Researchers Discover a Star's Minimum Possible Mass 112
paulmac84 writes "Stars that don't have enough mass never shine, dying billions of years before their bigger counterparts. But astronomers have never been able to measure the exact mass limit, because the lightest stars that do shine can be simply too faint to detect. Now, new images show for the first time how big a star must be to avoid impending doom. The long-awaited new images finally lay this question to rest, say the authors. The dimmest stars were measured as being 8.3% of the Sun's mass. All protostars that are smaller than this are headed for life as a brown dwarf."
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Finally a Definitive Answer! (Score:3, Insightful)
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Re:Finally a Definitive Answer! (Score:4, Informative)
Although the telescope would have been able to detect fainter stars, none could be found- so it appears that they simply don't exist. "We checked the instruments over and over again" said Professor Richer "but we don't see any stars fainter than this".
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And when they say "shine", what do they mean? In what spectrum? To what brightness? Another way to ask this is, what makes a brown dwarf "brown"?
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What I'm saying is that if it puts out energy, why is it not a star? Counter proposal: is a black ho
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What's the difference between an object like Jupiter and a brown dwarf or star? As I said earlier, what makes a brown dwarf "brown"? What spectrum range defines a star? What I'm saying is that if it puts out energy, why is it not a star? Counter proposal: is a black hole putting out energy? Is it a subset of "star"? What sort of energy need a "star" emit? How much of this energy? How often? Is a faded old white dwarf still a star? Define your terms, sirs.
These are things you don't understand, by your own
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This is possibly true, although the difference in energy being received and the observed temperatures are within a reasonable tolerance (~ 10%?); whether this is because Jupiter has some extra energy due to radioactive decay, or continued gravitational compression, or whether it's just a measurement error is not clear.
Is it not smaller than their lower limit?
Yes. It's not expected that Jupiter is fusing any significant amount of deuterium or n
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So the definition of a star is an object which emits radiation due to fusion, or which did at one time?
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If the object isn't heavy enough to undergo fusion by itself, it's not considered to be a true star...but objects which were heavy enough to be a star, and then went into the red supergiant phase or go nova, the left-over stellar core (a "white dwarf" or "neutron star", respectively) will still be considered a star until they cool below 1000K or so.
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Brown Dwarfs (Score:2, Funny)
Yeah, that's it, "vertically challenged stars of color".
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Your signature The "USAPATRIOT" Act has nothing to do with patriotism, so I pronounce it "the you sap at riot act" to avoid confusion. literally makes absolutely no sense and is annoying. While I am certainly not a fan of the PATRIOT act suggesting that its acronym means or should read something completely unintelligible is neither funny or interesting.
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Just like the USAPATRIOT Act, which makes no sense (for its purported purpose -- stopping terrorism), and is annoying to people who value their freedom.
The problem is that pronouncing it "the patriot act" or "the you ess eh (Canadian pronunciation of "eh") patriot act" lends it an air of legitimacy, like it's actually a
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There may be some truth in this comment. Could it be 8.2% instead?
Whenever you read an article like this, we should pay attention to the error bar. Is it 8.3% +/- 1, 5, or 50%?
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I know what you are getting at: you are basically talking about significant figures, which isn't a bad guess. But here I am referring to more traditional statistical errors that should be propagated through analysis.
I just read the actual paper and it doesn't have any good estimate on the error.
Just FYI.
Re:Finally a Definitive Answer! (Score:4, Interesting)
Although the telescope would have been able to detect fainter stars, none could be found- so it appears that they simply don't exist. "We checked the instruments over and over again" said Professor Richer "but we don't see any stars fainter than this".
So they could have detected much dimmer stars but didn't - so assuming a big enough sample, they discovered the minimum mass to initiate fusion. Pretty impressive.
So finally a Definitive Answer! Until someone bothers to look at a larger sample set,, finds dimmer stars, and they have to lower the minimum again.
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So finally a Definitive Answer! Until someone bothers to look at a larger sample set,, finds dimmer stars, and they have to lower the minimum again.
I'd rather say, finally a definitive answer, period. The reason why stars cannot be smaller than that limit is theorical, and the observation allows us to find that limit. A larger sample set will not lower the minimum, ever. It will only reduce the margin of error. The dimmest star you could ever find is comprised in the margin of error we got.
