Star\u2019s extreme proximity to Sagittarius A* means it could open new window onto black hole\u2019s fundamental properties<\/p>\n
Astronomers have detected the fastest known star in the Milky Way, hurtling around the supermassive black hole at the heart of the galaxy.<\/p>\n
The star, called S301, travels at about 25,000km (15,500 miles) per second, 100,000 times faster than a commercial plane. It is also the closest known star to the Milky Way\u2019s central black hole, Sagittarius A*, approaching it around the distance of Saturn to the Sun.<\/p>\n
\u201cWhat is special about this star is that it\u2019s orbiting Sagittarius A* on a very tight orbit, taking just 8.7 years to complete it, and is approaching the black hole at a mere 12 times the distance of Earth to the sun. That is unprecedented,\u201d said Felix Mang, a PhD student at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, and an author of the study published on the findings.<\/p>\n
The star\u2019s extreme proximity to Sagittarius A* means that it could open a new window on to the black hole\u2019s fundamental properties and the extreme environment surrounding it.<\/p>\n
Like many objects in the night sky, black holes are predicted to spin. According to Einstein\u2019s general theory of relativity, a spinning black hole drags spacetime along with it, warping the orbits of surrounding stars. This effect is only meaningful for objects orbiting fast-rotating black holes at close range.<\/p>\n
S301 appears to have the perfect combination of a highly eccentric (lopsided) and very tight orbit.<\/p>\n
\u201cFor the first time, we would actually be able to measure very directly the spin of a massive black hole, which would be a key test of Einstein\u2019s theory,\u201d said Dr Stefan Gillessen, a senior scientist at MPE and a co-author of the study, which is published in the journal Nature.<\/p>\n
Previously it had been assumed it would require measuring the motion of multiple stars for several decades to estimate the spin of Sagittarius A*. The scientists were able to trace S301\u2019s orbit back to 2017 and, by tracking it through its next closest passage in 2031, hope to have enough data.<\/p>\n
\u201cWith this star we hope to measure, within the next 10 years, the spin of the black hole,\u201d said Mang.<\/p>\n
The observations were made using the European Southern Observatory\u2019s Very Large Telescope Interferometer (ESO\u2019s VLTI) at the Paranal Observatory in Chile, which combines the light from four 8-metre telescopes.<\/p>\n
Although the star is unusually close to the central black hole, it is not expected to cross its event horizon, the point beyond which objects can never escape.<\/p>\n
\u201cBlack holes are perceived as these cosmic vacuum cleaners engulfing everything they can get a handle on,\u201d said Mang. \u201cBut it\u2019s just a massive object. It\u2019s not really much different from something orbiting the sun and it\u2019s going to remain on this orbit.\u201d<\/p>\n
Dr Ziri Younsi, an astrophysicist at University College London, who was not involved in the observations, said: \u201cThis is incredibly important as a discovery. It\u2019s very exciting because this thing comes insanely close to Sagittarius A* and it\u2019s travelling, at its peak, at about 8% of the speed of light, which is crazy.\u201d<\/p>\n
Younsi said that using the orbit to provide a measurement of the black hole\u2019s spin would be a gamechanger for understanding the evolution of the Milky Way.<\/p>\n