Astronomers Find Star-Less Galaxy

zavvy · Feb 23, 2005

Astronomers Find Star-Less Galaxy LINK Astronomers say they have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter. The team, led by Cardiff University, claimed it is the first to be detected. A dark galaxy is an area in the Universe containing a large amount of mass that rotates like a galaxy, but contains no stars. It was found 50 million light years away using radio telescopes in Cheshire and Puerto Rico. The unknown material that is thought to hold these dark galaxies together is known as 'dark matter', but scientists still know very little about what that is. The five-year research has involved studying the distribution of hydrogen atoms throughout the Universe, estimated by looking at the rotation of galaxies and the speed at which their components moved. Hydrogen gas releases radiation that can be detected at radio wavelengths. In the Virgo cluster of galaxies, they found a mass of hydrogen atoms a hundred million times the mass of the Sun. The mysterious galaxy has been called VIRGOHI21. Similar objects that have previously been discovered have since turned out to contain stars or be remnants of two galaxies colliding. However, the scientists from the UK, France, Italy and Australia found no visible trace of any stars, and no galaxies nearby that would suggest a collision. Dr Robert Minchin, of Cardiff University, said: "From its speed, we realised that VIRGOHI21 was a thousand times more massive than could be accounted for by the observed hydrogen atoms alone. "If it were an ordinary galaxy, then it should be quite bright and would be visible with a good amateur telescope." The astronomers say it is hard to study the universe's dark, hidden objects because of the Earth'

Saiph · Feb 23, 2005

that is cool, and disturbing. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

yevaud · Feb 23, 2005

One wonders if this sort of thing would explain the two "Great Attractors?" <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

zavvy · Feb 23, 2005

that is cool, and disturbing. Not to mention confusing. I always thought that, by definition, a Galaxy was a system containing stars... <img src="/images/icons/crazy.gif" />

astrophoto · Feb 23, 2005

Perhaps it's a galaxy yet to give birth to stars? Not yet coalesced? Very odd indeed. I have a hard time believing in 'dark matter' ... maybe we cant SEE it because its too far off and not lit by a star, but it is still just matter.

Saiph · Feb 23, 2005

well, it's galaxy like. They say it's rotating like a galaxy, as far as they can tell. Dark matter is a reality. Now, what it really is, is the debatable part. Large portions of it are definetely regular matter that isn't producing much light at all. Some of it is also likely to be various forms or arrangments of matter we haven't figured out yet. Unfortunately, doing that we can only, currently, explain 20% of the observed dark matter. so that leaves 80% unaccounted for. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Feb 23, 2005

right, at this point, and at that distance, it is about the age of the milky way. That means finding completely burned out stars is possible, but not likely (though we have, apparently, found ohters), and it still undergoing initial formation (very initial, no stars at all yet!) is also unlikely. The article indicates that the researchers see no evidence for it being a galaxy of burned out stars, though they wish to do further research. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

astrophoto · Feb 23, 2005

Hmmmm ... a bunch of really small black holes rotating around a central massive set of black holes...

claywoman · Feb 23, 2005

Please explain slowly and in little words an non-scientist can understand here....How, without stars, do they know there is a galaxy? How do they know with nothing to focus on, it is spinning or that anything, for that matter is spinning out there? Again, taking up the cry of another here, I thought galaxy meant full of stars....I'm so confused!!!

jatslo · Feb 23, 2005

Dark Matter does not reflect light, it absorbs light. This would explain why you are not seeing the few stars that exist. I do not understand why it is transparent though, I can see galaxies behind the object in question, as if I were looking through a window. You would think that the light from objects behind it would be blocked. But do not ask me, because I am just a Lepton ;o) --- Jatslo

tom_hobbes · Feb 23, 2005

Very intriguing Zav. Heard it on the news earlier. I'll see if I can get any extra details on Thursday at the SF group. I'll be seeing a friend from Joddrel bank, he's probably fairly up to date. jatslo, Do galaxies only appear opaque because of their luminosity? When dark, they may well be fairly transparent? (Shrugs, cluelessly.) <div class="Discussion_UserSignature"> I wish I could remember But my selective memory Won't let me - Mark Oliver Everett </div>

jmeyer · Feb 23, 2005

If a black hole has an entrance, could this be an exit? Perhaps portals, wormholes, etc... I know I'm stretching the imagination here, but this could really be any number of things. Pretty exciting. Personally, I'm hoping it's an alien colony with a lousy invisibility mechanism.

