January 31, 2013
Researchers Find New Way To Weigh Supermassive Black Holes
John P. Millis, Ph.D. for redOrbit.com — Your Universe Online
Black holes of any size are mysterious, seemingly breaking through the barriers of the physical laws that guide our Universe. Formed under extreme conditions -- such as the collapse of a massive star, some ten times the mass of our Sun or more -- these objects are very difficult to study under any conditions.
Most puzzling are a class of black holes that can range in size from millions to billions of solar masses. Such supermassive objects cannot be explained by the usual black hole formation methods.
Traditionally, in the field of astronomy, the way we seek to solve such problems is to study as many of the objects as we can, preferably in various states of evolution, and combine the information together to get a complete picture of the phenomenon. For instance, in order to discover how normal stars evolve, thousands upon thousands of stars, all at various stages, were studied and cataloged. By doing so, scientists were able to take the data and extract a roadmap for how stars are born, grow and die, and what properties dictate what path they take.
However, supermassive black holes present a problem. In the entire time that we have been aware of their existence we have only been able to get reliable data on about 60 of them. “Because of the limitations of existing telescopes and techniques we had run out of galaxies with supermassive black holes to observe,” notes Michele Cappellari of Oxford University's Department of Physics.
But Dr. Cappellari and her colleagues have discovered a new method to find and study supermassive black holes at the cores of galaxies. And the hope is that this will allow the catalog of data to expand, and perhaps help to explain some of the unanswered questions of these monstrous objects.
The first step is to measure the mass of the black hole in question. To do this, Tim Davis of the European Southern Observatory, and lead author of the team´s recent paper on the subject, explains, “We observed carbon monoxide molecules in the galaxy we were monitoring using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) telescope. With its super-sharp images we were able to zoom right into the center of the galaxy and observe the gas whizzing around the black hole. This gas moves at a speed which is determined by the black hole's mass, and the distance from it. By measuring the velocity of the gas at each position, we can measure the mass of the black hole.”
Making this discovery even more exciting is the knowledge that new telescopes nearing completion will allow researchers to search for these objects even more quickly, and with higher precision.
Another author of the paper, Martin Bureau of Oxford University's Department of Physics, reports, “The ALMA telescope [Attacama Large Millimetre/submillimetre Array] is now in the final stages of construction and our team is currently bidding for time to use it for our black hole survey. If all goes according to plan we could begin our survey by the end of this year.”
With this new technique, the inventory of supermassive black holes will expand; and with it the knowledge of how these mysterious objects are formed, evolve and interact with the galaxies in which they live.