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Astronomers Find Star-Less Galaxy
Wohngebaeudeversicherung writes "Astronomers have discovered a galaxy about 50 million lightyears away from earth that appears to be composed entirly of dark matter. This galaxy, dubbed VIRGOHI21 is rotating like a real galaxy, at speeds only explainable through massive amounts of matter, thought no single visible star could be detected."
I suggest we donate one of our stars. How about Ben Affleck?
...that I click on "Read More" to find out about matter that's invisible to us and all I get is:
"Nothing for you to see here. Please move along."
Brilliant.
"Backups are for wimps. Real men upload their data to an FTP site and have everyone else mirror it." -- Linus Torvalds
Astronomers have discovered a galaxy about 50 million darkyears away from Virgo that appears to be composed entirly of light matter. This galaxy, dubbed EARTHHI21 is rotating like a real galaxy, at speeds only explainable through massive amounts of matter, thought no single dark mass could be detected."
MORTAR COMBAT!
Aha! It's intelligent life! They must have engineered millions of Dyson Spheres over all the stars of their galaxy!
Do you like Japanese imports?
My favorite part of the article: Someone thought that circling the invisible galaxy in the picture was a helpful move.
Personally, I think articles with discoveries this exciting need to be written with more enthusiasm
You are checking your backups, aren't you?
"Um, Bill? The lenscap is still on..."
>
Nope, Goatse Galaxies have Goatse Stars
Sheesh, evil *and* a jerk. -- Jade
...and it doesn't require exotic quarks, leptons, or baryons to work.
Okay, that's an enormous (and highly unlikely) exaggeration, but I *have* thought of an interesting possibility. A Dyson Sphere surrounding several stars (or in a Type 3 civilization, an entire galaxy) would block visible light - the problem is it would glow in the infrared, so it wouldn't really be dark. Black holes are dark, but they tend to fling stuff around, and matter sucked into them gives off bursts of energy before they disappear.
The solution: a dark bubble. At the center of our galaxy there is a supermassive black hole, which is (according to some estimates) roughly three million solar masses. A civilization putting a bubble around it would have 1 (earth) gravity a little beyond the orbit of Pluto, perhaps 40-45 A.U. or so. The problem is that you still would need to stick some stars around it to supply energy, and a Klemperer rosette would be pretty noticeable.
Well, light falling onto a blackhole blue shifts, increasing its energy. Increase the bubble enough (remember, we're talking a civilization that can harness the energy of a galaxy), and the mass of the bubble itself starts to warp space around it. There comes a point where the size of the bubble and the mass that makes it up can be just under the Schwarzschild limit - a bit more massive and it would be a black hole - even without a central singularity. For humans, we'd want a bubble that has a surface gravity equal to earth's, and a blue-shifted energy equal to the average output from our sun.
As a back-of-the envelope calculation, using v^2=2*g*R, where v is the escape velocity, g is the gravitational attraction at the earth's surface, and R is the radius from the center of mass, and setting v=c (the speed of light) for the maximum size, you get a bubble with a diameter just a bit under a light-year across (354 light days, if I figured correctly). The surface area would be about 3 square light-years, 2.6 x 10^26 square kilometers, or 5.2 x 10^17 times the surface area of the earth. The mass would be equivalent to 1.5 trillion suns - roughly twice the mass of our galaxy. Assuming you use buckytubes as the material of choice, you'd have a shell 7000 kilometers thick of solid buckminsterfullerene.
Of course, this is the absolute maximum size and mass just before it becomes a black hole, so the actual construct would be a bit smaller and less massive, balancing surface gravity and blue-shifted energy hitting the surface. You'd also want to carve out mountain ranges and oceans for a bit of variety - a galactic Kansas would be kind of boring. For safety reasons, you would have to stick these bubbles in the empty space between galaxies, or just use all of the mass in one large galaxy (you'd have to be careful, though, to keep relativistic rocks from flying at the completed project). You'd have a sky that would look kind of like a slow-moving aurora, perhaps -- infrared would be shifted into visible light, visible stars would have their peak shifted to ultraviolet -- especially since the gravitational warping would slow down time considerably compared to the rest of the galaxy.
To detect them, you'd have to aim telescopes at the "empty" parts of the sky and see if there was any gravitational lensing. If something was there that was far too massive to be a neutron star but didn't have the characteristics of a supermassive black hole, that could be a sign of it. The largest ones would have the gravitational mass of a large galaxy, so if a supercluster appears to be missing a galaxy's worth of stars that stellar motions demand, it might not be exotic matter but instead bubbles of normal matter from some vast engineering project.
Of course, it might be too early in the evolution of the universe for a type 3 civilization to appear, or you might not be able to make a buckytube bubble big enough that would also support its own weight, so exotic forms of matter might still be necessary. One thing's for certain, though - a bubble like this would make Ringworld look as spacious as a phone booth.
It doesn't have anything to do with black holes.
If it was a black hole, it would be detected by the movement of visible objects around it, or x-ray and gamma-ray bursts from acceleration jets and from energy emitted by the accretion disk.
Dark Matter is simply "missing matter", or matter that cannot be detected through emitted radiation. It can, however, be detected through its (gravitational) effects on surrounding bodies.
Vivin Suresh Paliath
http://vivin.net
I like
It was easy to disprove the existence of aether with the Michelson-Morley experiment. Had that experiment not been possible it would have been very premature to jump to the conclusion that there is no aether. When it comes to dark matter, there is no easy experiment to disprove its existence and so it would be very rash to conclude that our understanding of gravity, which has worked extremely well for us for hundreds of years, is wrong.