Re:Finally a Definitive Answer! (Score:5, Informative)
Basicly, this observation is in reasonably close accordance with the theories about stellar fusion; basicly, an potential star needs to have about ten or fifteen times Jupiter's mass before deuterium fusion is possible, and about 70 times Jupiter's mass before normal hydrogen fusion happens (according to the models).
Jupiter weighs 1.899 * 10^29kg; Sol weighs 1.989 * 10^32 kg (or about 1050 times what Jupiter weighs).
8.4% of Sol's mass is 1.65 * 10^30, or 87 times what Jupiter weighs.
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Unless a star is nearby, planets are effectively invisible at stellar distances since they radiate no light of their own. Even with a star nearby, it's easier to notice the gravitational wobble of the planet shifting the star's orbit and causing doppler changes to the star's spectrum than to observe the planet directly via reflected light.
A "brown dwarf", sometimes referred to as a T-class star is something that emits enough
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Um... yay? (Score:4, Interesting)
Re:Um... yay? (Score:5, Informative)
True enough, but both back-of-the-envelope calculations and the best models give you an answer that's spot on, to within something less than a factor of two. It's not as though there's some great debate within the community about whether the minimum mass for pop-II stars is significantly different from
I'm a great fan of observational confirmations, and of giving Hubble time to people doing this sort of work, but it's hard to imagine why anyone who isn't a specialist in stellar modeling looking to test their code to within a few percent would care about this particular result.
It hardly seems like press release material. What's more, dressing up the article to make it seem like some great mystery has been solved is disingenuous.
But, I suppose, "this just in: astronomers have confirmed something that they've been rather confident is true for decades" doesn't sell papers.
Re:Um... yay? (Score:5, Insightful)
Perhaps it is a simple problem to answer mathematically. And now we've tested it. We have actual data. Does the data match up with the mathematical answer? Maybe, maybe not, I don't pretend to know. But I imagine people out there do - so either we've got another point of verification that our models are good, or it's time to figure out what's wrong with them.
Either way, this is what's called Science.
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Note that there's a lot of other factors such as air resistance which are important too, though.
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Bit of a problem in your argument there - heavy thing DO fall faster then light things!
It's just that on earth, the earth is so much larger then the falling item, that if the faller is a little bigger or a little smaller it's not much noticable.
OTOH if you get some nice large objects - say th
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Actually, if you go to a decent science museum, they should have an exhibit where they show something like a feather and lead shot being dropped in a vaccuum...really and truely, they fall at exactly the same speed and hit the ground at the same time.
If you plug in F=M1a and F = gM1M2/r^2, you discover that the gravitational attaction of a heavier object to the earth exactly counterbalances the weight of the heavier obje
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No, not "really and truely", only "approximately". I guess you missed where I wrote the difference on earth is not noticable. But just because you can't see it doesn't mean it's not there.
You have an error in your equation: you forgot about the acceleration o
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No, actually, I haven't.
Notice that both objects are being released at the same time; the motion of the Earth towards them is not different for one object versus the other, presuming it was significant at all (which it is not; the Earth weighs about 10^26 times what a 5kg lead pellet weighs). When you drop two objects from the same height, at the same time, in a vaccuum, they will hit the ground at ex
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You seem to have forgotten we are talking about how fast objects fall, not comparing them. Go back and read the post that started this.
"presuming it was significant at all (which it is not; the Earth weighs about 10^26 times what a 5kg lead pellet weighs)."
WOW! you don't say, I have never heard of this before, the earth is heavy? The fact I said this at least 3
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How do you measure velocity, eh? Measure the distance, divide by the elapsed time?
Well, in the specific example I gave, and in the historic example involving a leaning tower in Italy, the distance and the time are exactly the same for the two objects...so the the velocity ("how fast"), is also the same.
Go back and read the post that started this.
The post by ZorbaTHut, hmm? Modded +5 because it had a good point, wh
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Or the thing to point out is that atmospheric drag is a big deal. As for the miniscule amount that a slightly more massive object would have on gravitaional attraction, it isn't worth worrying about. And if you do the ma
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Of course-- that is so intuitively true that nobody [1] questioned it for the 2000-odd years between Aristotle & Gallileo.
