It is believed all large galaxies form around a supermassive black hole, providing a powerful gravity field and devouring any stars or other matter that approaches too close.
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Rather than imaging the black hole directly, ALMA gathered measurements of the gases trapped within the black hole’s gravitational well.
Scientists think every massive galaxy, like the Milky Way, has a massive black hole at its center, Baker said. They noted that these measurements were made possible by ALMA’s high-resolution observations of carbon monoxide emissions from the high-speed gas disk surrounding the black hole.
Being able to measure the mass of black holes allow scientists to better understand how they grow, change, and shape the universe around them. As we can’t see them (as there’s nothing to see as there’s no escaping light), astronomers have to look for black holes’ presence through other, indirect, means. “This is an exciting milestone for ALMA and a great demonstration of its high-resolution capability”, added Barth in a paper appeared in the Astrophysical Journal Letters.
73 million light-years away sits a supermassive black hole at the center of a galaxy known as NGC 1332.
About one in 10 elliptical galaxies contain disks of cold molecular gas and dust that orbit their centres.
“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 one of the researchers, Aaron Barth from the University of California, Irvine.
“Measuring the mass of a black hole accurately is very challenging, even with the most powerful telescopes on Earth or in space”, Barth said. By using the distance of the cloud from the black hole and clocking its speed, the team was able to estimate the mass of the black hole, and it was impressive.
Previous studies of NGC 1332 with ground- and space-based telescopes gave wildly different estimates for the mass of this black hole, ranging from 500 million to 1.5 billion times the mass of the Sun.
To weigh this supermassive black hole, a team at Rutgers University, led by Professor Andrew Baker, used the Alma radio telescope array in Chile.
The ALMA observations reveal details of the disk’s structure on the order of 16 light-years across.
Illustration of a blue star and black hole. The ratio of a black hole’s mass to a galaxy’s mass is important in understanding their makeup.
Part of understanding supermassive black holes is measuring their exact masses. “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”. However, ionized gas disks tend to exhibit more turbulent, chaotic motion, which lowers the precision of the mass measurement.
Barth’s group is analyzing ALMA investigations of several other elliptical galaxies from their study, and six more galaxies are in the queue to be studied during this year’s ALMA operating cycle.
“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”, Baker says.
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Scientists from Texas A&M University; the University of California, Irvine; the University of Colorado, Baker; and the Kavli Institute for Astronomy and Astrophysics at Peking University in Beijing are coauthors of the study.
