Tuesday, August 17, 2010

White dwarfs, day 1

Yesterday was the first day of the 17th bi-annual European White Dwarf Workshop, a weeklong-conference about white dwarf stars.

White dwarf stars are the slowly-fading embers left behind when most stars exhaust their fuel.  Stars shine due to nuclear reactions in their cores.  They fuse hydrogen atoms to make helium, and then they fuse helium atoms to make carbon and oxygen.  The heaviest (most massive) stars can even fuse carbon and oxygen atoms into still heavier elements, but these stars are rare.

Once a star has fused as many atoms as it can into as heavy of elements as it can, the star swells up into a red giant star (the red giant sun will swell from its current diameter of about 1 million miles into a diameter of about 200 million miles, swallowing Mercury, Venus, and maybe even the Earth in the process).  After spending some time as a red giant, a star will blow off its outer layers in a beautiful planetary nebula, exposing the white-hot nuclear reactor that was its core.  This core, which can contain up to half the mass of the original star, is only about the diameter of the  Earth.   This is what we call a white dwarf.

Because white dwarfs are formed in this way, they are one of the few glimpses we astronomers have into the central nuclear engines that power stars.   So, while you could say that this week is dedicated to studying dead stars, it is more like stellar forensics.

Yesterday one of the topics were white dwarfs with carbon and/or oxygen atmospheres.  I've worked in this field quite a bit, and I was part of the team that discovered that many of these carbon-atmosphere white dwarfs change their brightness.  Yesterday's talks made us wonder if maybe all of the carbon-atmosphere white dwarfs change their brightness.  Every single one of these stars that has been studied in enough detail do indeed vary, which is unheard of in other kinds of white dwarfs.

Today I give my talk.  I'll let you know how it goes.

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