossils of planetary systems once similar to our own, are not easy to find. Perhaps they are just harder to see than we thought. Perhaps they didn't survive the death of their parent star. Time will tell. If nothing else, we just need to wait six billion years and watch what happens to Jupiter, Saturn, Uranus and Neptune. One way or another, we'll learn what happens to planets when their parent star dies.

Wednesday, September 09, 2009

New Hubble pictures!

Hubble's new view of Stephan's Quintet
Image Credit: NASA, ESA and the Hubble SM4 ERO Team

Yes, I know I'm a whole 6 hours late to the game in bringing you these photos, during which time every other science-related blog in the world already posted them. But they are just so cool, I'm going to post them anyway.

Last May, the space shuttle Atlantis visited the Hubble Space Telescope for their fifth and final servicing mission. Hubble has certainly been one of the crowning achievements of NASA and the Space Shuttle program; the astronauts transformed a dud of a telescope into one of the most important astrophysical laboratories ever built. In May, astronauts replaced two instruments and repaired two others, plus gave Hubble new batteries, gyroscopes and some other minor repairs. Today, after nearly five months of sometimes frustrating checkout and calibration, NASA released its first images from the repaired Hubble.

You can look at all of today's images here. There are pictures of the colorful center of the Milky Way Galaxy's biggest globular cluster, omega Centauri. That picture shows the power of Hubble. From the ground, the center of omega Centauri looks like a blob of starlight, there are so many stars! Yet Hubble resolves them all. The Hubble also imaged the birth of a new star and the death of an old one.

For those of you who can speak spectra (the splitting of light into its component colors), there are some amazing spectra from the uber-massive star eta Carinae (a star nearly 100 times the mass of the sun, about as big as any single star can get!), spectra of gas near a supermassive black hole showing changes over the past 10 years, and more. While spectra are often less inspiring for the general public to look at, they carry far more information than you might guess. From a spectrum, we can determine the speed of a moving object, its atomic composition, its temperature, its atmospheric pressure, and other important quantities that a picture alone could never tell.

My favorite image (and the one at the top of this article) is of Stephan's Quintet, a tight grouping of five galaxies. Four of the galaxies (the yellowish ones) are located 290 million light years away and are so close together, gravity is ripping off pieces of the galaxies, creating streams of stars and rings of new star formation. The fifth galaxy, the whiter one in the upper left of this image, is not related to the others. It is only 40 million light years away, and just happens to be along the line of sight to the other galaxies. Just think -- when the light that Hubble saw left the more distant quartet of galaxies, the first dinosaurs were just starting to roam the Earth. When that light passed the closest galaxy, dinosaurs had already been dead for 25 million years, and the earliest humans were still 38 million years away. But the neatest part of this image is the zoomable version, so you can zoom in and around the image to see amazing details. You can see individual stars in the closest galaxy! Cool stuff.

Anyway, Hubble is now doing hard core science again (and has been for a few weeks). Thanks once again to the amazing team of astronauts and ground crew for fixing this marvelous telescope!

Note: At times I've been getting some errors when trying to access views of some images. If this happens to you, take a deep breath and try again. They must be popular!

Tuesday, September 08, 2009

News tidbits

It's telescope proposal time again, so I'm spending much of my day and energy writing short applications to use various telescopes. I'll take an easy path out here and just post some news snippets.

