“The story of A2261-BCG,” he said, referring to the galaxy’s formal name in literature, “is what happens with the most massive galaxies in the universe, the giant elliptical galaxies, at the end point of galaxy evolution.”īlack holes are objects so dense that not even light can escape their gravitational clutches. Over the past four decades, they have sought to elucidate the nature of galactic nuclei, using the sharp eye of Hubble and other new facilities to peer into the intimate hearts of distant galaxies. The group first came together under Sandra Faber of the University of California, Santa Cruz, in the early days of the Hubble Space Telescope.
Lauer is part of an informal group who call themselves Nukers. “What happens when you eject a supermassive black hole from a galaxy?” Lauer asked. He added that the upcoming James Webb Space Telescope would have the capability to shed light, so to speak, on the case. “It’s an intriguing mystery, and we’re on the case,” Postman said in an email. Proving the latter could provide insight into some of the most violent and dynamic processes in the evolution of galaxies and the cosmos, about which astronomers have theorized but never seen - a dance of titanic forces and swirling worlds that can fling stars and planets across the void. But another provocative possibility, Lauer and his colleagues say, is that the black hole was thrown out of the galaxy altogether. One possibility is that the black hole is there but has gone silent, having temporarily run out of anything to eat.
So where has nature stashed the equivalent of 10 billion suns? Comparatively, the black hole at the center of the Milky Way galaxy is only about 4 million solar masses. Using the standard rule of thumb, the black hole missing from the center of the 2261 galaxy should be 10 billion solar masses or more. It is about 2.7 billion light-years from here, in the constellation Hercules in the northern sky, not far from the prominent star Vega. The galaxy is the brightest one in a cluster known as Abell 2261. In the years since, the two researchers and their colleagues have been looking for X-rays or radio waves from the missing black hole. “Oh, my God, this is really unusual,” Tod Lauer, an expert on galactic nuclei at the National Optical Astronomy Observatory in Tucson, Arizona, and an author on the paper, recalled saying when Postman showed him the finding. Scientists are probing the knots at its core for signs of a supermassive black hole. In an image provided by NASA, a composite image of the galaxy cluster Abell 2261 made from X-ray, optical and infrared data. Moreover, the entire core, a cloud of stars some 20,000 light-years across, was not even in the middle of the galaxy. On the contrary, at the exact center of the galaxy’s wide core, where a slight bump in starlight should have been, there was a slight dip. Normally, the galaxy’s core would have a kink of extra light in its center, a kind of sparkling cloak, produced by stars that had been gathered there by the gravity of a giant black hole. So it was a surprise a decade ago when Marc Postman, of the Space Telescope Science Institute, using the Hubble Space Telescope to survey clusters of galaxies, found a supergiant galaxy with no sign of a black hole in its center.
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