Posted on 06/14/2007 8:50:35 PM PDT by annie laurie
An international team of astronomers have conclusive new evidence that a recently discovered "dark galaxy" is, in fact, an object the size of a galaxy, made entirely of dark matter. Although the object, named VIRGOHI21, has been observed since 2000, astronomers have been slowly ruling out every alternative explanation.
In a new research paper, entitled 21-cm synthesis observations of VIRGOHI 21 – a possible dark galaxy in the Virgo Cluster, researchers provide updated evidence about this mysterious galaxy.
They have now performed a high resolution observations of VIRGOHI21 using the Westerbork Synthesis Radio Telescope (WSRT), to better pin down the quantities of neutral hydrogen gas. They also did followup observations with the Hubble Space Telescope, looking for any evidence of stars.
Astronomers first suspected there was an invisible galaxy out there when they spied galaxy NGC 4254. This unusual-looking galaxy appears to be one partner in a cosmic collision. All the normal evidence is there: gas is being siphoned away into a tenuous stream, and one of its spiral arms is being stretched out.
But the other partner in this collision is nowhere to be seen.
The researchers' calculated that an object with 100 billion solar masses must have careened past NGC 4254 within the last 100 million years, creating the gas stream, and tearing at one of its arms. This was the clue that an invisible dark matter galaxy might be lurking nearby.
A detailed search turned up a mysterious object called VIRGOHI21, located about 50 million light-years from Earth. Were it a normal galaxy, you would be able to see it in a powerful amateur telescope. But there's nothing there. Even in the Hubble Space Telescope, not a single star is shining from this massive region of space.
It was only visible in radio telescopes, which could detect the radio emissions from neutral hydrogen gas located in the cloud.
When they first published their research a few years ago, the astronomy community was understandably skeptical, and proposed several alternative theories to explain the mysterious object.
For example, there could be additional mass associated with VIRGOHI21, and not just dark matter. The discovery of red giant stars in the region would give some indication that this was a more normal interaction. But Hubble turned up nothing.
Dr. Robert Minchin, lead researcher from the Arecibo Observatory, said, "not even the power of Hubble has been able to see any stars in it."
It's possible that VIRGOHI21 has always been this way, formed from primordial dark matter and neutral hydrogen after the Big Bang. It's been cruising the Universe ever since, disrupting galaxies as it goes.
However, there do seem to be ways that galaxies and their dark matter can be separated. Only a few months ago, a ring of dark matter was found surrounding a group of colliding galaxy clusters by the Hubble Space Telescope. Perhaps VIRGOHI21 is the wreckage from one of these cluster collisions; a shred of dark matter hurled out into space.
It could be that there are many of these dark galaxies out there. A new sky survey, carried out with the 305-metre (1000-foot) Aricebo radio telescope in Puerto Rico should tease out more of these objects in the future. The survey is called the Arecibo Galaxy Environment Survey (AGES).
This most recent paper has been accepted for publication in the Astrophysical Journal.
Why would I want to converse with someone not in charge of their own life? May as well talk to a toaster with attitude.
What's wrong with this question? Do you mean to say that 'dark matter' is every where in the universe but Earth?
L
I leave disappointed
youre welcome to the last word
.....yes, yes, I know, "dont leave disappointed...just leave"
the peanut gallery is yours for the evening
Cerebral vs creationism... nah. Too easy. You have a good night, and don’t forget to empty the crumb tray.
I guess you are better at theory than practical problem solving. In your scaled-down model, you neglected some very important physics concepts, namely the role of mass. If your example was even remotely correct, and dust motes have not graviational effeet on each other, then what is holding the galaxy together? And planets are a heck of a lot smaller than stars so what is keeping them in their orbits? Angels pushing stars and planets around?
No.
You failed to account for the scaled mass of the sun and the r^2 distance dependence of gravity. To model the scale experiment correctly, the mass of the sun-dust mote would be about 57 metric tons.
And if you were to have a dust mote sized model, why wouldn't there be any interaction? What other forced would swamp gravity? I don't know of any that have the same long distance effects as gravity does.
What's wrong with this question? Do you mean to say that 'dark matter' is every where in the universe but Earth?