  • Refurbished Hubble pictures come out tomorrow! It's hard to believe that the most recent and final Hubble Space Telescope repair mission was four whole months ago. Tomorrow, NASA will officially release its first pictures from the refurbished telescope (if you don't count those pictures of Jupiter from July). I've been seeing some colleague's new Hubble pictures for several weeks now, despite threats from NASA that they'll never get Hubble time again if they show the pictures. Astronomers can't keep secrets, even when dire threats are made. Anyway, Hubble is now mostly doing science again, with some final calibration and engineering activities filling up the rest of the its time. If you want to see the release of the new images, check out NASA TV at 11am EDT (8am Pacific, 15:00 UT).
  • NASA's Review of U.S. Human Space Flight Plans Committee's Summary Report is out. This was a committee charged with reviewing NASA's future plans for manned space flight. A description of the committee and a link to the 12-page summary itself can be found on this page. The two major findings are (a) that the shuttle program will have to rush to finish its current launch program by the end of 2010, potentially risking safety, so NASA should be given some funding to allow the schedule to expand into the first half of 2011, and (b) that, at current NASA budget levels, the International Space Station (which isn't even finished being built yet!) will have to be de-orbited in 2015, NASA's newest Ares rockets will not be ready until at least 2016, and that a return to the moon could not happen before 2030. The committee also outlined several options where, for an extra $3 billion / year, the space station can be run to at least 2020, and missions to the moon or other near-Earth places could begin in the early 2020s.
  • Neil Armstrong admits the moon landings were faked. Or not. Last week, the satirical newspaper The Onion published an article claiming that Armstrong had been convinced by a conspiracy theorist that he had not, in fact, landed on the moon (warning: the Onion often contains adult language). Evidently some foreign newspapers, not realizing that the Onion is satirical (i.e., it makes everything up), picked up the story and unknowingly presented it as real. This just goes to show that you shouldn't believe everything you read. Not even on the Internet.

Tuesday, September 01, 2009

Happy New Year!

It's the start of a new school year here at the University of Texas. The building is full of freshmen wondering why the elevator doesn't stop at certain floors, our large number of weekly seminars are starting up again, and we've welcomed a dozen or so new graduate students into our program, and we're awaiting the arrival of a new faculty member and a few new postdocs.

Life in academia is centered on the school year, not on the calendar year. And, because of the incredibly slow bureaucracies common at universities, it's already time to start thinking about applying for money and jobs that would start next September.

For the past three years, my position here has been financed by a fellowship from the National Science Foundation. That money enabled me to expand my research programs, explore new and exciting areas of astronomy, and spend a lot of time writing blog posts and surfing the astronomy internet. That changed at the stroke of midnight last night, as my research fellowship came to an end.

In reality, there's not much change for me in the short term. For the next several months, I'm getting paid out of a different research grant from the National Science Foundation. It means a slight pay cut and some new research responsibilities, but otherwise few changes. I'll still be blogging as I can, I'll still be studying white dwarfs, and I'll still be looking for that ever-elusive permanent, tenure-track position.

So, sit back, relax, and enjoy the ride. With the start of a new year, the possibilities seem endless.

Wednesday, August 26, 2009

Help astronomers understand the weird star epsilon Aurigae

An artistic envisioning of what epsilon Aurigae may look like up close
By Nico Comargo and courtesy www.citizensky.org
The star epsilon Aurigae is one of the most mysterious objects that you can see without the need for a telescope. With your eye, it looks like a pretty normal star in the constellation Auriga. But every 27 years, it gets noticeably fainter for almost two years, then it returns to its normal brightness for another 25 years. And the cool thing is, nobody is really sure why (read an older post of mine for a little more info, or read articles on this star in the May 2009 issue of Sky and Telescope (click here for the PDF version of the article) and in the October 2009 issue of Astronomy magazine.

Epsilon Aurigae is just beginning its first eclipse since the early 1980s. In order to better understand this system, a large team has been assembled by the American Association of Variable Star Observers, Denver University, Adler Planetarium and Astronomy Museum, Johns Hopkins University, and the California Academy of Sciences.

Best of all, this team wants and needs your help to study this weird star! As part of the International Year of Astronomy, the CitizenSky project has been created to recruit, train, and coordinate public participation in the study of epsilon Aurigae. It doesn't matter whether you have a PhD in astronomy or whether you wouldn't know which end of a telescope to look through, you are heartily welcome to help. (If you have a PhD in astronomy and still don't know which end of the telescope to look through, that's okay, too! It means you're a theorist, and you can probably come up with 30 new explanations for epsilon Aurigae for observers to test in the coming year.)

