Astronomers Find Unusual Star

First time accepted submitter JoshuaZ writes "Astronomers have found an unusual small star. SDSS J102915+172927 is a small faint star with very little of any elements other than hydrogen or helium. The star's composition is surprising (Pdf) since standard theories of star formation require heavier elements in small stars in order to allow the stars to be heavy enough to come together. Possibly the most unusual aspect of this star is the complete non-detection of lithium which would be expected in a star of this size. The only elements created shortly after the Big Bang were lithium, hydrogen and helium, and the star should have lithium levels much higher since they should correspond closely with the levels believed to have been formed shortly after the Big Bang."

Comments

have direction, but not distance

[rubycodez]

I always like to know how far away something is from us. Most articles on the web give direction toward Leo, but for distance I only found one reference that said it was hovering 3,500 light-years above the disk of the Milky Way. So it's near our Milky Way

http://www.cosmosmagazine.com/news/4690/impossible-star-discovered

Re:have direction, but not distance

[Michael Woodhams]

For a main sequence star, the procedure would normally go something like this:
From the star's spectrum, you know its temperature. (With a good enough spectrum, you can also confirm that it is main sequence.) From the temperature and the fact it is main sequence you know its intrinsic luminosity pretty well. From its temperature you know its intrinsic colour well. Comparing this to the observed colour, you infer how much dust there is between you and the star. (Dust blocks blue light more strongly than red light, so more dust means redder colour.) Knowing how much dust there is, you know how much its observed brightness has been reduced by the dust. Knowing what its brightness would be without dust and its intrinsic luminosity, you use the inverse square law to figure out how far away it is.

However, this star would have a really weird spectrum. If I recall correctly, hydrogen and helium only show spectral lines in much hotter stars, so presumably the only lines are calcium (the only metal they did detect). I don't know how well they can determine temperature with just calcium lines. I'm also not sure how precise this procedure is on ordinary stars, but I'd guess the uncertainty in distance would be about 10-30%.

IAAFA also, but I've never actually used the procedure I describe above.

Re:So, it's like Jupiter?

[sFurbo]

The mass fraction of elements heavier than helium in this star is less than 1ppm. The sun is 99.9% H and He and only 0.1% heavier stuff, this star has some 50.000 times less than that. Compared to this star, Jupiter is solid iron, so no, not like Jupiter at all.

Re:Occam's Razor

[TheRaven64]

While I agree with the contention that the simplest explanation is likely the right one

Why would you agree with something so nonsensical? And why would you state such a belief in the context of Occam's Razor, which says nothing of the kind. Occam's Razor says that, if a model works without one of its factors, then it is safe to remove that factor. It's a rule about logic, not about science. If you start with a set of axioms and develop a system, then there are an infinite number of axioms that you can add without changing the validity of any of your interred rules, but adding these does not gain you anything.

An example of its application in science is the idea of guided evolution. One model suggests that species change via random mutations. Another model suggests that these changes are not random, that they're guided by a higher power in such a way that is indistinguishable from random change. Occam does not say that the second hypothesis is wrong, merely that it adds nothing useful to the model. You could also add another factor to that saying that it's guided by a higher power who makes decisions based on what an angel tells him. You could go on adding extra layers to this hypothesis forever, without altering the predictions that are made. You can, therefore, save yourself some mental effort by ignoring the factors that are irrelevant.

That doesn't mean that the first theory is 'right', or true, it just means that it's simpler and equally useful.