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Discipine of Physics
Faculty of Science, Engineering & Technology

Astrophysics Research


UTAS People Involved
Some galaxies produce much more light at radio, x-ray and other wavelengths than can be explained by the stars that we see.  The excess emission normally comes from the very central regions of these galaxies, which are called active galaxies.  Most astronomers think that these active galaxies have a giant blackhole at their centre and that it is the material being heated as it falls towards the blackhole that produces the excess emission.  However, it is very hard to prove conclusively that a blackhole is responsible.  The best evidence for a blackhole at the centre of an active galaxy comes from observations of maser emission from the water molecule in a galaxy called NGC4258. These observations show that there is a total mass more than 36 million times greater than our Sun in a region of less than half a light-year (much less than the distance from the Sun to the nearest star).

One of the astrophysical environments that produces masers is the nucleus of active galaxies.  The masers associated with active galaxies are about a million times brighter than those typically found in star formation regions in our galaxy and for this reason are called megamasers.  The material being drawn into a blackhole cannot fall straight in, instead it forms a large flat (accretion) disk and slowly spirals towards the blackhole.  Some of the megamasers have been found to lie in the accretion disk and it is this which has enabled them to be used to measure the mass of the central blackhole.  As well as providing very detailed information on the regions near a blackhole, some megamasers can also be used to geometrically measure the distance to their galaxies.

Measuring distance is one of the most difficult and important tasks in astronomy and is fundamental to our understanding of the Universe.  A team of astronomers from the Harvard-Smithsonian Center for Astrophysics, the Australia Telescope National Facility and the University of Tasmania are conducting a sensitive search for new megamaser galaxies.  Studies of the megamasers we discover are yielding new insights into the what goes on at the centre of active galaxies and will allow us to directly measure the distance to some.

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Dr Simon Ellingsen
Simon Picture

Jamie McCallum

Lincoln Greenhill (Harvard CfA)
Paul Kondratko (Harvard CfA)

Created: September 2009 by Tammy Riley
Last modified: September 2009
Copyright School of Mathematics & Physics, University of Tasmania Australia, 2009