CitizenSky got a big boost earlier this week when it received three years of funding from the National Science Foundation for the project. So, instead of worrying how to pay for everything, the organizers can focus on getting the best science, instead.

Some professional astronomers will be studying epsilon Aurigae with big telescopes, too, but we can't look at the star 100% of the time for the next two years. In fact, the biggest telescopes can't even look at the star, because it is too bright. And, besides, there're other neat things going on in astronomy, too! So if epsilon Aurigae does anything unexpected, especially on day-by-day or even hour-by-hour basis, there's a good chance professional telescopes won't be looking. This gives you the chance to be the one making observations of epsilon Aurigae when something cool happens.

In order to succeed, CitizenSky needs your participation and help. If you have a nice telescope with some digital imaging equipment, great! If all you have is two eyeballs and a scrap of paper, that will work too! Just click on over to CitizenSky.org to read more about the project and how you can contribute valuable data to help solve the mystery of epsilon Aurigae.

And, if you know anyone else who might be interested, spread the word!

Tuesday, August 25, 2009

More thoughts on Pluto and the scientific method

While ruminating on my post on Pluto and the definition of planets yesterday, I thought of a couple other points on the topic that I wanted to make, though not necessarily related.

1. The story of the status of Pluto is a great illustration of the scientific method. The discussion of the discovery of Pluto, the much later discovery of the Kuiper Belt, and Pluto's subsequent demotion is (with one big exception I'll get to in a couple of paragraphs) an excellent illustration of the way that science actually works. When new data comes to light, we should never be afraid to re-examine even the most dear of scientific ideas. No matter how much we love Pluto (and it's okay to love Pluto, to study Pluto, to spend multiple careers working on Pluto, and to revere Clyde Tombaugh and the amazing amount of work he did to discover Pluto), we have to be willing to reconsider its status. To say, "Nope, it's a planet, end of story" or to say, "Nope, it's not a planet, end of story" is to be unscientific.

Further, science rarely gives us clear-cut answers, especially in the short term. Different teams of excellent scientists can examine the same evidence and come to different conclusions. Only through further study and analysis and debate can the deeper, underlying truths of science be brought out. The discussion of what Pluto is continues (though not always in the public eye), and the vast majority of scientists involved, deep down inside want to know the truth as to what is going on. If you want to learn how science really progresses, keep watching the unfolding saga of Pluto. In the end, the truth will be discovered. It just takes time and lots of work.

2. The International Astronomical Union's demotion of Pluto was far more a decision to solve a bureaucratic nightmare than a decision on the underlying science. Three years ago, the International Astronomical Union found itself with a problem. The IAU has, by consensus of the astronomical community, the final say in the naming of objects. And the IAU has devised specific rules for how to name objects, from planets to moons to asteroids. The rules differ greatly -- planets are named after Roman gods, moons of planets have restrictions also based on mythology, but asteroids ("minor planets") can have many other names, such as the asteroid Misterrogers.

With the discovery of Kuiper Belt objects larger than Pluto, the IAU needed to decide what set of rules the naming conventions should follow. What if someone found a Mars-sized Kuiper Belt Object and wanted to name it Bartsimpson? And which committee in the IAU would get to choose the name? Would the discoverer get a say in the name?

So the IAU decided to create the classification of "dwarf planet" to include all the smaller things that were generally round in shape (the biggest asteroids and Kuiper Belt objects), but were not moons and were not one of the classical planets. This designation allowed the IAU to come up with new naming rules, and everyone could be happy.

This turned into a disaster. What should have been simply a rule on how to name bigger round things turned into a vote on what constitutes a planet. And, as I pointed out yesterday, there are many ways of drawing lines, none of which seems inherently obvious. And this definition went through revisions, and astronomers voted on it. Yet this is not how science works. Scientific truths and laws are not decided by vote. The laws of nature are what they are, and it is our job as scientists to figure out what those laws are over time. This can take years, decades, or even centuries, yet the IAU definition was debated, altered, and approved in a couple of weeks.

