As black holes are proverbially black, astronomers have to come up with intuitive ways to work out how big they are. One way to do so is to look at how fast gas around them moves, a technique astronomers used with the Atacama Large Millimeter Array (ALMA) to get the most accurate mass measurement yet.
The supermassive black hole (SMBH) in question is estimated to have a mass of 660 million Suns, based on the gas around it moving at 500 kilometers (310 miles) per second. The SMBH is located 73 million light-years from Earth in galaxy NGC 1332.
The measurement was possible thanks to the power of ALMA, which scans the sky with its 66 radio antennas. The observatory looked at the emission from carbon monoxide circling the SMBH, and was able to map it to a resolution of about 15 light-years (0.044 seconds of a degree in the sky). The results were published in the Astrophysical Journal Letters.
“This is a case where new instrumentation has allowed us to make an important new advance in terms of what we can say scientifically,” senior co-author Andrew J. Baker of Rutgers University in New Jersey said in a statement. “This has been a very active area of research for the last 20 years, trying to characterize the masses of black holes at the centers of galaxies.”
NGC 1332 and its supermassive black hole as seen by Hubble and ALMA. NASA/ESA/NRAO/ESO/NAOJ/Carnegie-Irvine Galaxy Survey
Astronomers are confident that every major galaxy has an SMBH at its center, and there is extensive evidence that the growth of each black hole is closely linked to the growth of its host galaxy.
“The ubiquity of black holes is one indicator of the profound influence that they have on the formation of the galaxies in which they live,” Baker added.
Learning as much as we possibly can about black holes provides us with new insights on galaxies, and takes us a step closer to understanding how galaxies form and evolve.