L
Dark matter has mass, but it does not interact with regular matter. Sure, the stuff may be splashing through the Earth all the time, but since it has no interactions with regular matter, you'd never notice it except for effects related directly to mass. The only force mass can exhibit is gravity. You can't see it with light because it has no eletromagnetic interations. Same reason why regular matter can't capture or bond with it. It has no chemical interactions, which is based entirely on electromagnetism. It has no nuclear interactions either, other wise nuclear effects could be observed. The stuff appears to have only mass interactions.
So to answer the question directly, the stuff could be passing right through you and you'd never know it. It would never pile up on your carpet because there is nothing to hold it on your carpet. And you could not vacuum it up because suction, via air movements, would have no effect on it either.
It is only detectable by it's gravitational effects on matter. In othr words, we see things moving and the pattern of the motion indicates a gravitational effect of a certain magnitued and in a certain location, but there is nothing visible where it should be. Without dark matter, things in the universe would not be moving the way they are. These are highly quantifiable parameters that are involved and not some kind of guess.
So let me get this straight. It has mass, which means it must have gravity. Right?
The only force mass can exhibit is gravity
OK, so it has gravity. That must mean that it's attracted by gravity to other objects that have mass. Like my carpet.
The stuff appears to have only mass interactions.
OK I get it. Here's where you lose me:
It would never pile up on your carpet because there is nothing to hold it on your carpet
My carpet doesn't have gravity? Earth has gravity. My carpet is on Earth. Therefore my carpet has gravity. Therefore this 'dark matter' stuff must be on my carpet.
These are highly quantifiable parameters that are involved and not some kind of guess.
Bull. There's stuff going on you scientists can't explain so you made up this 'dark matter' hooey and pounded on your little theory hard enough to make it 'do' what you see happening. That doesn't 'prove' anything.
L
Mainly electrical and electromagnetic forces, which are many orders of magnitude more powerful than gravity.
The sun and Alpha Cent actually don’t have much of a gravitational effect on each other. But, there are 100 billion other stars and a lot of other things in the same system, so just looking at those two gravitating bodies would probably not give a satisfactory explanation of what is going on.
Apparently from what I read, even in the case of star clusters in which the light of the stars unifies, the distances between any two stars are not that much different than that between our sun and AC.
While most stars appear to be binary, that is, two orbiting their combined center of mass, most stars would be well beyond their relative escape velocities from most other stars. They all, inside the galaxy, orbit a center of mass; the problem: that mass is not a simple point center but some kind of figure like a disk. You might be interested in this from a math point of view. Dark matter is one possible explanation, but a modification to theory of gravitational fields is open to development.
Also, if '95%' of the Universe is this dark matter stuff, and the only quality it has is mass and gravity, how come we aren't all being crushed to death by stuff we can't see?
I mean eventually enough of the mass from this invisible, undetectable stuff would be drawn to Earth by our gravity that we would all be getting heavier over time. Right?
L
Although the mass represented by the dark matter hypothesis, and it is only a hypothesis, is large, it would only represent a few more stars in our neighborhood if we could see it. Most of near sunspace would still be empty.
If you wish to model the galaxy motion by individual stars you will quickly come to a computability problem, but if you model it by the gravitational field the problem is immensely simpler. Still, a modification to the inverse square format of the gravity field might also produce a solution. So, a chance to try some calculus.
Our solar system by all acounts works very nicely without dark matter and you have to assume that if you add dark matter equivalent to 20 times the mass of the observable bodies in our system into our system, the rest of it would cease working according to the mathematical models which Kepler, Newton et. al. so graciously provided us with.
What we have here is something like Cotton Mather's invisible world wonders or the emperor's new suit of clothes, i.e. the stuff is 95% of the universe EXCEPT in our own solar system where we could have any experience with it.
You really are pig ignorant about physics. So all of Newton's and Einstein's work is wrong! Laughable! Gravity is solely attractive. Mass is attracted to mass. Electromagnetic forces can be attractive and repellant. But for astonomical bodies on astronomical scales, it's all attractive forces that have been observed. In any system with more than 2 bodies, if electromagnetic forces were involved, then at least one body would be repulsive in nature!
Not only that but gravity is the dominant force over astronomical distances. The magnitude of a charged system, either electrically or magnetically, would have to be multiple orders of magnitude different than what actually exists in nature in order to have any effect. Only on very small scales does electromagnetism trump gravity.
No, that is incorrect. The scale is such that we would hardly notice dark matter accumulating on our tables and windowsills. Order of magnitude rules.
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