I think the IAU should probably just have said something like, "We're making a new class of objects for the purposes of naming conventions. Objects orbiting the sun and large enough to be made round by their own gravity shall be named after mythological gods, and not just Greco-Roman gods, and Committee X has the right to decide how such names are to be selected." That would have solved the naming crisis yet allowed the scientific community to continue to debate exactly what makes a planet, and whether there is a fundamental physical difference between different types of rocky bodies.

Alas, this isn't what happened. They shoulda asked me.

3. What should the role of public opinion and historical precedence be, if any? I'm not going to do much more than open this can of worms, but to what extent can or should public opinion matter? After all, even if 100% of the world's people felt that the moon was made out of green cheese, the moon wouldn't magically transform into a giant Limburger; it would stay a round body made of metal and rock. And if 95% of Americans wrote letters to Congress demanding that Saturn be declared imaginary, and even if Congress passed a law declaring Saturn imaginary, it wouldn't suddenly vanish into the (non-existent) ether. Saturn would continue to circle the sun as always.

So, what should be scientists do about the millions of people still angry about Pluto? We can give in and say, "you're all right, Pluto's a planet." That solution would make people happy, but it completely ignores the scientific process. We could come to a scientific consensus, announce the result, and tell people to "deal with it." That solution would reach the scientific truth (whatever that result might be), but it clearly doesn't work (see point 2 above), and it would really tick off the people who pay our salaries. Maybe we should acknowledge the public's interest in the topic while doing our research, reach a scientific conclusion, and all the while try and teach y'all what we are doing, why, and how we reach the conclusions we do? Nah -- that would be hard. And make too much sense.

Monday, August 24, 2009

The never-ending saga of Pluto

Pluto and its moons
Image Credit: NASA / ESA /H. Weaver (JHU/APL), A. Stern (SwRI), and the HST Pluto Companion Search Team

I get back from a fun week of supernova discussions, and the top astronomy news story I spy is on CNN, which says, "Debate over Pluto rages on." Alas. It's the three-year anniversary of the International Astronomical Union's vote to revoke Pluto's planetary membership card, so I guess these stories are bound to come up. The problem is, there's really nothing new, it's just the Earth has gone around the sun three times since the vote was taken.

So, I thought I'd sum up my opinion on the matter. And this opinion starts with one crucial bit of information: I'm taking as pure of a scientific stand as I can, which means setting aside history, public opinion, and as much human emotion as possible. That's part of my job as a scientist. I am supposed to be able to look at factual evidence and see if that evidence supports a hypothesis, no matter where that evidence or hypothesis came from.

So, let's look at the Solar System and start with something easy. Our Solar System is dominated by the sun. Roughly 99.987% of the mass in the solar system is found in the sun. The sun is almost at the dynamical center of the Solar System. The sun is the only thing in our Solar System that produces its own energy by fusion reactions. The sun is clearly different from everything else in our Solar System. So we can set it apart.

Alrighty, let's look at what is left. Jupiter has about 3/4 of the remaining matter in the Solar System. It is a big, almost spherical collection of gas (with maybe some rocks in its core, but we can't see those). It's mostly made out of hydrogen and helium, but has never performed nuclear fusion. But Jupiter has a smaller sibling, Saturn, and a couple of similar cousins, Uranus and Neptune. So, although there are some differences between these four objects, they are all similar enough that we'll lump them together for the time being. For the lack of a better term, let's call them "gas giant planets".

Okay, now we are getting to the hard stuff. There remains about two or three Earth masses of material left in the Solar System, and this material is distributed among a bunch of rocky things. Ordered by decreasing diameter, Earth is the biggest, Venus a close second, and Mars a distant third. These rocky bodies are able to hold on to an atmosphere. Next, in radius, comes Ganymede, Jupiter's largest moon, which doesn't have an atmosphere. Then we have Titan, Saturn's largest moon, which has an atmosphere as thick as Earth's. Now we get to Mercury. Next come a bunch of moons: Callisto, Io (Jupiter), the Moon (Earth), Europa (Jupiter), and Triton (Neptune). Then comes Eris, the largest known member of the Kuiper Belt, a collection of icy bodies further from the Sun than Neptune. Finally, in 13th place among the rocky/icy things in our Solar System, we get to Pluto.