Saiph · Feb 24, 2005

To be fair, this isn't a galaxy as you normally think of it. It does, however, have the size and general behavior of a galaxy (so it's similar to a galaxy in many ways, and doesn't have a classification of it's own yet). The way they detected it is by using a radio telescope to observe the "21 cm line". Normally atoms emit, or absorb, light by electrons moving from one part of an atomic orbital to another. This usually means they need to be pretty warm, basking in the glow of a nearby star. When the electron shifts down (spontaneously, and randomly), it goes to an orbital with less energy, and the energy difference between the two locations (or states) is emitted as a photon. However there is a second type of transition, called a "fine" transition. As electrons orbit an atomic nucleus, they have a "spin". This can be up, or down. Each one has a slightly different energy, just as there is a different energy to regular orbitals, that are the source of normal light in the previous paragraph. Occassionally an electron in the "up" position will spontaneously flip, and go to the "down" position (this is the same spontaneous reaction that cuases orbital transitions normally), releasing a photon in the process. Since the difference in energy in this "fine" transition is so much less than the energy of a typical transition it has a much longer wavelength, of ~21 cm (thus the name). The key here, is no nearby star is needed to heat the gas. Normally you need a nearby star to give photons for the atom to absorb, moving the electron up, so it has a place to start from. For the fine transition the electron can already be in the lowest possible level, and then do it's flip. This means the hydrogen can do this in a very, very, cold environment. Add to it the fact that in a hot environment, the electron is likely bumped around by ambient photons, that it doesn't get a chance to do this flip. The flips h <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Feb 24, 2005

any stars that do exist could very well be obscured from our view by a shroud of dust (and/or darkmatter). It's not uncommon to see objects through galaxies, so that doesn't suprise me to much. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

jatslo · Feb 24, 2005

I don't know, maybe the light is arching around the object and our brains are filling the blanks, gaps, and what not. It will be interesting to analyze the light that appears through the looking glass, and compare it to something else. I bet the light is chalk full of holes. We could utilize what we learn and find others. I was analyzing that particular point in space for some time, and I saw numerous symmetrical points in space that were absent of anything. Could these areas of dark symmetry be others? Black Holes? Look at those Hubble deep view pictures, and you will see what I mean for yourselves. ---Jatslo

Saiph · Feb 24, 2005

actually studies have been done on the distribution of galaxies and such in various images. The findings are that they are distributed randomly, and in an isotropic manner (i.e. uniformly scattered, no overall clumping) when you get beyond the size of galactic superclusters. even the great voids, and strings of galaxies form in a random fashion, all over the place. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

bobvanx · Feb 24, 2005

I especially like the picture they've released, with an ellipse to show us where to look for what we can't see. Something very dada about that.

jatslo · Feb 24, 2005

This rule should be applied to incluse dark matter, as well? Go get em, I bet there are trillions upon trillions ;o) ---Jatslo

astrophoto · Feb 24, 2005

I am still not buying "Dark Matter" as somehow radically different, if at all, from normal matter. Can anyone explain to me the various proof we have for this theory and how it cannot be explained by Matter not emitting enough light to be visually detected?

j8hart · Feb 24, 2005

The article says “Hydrogen gas releases radiation that can be detected at radio wavelengths.” Which suggests 1) they know it’s there because even without the stars the Hydrogen has enough energy to emit in the radio frequencies, and 2) they are using the Doppler shift of the Hydrogen spectrum to prove that it is revolving. I.e. One side of the “galaxy” is turning towards us, the other away from us shifting the frequency of the hydrogen lines by different amounts depending on which side of the “galaxy” you are observing.

alkalin · Feb 24, 2005

Hydrogen is very very likely not the only ordinary matter involved in this swirl. It just seems so likely that we might be witnessing a creation of a new proto-galaxy.

Saiph · Feb 24, 2005

By looking at galaxies and how the stars move in them, we know there is unseen matter (or rather a source of gravity). Since it isn't giving off light (or we'd see it) we call it dark matter. The astronomy community has looked around and dredged up all the types of objects, and material that are very hard to detect (i.e. don't give off light) and figured out how much there is (extrapolated the figures). This includes cold hydrogen for instance. Brown dwarfs, quiescent black holes, and anything else we can think up. Unfortunately, even using optimistic estimates of how much there is, only accounts for 20% of the required dark matter. Some of it may be regular stuff, but that's a big difference. And so people are looking for anything else that will fill the gap (or remove the gap by modifying the laws of gravity via MOND). So do we say Macho's and Wimp's exist? No, do we say they may? Yes. Do we look for them, Yes. Have we found them? No. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

vogon13 · Mar 12, 2005

Was I the only one to think George Carlin will probably add this to his routine? You know the one, scientists discover a disease with no symptoms, archeologists find evidence of past civilization that left no artifacts, mathematicians discover a new number between 6 and 7, etc. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

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