New Evidence Shows Black Hole Growth Preceding Galactic Formation

The co-evolution of black holes, almost unfathomable in their bulk, and the even more massive galaxies that host them remains poorly understood—a kind of chicken-and-egg problem on mammoth scales. Do black holes, such as the lunker in our own Milky Way Galaxy, which contains the mass of four million suns (that’s about eight undecillion, or 8 x 10^36 kilograms), drive the evolution of galaxies around them; or do galaxies naturally nurture the gravitational gobblers at their centers; or perhaps do they come into being together, as a matched pair?

A serendipitous discovery in a relatively close-by dwarf galaxy may help answer that question. Amy Reines, a graduate student in astronomy at the University of Virginia (U.V.A.), was looking at bursts of star formation in a galaxy known as Henize 2-10, which serves as a kind of observational proxy for galaxies that existed in the early universe. She noticed a suspicious radio wave source coming from a small region of the galaxy, a good distance removed from the active stellar nurseries. A comparison with archival data showed x-ray radiation from the same location within Henize 2-10; the balance of radiation levels in different wavelengths pointed to the presence of a giant black hole accreting material from its surroundings.

That is notable because Henize 2-10 lacks a detectable spheroid, or galactic bulge, in its center, which is usually directly related to the mass of a galaxy’s black hole. “That suggests that you just don’t need one to make a black hole,” Reines says. “People have thought that galaxies and their black holes have grown synchronously,” she adds. “This really challenges this notion and suggests that a massive black hole could form ahead of its galaxy.” Reines and her colleagues from U.V.A. and the National Radio Astronomy Observatory, headquartered in Charlottesville, Va., reported the finding online January 9 in Nature

via Scientific American.

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