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The Starry Sky Just Got Starrier
An anonymous reader writes "Astronomers have surveyed eight elliptical galaxies, and found that we've vastly underestimated the number of dim red dwarf stars in these giant galaxies. When they used the new number of red dwarfs in their calculations, they tripled the total number of known stars in the universe."
dark matter much?
It's full of three times the stars.
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dark matter much?
Apparently less :)
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To phrase that as a real question: What effect does this discovery have on the current estimates of the amount of dark matter in the universe?
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Good question. Assuming you are asking something along the lines of "How does this finding effect the ratio of dark to regular matter?" My guess is, not much, because I don't think the ratio ever really depended on observations of stars, per se.
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Really? I thought that they used gravity to determine the approximate mass of the galaxy, and then subtracted the amount of visible matter to yield the amount of dark matter. If that's how they did it, then increasing the amount of visible matter would have to decrease the amount of dark matter.
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Good question. Assuming you are asking something along the lines of "How does this finding effect the ratio of dark to regular matter?" My guess is, not much, because I don't think the ratio ever really depended on observations of stars, per se.
What was the need for there to be dark matter in the first place? Wasn't it invented as a concept to explain why the universe is the way it is assuming it has a specific amount of stars in it? Has anyone proven that dark matter exists or is it just a convenient kludge to make a model of the universe fit observations?
If they discovered that there are 3 times as many stars as previously believed then what purpose does the concept of dark matter serve?
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Non-baryonic dark matter has to exist in order for certain observations made on the cosmic background radiation to make sense. Basically, the Big Bang couldn't have happened without it. There's a lot more to it than just missing mass.
As for evidence, there's enough to infer it exists, but its exact composition remains elusive, so far as I know with my layman's understanding of this stuff.
Minor corrections:
- Not only the visual spectrum, but the entire electromagnetic spectrum.
- Black holes are also added to the baryonic matter count, and their masses are estimated based on their effect on observable matter. For faraway objects, one can assume that the number and sizes of black holes compared to visible matter is lower than the ratio in our neighbourhood, simply because faraway galaxies are much younger, giving black holes less time to appear and grow.
Anyhow, I see this as good news for our descendants. Red and brown dwarves are likely better targets for extrasolar exploration than bigger stars are.
They don't determine the mass of a galaxy by counting stars.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
it's more full of stars!
> True, Dark Matter, like Dark Energy, is just a placeholder name for something that we _think_ is there.
FTFY.
Probably will get modded down, but if you "knew" it, then you would be able to prove it exists. Since no one has seen it, touched it, tasted it, smelt it, or felt it, therefore it is a mathematical kludge, aka, the aether of the 1900s. (Yes, I'm aware of http://www.nasa.gov/home/hqnews/2006/aug/HQ_06297_CHANDRA_Dark_Matter.html )
Ergo, while said more politely, "it falls out of the math", which will allthough appear quite reasonable at first, given the current limitations of understanding gravity / light / mass & energy, it is still one a big hack-job based on one assumption after another, namely:
a) that there is only one type of gravity and
b) gravity is universal (which is a little preposterous / pretentious to base how the WHOLE universe works based on one tiny little planet.)
c) redshift is accurate (ARP has interesting evidence that calls into question this assumption)
This prof. provides a half-decent summary though:
http://zebu.uoregon.edu/1999/ph123/lec08.html
I believe this is one piece of very strong evidence for some sort of pervasive weakly interacting massive stuff. Two galaxies collide. The normal matter interacts with other normal matter and slows down, The "other stuff" does not interact, and keeps moving. We know it is there because it creates a gravitational lens. If the lensing were caused by any sort of matter that interacted with other matter, these lenses would not be located where they are.
So the theory of Dark Matter is more than just "there is more stuff than we can see." We can see specific phenomenon that normal matter just can not produce.
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
Actually, last I heard it was 5 to 1. So those tiny stars and any rocks orbiting them could have a bigger impact on those numbers than you think.
The best evidence is that, by observing galaxy rotations, it seemed like the galaxies needed to be about 80% dark matter for the rotations to make sense (there were several competing theories at that point). Then the CMBR observations pegged the composition of the universe at that early time at about 80% dark matter. The unrealted theories agreed to a couple of significant digits, which pretty much settled the matter (as much as anything in cosmology can ever be known).
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Since they can make predictions with it, and have tons a data supporting there is an effect going on, you're wrong.
"Since no one has seen it, touched it, tasted it, smelt it, or felt it."
the same can be said for gravity.
Now if you added 'measured it' then it couldn't be said for gravity. Of course then it couldn't be said for dark energy and dark matter.
a) There is no evidence of any other kind. Should some good evidence actually come in, then great.
b) Every measurement we have made using our understanding of gravity seems consistent. Again, if there is actual evidence of something else, then thing will change.
c) interesting evidences doesn't matter, strong* evidence does.
