A team of astronomers from the University of California, Irvine (UCI) has used the Atacama Large Millimeter/submillimeter Array (ALMA) astronomical interferometer of radio telescopes to determine the mass of a supermassive black hole at the center of a close-by elliptical galaxy to be 600 million times that of the sun.
The scientists first determined the speed of a disk of molecular dust and gas orbiting the black hole at the center of galaxy NGC 1332, a measurement that laid the foundation for the subsequent determination of the mass.
"This is the first time that ALMA has probed the orbital motion of cold molecular gas well inside the gravitational sphere of influence of a supermassive black hole," said Aaron Barth, a professor at UCI and lead author of the study. "We're directly viewing the region where the cold gas is responding to the black hole's gravitational pull. This is an exciting milestone for ALMA and a great demonstration of its high-resolution capability."
The mass measurement that they obtained was very precise due to the speed of the dust and gas that they were able to determine.
"For a precise measurement, we need to zoom in to the very center of a galaxy where the black hole's gravitational pull is the dominant force," Barth said. "ALMA is a fantastic new tool for carrying out these observations."
The supermassive black hole lies at the heart of galaxy NGC 1332, a massive elliptical galaxy that is located in the southern sky approximately 73 million light-years from Earth. Not only are elliptical galaxies known to contain massive central black holes, approximately one in 10 of them contain disks of cold molecular gas and dust orbiting their centers, which makes them prime candidates for a precise black hole measurement.
In addition, dense disks of cold molecular gas - like the one in NGC 1332 - are easier for ALMA to measure due to the lower level of turbulence in their motion, allowing for a more precise measurement.
"This observation demonstrates a technique that can be applied to many other galaxies to measure the masses of supermassive black holes to remarkable precision," said Benjamin Boizelle, a UCI graduate student and co-author of the study.
The findings were published in the May 5 issue of The Astrophysical Journal Letters.