On the other hand, you can take two pieces of paper, which weigh the same, and have the same density, and crumple one into a tight ball, and
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This BTW is a serious problem with other scientific investigations, where some "theories" are offered, but realisticly eliminating extra factors that influence the results is often difficult or impossible to do. The whole issue of global warming, for instance, has so many variables that the one often used conclusion, that human-caused pollution is directly causing global warming
Re:Um... yay? (Score:4, Interesting)
Here's just some of what makes it more complex for the real world though, and I'm probably missing plenty of other complexifying factors:
Spinning Star? What range of rotation rates occurs in low-mass stars, How much pressure does it relieve at the core at a minimum? (Is there any real occurance of a low mass star with absolutely no rotation?)
Which Population (I or II). Low mass stars can be very old, as they burn their fuel so slowly. This affects how much of the heavier elements are found in their cores. Just where newer generation stars formed makes a big difference in how much of what heavier elements are in them, but there's not much of a difference theoretically possible for the first generation. Are their faint stars can we observe, but not get enough of a spectrum on to be confident of their composition?
Are there any convection currents in low mass stars? Do such, as yet unproved, currents include the full range of modalities found in a star the size of our Sun, or fewer? (or maybe even something truly novel, completely different than in bigger stars?). We're not even real sure how typical current patterns within our Sun are for stars of its general type, last I looked.
Can having a large, close companion star significantly reduce the minimum mass threshold, or would any such received radiation effects be trivial?
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The rotation of a star would presumably be a result of its original collapse. Conservation of angular momentum. Hence the really enormously fast rotation of extremely collapsed objects like pulsars.
A low-mass star, then, would probably spin relatively slowly. Less mass means less angular momentum. Si
Model stars (Score:2)
I bought a model star once. Probably a Revell kit. It was quite simple. Too simple. Two halves of a ball, with a page of assmbly instructions, three pages of instructions on the proper use of model glue, two pages of instructions on the proper application of model paint, and seven pages of disclaimers. All in 8 languages.
I filled it with hydrogen and detonated it. Made a really nice star for a few milliseconds...
AstroPhysics, not Taxonomy (Score:2)
8.3%? (Score:2, Funny)
For those who are wondering... (Score:5, Informative)
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In the book I believe Clarke just said "heavier elements." The monoliths were sucking up Jupiter's high clouds and turning the material into heavy elements, which would have the same effect, you'd just need more of it.
Whether it would work for the millions of years mentioned in the book,
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Plus, it was just a book =)
Re:For those who are wondering... (Score:4, Funny)
Re:For those who are wondering... (Score:4, Insightful)
What we really need to know is how many clown-laden Bugs is that?
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Re:For those who are wondering... (Score:4, Insightful)
Holy crap, you mean the Library of Congress is massless?!
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No, just that it's not of fixed mass. You can put several books on a DVD, and the DVD weighs less. Or you could put them on stone tablets instead if tha's your thing.
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Holy crap, you mean the Library of Congress is massless?!
Now if we could just make it spherical ...
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I'm not really sure how to express it in LoC, but knowing that Burning Library of Congress (BLoC) is roughly 4 petajoules [slashdot.org] and also that E = mc^2,
E = 0.83 * solar mass * c^2 = 1.48e47 J = 1.48e32 PJ = 3.7e31 BLoC
which allows us to truly appreciate the order of magnitude in question.
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That said, relative composition IS different; Jupiter has a dense rocky core of heavier elements (the same sort of stuff the inner planets are made of), surrounded by metallic, liquid, and gaseous hydrogen and some helium. The sun is almost completely made of hydrogen and helium, with a reside
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* That wouldn't be a great idea, since they were trying to help Europa's life. I bet 87 times bigger would be big enough
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I thought we knew that decades ago. (Score:5, Funny)
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So what? (Score:3, Funny)
Brown Dwarf? (Score:5, Funny)
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We've know the answer for a while ... (Score:1)
Orson Welles (Score:3, Funny)
Ironic.
For a little perspective... (Score:3, Interesting)
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That's kinda meaningless. I'm sure that from time to time nuclei in my immediate vicinity decide to tunnel close enough for fusion. But once something's that small, you simply ignore it.
Hmmm..