Your post shows a large amount of ignorance on this matter, and ignorance on the scientific process.
*no pun intended.
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No, it's out there. Things like the bullet cluster pretty much prove that there must be large amounts of some sort of weakly interacting matter. Basically, two galaxies collide. Normal matter in one galaxy interacts with normal mater in the other, slowing it down. But something massive wasn't slowed down and kept right on trucking along the same path at the same speed as before. We only know it is there because of the gravitational lensing it produces. So, we have direct evidence of matter that we can not see, and that does not interact with other stuff except through gravity. Call it whatever you like, it's out there. And that is just one piece of evidence. Galaxy rotation and the CMB are others.
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
From Popular Science you can read:
" 'Within these galaxies, a good chunk of the mass that had been ascribed to dark matter is probably stars,' said Pieter van Dokkum, the lead researcher on the project."
So I bet "a good chunk of the mass" is a bit more than "a minor change".
But we will probably soon get an exact new ratio after the smart guys have made new calculations, other than any of the above.
Five to one or twenty to one, you still have a significant amount of mass.
Then, as you mention, you have to add all the hard to detect planets for another small fraction. (If weren't seeing the star you can bet they weren't measuring its wobble). Admittedly its probably a small addition relative to the stars themselves.
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Nice, more stars.
can't wait to take my telescope out and look at them.
wait, what?
Be seeing you...
Bah.
Postulating Dark {Matter, Energy} is the height of hubris, since it implies that Astronomy Has Seen All There Is To See from our tiny little glasses on our tiny little rock in a backwater arm of the Galaxy.
Thank The FSM that there are still a few rational scientists out there actually *looking* for stuff.
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By that standard virtually all of science is based upon hubris as we haven't actually discovered everything there is to discover before coming up with hypothesis to test. By that measure it was arrogant of people to come up with the second without realizing that relativity is involved and that time doesn't exist at 0 kelvin.
Now, if you want legitimate arrogance, just look at those guys with their "string theory." It's been decades and they still haven't managed tho have a single testable hypothesis coincide with their ideas. A lot of things look good on paper as theory and then completely disintegrate when applied to the real world.
To say the sky got 'starrier' would imply that more stars are there than before...
No, it means there are more stars than we knew about before.
It's just the opposite, Dark Matter is something we know we haven't seen, yet. It is a way to measure the "unexplored".
It's like saying that I know that of 20 persons in this room I can see 5 (and I can describe them).
If I have some way of knowing (gravity for example) that it must be equal to 20 persons, I can call the missing persons Dark People. They might be 15 normal people, its just that they are behind stuff (my self for example) so I cant see them straight on. I might catch a glimpse in a reflective surface and so on. But I might also have a number of persons and the rest are dogs, just because I haven't seen a dog doesn't mean there aren't any.
So Dark Matter might be known stuff (new stars like this) or unknown stuff (like the dogs).
Really dim baryonic matter would only explain some of the many different lines of evidence.
I don't really have a horse in this race, I mean, I could care less which theory turns out to be correct. It just seems like the preponderance of evidence points to a non-baryonic source of mass at this point.
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
That reminds me. There's a few wags at my institution who like to send examples to a certain mailing list of kookie religious people being kookie. Someone posted a discussion on a Christian web site of some fundamentalist "physicists" talking about how the reason regular physicists had to invent dark matter is because they weren't taking into account the mass of Heaven and Hell.
I am not making this up. When I get time I'll try to find the link and I'll post it to a journal here. Some of you godless heathens might get a kick out of it.
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Not quite. It's just matter we haven't seen and so can't account for, if we have the mass estimates for the universe right, which is in itself doubtful. For instance, a small galaxy directly behind a large one in a position that doesn't allow us to see it -- that's "dark" from the dark matter point of view, even though it's glowing like crazy. Some of it might not be radiating, or radiating too dimly; but on the other hand, our math may just be entirely wrong.
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Postulating Dark {Matter, Energy} is the height of hubris, since it implies that Astronomy Has Seen All There Is To See from our tiny little glasses on our tiny little rock in a backwater arm of the Galaxy.
Thank The FSM that there are still a few rational scientists out there actually *looking* for stuff.
There are observations that have been made which cannot be explained by any quantity of unseen "regular" aka Baryonic matter. This is the result of people actually looking for stuff, and not in their hubris assuming that we have Seen All There Is To See. Indeed it is very much a case of realizing that we have not seen it all.
Hubris is dismissing (the non-Baryonic subset of) Dark Matter because it's not the same as the "regular" matter we are familiar with in a much more extreme case of assuming we have Seen All There Is To See. Red dwarfs are nothing new; and you're strongly implying you think such examples of normal objects will explain away the need for Dark Matter, as in we won't find anything new. We Have Seen It All.
