Astronomers using the Atacama Large Millimeter/submillimeter Array, or ALMA, a network of several dozen radio dishes located in the high-elevation desert of northern Chile, have measured the mass of the supermassive black hole at the center of the barred spiral galaxy NGC 1097.
In this image, the larger-scale structure of NGC 1097 is easily visible. Image credit: ESO / R. Gendler.
NGC 1097 lies in the southern constellation Fornax at a distance of only 45 million light-years. Lurking at the very center of this face-on galaxy, a supermassive black hole is gradually sucking in the matter around it. The area immediately around the black hole shines powerfully with radiation coming from the material falling in.
The distinctive ring around the NGC 1097’s black hole is bursting with new star formation. An inflow of material toward the central bar of the galaxy is causing the ring to light up with new stars. The ring is around 5,000 light-years across, although the spiral arms of the galaxy extend tens of thousands of light-years beyond it.
A team of astronomers led by Dr Kyoko Onishi of the Graduate University for Advanced Studies (SOKENDAI) in Japan determined that NGC 1097 harbors a black hole 140 million times more massive than our Sun. In comparison, the black hole at the center of the Milky Way is a lightweight, with a mass of just a few million times that of our Sun.
This composite image shows the barred spiral galaxy NGC 1097. By studying the motion of two molecules, astronomers were able to determine that the supermassive black hole at the center of this galaxy has a mass 140 million times greater than our Sun. Image credit: ALMA / NRAO / ESO / NAOJ / K. Onishi / NASA / ESA / Hubble Space Telescope / E. Sturdivant / AUI / NSF.
First, Dr Onishi and co-authors measured the distribution and motion of two molecules – hydrogen cyanide and formylium – near the central region of NGC 1097.
They then compared the ALMA observations to various mathematical models, each corresponding to a different mass of the supermassive black hole.
The ‘best fit’ for these observations corresponded to a black hole weighing in at about 140 million solar masses. The results are published in the
“This is the first use of ALMA to make such a measurement for a spiral or barred spiral galaxy,” said Dr Kartik Sheth of the National Radio Astronomy Observatory in Charlottesville, Va., who is a co-author of paper about the results available online in the Astrophysical Journal.
“When you look at the exquisitely detailed observations from ALMA, it’s startling how well they fit in with these well tested models.”
“It’s exciting to think that we can now apply this same technique to other similar galaxies and better understand how these unbelievably massive objects affect their host galaxies.”
“Future observations with ALMA will continue to refine this technique and expand its applications to other spiral-type galaxies,” the astronomers said.
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K. Onishi et al. 2015. A Measurement of the Black Hole Mass in NGC 1097 Using ALMA. ApJ 806, 39; doi: 10.1088/0004-637X/806/1/39
