dark matter - "dark galaxy" found!

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foxy

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Jul 4, 2002
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Just found out today that radio astronomers have found the first ever galaxy (VIRGOHI21) composed entiredly of dark matter! For those that don't know dark matter was proposed originally to explain why galaxies rotate and move apart from each other much faster than can be explained by the visible amount of matter they contain.

Anyway it was found by a team of astronomers led by those at Cardiff University in the UK UK UK UK (cheers) using the Lovell telescope at Jodrell Bank. They found it using a technique where astrophysical objects are detected and analysed by looking at their hydrogen content only (this allows places where no large objects such as stars exist to be looked at - big advancements in this field recently).

They found it in the Virgo cluster (about 50million light-years away). It is rotating as a normal galaxy but but doesn't contain any stars or black holes. There is a cloud of hydrogen atoms there 10^8 times heavier than our sun. Robert Minchin and his team at Cardiff and co-workers in Italy, France and Austrailia have studied the galaxy in detail and all agree the galaxy is 1000 times more massive than can be accounted for by the hydrogen it contains! This was done by looking at the gravitational field etc around it - nothing at visible wavelengths of light have been deteced as would be if it were a normal galaxy! No stars detected, dead or otherwise. Nothing like this has been found ever before, the only similar things turned out to have stars or debris from nearby optical galaxies in them.

fs this is exciting :) Me goes to find the published paper - it's in Astrophys. J. 662 L21-L24 for any interested fellow scientists with access to that journal.
 
wasnt dark matter just something that the physics boffins made up so that all there calculations about the universe actually worked? or am i thinkin of anti-matter. hmm my head hurts and uni is finished so im off to pub :D
 
Cant believe they finally found some (illusive) dark matter... about time!
I bet all those scientist proclaiming dark matter is real were getting nervous because nothing was found and they would look silly, I'm sure they are quite relieved.. ;)
 
I am just wondering. I heared somewhere the galaxy/cosmos is expanding as we speak/chat/forum/wahtever.
Isn't everything 'stretching' out that way?


foxehh said:
They found it in the Virgo cluster (about 50million light-years away).
Click to expand...

If the galaxy would be expanding (getting bigger ;x), those light years change aswell?
 
And a second note: U say it is 50 million light years away. Isn't this old news for us? This stuff happened 50 million years ago ?
 
Hmm where to start.

It's true that things we observe now that are 50million light years away look as they did 50million years ago...just because the light from them takes that long to reach earth....the same is true even of our Sun...when you look at the sun you actually see it as it was 8mins ago (takes about 8mins for light to reach us from sun). Many of the stars you see in the sky might have actually blown up and diasappeared millions of years ago.

This isn't really a problem though and due to the vastness of the universe it can't be avoided. Quite the opposite it is very usefull. Look at galaxies very far away and you can see close to what the universe was like very early on, look at closer ones for a more recent picture. Loads is/has/will be learned in this way about how stars/galaxies etc change as they mature. If the universe wasn't so big this wouldn't be possible, as it is we can see billions of years of history all at the same time in the sky...amazing...well I think so.

As for the universe expanding: yes it does and after various discoveries regarding Neutrinos recently it is generally accepted that it will expand and cool for trillions of years untill the background radiation becomes so low that black holes will start to radiate matter rather than absorb it (oops tangent, don't get me started on physics stuff lol!). Ok so galaxies that are close to each other eg our milky way and andromeda actually are getting closer due to their gravity. (Galaxies often collide because of this - in fact that is why our galaxy is spiral shaped - because at some point in history another galaxy collides with us). But almost all other galaxies are moving apart from each other. Also galaxies further away are moving faster, for example two galaxies I was looking at recently, Hydra which is 4000LY away is moving at 65,000km/s away from us whereas Corona B. which is 1800LY away from us is moving at 25,000km/s. This agrees with the linearity of Hubbles law. As with all things the Universe is evolving all the time. (numbers are from memory and are quite approximate).

In case you are interested I'll tell you how the speed of galaxies is measured - it's done using the doppler effect. A good example is a F1 car screaming past you: as it gets closer to you the sound is quite high pitched then as it passes you and gets further away the sound gets lower. This is because of the relative spped of sound and the car as it gets closer to you the sound waves are closer and as it moves away the sound waves are further apart. Anyway the same effect can be observed in electromagnetic waves such as light waves. By looking the light spectrum from galaxies different distances away you see the further away a galaxy is the more red it is (the light waves are redshifted as the wavelength is greater) closer galaxies are less red. This redshift can be measured and used to calculate the speed of even very distant galaxies.

Doppler effect is ace...I remember lying on my back in St Andrews years ago in a field near Lucas airbase. Suddenly a fighter jet absolutely belted past at low height...nearly had a heart attack. But there was no sound and I hadn't heard it coming...weird seeing a massive plane right above you making no sound....until 1 second later and I heard a deafening roaring sound of the engines. This meant the jet was travelling at supersonic speeds - it was travelling towards me faster than the sound it was making so I saw it before I hear it...if you look into the doppler effect more closely you can see why you get the supersonic boom when something breaks the sound barrier. Fs off on a tangent again lol.

Yeh what was the point again.....ah yeh....so what you say is true sneez but since the universe is so big it doesn't matter. A galaxy sized "blob" of dark matter 50million LY away won't have an "apparent" motion in the sky fast enough that it will cause a problem or indeed be discernable. As for the time 50million years is not that long in terms of the age of the universe so when we are trying to understand the universe it is not bad it's good that we can look at very old and very new celestial objects at the same time. Hope that answered your points there sneez.
 
sneez said:
And a second note: U say it is 50 million light years away. Isn't this old news for us? This stuff happened 50 million years ago ?
Click to expand...

foxy said:
As for the time 50million years is not that long in terms of the age of the universe so when we are trying to understand the universe it is not bad it's good that we can look at very old and very new celestial objects at the same time. Hope that answered your points there sneez.
Click to expand...

Guys, a Light Year is a measure of distance, not time. Specifically, it's the distance that a particle of light travels in a year. Approx. 5,878,668,575,518 miles.
 
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