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Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Dark Matter Survives Another Test
28 September 2005 (All day)
The cosmic lost-and-found department now contains an important "found" item: dark matter. A new simulation of the orbits of stars after galaxy collisions concludes that invisible cocoons of matter do indeed exist around large nearby galaxies. The study refutes a recent claim that some of those galaxies have little or no dark matter--a provocative idea that flew in the face of leading theories of galaxy formation.
In the earlier research astronomers examined nebulae of gas in the outskirts of three giant blobs of stars called elliptical galaxies. The nebulae form when dying stars similar to our sun expel their atmospheres. A team led by Aaron Romanowsky, now at the Universidad de Concepción in Chile, found that about 100 nebulae in each galaxy seemed to orbit very slowly. The researchers maintained that if the galaxies held far more dark matter than visible stars, then the nebulae should orbit faster under the matter's gravitational influence.
But there's no need to rewrite the theories of galaxy formation, says astrophysicist Avishai Dekel of Hebrew University in Jerusalem, Israel. Dekel and coworkers scrutinized the mergers between big spiral galaxies that probably form elliptical galaxies. Computer models showed that the collisions fling arcs of stars deep into space. The team's virtual galaxies included dark matter, which pulled most of the stars back toward the merged galaxies and forced them into swooping, cigar-shaped paths.
The model matches the observations of slow-moving nebulae by Romanowsky's team, Dekel says, because telescopes would see most of the nebulae at the farthest and slowest points of their long orbits. The simulation also suggests that the nebulae actually move through space more quickly than Romanowsky's team deduced, because telescopes can only measure the component of their motions directly toward or away from Earth. Faster motions toward the sides of the galaxy would not have shown up, says Dekel, whose team describes its findings 29 September in Nature.
"This is a plausible and simple interpretation," says astrophysicist Julio Navarro of the University of Victoria, British Columbia. "It demonstrates that with just 100 [nebulae] for each galaxy, it's hard to rule out well-established dark matter scenarios." Romanowsky calls the work by Dekel's team "important," but he adds a caveat: "It's not clear their model explains everything we see." Ongoing analysis of nebulae in 12 elliptical galaxies still points to less dark matter than expected, he says.