A star orbits the Milky Way’s black hole at 18 million miles per hour

A star orbits the Milky Way's black hole at 18 million miles per hour
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A recently discovered star, now designated S4716, is traveling at a mind-boggling speed of 5,000 miles (8,000 km) per second around the black hole at the center of our Milky Way galaxy. reported.

The vast expanse of our universe means astronomers always find something they’ve never seen before. Earlier this week, astronomers detected two bus-sized asteroids heading for Earth, which will pass at distances barely a quarter of what separates the Moon from us.

Aside from asteroids, our galaxy is also of special interest to astronomers looking for signs of other planets harboring life. However, right in the center of the Milky Way, there is a supermassive black hole that has been dubbed Sagittarius A* or Sgr A* and S4716 is orbiting this black hole at a ferocious rate.

What we know about S4716

From observations made so far, we know that at 5,000 miles (8,000 km) per second or 18 million miles (29 million km) per hour, S4716 is the fastest star orbiting Sgr A*. Completes an orbit around 14.6 million (23.5 million km) in diameter black hole in just four years.

S4716 is part of a dense group of other stars that also orbit Sgr A*, which astronomers refer to as the S cluster. All the stars in this cluster move at high speeds but vary in their mass and brightness. Another star in this cluster, known as S2, is more popular and is much larger than S4716.

However, S2’s orbit around the black hole takes 16 years and comes within 11 billion miles (18 billion km) of Sgr A*. By comparison, S4716 comes within 9.2 billion miles (150 million km) of the black hole, that’s about 100 times the distance between Earth and the Sun.

The discovery of a star so close to a black hole could change our understanding of the evolution of our galaxy and its fast-moving stars. “S4716’s short-term compact orbit is quite puzzling,” said Michael Zajaček, an astrophysicist at Masaryk University. statement. “stars it cannot form so easily near the black hole. S4716 had to move inwards, for example by getting closer to other stars and objects in the S cluster, which caused its orbit to shrink significantly.”

How did astronomers detect the fastest star?

While S2 has helped us understand more details about Sgr A*, it does have drawbacks. “S2 behaves like a large person sitting in front of you in a movie theater: it blocks your view of what’s important. Therefore, the view towards the center of our galaxy is often obscured by S2,said Florian Peissker, an astrophysicist at the University of Cologne, who participated in this research, in a statement.

Peissker and his team used data from five telescopes, NIR2 and OSIRIS, at the Keck Observatory in Hawaii, and the Very Large Telescopes SINFONI, NACO and GRAVITY and refined their analytical techniques over two decades to confirm the orbital period of S4716. “For a star to be in a stable orbit so close and so fast in the neighborhood of a supermassive black hole was completely unexpected,” added Peissker.

The research was published in the astrophysical journal.


Continuous tracking of the galactic center and Sgr A*, the central supermassive black hole, produces surprising and unexpected findings. This goes hand in hand with the technical evolution of telescopes and instruments on the ground and in space, but also with the progression of image filtering techniques, such as the Lucy-Richardson algorithm. As we continue to track the members of the S cluster near Sgr A* on their expected trajectory around the supermassive black hole, we report the finding of a new stellar source, which we call S4716. The newly discovered star orbits Sgr A* in about 4.0 years and can be detected with NIRC2 (Keck), OSIRIS (Keck), SINFONI (VLT), NACO (VLT), and GRAVITY (VLTI). With a periapse distance of approximately 100 au, S4716 shows an equivalent distance towards Sgr A* as S4711. These fast-moving stars undergo similar dynamical evolution, as S4711–S4716 share comparable orbital properties. Furthermore, we will make a connection between the recent discovery of a faint new star called S300 and the data presented here. Additionally, we observed a mixed star event with S4716 and another newly identified S star S148 in 2017.

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