ALMA | National Radio Astronomy Observatory | 2019 Aug 07
Capturing Orbital Motion around a Black Hole in Unprecedented Clarity
What happens inside a black hole stays inside a black hole, but what happens inside a black hole’s “sphere of influence” – the innermost region of a galaxy where a black hole’s gravity is the dominant force – is of intense interest to astronomers and can help determine the mass of a black hole as well as its impact on its galactic neighborhood.ALMA has made the most precise measurements of cold gas swirling around a
supermassive black hole — the cosmic behemoth at the center of the giant elliptical
galaxy NGC 3258. Credit: ALMA (ESO/NAOJ/NRAO), B. Boizelle; NRAO/AUI/NSF,
S. Dagnello; Hubble (NASA/ESA); Carnegie-Irvine Galaxy Survey
New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) provide an unprecedented close-up view of a swirling disk of cold interstellar gas rotating around a supermassive black hole. This disk lies at the center of NGC 3258, a massive elliptical galaxy about 100 million light-years from Earth. Based on these observations, a team led by astronomers from Texas A&M University and the University of California, Irvine, have determined that this black hole weighs a staggering 2.25 billion solar masses, the most massive black hole measured with ALMA to date.
Though supermassive black holes can have masses that are millions to billions of times that of the Sun, they account for just a small fraction of the mass of an entire galaxy. Isolating the influence of a black hole’s gravity from the stars, interstellar gas, and dark matter in the galactic center is challenging and requires highly sensitive observations on phenomenally small scales. ...
During the past few years, ALMA has pioneered a new method to study black holes in giant elliptical galaxies. About 10 percent of elliptical galaxies contain regularly rotating disks of cold, dense gas at their centers. These disks contain carbon monoxide (CO) gas, which can be observed with millimeter-wavelength radio telescopes.
By using the Doppler shift of the emission from CO molecules, astronomers can measure the velocities of orbiting gas clouds, and ALMA makes it possible to resolve the very centers of galaxies where the orbital speeds are highest. ...
A Precision Measurement of the Mass of the Black Hole in NGC 3258
from High-resolution ALMA Observations of Its Circumnuclear Disk ~ Benjamin D. Boizelle et al