September 16, 2011
Supermassive Black Holes Found In Small Galaxies
With the help of the Hubble Space Telescope, a researcher at the University of California, Santa Cruz (UCSC) and colleagues have discovered supermassive black holes growing in shockingly small galaxies, the university announced on Thursday.
The findings, according to a UCSC press release, suggests that central black holes, which can be found in all massive galaxies, had formed at an earlier stage of galaxy evolution, since they are rarely observed in smaller "dwarf" galaxies. The galaxies were discovered by a team led by UCSC postdoctoral researcher Jonathan Trump, and are located an estimated 10 billion light-years away.
"It's kind of a chicken or egg problem: Which came first, the supermassive black hole or the massive galaxy? This study shows that even low-mass galaxies have supermassive black holes," Trump said in a statement. "When we look 10 billion years ago, we're looking at the teenage years of the universe. So these are very small, young galaxies."
The research, which is scheduled to be published in The Astrophysical Journal, is part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and used a powerful new tool on the Hubble, known as a "slitless grism."
This device is installed on the telescope's WFC3 infrared camera and can give scientists detailed data about different wavelengths of light originating from these galaxies, the press release stated. Using spectroscopy, the scientists then broke down the light into its component colors and/or wavelengths, and because of the high spatial resolution of the Hubble, they were able to receive separate spectra from both the center and the outer part of each galaxy.
Using this information, they identified emissions from the central black holes, according to UCSC.
"This is the first study that is capable of probing for the existence of small, low-luminosity black holes back in time," coauthor Sandra Faber, UCSC Professor of Astronomy and Astrophysics as well as a CANDELS principal investigator, said. "Up to now, observations of distant galaxies have consistently reinforced the local findings--distant black holes actively accreting in big galaxies only. We now have a big puzzle: What happened to these dwarf galaxies?"
Trump speculates that some of them may remain small, while others may eventually grow to be similar in size to the Milky Way. However, Faber notes that, in order to have become big galaxies, the dwarf galaxies would have had to grow much more quickly than standard models predict. If they remained small, then similar galaxies located nearby should also have central black holes.
"There might be a large population of small black holes in dwarf galaxies that no one has noticed before," she said.
The research was funded by NASA and the National Science Foundation (NSF), and co-authors of the paper include representatives from UCSC, the Steward Observatory, the University of Minnesota, the University of Michigan, Imperial College London, New York University, the Spitzer Science Center, the National Optical Astronomical Observatories, the Space Telescope Science Institute, the University of Edinburgh, Texas A&M University, Carnegie Observatories, the Max Planck Institute for Extraterrestrial Physics, the University of Pittsburgh, Johns Hopkins University, and the Goddard Space Flight Center.
Image Caption: Astronomers detected supermassive black holes in 28 distant, low-mass galaxies, including the four shown in these Hubble Space Telescope images. Image credit: A. Koekemoer, Space Telescope Science Institute.
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