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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."
That is unusual.
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.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Many parts of the bible lend credence to your theory that He runs out of lithium from time to time.
How can I believe you when you tell me what I don't want to hear?
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.
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.
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Jesus.
1) People calling something "dark" doesn't mean they literally believe that, for instance, "dark energy" exists. What they know is that observations cannot be accounted for without something that acts the way "dark energy" acts, in the equations they currently employ. There is enormous research in this field pursuing a wide range of approaches to reproducing the observations theoretically. The simplest models employ a "dark energy" -- literally, something that does not interact with light, and which has a pressure sufficiently negative as to accelerate the expansion of the universe. No-one -- and I mean NO-ONE -- who works in the field treats these as anything other than toy models. Phenomenology, to use the jargon. More complex models attempt to see what changes to the assumed laws of gravity are necessary to reproduce the effect. No-one who does this pretends that their model is anything other than a toy model. (Indeed, most modifications to gravity can be rephrased as a dark energy of the first kind anyway, albeit a really weird, ugly one. It's the motivation that's different.) More controversial models attempt to reproduce the observations by changing one of the fundamental assumptions that lead to the standard cosmological model: homogeneity. Violate homogeneity and you can influence the paths of photons around us in ways that mimic "dark energy". No-one working on this pretends that it's anything other than a toy model. Yet another approach is to point out that the universe is intrinsically inhomogeneous and anisotropic and attempt to reconstruct the homogeneous universe we employ in cosmology from that. No-one working on this pretends that the models studied so far are anything other than toy models.
It's not "scientists" "making up" "dark" "somethings" that can be "plugged into equations" but "never detected", it's people tagging a puzzling observation with a placeholder ("dark energy" for the anomalous acceleration of the universe; "dark matter" for the apparent necessity across a massive range of scales for large amounts of clustering matter that doesn't interact with light) and then exploring potential explanations.
I don't care if you were trying to joke. This kind of accusation really annoys me because it suggests that either we're terrible at explaining what's going on, or people simply aren't listening to us;, or both and people who argue this way tend to insinuate that those of us in astrophysics are a pack of idiots or charlatans fraudulently inventing arbitrary and unobservable physics in order to screw millions upon millions of euro from the honest taxpayer. And that's frankly offensive.