Researchers have believed for decades that normal, visible matter makes up only around a sixth of the material in the universe. The rest is an unseen, enigmatic â€œdark matter,â€ which reveals itself only through its gravitational pull.
Some scientists, though, propose that there is no dark matter, and that our understanding of the laws of gravity is wrong instead.
The new finding was based on observations from five telescopes including NASAâ€™s Chandra X-ray Observatory, an orbiting station that captures X-rays emanating from cosmic structures.Â â€œThis is the most energetic cosmic event, besides the Big Bang, which we know about,â€ said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.Â Researchers have produced an animation of the collision (see sidebar).
â€œThese results are direct proof that dark matter exists,â€ added Doug Clowe of the University of Arizona at Tucson, and leader of the study. He acknowledged, though, that the finding reveals nothing about what dark matter actually is.In clusters of galaxies, the normal matter, like the atoms that make up the stars, planets, and everything on Earth, mainly takes the form of hot gas and stars. The hot gas between the galaxies far outweighs the stars in all the galaxies.Â
This normal matter is held in a cluster by the gravity of an even greater mass of dark matter, most astronomers think. Without that, the fast-moving galaxies and hot gas would fly apart.Â
Cloweâ€™s team studied a galaxy cluster designated 1E0657-56, also called the â€œbullet clusterâ€ because it contains a spectacular bullet-shaped cloud of scorching gas. X-ray images show the bullet shape is due to a wind produced by the recent collision of a smaller cluster with a larger one, the researchers said.
before it's in the papers"
June 04, 2013
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Stupendous crash proves "dark matter"
exists, astronomers claim
Aug. 21, 2006
and World Science staff
A colossal crash between two clusters of galaxies has
wrenched apart â€œdark matterâ€ and normal matter, proving the mysterious
dark substance exists, astronomers say.
Researchers have believed for decades that normal, visible matter makes up only
around a sixth of the material in the universe. The rest is
an unseen, enigmatic â€œdark matter,â€ which reveals itself only through its gravitation­ pull.
|Hot gas is seen as the two pink clumps in the image.
This contains most of the normal, or "baryonic," matter in the two
galaxy clusters. The bullet-shaped
clump on the right is the hot gas from one cluster, which plowed through the hot gas from the other, larger cluster during the collision.
The blue areas show where astronomers found most of the mass concentrated.
They determined this using "gravitational lensing," an effect in
the material distorts light from objects far behind the galaxy cluster.
The separation of blue and pink are evidence of the breakup of dark and
regular matter, astronomers say. (Courtesy Chandra X-ray Center).
ANIMATION OF COLLISION: As two galaxy clusters collide, the hot gas in each cluster
is slowed by a drag force. In contrast, the dark matter is not slowed by the impact because it doesn't interact directly with itself or the gas.
Thus, the dark matter clumps from the two clusters move ahead of the
Quicktime format (download here):
Some sciÂenÂtists, though, proÂpose that there is no dark matÂter, and that our unÂderÂstandÂing of the laws of gravÂiÂty is wrong inÂstead.
The new findÂing was based on obÂserÂvaÂtions from five teleÂscopes inÂcludÂing NASAâ€™s ChanÂdra X-ray ObÂservÂaÂtoÂr, an orÂbitÂing staÂtion that capÂtures X-rays emÂaÂnatÂing from cosÂmic strucÂtures.Â
â€œThis is the most enÂerÂgetÂic cosÂmic event, beÂsides the Big Bang, which we know about,â€ said team memÂber MaxÂim MarkeÂvitch of the HarÂvard-SmithÂsoÂnian CenÂter for AsÂtroÂphysÂics in CamÂbridge, Mass.Â ReÂsearchers have proÂduced an anÂiÂmaÂtion of the colÂliÂsion (see sideÂbar).
â€œThese reÂsults are diÂrect proof that dark matÂter exÂists,â€ added Doug Clowe of the uniÂverÂsiÂty of ArÂiÂzoÂna at TucÂson, leadÂer of the studÂy. He acÂknowlÂedged, though, that the findÂing reÂveals nothÂing about what dark matÂter acÂtuÂalÂly
In clusÂters of galaxÂies, the norÂmal matÂter, like the atoms that make up the stars, planÂets, and eveÂryÂthing on Earth, mainÂly takes the form of hot gas and stars. The hot gas beÂtween the galaxÂies far outÂweighs the stars in all the galaxÂies.Â
This norÂmal matÂter is held in a clusÂter by the gravÂiÂty of an even greatÂer mass of dark matÂter, most asÂtroÂnoÂmers think. WithÂout that, the fast-movÂing galaxÂies and hot gas would fly apart.Â
Cloweâ€™s team studÂied a galÂaxÂy clusÂter desÂigÂnatÂed 1E0657-56, alÂso called the â€œbulÂlet clusÂterâ€ beÂcause it conÂtains a specÂtacÂuÂlar bulÂlet-shaped cloud of scorchÂing gas. X-ray imÂages show the bulÂlet shape is due to a wind proÂduced by the reÂcent colÂliÂsion of a smaller clusÂter with a largÂer one, the reÂsearchers said.
The astronomers used the telescopes to determine where the mass was
located in the clusters. They found that the hot gas in the collision was slowed by a drag force, similar to air resistance. But the dark matter wasnâ€™t slowed at all, they
said, because it doesnâ€™t interact directly with itself or the gas, except through gravity.
Thus dark and normal matter came apart, they added, which wouldnâ€™t have happened if theories that propose alternatives to dark matterâ€”by suggesting revisions to our laws of gravityâ€”were
correct. These theories, they continued, propose the mass would be distributed
differently, since the separation wouldnâ€™t occur.
â€œThis new result will be impossible to ignore,â€ said University of Chicago cosmologist Sean Carroll, who wasnâ€™t involved with the study. The findings are to appear in an upcoming issue of
The Astrophysical Journal Letters.
The new findings donâ€™t address the so-called dark energy, which is distinct from dark matter. Dark energy is an additional force that is believed to be speeding up the expansion of the universe. Current estimates suggest regular matter comprises only 5 percent of the universe, dark matter 25 percent, and dark energy 70 percent, Carroll said.
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