The Laser Guide Star (LGS) is launched from the VLT’s 8.2-metre Yepun Telescope and aims at the centre of our galaxy, in the heart of the brightest part of the Milky Way. The laser beam is part of the VLT’s adaptive optics system. It creates an artificial star at 90km altitude in the Earth´s mesosphere. This star is used as reference to correct images and spectra for the blurring effect of the atmosphere. The plane of the Milky Way is crossed by prominent dark lanes, huge clouds of interstellar dust that block the visible light. Thanks to the infrared instruments mounted in the Yepun Telescope, astronomers can ‘see through’ and study the complex and turbulent core of our galaxy, where a supermassive black hole is lurking. The ESO’s Very Large Telescope is composed by four 8.2-metre Unit Telescopes (UTs, where Yepun is UT4) plus four 1.8-metre movable Auxiliary Telescopes (ATs). Credit: G Hüdepohl (atacamaphoto.com)/ ESO.
Astronomers have announced that the first ever binary star has been found near to our galaxy’s supermassive black hole.
An international team of researchers has detected a binary star orbiting close to Sagittarius A*, the supermassive black hole at the centre of our galaxy.
It is the first time a stellar pair has been found in the vicinity of a supermassive black hole.
The discovery, based on data collected by the European Southern Observatory’s Very Large Telescope (ESO’s VLT), helps us understand how stars survive in environments with extreme gravity, and could pave the way for the detection of planets close to Sagittarius A*.
Lead author of the study, Florian Peißker, a researcher at the University of Cologne, Germany, said: “Black holes are not as destructive as we thought.”
Binary stars, pairs of stars orbiting each other, are very common in the Universe, but they had never before been found near a supermassive black hole, where the intense gravity can make stellar systems unstable.
This new discovery shows that some binaries can briefly thrive, even under destructive conditions.
D9, as the newly discovered binary star is called, was detected just in time: it is estimated to be only 2.7 million years old, and the strong gravitational force of the nearby black hole will probably cause it to merge into a single star within just one million years, a very narrow timespan for such a young system.
Co-author Emma Bordier, a researcher also at the University of Cologne and a former student at ESO, said: “This provides only a brief window on cosmic timescales to observe such a binary system — and we succeeded!”
This image indicates the location of the newly discovered binary star D9, which is orbiting Sagittarius A*, the supermassive black hole at the centre of our galaxy. It is the first star pair ever found near a supermassive black hole. The cut-out shows the binary system as detected by the SINFONI spectrograph on ESO’s Very Large Telescope. While the two stars cannot be discerned separately in this image, the binary nature of D9 was revealed by the spectra captured by SINFONI over several years. These spectra showed that the light emitted by hydrogen gas around D9 oscillates periodically towards red and blue wavelengths as the two stars orbit each other. Credit: ESO/ F Peißker et al., S. Guisard.
Harsh conditions
For many years, scientists also thought that the extreme environment near a supermassive black hole prevented new stars from forming there.
Several young stars found in close proximity to Sagittarius A* have disproved this assumption.
The discovery of the young binary star now shows that even stellar pairs have the potential to form in these harsh conditions.
Co-author Michal Zajaček, a researcher at Masaryk University, Czechia, and the University of Cologne, said: “The D9 system shows clear signs of the presence of gas and dust around the stars, which suggests that it could be a very young stellar system that must have formed in the vicinity of the supermassive black hole.”
Enigmatic
The newly discovered binary was found in a dense cluster of stars and other objects orbiting Sagittarius A*, called the S cluster.
Most enigmatic in this cluster are the G objects, which behave like stars but look like clouds of gas and dust.
It was during their observations of these mysterious objects that the team found a surprising pattern in D9.
The data obtained with the VLT’s ERIS instrument, combined with archival data from the SINFONI instrument, revealed recurring variations in the velocity of the star, indicating D9 was actually two stars orbiting each other.
Peißker said: “I thought that my analysis was wrong, but the spectroscopic pattern covered about 15 years, and it was clear this detection is indeed the first binary observed in the S cluster.”
The results shed new light on what the mysterious G objects could be. The team proposes that they might actually be a combination of binary stars that have not yet merged and the leftover material from already merged stars.
The precise nature of many of the objects orbiting Sagittarius A*, as well as how they could have formed so close to the supermassive black hole, remain a mystery.
But soon, the GRAVITY+ upgrade to the VLT Interferometer and the METIS instrument on ESO’s Extremely Large Telescope (ELT), under construction in Chile, could change this.
Both facilities will allow the team to carry out even more detailed observations of the Galactic centre, revealing the nature of known objects and undoubtedly uncovering more binary stars and young systems.
Peißker concluded: “Our discovery lets us speculate about the presence of planets, since these are often formed around young stars.
“It seems plausible that the detection of planets in the Galactic centre is just a matter of time.”
The study is published in Nature Communications.