If we keep going down in size, we quickly pick up many more icy objects in the Kuiper Belt and the largest asteroids in the asteroid belt between Mars and Jupiter. Ceres, the largest asteroid, is less than half the diameter of Pluto, and only about 1/6000th the mass of the Earth. As we keep looking smaller, we find more and more asteroids down to the smallest sizes we can see -- objects only a hundred meters across or even less!

There's an important point here. Once we start looking at rocky things in our Solar System, there's no obvious demarcation between types of objects. The bigger "terrestrial planets" all have atmospheres, but so do some moons. A couple of moons are larger and more massive than the classical planet Mercury. Some things are icy, some are rocky. Things the size of the largest asteroids and bigger are all round in shape. So, from considering the size, mass, shape and compositions, there are some lines that could be drawn, but none of these classifications seem obvious.

Okay, so let's look at something else. Let's look at the structure of the Solar System. Sun near the middle, all by itself. Then comes some of the small rocky things: Mercury, Venus, Earth (with its moon) and Mars, with a few tiny asteroids scattered about in there. In this case, the asteroids in this region are so small compared to the big five rocky things that they look fundamentally different. Continuing outward, we next find the asteroid belt, the collection of most asteroids, including the biggest ones: Ceres, Pallas, and Vesta. Next come the four big gas giant planets, each of which has a bevy of much smaller moons, and with a few asteroids and other small icy things swimming about. Last comes the Kuiper Belt, which has a lot of icy things of all sizes. Eris and Pluto are both clearly in this Kuiper Belt -- they're the biggest things in the Kuiper Belt, but otherwise they share similar orbits at similar distances from the Sun.

In this structural view of the Solar System, the four gas giants and four of the rocky bodies (Mercury, Venus, Earth and Mars) all stand out as unique, dominating their respective parts of the Solar System. The asteroid belt is its own thing, and the Kuiper Belt is its own thing. In this view, we can call the eight unique things "planets", and everything else "non-planets". It seems a natural division, and we can define mathematical and physics-related definitions that would include the eight planets in the "planet" category and relegate everything else to the "other" category.

But this definition is also not satisfactory. If we were to take the Earth, stick it on a circular orbit in the middle of the Kuiper Belt, and let billions of years go by, the result would be a round ball of ice the size of the Earth in the middle of a bunch of other smaller balls of ice. An astronomer looking at this Solar System would probably just include Earth as a giant member of the Kuiper Belt. Mars or Mercury certainly would just be considered larger Kuiper Belt objects. But if we moved Jupiter into the Kuiper Belt, it would quickly fling every tiny ice ball out into deep space or down into the sun, and the Kuiper Belt would quickly cease to exist, other than the colder version of Jupiter happily orbiting the sun. In similar thought experiments, Jupiter, Saturn, Uranus and Neptune would still be unique objects, but the smaller rocky planets would not be.

So, from a scientific-motivated standpoint, I think it is unclear if even the Earth should qualify as a planet. Certainly the Earth is unique given its current place in the Solar System, but if it were a moon of Jupiter or out in the far reaches of the Solar System, it would be just another ball of ice. In short, I would argue that there is no good definition for a planet, at least one that would include the Earth and Mars and Mercury while excluding Jupiter's larger moons or giant ice balls in the Kuiper Belt. The rocky things in our Solar System form a continuum of sizes and relevance, and any lines we draw are, to some extent, arbitrary. I'd argue that this is true even if these distinctions are motivated by physics (such as whether an object's gravity dominates part of the Solar System, or if its gravity is strong enough to make it round)!

So, back to poor Pluto. What should we call it? I think that, had we not known about Pluto and we were to discover it today, we would not call it a planet. We'd call it a member of the Kuiper Belt. But, as I've described in far too many words, even a scientifically-motivated definition is, in the end, arbitrary, at least among the rocky and icy things in our Solar System. So I'm perfectly happy to allow history and sociology to help us define what we'll call a planet in our Solar System, and I won't argue with anyone who wants to say that there are nine planets, or even thirteen (let's make Eris, Ceres, Pallas and Vesta planets, too!)

