Posted on 08/21/2006 6:13:30 PM PDT by vikingd00d
Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.
"This is the most energetic cosmic event, besides the Big Bang, which we know about," said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
These observations provide the strongest evidence yet that most of the matter in the universe is dark. Despite considerable evidence for dark matter, some scientists have proposed alternative theories for gravity where it is stronger on intergalactic scales than predicted by Newton and Einstein, removing the need for dark matter. However, such theories cannot explain the observed effects of this collision.
"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."
In galaxy clusters, the normal matter, like the atoms that make up the stars, planets, and everything on Earth, is primarily in the form of hot gas and stars. The mass of the hot gas between the galaxies is far greater than the mass of the stars in all of the galaxies. This normal matter is bound in the cluster by the gravity of an even greater mass of dark matter. Without dark matter, which is invisible and can only be detected through its gravity, the fast-moving galaxies and the hot gas would quickly fly apart.
The team was granted more than 100 hours on the Chandra telescope to observe the galaxy cluster 1E0657-56. The cluster is also known as the bullet cluster, because it contains a spectacular bullet-shaped cloud of hundred-million-degree gas. The X-ray image shows the bullet shape is due to a wind produced by the high-speed collision of a smaller cluster with a larger one.
In addition to the Chandra observation, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes were used to determine the location of the mass in the clusters. This was done by measuring the effect of gravitational lensing, where gravity from the clusters distorts light from background galaxies as predicted by Einstein's theory of general relativity.
The hot gas in this collision was slowed by a drag force, similar to air resistance. In contrast, the dark matter was not slowed by the impact, because it does not interact directly with itself or the gas except through gravity. This produced the separation of the dark and normal matter seen in the data. If hot gas was the most massive component in the clusters, as proposed by alternative gravity theories, such a separation would not have been seen. Instead, dark matter is required.
"This is the type of result that future theories will have to take into account," said Sean Carroll, a cosmologist at the University of Chicago, who was not involved with the study. "As we move forward to understand the true nature of dark matter, this new result will be impossible to ignore."
This result also gives scientists more confidence that the Newtonian gravity familiar on Earth and in the solar system also works on the huge scales of galaxy clusters.
"We've closed this loophole about gravity, and we've come closer than ever to seeing this invisible matter," Clowe said.
These results are being published in an upcoming issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center, Cambridge, Mass. For additional information and images, visit:
http://chandra.nasa.gov
No it is not an ether.
(I'm gonna get clobbered for that one :) )
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If an inch represents the difference in the knowledge of Kepler and Galileo and todays observers, then a miles represents how much more knowledge there must be before we begin to explain it all. We may never travel that mile.
Why not? An invisible, odorless realm that affects gravity and light. Whys it not an ether?
Now back to the future?
In 1998 astronomers blew the lid off of the oscillating universe theory (first a big bang occurs, galaxies fly away from each other then slow down, slower and slower then gravity starts pulling them together again until they collide together and BOOM another big bang) because they discovered that the expanding galaxies were not slowing down, but actually accelerating aqwy from each other faster and faster.
Previous theories were tossed out, and new ones were needed.
One prominent theory suggested that there was additional matetr out there beyond the galaxies and the gravitation of that unseen matter is pulling the galaxies away faster and faster.
The frantic search for the elusive "dark matetr" began.
It has been one of the greatest hunts in the history of physics.
Now, apparently the hunt is over.
But.....
They really do not understand the nature of this exotic stuff. It is not like normal matter. Some theories suggest it is actually matter at the intersection of other dimensions, neither totally in our dimensions nor in the other dimensions.
Kinda like light which has properties of both matter and electromagnetic waves at the same time.
This is very big news.
I affect gravity and light but I am not an ether either.
Hmmmm... Light matter/energy vs. dark matter/energy...
The bigger question is why it is important to understand the world we live in.
Thanks for the ping.
BuMpiTy, BuMp, BuMp, ...BOOM!
Sorry. I'm just being obstinate.
It will be fascinating to find out where we fit dark matter/energy into our scientific worldview though. Not atoms/protons/neutrons/electrons/quarks or other normal matter constituents that would fit into the Periodic Table, then just what the he!! IS it?
It's sorta deflating to find out that we only know what a small fraction of everything is.
Godspeed
Very elegant--finding a spot where natural forces ought to separate the dark and luminous matter. It must have been a very cool moment when they first overlaid the IR chart with the lensing chart.
At a minimum, future work is going to have to explain gravitational centers that are completely separate from the IR centers. Dark matter seems like a pretty good way to do it. And, the dark matter theory obviously predicted this result in this oddball situation before the observations were made--they wouldn't have gotten 100 hours on the scope without a pretty compelling case that this was a way to test the dark matter theory. Sometimes science is just beautiful.
This result is, I think, almost as important as the confirmation of relativity by gravitational bending of light.
[Raising my hand ...] I have a question. As these clusters pass through each other, and the visible matter gets slowed down so that the dark matter sails through faster, the dark matter leaves the visible galaxies behind. Fine. Now then, I thought the first clue to the existence of dark matter was that galaxies were rotating as if there were lots more mass than we could detect. So, won't the rotation of these "naked" galaxies (stripped of their dark matter) cause them to fly apart? Is that going to be observed?
I'd need to have a better understanding of exactly what's going on to answer that; I'll have to punt until the heavy hitters show up.
The expansion of the universe is a large-scale effect; it doesn't affect the local motion of galaxies. Example: Andromeda is 2.2 million LY away from our galaxy, yet the two are moving towards each other.
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