No, the speed of dark is still unknown, but it is expected to be a lot faster than speed of light. Because where ever the light goes, the dark is already there waiting for it.
Having never seen an invisible galaxy before, I'm glad they circled it...
Sometimes I get the feeling that scientists are just fucking with me.
No, black holes by themselves do not emit light since nothing can escape from beyond the event horizon. The light is just a small part of a large range of electromagnetic radiation released by the black hole. This radiation comes from the accretion disk around a black hole, where matter that is spiralling into the black hole starts heating up immensely due to friction. Occasionally, matter escapes (from above the event horizon) in the form of bipolar acceleration jets. Scientists are not sure exactly why this happens.
The other form of radiation emitted by black holes is Hawking Radiation. Space is teeming with particle-antiparticle pairs that are constantly created and annhilated. In the vicinity of a black hole, one member of the pair can be sucked in (consequently annhilating its evil twin inside the black hole) while the other escapes. This gives the impression of the black-hole emitting radiation. Hawking came up with this theory when it was found that black-holes have temperature. That would seem preposterous since it means that the black hole was emitting energy, which it shouldn't.
Vivin Suresh Paliath
http://vivin.net
I like
Congressman (skeptical): Well, I dunno...I don't really see anything there.
Astronomer: Oh, one moment...let me circle it for you!
Congressman: Yes, yes I see it!
Astronomer: Now I was wondering, Congressman...how much additional funding might we get for this discovery?
Congressman: Hm. I'm not sure we have additional funds for such an admittedly amazing find. Now, if you had TWO dark matter galaxies, we'd have something to discuss.
Astronomer (uncapping pen): Funny you should mention that...
...with my tax return?
IRS Auditor: We've added up all of the income your employers have reported for you and it is much greater than what is reported on your tax form. How do you explain that.
Me: While you can usually detect income through tax forms, some types simply don't register. I believe that it is called...dark income.
IRS Auditor: I believe that it is called...tax evasion.
Me: gulp...
Some common objections to dark matter I constantly see whenever the topic comes up on Slashdot:
...
Can't dark matter just be brown dwarves or black holes or something? Why do scientists postulate crazy exotic invisible particles?
Dark matter is postulated to come in two kinds, Massive Compact Halo Objects (MACHOs) and Weakly Interacting Massive Particles (WIMPs). MACHOs are things like brown dwarves, etc.; WIMPs are the new kind of matter. We have already detected some MACHOs through gravitational microlensing experiments (looking for them by how they gravitationally deflect light). But if all the dark matter were MACHOs or something else mundane and baryonic, we would have detected more of them by now. That leaves WIMPs. Also, MACHOs and WIMPs have different physical properties (e.g., they cluster differently, and thus seed the formation of the large-scale galactic clusters we see today in different manners), and an all-MACHO universe doesn't cluster right, though it works out if you let some WIMPs into the mixture.
Ordinary neutrinos don't do the trick, either; we evidently need some new kind of particle. We don't know what WIMPs are, but some have postulated axions, neutralinos or other supersymmetric particles, WIMPZILLAs, solitons, sterile neutriono (that only interact gravitationally),
Dark matter is unscientific; it can't be tested or falsified.
Dark matter theories can be tested indirectly by observing the different predictions they make for galactic rotation curves, early-universe structure formation, cosmological expansion, etc. Already such observations have excluded a number of dark matter theories. And there are experiments underway that try to directly detect them, similarly to how we detect neutrinos.
Dark matter is just epicycles all over again, a fudge factor to preserve a wrong theory of gravity.
Once upon a time, irregularities were noted in the orbit of Uranus. It could have been postulated that the laws of gravity were wrong. Instead, it was postulated that an unseen bulk of matter was perturbing Uranus's orbit. Eventually, that bulk of matter was seen: the planet Neptune.
On the other hand, once upon a time, irregularities were noted in the orbit of Mercury. It was postulated that maybe a new planet caused them (Vulcan), but that turned out to be wrong; instead, a new theory of gravity was needed (general relativity).
The moral: you can attempt to explain away the observations with either dark matter or a new theory of gravity; both are scientifically valid approach. The problem with the latter is that it has proven extraordinarily difficult to produce a modified theory of gravity that is consistent with all observations, whereas there are dark matter theories that appear to do the job. Believe me, scientists don't ignore the possibility of a new theory of gravity any more than they ignore the possibility of a new type of matter; it's just that new theories of gravity don't seem to work as well as new theories of matter in explaining the observations.
What about MOND?
MOdified Newtonian Dynamics is the leading candidate for a non-dark matter alternative, modifying the laws of gravity. (Note that this page is by MOND's inventor, and may be biased.) However, it has had trouble with a number of observational tests; you can search the astro-ph arXiv for critiques of MOND. In particular, although it seems to work for galactic rotation curves, it's hard to get it to also work for cosmological expansion and structure formation. It's also very difficult to make it into a theory compatible with observed tests of relativity.
What about Bekenstein's MOND theory?
Bekenstein recently proposed a relativistic version of MOND called
I'm sure I speak for many here when I say I was extremely reluctant to click on that link.
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- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
Still seeing only "clusters" of stars? Check out this view from our old friend Hubble!
This image and the TERAbytes of data like it that have been collected over such a short time are testimony to why losing Hubble is going to be such a tragedy -- whether or not we understand or accept the reasons it's going to happen.
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Only on Slashdot will you see calculations for accelerating a Dyson sphere with starlight so you can go visit your girlfriend in another part of the galaxy.
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