More important than which little objects are planets is that we realize there is a hierarchy of objects in the Solar System, and that the Earth is not in the first or second tiers of that hierarchy. So, if we are looking for other Earth-like planets in other Solar Systems, we will have to look past a lot of big balls of gas before we find the insignificant rocks that may be home to other astronomers studying the four planets of our Solar System.

One last note, for those who have read more about these arguments at other places or even been involved in the discussions of definitions of the word "planet" themselves. I'm NOT arguing that concepts like Hill spheres and formation mechanisms are useless; I actually find them very appealing. But, in the end, those are definitions that leave as much to chance as they do to deeper truths. No matter where a Jovian planet is in a solar system, we would call it a planet. The same is not true for the Earth. This bothers me. Maybe I shouldn't think so hard about it.

Saturday, August 22, 2009

Weird things in the night

The weird transient event SCP 06F6
Image Credit: NASA / ESA / K. Barbary

In spite of everything we know about the Universe, there are still some things out there that we cannot yet even provide a basic explanation for. At the supernova conference I attended this last week, we heard a talk about a new type of object that is not yet explained.

In 2006, the Hubble Telescope was watching a patch of sky for supernovae in very distant galaxies. Hubble finds supernovae by watching for "new" sources of light that get brighter and then fade away; different types of supernovae brighten and fade in specific ways, and so the most interesting ones could be flagged for additional observations.

One such event with the boring name of SCP 06F6 (pictured above) was very curious. It got brighter over a period of 100 days, and then faded away over a similar length of time. That time scale is very long for supernovae. Also, SCP 06F6 did not take place in a detectable galaxy, so if it is not in our own Milky Way galaxy, it took place either on the far edge of the Universe, or it took place in a very wimpy galaxy. But we don't know.

Astronomers took a spectrum of SCP 06F6. Spectra, or the splitting of light into component colors, are a very powerful tool for studying astronomical objects. We can learn the composition of stars and the distances of other galaxies by studying spectra. Different types of supernovae all have different types of spectra. But the spectrum of SCP 06F6 is like no other supernova spectrum. It shows what looks like carbon molecules in a galaxy at a distance of 1.8 billion light years (z=0.14, for those of you who speak redshift).

1.8 billion light years is a big distance, but it's not that big for today's large telescopes and the Hubble Telescope. We should be able to see most small galaxies at that distance, and, again, we don't see a galaxy here. Also, supernovae are very powerful explosions, and carbon molecules are easily broken apart in such extreme conditions. This explanation doesn't add up. It could also be possible to explain the lines as calcium at a distance of 6 billion light years (z=0.5), but even that isn't all that far for supernovae.

Since the discovery of SCP 06F6, supernova searches have started to find many similar events, with the same long rise times, the same weird spectra, and the same lack of a host galaxy. Odd. Very odd.

So, what else could these events be? Astronomer Andy Howell showed the spectrum of a couple of these things, and my first thought was that they look like a rare type of white dwarf called "peculiar DQ" white dwarfs. These white dwarfs show what looks like carbon in their spectra, but at slightly the wrong wavelengths. This could be due to magnetic fields on the white dwarfs, or maybe due to hydrogen adding itself to the carbon molecules (making hydrocarbon white dwarfs!). White dwarfs would be in our own galaxy, so you wouldn't expect to see a host galaxy in Hubble pictures (we're in it!). These peculiar white dwarfs are also very faint, so if they are thousands of light-years away in our galaxy, we would not see the star before or after the event.

