Researchers at the University of Cologne and Masaryk University in Brno (Czech Republic) have clocked a star, labeled S4716, orbiting Sagittarius A*, the black hole at the center of our Milky Way Galaxy, at 8000 kilometers (4971 miles) per second, currently making it the fastest known star. The findings were published in The Astrophysical Journal.
While S4716 displays incredible speeds while orbiting Sagittarius A*, it still takes about four years to complete one orbit while coming as close as 100 AU (astronomical unit) to the black hole. For context, one astronomical unit is equivalent to the distance from the Sun to the Earth. While 100 AU might seem large, this is still relatively small distance by astronomical standards.
“The short-period, compact orbit of S4716 is quite puzzling,” said Michael Zajaček, an astrophysicist at Masaryk University in Brno and co-author on the study. “Stars cannot form so easily near the black hole. S4716 had to move inwards, for example by approaching other stars and objects in the S cluster, which caused its orbit to shrink significantly.” The S cluster is a densely packed cluster of stars in the vicinity of Sagittarius A*. It is home to well over a hundred stars that differ in mass and brightness and are known to move particularly fast such as S4716.
“One prominent member, S2, behaves like a large person sitting in front of you in a movie theatre: it blocks your view of what's important,” said Dr Florian Peissker, lead author of the new study. “The view into the center of our galaxy is therefore often obscured by S2. However, in brief moments we can observe the surroundings of the central black hole.”
The comprehensive study was carried out using observations covering almost 20 years using five telescopes to observe S4716, four of which were combined into one large telescope to allow for even more accurate and detailed observations of S4716.
“For a star to be in a stable orbit so close and fast in the vicinity of a supermassive black hole was completely unexpected and marks the limit that can be observed with traditional telescopes,” said Peissker.
Sources: The Astrophysical Journal
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