The odds of seeing such an event for an isolated black hole were slim, but given that millions of stellar-mass black holes are predicted to be drifting through our galaxy, some might turn up in sufficiently broad and deep surveys of the sky.
Eddington’s work, however, suggested these outcasts could be found by observing their lensing effects-typically a telltale transient brightening of any background stars the black holes flit across within our field of view. That cosmic wanderlust-plus the black holes’ small sizes and inherent darkness-should make them almost impossible to see. These forces can be so great they sometimes kick the newborn black hole right out of its womb on an endless interstellar cruise. The birth of such a stellar-mass black hole-a city-sized sphere containing up to dozens of times our sun’s mass-is often accompanied by a bright supernova from the enormous energies released by the core collapse. Stars greater than about 20 times the mass of our sun should form black holes at the end of their lives, when their heavy cores collapse under their own weight following the exhaustion of their thermonuclear fuel. In the subsequent decades, scientists realized a novel use for this technique. “The apparent position of the stars had a tiny shift,” says Feryal Özel from the University of Arizona, who was also not involved in the paper. Using a technique known as astrometry, he carefully noted these stars’ positions before and during the eclipse, revealing a subtle change in their apparent locations in the sky due to their light being warped by our star’s considerable gravitational pull.
Eddington proved this to be true during a total solar eclipse, when the sun’s glare was minimized so that background stars adjacent to it in the heavens could be seen. Einstein’s theories of special and general relativity had postulated that massive objects should cause a dent in spacetime, bending nearby rays of light in a process known as gravitational lensing. In 1919, the British astronomer Arthur Stanley Eddington performed a famous experiment. “It’s the tip of the iceberg,” says Kareem El-Badry from the Harvard-Smithsonian Center for Astrophysics, who was not involved in the paper. “We can actually prove that isolated black holes are there.” This discovery may be just the start ongoing surveys and upcoming missions are expected to find dozens or even hundreds more of the dark, lonely travelers. “It’s super exciting,” says Marina Rejkuba from the European Southern Observatory in Germany, a co-author on the paper. The result, which appeared January 31 on the arXiv preprint server but has not yet been peer-reviewed, represents the culmination of more than a decade of ardent searching. Scientists have announced the first-ever unambiguous discovery of a free-floating black hole, a rogue wanderer in the void some 5,000 light-years from Earth. Never before, though, have we seen a long-predicted phenomenon: an isolated black hole drifting aimlessly through space, born and flung out from the collapsing core of a massive star. Closer to home, we have witnessed the dramatic celestial fireworks produced when the Milky Way’s own supermassive black hole and its more diminutive cousins feed on gas clouds or even entire stars. Meanwhile, researchers now routinely detect gravitational waves rippling through the universe from smaller merging black holes. The biggest ones-supermassive black holes that can weigh billions of suns-have been found at the centers of most every galaxy, and we have even managed to image one. These are boom times for astronomers hunting black holes.
0 kommentar(er)