But the white dwarf explanation doesn't explain how these things get brighter and fainter. Gravitational lensing is one possibility. If another star passes between us and the distant white dwarf, the gravity of the interloping star can focus the light and make a star get much brighter than it was, even over a timescale of weeks and months. This would seem like a natural explanation to me, with one major problem. Gravitational lensing does not change the color of a star, only its brightness. But there is pretty good evidence that SCP 06F6 and its kin are changing color. If true, that would seem to rule out a gravitational lens. Maybe. (I can think of ad-hoc ways to save it, but then why should these ad-hoc ways happen more than once in different parts of the sky?).

There are many other ideas astronomers have proposed, from Texas-sized asteroids running into white dwarfs in our galaxy to carbon-rich stars halfway across the universe being shredded by distant black holes to exotic types of supernovae. We know so little about these events, it is hard to rule any weird things out yet. As we discover more of these, though, hopefully we can build up enough information to explain these rare and mysterious events.

Friday, August 21, 2009

Light echoes

Light echoes from old supernovae in the Large Magellanic Cloud
Image credit:
X-ray: NASA/CXC/Rutgers/J.Warren, J.Hughes; Optical (Light Echo): NOAO/AURA/NSF/Harvard/A.Rest et al.; Optical (LMC): NOAO/AURA/NSF/S.Points, C.Smith & MCELS team

In 1572, the astronomer Tycho Brahe noticed a "new" star in the sky that grew in brightness until it was visible in the daytime, and then slowly faded away. This star challenged ideas that the heavens were unchanging, and led Tycho to start studying the heavens. Thirty years later, in 1604, Tycho's protege Johannes Kepler noticed a new star in the constellation Ophiuchus; this "star" also became the brightest star in the sky for some time before fading away.

Today, we know these two events were the explosions of stars, known as supernovae. Using optical and X-ray telescopes, we can study the nebulae left from these explosions. Therefore, Kepler and Tycho's supernovae are important bits of data for studying exploding stars. Unfortunately, no supernovae have been observed in our galaxy since 1604. We would very much like to observe a nearby supernova with all of our modern astronomical instruments. Alas, the closest supernova we've gotten was in 1987, when a star exploded in the Milky Way's companion galaxy the Large Magellanic Cloud. And while we see supernovae in more distant galaxies fairly often, it is often impossible to study these events more than a year later.

About 5 years ago, astronomer Armin Rest and his collaborators discovered filaments of light in the Large Magellanic Cloud that appeared to be moving away from three former supernovae. Further analysis found that this light was an echo, or reflection, of light released in supernovae explosions hundreds of years ago. The light started off moving away from the explosion in random directions, and then it hit a cloud of dust, which reflected the light toward the Earth. The light ended up having to travel a few hundred light-years further than the original light from the supernova, so it is just now arriving at the Earth. What this means is that we can see the original light from those explosions and study it as if the supernova were happening now. The picture at the top of this post is from that study.

A couple of days ago, Dr. Rest presented some newer work on light echos. He and his collaborators have now found light echos from both Tycho's supernova and Kepler's supernova. Using telescopes, Rest has managed to use modern instruments to study light from the same explosions that Kepler and Tycho saw. He's been able to confirm what kind of supernova Kepler and Tycho saw -- Tycho saw a Type Ia supernova (an exploding white dwarf), and he saw a very normal Type Ia. Kepler saw a Type IIL supernova (a rare type of exploding massive star).

One of the exciting things about this research is that not only can we study the explosions themselves 400 years later, but we also do not have to wait to look at the final supernova remnant -- we already see those! We are just now starting to see the new nebula that Supernova 1987A is forming; for Kepler and Tycho, 400 years have already passed, so the nebula is already well-formed and has been well-studied by all kinds of telescopes.

One other great thing about light echoes is that they allow us to see the explosion from different directions, like mirrors held hundreds of light years on either side of the explosion. Tycho looks the same from different directions, but Supernova 1987A looks slightly different. With a little luck and a lot of hard work, we may be able to piece together an even better picture of these explosions.

These light echoes are therefore letting us study the past and present of famous supernovae. We can use modern telescopes to study these famous supernovae, and get information almost as good as if Tycho had today's observatories at his disposal. And we don't have to wait decades or centuries for the next nearby supernova explosion.

