April 16, 2010

Black Holes Linked To Galaxy Death

Black holes are thought to reside at the center of almost every galaxy, with some growing to more than a billion times the mass of the Sun. Now a team of UK astronomers believe that these supermassive black holes are commonplace, release more than enough energy to strip their host galaxies apart and in the process shut down these galaxies' star formation for good. On Friday April 16th, team member Asa Bluck of the University of Nottingham, who led this research, will explain the dramatic impact of these monster black holes in his talk at the RAS National Astronomy Meeting (NAM 2010) in Glasgow.

For many years black holes have fascinated scientists and the public alike, with their peculiar ability to warp space and time and their almost sinister tendency to devour everything they encounter. Before it falls in, as matter swirls around the black hole it forms an "accretion disk", where it heats up and radiates energy. The supermassive black holes have such a strong gravitational field that the infalling matter releases a vast amount of energy, making each accretion disk far brighter than the combined output of the hundreds of billions of stars in the galaxy around it.

One of the consequences of this outpouring of energy is that it drives away cool gas and dust, the raw ingredients of new stars. This permanently shuts down star formation in the surrounding galaxy, dooming it to a slow death, where the remaining stars age, grow red, end their lives and are never replaced.

The new study considered the role of supermassive black holes in the development of galaxies. To search for them, the team used the Hubble Space Telescope and the Chandra X-ray Observatory to image the Universe to unprecedented depth and resolution in optical, near infra-red and X-ray light. In particular, the astronomers looked for galaxies which have a very high emission of X-rays, a classic signature of black holes devouring gas and dust.

From the space telescopes' data Asa and the other team members find that at least 1/3 of all the massive galaxies in the Universe not only contain supermassive black holes, but that at some point in their histories the emission from the holes' accretion disks far outshines their host galaxies. The energy output of regions around the black holes is high enough to strip apart every massive galaxy in the cosmos 25 times over, whilst the X-ray emission from them turns out to dwarf that from every other source in the Universe put together.

Asa sums up the new results: "We are left with a startling picture of the formation history of massive galaxies, where dramatic violence in the form of the torrent of radiation from matter falling into black holes leads to the death of galaxies they inhabit."

The results of this study are to be submitted to Monthly Notices of the Royal Astronomical Society for publication.


Image Caption: The image is a multi-wavelength image of the galaxy NGC 1275 which is a local equivalent to many of the distant massive galaxies studied by Asa Bluck and the other members of the Nottingham / University College London team. It shows the phenomenal power of supermassive Black Holes to rearrange the gas of a galaxy, and represents a window onto a violent past to the lives of galaxies. Over the history of the Universe at least 1/3 of all galaxies went through a phase of development similar to this one. Credit: A. Fabian (Cambridge) / STScI / NASA.


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