Friday, July 02, 2010

Random neat things in the sky

Today I was working on one of the many projects on which I am dreadfully behind.  Usually that means I just plow through the work as quickly and accurately as I can.  This particular project involves taking deep (very faint) photographs of what, to many astronomers, are large areas of the sky  -- patches about as large as the moon.  These pictures often contain 20,000 or 30,000 galaxies, too many to work on by hand.  So I use automation to measure the position, brightness and color of each galaxy.  I then spot check each data set to make sure the automation worked.

When I spot checked this particular image, I noticed lots of really cool galaxies. So I made a color image from our photographs, and I made cutouts of some of the more interesting things.  For each of the images below, click on them to get a larger view.  And, in case you wonder, the blue and white vertical streaks are artifacts from stars that are so bright they overwhelm the camera.  Even so, these stars are typically 1000 to 10,000 times fainter than the faintest star your eye can see on a dark, crystal-clear night.  All descriptions refer to the picture above them.

The above picture is the center of our entire photograph (which is WAY too big to post), and is about 5 arcminutes (1/6th of the moon's diameter) across.  The tiny yellow arrow marks the faint galaxy that led us to this patch of the sky.  The galaxy is a gravitational lens, meaning that its gravity bends and focuses the radio waves from a much more distant black hole into a distorted picture of the background black hole.

The faint galaxy, called MG J1131+0456 is about 7 billion light years away.  We don't know how far away the black hole is; it is too faint to study with current telescopes, but some astronomers have guessed it is at least 10 billion light years away.  Here you can see some false-color images of the galaxy and the arc-shaped distorted picture of the black hole taken with the Hubble Space Telescope; our image is not sharp enough to see detail.

Our interest is to study how the gravity from all the other galaxies in this picture change the distortions that we can see in the Hubble Space Telescope image, you can read more about that in a post I wrote last month.  The thousands of galaxies in this small patch of sky lie at all different distances from the Earth; the bigger galaxies in the upper left are "close", only 1 billion light years away, while many of the faintest fuzzy galaxies could be five to eight billion light years away.  I just love all the different shapes and sizes of galaxies in this part of the image.
This pretty spiral galaxy just happened to be in the field of view of our camera.  Like many galaxies, it has a name: MCG +01-29-047.  It is located about 450 million light-years away, and it reminds me a little of the nearby spiral galaxy Messier 101.  The brightest galaxy above and to the right of the spiral is related to the spiral -- it's at the same distance.  I think that the spiral's gravity is messing with the companion galaxy, because the companion looks a little odd-shaped and like it may have a shell around it.
Here is another portion of my big image.  In the center-left is another spiral galaxy, this time seen almost from the edge.  On the center right is another distorted shell galaxy.  The spiral is about 250 million light years away; I don't know if the distorted shell galaxy is related. 

Just to the right of the spiral galaxy is a tight group of at least five galaxies (click on the picture to see a larger version and get a better view).  From the colors I measure, I think this group is a lot further away than the spiral, but I don't know how far away it is -- maybe 1 or 2 billion light years.  But really cool is the wispy tail coming out of the tight group toward the upper right and then making a sharp bend to the left. 

That wispy structure is called a tidal tail, and it is made out of stars that used to belong to one of the group galaxies but got tossed out by another galaxy's gravitational pull.   Here's a Hubble picture of a tidal tail being pulled from a galaxy called Arp 188.  Hubble has also imaged a closer tight group of galaxies called Stephan's Quintet; I suspect this tight little group of galaxies is very similar.

To the best of my knowledge, nobody has published a study of this group of galaxies or this tidal tail before!  Alas, I don't have time to do any follow-up work at the moment.
Here is a last bit of the image with two more distorted galaxies.  In the lower left is a galaxy with at least one and probably more faint loops around it, perhaps the remains of small galaxies that got too close to the big one and have been shredded beyond recognition.  The galaxy in the upper right looks a little like a more distant version of the Hubble Arp 188 picture, but without the long tidal tail.   Neither of these galaxies have anything published about them, so I don't know much more!

These four images make up just a tiny fraction of the entire full-moon sized image.   I also spied a cluster of galaxies (which doesn't look that great in this image, but if it were a few billion light-years closer would be very impressive) and many more distorted galaxies.   An astronomer could spend an entire career trying to understand the tiny portion of the Universe in my photograph.  Alas, I don't have more than half an afternoon to give for now.

Image Credits: NOAO / KPNO / K. Williams


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  2. Pretty! I wonder if either of these made the group catalog.

  3. I find tidal force absolutely fascinating. It is awesome to think that one astronomical body could be altering the shape of another on such a large but slow scale.