Even though what astronomers have seen strongly suggests that is not true, and there is stuff out there completely different than what you are comfortable with.
It is kinda funny how often people give "arrogance" as the reason why scientists put forward certain hypothesis when they are completely unaware of the actual scientific reasoning behind the hypothesis. By attributing arrogance to others as a consequence of their own ignorance, they demonstrate tremendous hubris.
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The galaxy rotation problem is basically this: Stars towards the edge of galaxies (mainly spiral galaxies) rotate much faster than they should based on Newtonian gravitation using only the visible material (the Einstein corrections are negligible at the speeds and distances being talked about, so they can't account for the differences). To explain this, you have basically two options: MOND, MOdified Newtonian Dynamics (ie., changing the laws of the universe at large distance scales like kiloparsecs), or dark matter (which can include baryonic dark matter as well, but generally refers to non-baryonic things), which corrects for it by assuming that there's a vast halo of objects that outweighs everything else in the galaxy and thus speeds up the rotation of objects far away from the galactic core.
The evidence at the moment seems to be in favor of dark matter, and in any event I have some doubt that we will ever see "examples at the same scale of pure baryonic matter interactions" as you put it; it may be that the phenomena in question are simply things that appear on the very large scale and aren't observable on the small scale, just the same way that relativity only becomes important under certain conditions and Newtonian dynamics works perfectly well in our "normal" world. (But I'm not an astrophysicist, just aiming to be one!)
Rocks that orbit the stars are irrelevant for the purposes of mass calculation. All the mass in our solar system that isn't the Sun or Jupiter is less than Jupiter. Jupiter's mass is less than 1/1000th of the Sun's. Granted, our solar system may not be representative of other star systems, I bet it would be. Due to the process of stellar formation, there's always a shit-ton more Hydrogen and Helium than anything else.
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Dark matter and dark energy are two totally different things. They're placeholders for vastly different phenomena. Dark matter explains why galaxies rotate at the speeds they do, even though their visible mass is much, MUCH, lower than the spinning speed shows it should be. Dark energy is the pressure that's causing the universe to accelerate outward. The universe isn't just expanding, the rate of the expansion is increasing, not decreasing as you would expect. Some force is being exerted on the fabric of the universe that's causing it to expand at a faster rate every second.
So, to recap:
Dark matter = mass that's causing galaxies to spin faster than they should be
Dark energy = force that's pushing the universe apart
Learn something new.
Before Van Dokkum wrote his paper, the DM/DE proponents thought they'd found all the matter there is to find.
No astronomer thought they had found all the normal matter there is to find. In fact the search for dim red dwarfs in specific was part of trying to answer the Dark Matter mystery -- which originally only meant matter we had not seen yet, and only came to mostly refer to non-Baryonic Dark Matter when observations suggested that most of it was.
In fact, would you believe that when "DM Proporents" estimated the amount of non-Baryonic matter and added it to the known visible matter in galaxies, they still saw a discrepancy in observed gravity in elliptical galaxies? And that finding more normal matter was one prediction to explain it, and in fact this new observation may end up explaining the difference, solidifying our calculations of dark matter.
Suddenly there's 3x more. Which is a slight reduction in the need for DM.
3x the stars is not 3x the mass (particularly when the discovered stars are red dwarfs), but regardless...
Who's to say that in 1-20 years other heretics find 10x more baryonic matter, thus reducing even more the necessity for DM.
Indeed, who's to say? But as long as there are observations that cannot be explained by baryonic matter, it will be necessary.
I really like the characterization of this researcher as a "heretic", btw. I like it because this "heretic" was given access to the Keck Interferometer -- the combination of two of the largest telescopes in the world and thus a highly sought-after instrument -- in order to conduct his research. And then said research was published in Nature.
Because that's how we do things in science: we invite the "heretics" to make observations and disprove our current theories and hypothesis so we can create even better ones. They are not shunned, they are not shut out from access to the tools they would need to prove themselves,. Quite the opposite. Indeed, quite the opposite of a "Church" and "heretic" relationship. Which is why it's funny.
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The big bang is just hand-waving at this point in time.
Hand-waving, one of the most successfully predictive theories of the last century, these are both the same. I'll make them seem like they're both the same by... wait for it... waving my hands.
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Me neither. But it really seems odd that so many Slashdotters are so rabidly against the idea of dark matter.
The story of humanity is full of whole chapters which basically boil down to a bright spark being smothered by a bunch of ignorant fuckwads attached to their idea of how the world works. Every once in a great while the spark lands in a pile of tinder not in the furnace-equipped basement of a firetrap and something wonderful is born, but mostly people shun what they don't understand and it's their children or their children's children who are willing to incorporate it into their lives as an escape from the previous generation who doesn't "get it". This is why the technological singularity is the religion most appealing to the technological elite...
