March 3, 2012
Hubble Findings Cast Doubt On Dark Matter Theories
The discovery of a dark matter mass left behind after what is being called a wreck between massive clusters of galaxies has experts questioning current theories regarding the invisible substance believed to make up more than 80% of the universe.
According to a Friday press release from NASA, currently scientists theorize that galaxies should be anchored to dark matter, even in the event of a collision. However, astronomers using information gathered from the Hubble Telescope have discovered a "dark core" of the substance that contained fewer galaxies than it would have if the dark matter and the galaxies had stuck together, leading them to believe that most of the galaxies had become separated.
"This result is a puzzle," James Jee of the University of California in Davis, the astronomer in charge of the study, said in a statement. "Dark matter is not behaving as predicted, and it's not obviously clear what is going on. It is difficult to explain this Hubble observation with the current theories of galaxy formation and dark matter."
The observations originate from a merging galaxy cluster known as Abell 520, which NASA says is located 2.4 billion light years away. While dark matter cannot be seen, the scientists were able to detect it because of an effect known as gravitational lensing -- in other words, the substance can bend and distort light from galaxies not unlike a magnifying glass, allowing astronomers to infer that it is present. Their observations in this case revealed that there far fewer galaxies present in the Abell 520 cluster than there should have been.
The findings have been published online in The Astrophysical Journal.
The phenomenon had originally been spotted five years ago, in 2007, but were dismissed as unreal due to poor data, NASA said. According to a separate San Francisco State University (SFSU) press release, SFSU researcher Andisheh Mahdavi and his colleagues were the ones who made those observations, in part using ground-based telescopes which were only able to detect a few of the galaxies behind the cluster and which may have had their results distorted by Earth's atmosphere, the university said.
The researchers declared that they needed additional observations originating from the Hubble Telescope in order to confirm Mahdavi's findings, which the researcher called "a result that basically everyone wished would go away." It has not, however, and these new findings all but confirm that "without a doubt that there is a dark matter concentration in that piece of the sky," he added in the SFSU press release.
Dark matter, which is believed to be sort of a gravitational "glue" that keeps galaxies held together, was first detected approximately 80 years ago, according to a report published on HubbleSite Friday. Little is known about the material, although scientists know that it is not comprised of the same type of material found in other celestial objects and that it seems to have an almost supernatural gravitational influence on regular matter.
Studies of Abel 520 seem to cast what little they have learned and theorized about dark matter in doubt, however.
"The original observations found that the system's core was rich in dark matter and hot gas but contained no luminous galaxies, which normally would be seen in the same location as the dark matter," the HubbleSite report said. "NASA's Chandra X-ray Observatory detected the hot gas. Astronomers used the Canada-France-Hawaii and Subaru telescopes atop Mauna Kea to infer the location of dark matter by measuring how the mysterious substance bends light from more distant background galaxies, an effect called gravitational lensing."
"The astronomers then turned Hubble's Wide Field Planetary Camera 2 to help bail them out of this cosmic conundrum. Instead, to their chagrin, the Hubble observations helped confirm the earlier findings," it added.
Dr. Arif Babul, senior theorist on the study and an astrophysicist with the University of Victoria, called the observations "humbling," explaining that "in spite of all the leaps and bounds in our understanding, every now and then, we are stopped cold."
Image Credit: NASA, ESA, CFHT, CXO, M.J. Jee (University of California, Davis), and A. Mahdavi (San Francisco State University)
On the Net:
- Hubble Space Telescope
- University of California in Davis
- San Francisco State University
- The Astrophysical Journal
- University of Victoria