At edge of black hole, a star Albert Einstein would have loved
Scientists have found a star orbiting very close to the supermassive black hole at the center of the Milky Way. It could help scientists give Einstein's brilliance one of its sternest tests yet.
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Beyond the attraction of getting results before getting a gold watch, the discovery could represent the first in a larger population of dim stars at the galactic center.Skip to next paragraph
In Pictures Space photos of the day: Black Holes
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The star at the center of Friday's report, dubbed S0-102, is substantially dimmer than the star with the 16-year period, dubbed S0-2. In the rest of the galaxy, faint stars outnumber bright stars, so detecting such a dim star in this region "opens the door to detecting many more in that environment, if they exist," he says, allowing for increasingly precise tests of general relativity, Dr. Loeb suggests.
The effects related to general relativity can be seen in the impact supermassive black holes have on the stars' orbits as they make their closest approach, he adds.
Like Earth orbiting the sun, stars do not travel around black holes in circles, but ellipses – meaning they are sometimes closer and sometimes farther away. But instead of tracing the same elliptical orbit repeatedly, as the Earth does around the sun, the elliptical orbits of short-period stars should shift with time, tracing a rosette pattern around the behemoth.
In addition, changes in the intensity of the black hole's enormous gravitational pull as the stars make their closest approach should also affect the apparent speed at which light travels from the star, as seen from Earth. Dr. Ghez and colleagues note that this effect is too weak to see around an object like the sun, or even around more massive objects such as neutron stars. But with S0-102 and S0-2, the effect should appear as light shifting further into the red end or blue end of the spectrum as the stars orbit nearer the black hole. If Einstein is correct, the black hole's warping of space should make the shift in light more pronounced than under than would be the case under the picture of gravity Sir Isaac Newton drew.
Beyond putting Einstein to yet another set of tests, Leob says, these short-period stars also could help answer a question that continues to dog astrophysicists: What's feeding the Milky Way's black hole?
The black hole at the Milky Way's center is dormant – it's not emitting the vast amounts of radiation that supermassive black holes on a feeding frenzy do. Yet infalling matter is emitting enough radiation to let researchers know that the black hole is partaking in the cosmic equivalent of light snacks.
The source of the snacks could merely be interstellar gas close to the black hole. It also could be gas shed in the form of stellar winds from close-in stars. "The more stars we find, the better the constraints we will get about the origin of the gas that reaches the black hole," he says.
Ghez's team discovered both short-period stars using the Keck telescopes, which sit atop Hawaii's Mauna Kea. But the ability to make precise measurements needed to test Einstein's theories will have to await the construction of a new generation of Earth-based telescopes with light-gathering mirrors are three times the size of Keck's the team holds.