More news from the IAU meeting: for the first time, astronomers have found direct — and to my eye, fairly convincing — evidence of dark matter. Indirect evidence is all over the place, but no direct evidence, until now, has been found.
Now I was gonna write all this stuff about the history of dark matter, and how they made these observations, and why this is not only terribly important, but also very, very cool– but then I found that those folks at Cosmic Variance already did. So my work here is done.
August 21st, 2006 at 11:37 pm
My Mighty Meteorite…
The Bad Astronomy guy (not a bad astronomer, himself) performed yet another random act of kindness. He mailed me something out of this world: a meteorite! Not the entire thing, mind you - but a bit of “Canyon Diablo” history…….
August 22nd, 2006 at 6:01 am
Site linked got spammed. Can’t get in to read it =(
August 22nd, 2006 at 6:15 am
The error that the site is showing:
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August 22nd, 2006 at 6:17 am
Cosmicvariance got slashdotted.
Things seem to be better now; try again.
August 22nd, 2006 at 6:19 am
It worked for me. Thanks. Nice illustration, though they leave the impression dark matter is blue, at least for the novice reader.
August 22nd, 2006 at 6:24 am
They got hit by Fark.
Not many servers can handle Fark traffic.
August 22nd, 2006 at 6:29 am
[…] 请看官方新闻，SpaceFlightNow 报é“Bad Astronomy说：”… this is not only terribly important, but also very, very cool…” […]
August 22nd, 2006 at 6:52 am
The link worked for me.
At last, the dark side has emerged!
NASA also has a similar article. Quite an exciting time here. Goes to show how important those science missions are (ya hear me, Congress!).
August 22nd, 2006 at 7:43 am
You can see “how strong the dark side really is”
The future will show if this all is true at all. I´m still sceptical but it´s an interesting “proof”. It will be very exciting!
August 22nd, 2006 at 7:56 am
To heck with the reclassification of Solar System objects. I think THIS is the biggest astronomy story of the year.
Now what I want to know is what does this do to M-THeory?
August 22nd, 2006 at 8:07 am
Wonderful! I never subscribed to the idea of dark matter because of a lack of direct evidence, but I’m happy to be proven wrong!
One thing though that the article didn’t mention was the idea of explaining the behavior of galaxies via dark matter and by giving mass to the neutrino. I guess thats the next step in the cosmilogical game.
August 22nd, 2006 at 12:01 pm
A dumb question from a newbie to all this: the gravity maps show that the matter responsible for the lensing is concentrated in the clusters. How does this indicate the presence of dark matter? Could the lensing not be from the galaxies alone? Is there a way of determining that the amount of matter in the galaxies is not sufficient for the degree of lensing observed?
From a genuinely interested, though slightly confused, reader. Thanks!
August 22nd, 2006 at 12:54 pm
You astronomers always give us the best damn stuff in the universe! This is an amazing discovery.
August 22nd, 2006 at 1:35 pm
Is there a way of determining that the amount of matter in the galaxies is not sufficient for the degree of lensing observed?
Yes the way weak lensing algorithms works is that you end up with a model of what the mass that is causing the weak lensing looks like. This model for the Galaxy clusters shown indicates there is many times the mass in the “blue” areas of the picture than can be accounted for by the visible matter. That is, there is something that causes gravity (matter) that we can’t see electromagnetically (dark) in those areas.
August 22nd, 2006 at 2:06 pm
How does anti-matter relate to dark matter?
August 22nd, 2006 at 8:36 pm
Don’t ask me why I did this, but I copied the picture above to my hard drive, brought it into Photoshop, and inverted the colors (made it a negative). If you do that, it appears that you can see an area of optical dark matter near the top of the picture as well. Probably doesn’t mean anything, but I thought I’d mention it.
And please, no comments about the Shroud of Turin ; )
J. D.
August 23rd, 2006 at 4:13 am
A dumb question from a newbie to all this: the gravity maps show that the matter responsible for the lensing is concentrated in the clusters. How does this indicate the presence of dark matter? Could the lensing not be from the galaxies alone? Is there a way of determining that the amount of matter in the galaxies is not sufficient for the degree of lensing observed?
IIRC, the amount of lensing gives an idea of the total mass of the object(s) causing the lens effect. The visible mass of the galaxies in the cluster can be estimated with some accuracy - if that number is very different from the total mass required to do the lensing then there must either be dark matter, or wildly inaccurate estimates of the masses of the galaxies.
August 23rd, 2006 at 10:30 am
A follow-on (of sorts) to Christopher’s question:
I understand how the results show that the majority of each cluster’s original mass did not interact during the collision. And given that much of this un-reactive mass can’t be seen, it must (by definition) be dark matter.
My question is; how can we know that it’s nonbaryonic dark matter?
The assumption here seems to be that all of the matter in the clusters was either hot X-ray emitting intergalactic gas, visible galaxies, or nonbaryonic dark matter. Isn’t it possible that the clusters originally consisted of baryonic dark matter which, like the galaxies, did not interact during the collision?
Presumably, the galaxies themselves are ordinary (baryonic) visible matter, and they did not interact during the collision. Couldn’t galaxy-sized “blobs” of baryonic dark matter also behave as non-interactive particles during the collision?
August 23rd, 2006 at 3:50 pm
TR: the best models for nucleosynthesis and the structure of the CMB puts very strong bounds on the amount of baryonic matter. And it turns out that there is much more matter than can be explained by invoking baryonic dark matter. So it seems that they’re looking for exotic particles. If I am not mistaken, the #1 suspect is a stable remnant of supersymmetric interactions.
August 23rd, 2006 at 3:55 pm
I guess these specific observations indicate that Modified Newtonian Dynamics (MOND) does not work without becoming horribly complicated. So this might be the dark matter equivalent of Rutherford’s demonstration that atoms have nuclei.
August 23rd, 2006 at 6:18 pm
It’s fairly simple. Of the light matter, as you mentioned, you have either gas clouds or galaxies. The galaxies only make up about 10% of the light mass, and they’re relatively compact, so they made it through the collision pretty much without, erm, collision. The gas, though, collided a lot.
Now, the mass of the dark matter and the properties of the lensing indicate that there was a *lot* of it. There was definitely more dark matter than there was light gas. If it was baryonic, it would have interacted in the same fashion as the light gas - it would have collided and produced shockwaves. Since it didn’t, we can be fairly certain that it wasn’t baryonic.
Plus, baryonic matter interferes with light (because it interacts with the electromagnetic force). Clouds of gas dim or block out light, or they glow from within because they’ve got stars inside of them. However, the giant mass of dark matter isn’t interfering with light at all, except for the gravitational lensing. Thus, another indication that its nonbaryonic.
August 23rd, 2006 at 6:22 pm
It doesn’t. Anti-matter is essentially the same as ordinary matter with its charge reversed. Otherwise, it acts exactly like ordinary matter.
Dark matter is a special form of ordinary matter that’s non-baryonic. This means that it doesn’t interact with the electromagnetic force. Light goes straight through it without stopping, slowing, or scattering. Magnetic fields don’t move it. Nothing EM can affect it in any way. I believe that it still interacts with the weak and strong forces at least somewhat (someone correct me if I’m wrong), though those are absolutely useless on astronomical scales. Thus, we’re left with gravity being the only significant force that affects dark matter.
August 23rd, 2006 at 6:27 pm
Thanks PK.
August 23rd, 2006 at 6:32 pm
Xanthir, your first and second paragraphs seemed to repeat the supposition that I was questioning, but your third point is pretty compelling.