Two of the knots, they concluded, have been in all probability small galaxies with small inner motions being cannibalized by the massive galaxy. Measurements of the third knot had such giant error bars that it couldn’t but be dominated in or out because the black gap’s location.
The fourth, very compact knot close to the underside fringe of the core was too faint even for the Hubble, Dr. Burke-Spolaor reported. “Observing this knot would have required an overblown amount of time (hundreds of hours) observing with Hubble Space Telescope,” she mentioned in an e mail, and so it additionally stays a candidate for the black-hole hiding spot.
The galaxy core additionally emits radio waves, however they didn’t assist the search, Dr. Burke-Spolaor mentioned.
“We were originally hoping the radio emission would be some kind of literal smoking gun, showing an active jet that points directly back to black-hole location,” she mentioned. But the radio relic was no less than 50 million years outdated, based on its spectral traits, which meant, she mentioned, that the massive black gap would have had ample time to maneuver elsewhere because the jet turned off.
Next cease was NASA’s orbiting Chandra X-ray Observatory. Kayhan Gultekin of the University of Michigan, one other veteran Nuker who was not on the unique discovery staff, aimed the telescope on the cluster core and people suspicious knots. No cube. The putative black gap must be feeding at one-millionth of its potential charge if it have been there in any respect, Dr. Gultekin mentioned.
“Either any black hole at the center is very faint, or it isn’t there,” he wrote in an e mail. The similar goes for the case of a binary black-hole system, he mentioned; it could have to be consuming little or no gasoline to remain hidden.
In the meantime, Imran Nasim, of the University of Surrey within the U.Okay., who was not a part of Dr. Postman’s staff, has printed a detailed analysis of how the merger of two supermassive black holes may reform the galaxy into what the astronomers have discovered.
“Simply, gravitational wave recoil ‘kicks’ the supermassive black hole out of the galaxy,” Dr. Nasim defined in an e mail. Having misplaced its supermassive anchor, the cloud of stars across the black gap binary spreads out, turning into extra diffuse. The density of stars in that area — the densest a part of your entire large galaxy — is simply one-tenth the density of stars in our personal neighborhood of the Milky Way, leading to an evening sky that would seem anemic in contrast with our personal.
