An international team of astronomers led by Dr. Aaron Barth of the University of California, Irvine, has derived a precise measurement of the mass of a supermassive black hole at the center of the giant elliptical galaxy NGC 1332.
This image shows NGC 1332, a giant elliptical galaxy with a black hole at its center whose mass has been measured at high precision by ALMA. Image credit: Carnegie-Irvine Galaxy Survey.
NGC 1332, otherwise known as ESO 548-18 and LEDA 12838, is an almost-edge-on elliptical galaxy in the direction of the southern constellation Eridanus.
The galaxy is a member of the NGC 1315–1332 group, which is approximately 80 million light-years from Earth.
Like other giant elliptical galaxies, NGC 1332 hosts a supermassive black hole at its center.
Working with high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) — a powerful array of 66 radio telescopes designed to conduct observations at millimeter and submillimeter wavelengths — in Chile, Dr. Barth and his colleagues from the United States and China were able to determine the speed of a disk of cold molecular gas and dust orbiting the galaxy NGC 1332’s central, supermassive black hole.
The ALMA data show that near the disk’s center, the rotation speed of the gas reaches about 1.1 million mph (492 km per second).
By mapping the disk’s rotation with the high-resolution data, the team determined that the NGC 1332’s black hole has a mass of 660 million solar masses, with a measurement uncertainty of just 10%.
This is among the most precise measurements for the mass of a galaxy’s central black hole.
“Measuring the mass of a black hole accurately is very challenging, even with the most powerful telescopes on Earth or in space,” Dr. Barth said.
“ALMA has the revolutionary ability to observe disks of cold gas around supermassive black holes at small enough scales that we can clearly distinguish the black hole’s influence on the disk’s rotational speed.”
“The ALMA observations reveal details of the disk’s structure on the order of 16 light-years across,” the astronomers said.
“They also measure the disk’s rotation well within the estimated 80 light-year radius of the black hole’s ‘sphere of influence’ – the region where the black hole’s gravity is dominant.”
The results have important implications for how galaxies and their central supermassive black holes form.
“The ratio of a black hole’s mass to a galaxy’s mass is important in understanding their makeup,” Dr. Baker said.
The team’s findings have been accepted for publication in the Astrophysical Journal Letters (arXiv.org preprint).
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Aaron J. Barth et al. 2016. Measurement of the Black Hole Mass in NGC 1332 from ALMA Observations at 0.044 Arcsecond Resolution. ApJL, accepted for publication; arXiv: 1605.01346