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It probably depends on what you're talking about really, from WP:
dark matter accounts for 23% of the mass-energy density of the observable universe, while the ordinary matter accounts for only 4.6% (the remainder is attributed to dark energy).[2] From these figures, dark matter constitutes 80% of the matter in the universe, while ordinary matter makes up only 20%.
So ordinary matter accounts for 4.6% (1/20th) of all mass+energy in the universe - this I suppose has to do with Einstein's E=mc2 that allows for mass to be converted to energy and the other way around. And looking at actual mass, not taking the energy into account, this would end up at 1/5th. So both numbers are in a way correct, depending on context. I thought actually it was about 90% dark matter, so let's call that number the average. Then at least I'm not wrong myself.
Now I don't really know what they mean with the "dark energy" part or how that's measured, the "dark matter" I understand somewhat as it has to do with gravity.
Anyway this whole "dark matter" thing sounds to me like the hypothetical "aether" - we don't know what it is so make up something to make the formulas work. So now we found that there is 3-4 times as much "visible" matter in our universe than we thought before. Oh well that's quite some "dark matter" that has come to light. I'm quite sure the rest will follow sooner or later.
The human mind just can't really cope with large numbers. The universe is just so shockingly enormous, on the order of 10^80 atoms.
However, this is a tiny number in comparison with others. The number of possible chess games is on the order of 10^123. You'd have to encode 100000000000000000000000000000000000000 games of chess into a single atom to store every possible game.
Of course, you'd need 10^183,800 monkeys to write Hamlet on the first go.
These number all seem the same to me though, on the same order of 10^50 (number of atoms on the earth)
[rollseyes] Oh, please. Horizon problem? Doppler problem? CMBR problem (well, two of them, really)? Anti-matter problem? Dark matter / energy fudge factor / problems? Large scale void problem? Speaking of fudge, inflation? Really? Distant young galaxy problem? And the really big one, the singularity: BB theory doesn't actually oblige us by conforming to what we know about physics. It's just a math model, and it looks a good deal more like dividing by zero than it does 2+2 at this point in time.
I really don't think "successful" in this context means what you think it means. When a theory is riddled with errors and wrong predictions and fails to match the available evidence, "success" isn't exactly the word of choice, even if it's been fudged (and that is the correct word) to match some, though certainly not all, of the observations.
I guess since you can't refute the physics (specifically the fact that our physics don't allow for any of the early stages of what the big bang hypothesis describes), I'll just have to watch your hand-waving. But someone should really sit you down with a cosmologist someday and explain all this to you. It's pretty simple, really; you can only fit so much in a particular amount of space. BB theory doesn't actually work because of that slight inconvenience. So, no matter what it predicts, and no matter what it gets right, something else is wrong: Either it's the theory, or its the physics. But again, you need to hear this from a cosmologist. Or perhaps read up on it a bit.
You'll note I don't refute BB theory. I just point out that it is far from settled. Hilarious that you were knocked so off kilter by that, and even funnier that some slashdot moderator came in here and pulled a "moderator disagrees." Sometimes this place is just a circus of the incompetent. Other than that moment of fine humor, though, how have you been, Chris?
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Every alternative theory to dark matter explains *less* of the observations than dark matter does (typically only one thing ie galactic rotation, but not CMB or large scale structure). Like or love it, its the best theory that fits the data that we have. And despite the fact that its wasn't well like for a long time, a better theory just have not been put forward.
If information wants to be free, why does my internet connection cost so much?
effect does this discovery have on the current estimates of the amount of dark matter in the universe?
The what?
The term "dark matter" on its own, unless you an scientist using it in a specific context, is not meaningful. When a layperson uses it as you have it is meaningless.
You have to specify which dark matter you mean. There is "missing matter" at all distance scales above some relatively modest threshold, but there are quite different constraints on what it might be depending on the scale you're observing.
When anti-scientific nutjobs on /. bitch out the purported arrogance of scientists who postulate "dark matter" they never mention which "dark matter" they are talking about, which does nothing but demonstrate their profound ignorance of the issue.
Galactic dark matter, which is what is relevant to this discovery, is potentially entirely baryonic. That means it could be made of the same stuff we are.
But the H/He ratio in the early universe, and other primoridal isotope ratios that we can estimate quite well based on numerous observations and very solid theory, puts a strong limit on the amount of baryonic matter the universe can contain.
Ergo, at larger scales there is evidence for non-baryonic dark matter, which is a quite different animal, and warrants more skepticism.
There is also "dark energy" on the largest scales, which acts as a cosmological constant and which personally I'm a good deal more skeptical about.
People who are dismissive of all dark matter hypotheses but who do not understand the different roles that different types of dark matter and dark energy play in different theories at different scales are simply enemies of scientific inquiry.
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