Star discovered with the shortest orbital period around a black hole

Black hole illustration stars

Artist’s impression of a black hole. A star has been discovered orbiting the black hole at the center of our galaxy, the Milky Way, at an amazing speed of 8,000 km/s.

It takes a newly discovered star just four years to orbit the black hole at the center of our Milky Way.

Astronomers have discovered the fastest known star traveling around a[{” attribute=””>black hole in record time. The star, S4716, orbits Sagittarius A*, the black hole in the center of our galaxy, in four years and reaches a speed of around 8,000 kilometers per second (5,000 miles per second) which is about 30 million kilometers per hour (18 million miles per hour).

S4716 comes as close as 100 AU (astronomical unit) to the black hole – a small distance by astronomical standards. One AU is the approximate mean distance from the Earth to the Sun and corresponds to 149,597,871 kilometers (92,955,807 miles). The study was conducted by researchers at the University of Cologne and Masaryk University in Brno (Czech Republic) and published on July 5, 2022, in The Astrophysical Journal.

In the area near the black hole at the center of our galaxy is a densely packed cluster of stars. This cluster, called the S cluster, is home to well over a hundred stars that differ in their brightness and mass. S stars move particularly fast.

“One prominent member, S2, behaves like a large person sitting in front of you in a movie theater: 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.”


Stars in the S cluster are orbiting the black hole at the center of our galaxy at high speed. S4716 is the fastest. Photo credits: Florian Peißker, University of Cologne

Through more and more refined analytical methods and observations over almost twenty years, the astronomers have now unequivocally identified a star that is orbiting the central supermassive black hole in just four years. A total of five telescopes observed the star, with four of those five being combined into one large telescope for even more accurate and detailed observations.

“For a star in a stable orbit to be so close and fast to a supermassive black hole was completely unexpected and marks the limit that can be observed with conventional telescopes,” Peissker said.

Star discovered with shortest orbital period around black hole

The K-band view of the GC observed with NIRC2 (Keck) in 2019.30. This image is high-pass filtered and shows the position of several S stars near Sgr A*, indicated by a black cross. The star in the white dashed circle shows a K-band magnitude of 16.3 mag, while the star in the blue circle is faint at 17.0 mag. Both K-band sizes agree with the values ​​reported for S62 by Peißker et al. match. (2020a) and those for S29 by Gillessen et al. (2017) and Peißker et al. (2021b). Here north is up and east is to the left. Image credit: The Astrophysical Journal, DOI: 10.3847/1538-4357/ac752f

In addition, the discovery sheds new light on the origin and evolution of the orbits of fast-moving stars at the heart of the planet[{” attribute=””>Milky Way. “The short-period, compact orbit of S4716 is quite puzzling,” Michael Zajacek, an astrophysicist at Masaryk University in Brno who was involved in the study, said. “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,” he added.

Reference: “Observation of S4716—a Star with a 4 yr Orbit around Sgr A*” by Florian Peißker, Andreas Eckart, Michal Zajacek and Silke Britzen, 5 July 2022, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ac752f