The topic of light echoes also reminded me of the famous Diana Ross song Reflections. "Reflections of...the way light used to be." (Or something like that)

Wednesday, August 19, 2009

The continuing mystery of Type Ia supernova

After two days at a conference on stellar death and supernovae, it's become pretty obvious that the more we learn about Type Ia supernovae, the less we seem to know or understand. It's fairly amazing that after 40 years of intensive work on the problem, our understanding is still so muddy.

First, what do we know? Type Ia supernovae are a type of exploding star. In these explosions, we do not see any hydrogen or helium, which are the most common elements in the Universe. We also see lots of silicon and iron, which are the products of explosive nuclear reactions involving carbon and oxygen. These two facts make it seem likely that the exploding star is a white dwarf. White dwarfs are the nuclear ashes remaining after most stars finish their lives; they're made mainly of carbon and oxygen, and they have very little hydrogen and helium.

We also understand pretty well what happens after the explosion. Type Ia supernovae have a relationship between how bright they are and how long they take to fade away. This is very useful, because if we see Type Ia supernova in the distant universe, and if we can measure how long it takes to fade away, we know how bright it was. This allows us to figure out how far away the explosion was (because things appear fainter the further away they are). This relation allowed astronomers to find some of the first evidence for "dark energy."

But there are some mysteries. First, how do you get a white dwarf to explode? The typical white dwarf is very stable and resistant to explosion. If we can take a white dwarf and add more and more material to it, eventually it will get big enough that gravity will squeeze the white dwarf, cause it to heat up, and set off nuclear reactions. We think.

But how can you add material to a white dwarf? There are several ways. If you take two white dwarfs and merge them together, you might get a big enough white dwarf to explode. But colliding white dwarfs is hard, and we've never actually seen two white dwarfs that are going to collide and be massive enough to explode. This doesn't mean it can't happen, because it is hard to confirm that you have two white dwarfs in such a system, but until we find such a system, this is just an idea.

Another way to grow a white dwarf is to have it orbiting a normal star. If the white dwarf is close enough to the normal star, the white dwarf's gravity will siphon gas off of the normal star and onto the white dwarf. We actually do see several stars where this is happening; these are called cataclysmic variables. But in cataclysmic variable stars, there is usually too little material being transferred to build up the white dwarf to an explosive mass. There are some special types of these cataclysmic variables that may work, with names such as supersoft X-ray sources and recurrent novae, but we still can't be sure that they will explode.

Either of these methods, colliding white dwarfs or cataclysmic variables, take time to work, perhaps billions of years. But about 5 years ago, astronomers started discovering more and more evidence that the number of type Ia supernovae in a galaxy depends on how fast the galaxy is making new stars. That was a complete shock -- how can a process that takes billions of years to work know how fast a galaxy is making stars right now? Maybe there is a way of adding material to brand new white dwarfs in very short times.

Supernova scientists have just been coming to terms with that finding and developing explanations, when yesterday one of the teams counting Type Ia supernovae stirred the pot further. They said, essentially, that maybe they had made a mistake, and the rate of Type Ia supernovae in a galaxy doesn't depend on its current rate of making stars, but is just an artifact of how we were doing the observations. That claim caused a lot of controversy and discussion, and needs a lot of further exploration.

So, in short, we don't know exactly what causes Type Ia supernovae, and we have mixed signals as to how long it takes to start getting these supernovae. I'm cool with this, because it means there is a lot of work yet to be done, and lots of ways I can contribute to understanding these supernovae.

But there should be some concern, too. Scientists are using Type Ia supernovae to try and understand dark energy and to see whether it changes over time in our Universe. But can we believe the results that supernovae give us if we don't understand the explosions even moderately well? There are certainly other lines of evidence that dark energy exists, so the Type Ia supernovae are clearly pretty good for this purpose. But if Type Ias change at a slight level over time, that change in the supernovae could be interpreted as a change in dark energy instead. For this reason, we need to keep studying Type Ia supernovae and the stars that they come from, whatever those stars might be.