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

A recently discovered star, designated S4716, is orbiting the black hole at the center of our galaxy, the Milky Way, at an astonishing speed of 5,000 miles (8,000 km) per second. Space.com reported.

The vastness of our universe means astronomers are always finding something they’ve never seen before. Earlier this week, astronomers spotted two bus-sized asteroids heading toward Earth that will pass at distances just a quarter of what separates the moon from us.

Aside from asteroids, our galaxy is also of particular interest to astronomers looking for signs of life on other planets. However, right at the center of the Milky Way is a supermassive black hole dubbed Sagittarius A* or Sgr A*, and S4716 is orbiting this black hole at breakneck speed.

What we know about S4716

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

S4716 is part of a dense cluster of other stars also orbiting Sgr A*, dubbed the S Cluster by astronomers. All of the stars in this cluster are moving at high speed, but vary in mass and brightness. Another star in this cluster, known as S2, is better known and much larger than S4716.

However, S2’s orbit around the black hole takes 16 years and comes up to 11 billion miles (18 billion km) from Sgr A*. By comparison, S4716 comes as close as 92 million miles (150 million kilometers) from the black hole, 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 brief, compact orbit is quite puzzling,” said Michael Zajaček, an astrophysicist at Masaryk University in a Expression. “Stars cannot form so easily near the black hole. S4716 had to move inward, for example by getting closer to other stars and objects in the S cluster, causing its orbit to shrink significantly.

How did astronomers discover the fastest star?

While S2 helped us understand more details about Sgr A*, it does have downsides. “S2 behaves like a large person sitting in front of you in a cinema – it blocks your view of what is important. The view into the center of our galaxy is therefore often obscured by S2,” said Florian Peißker, astrophysicist at the University of Cologne who was involved in this research, in a statement.

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

The study was published in The Astrophysical Journal.


Ongoing monitoring of the galactic center and Sgr A*, the central supermassive black hole, is yielding surprising and unexpected results. This goes hand in hand with the technical development of ground- and space-based telescopes and instruments, but also with the advancement of image filtering techniques such as the Lucy Richardson algorithm. As we continue to follow the members of the S cluster near Sgr A* on their expected trajectory around the supermassive black hole, we present the discovery of a new stellar source 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 periaptic distance of about 100 AU, S4716 has an equivalent distance to Sgr A* as S4711. These fast-moving stars experience a similar dynamic evolution as S4711–S4716 share comparable orbital properties. We will also link the recent discovery of a new faint star called S300 to the data presented here. In addition, in 2017 we observed a blend star event involving S4716 and another newly identified S star, S148

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