They are the closest and sharpest images of the Milky Way’s core, where the giant Sagittarius A* black hole is located.
The destination is far away, the center of the Milky Way is about 27,000 light years from us. To get there, you must first cross a region invaded by cosmic dust in the constellation Sagittarius (the Archer). Behind the dust, a swarm of stars appears, orbiting an invisible monster, Sagittarius A*.
Sagittarius A* is a supermassive black hole, 4.3 million times the mass of the Sun. As the images get closer, it is possible to see a cluster of stars as seen by ESO’s Very Large Telescope NACO instrument (the last observation is from 2019). But the zoom zooms in even further, until almost everything goes dark. But it is possible to see the last stars, those closest to the black hole, observed with the GRAVITY instrument in ESO’s Very Large Telescope interferometry in mid-2021. The video capturing the journey into the galaxy’s interior was created by ESO / GRAVITY / L Sidewalk / N Risinger / DSS. The music is by Johan Monel. The journey starts here:
The last stars of the Milky Way
There are many stars around the black hole. In fact, millions are estimated to exist within 1.6 light years of the Milky Way’s central black hole. S29 is the closest known star to Sagittarius A* and, in their observations, astronomers have seen it approach the black hole at a distance of just 13 billion kilometers. That’s only about 90 times the distance from land to sun. The star was moving at a record speed of 8,740 kilometers per second.
Another of the stars close to the cosmic monster is S62, which is the fastest (known) star orbiting Sgr A*, with an orbital period of 9.9 years.
This animation, taken with images taken with the GRAVITY instrument on the ESO Very Large Telescope (VLTI) interferometer between March and July 2021, shows stars orbiting very close to Sgr A*, the supermassive black hole at the heart of the Milky Way.
Movement of stars around the black hole Sagittarius A *
Unraveling Secrets of the Black Hole of Sagittarius A *
The inner black hole at the center of the Milky Way does not emit light, it cannot be observed directly. Astronomers can only learn about their properties by studying the motions of stars in their vicinity.
‘Following stars in close orbits around Sagittarius A* allows us to accurately probe the gravitational field around Earth’s closest massive black hole, test general relativity and determine the properties of the black hole, “explains Reinhard Genzel, director of El Max Planck Institute for Extraterrestrial Physics and winner of the 2020 Nobel Prize in Physics for his research on Sagittarius A*
Measurements, taken between March and July 2021, revealed that Sagittarius A* has a mass of 4.3 million suns and is located at a distance of 27,000 light-years from Earth. Both numbers are the most accurate estimates of their kind to date.
The research is part of an international project called GRAVITY, which is developing new techniques to analyze images of the Milky Way’s galactic center in order to map the surroundings of Sagittarius A* in as much detail as possible. The project takes place in the Very Large Telescope , one of the most advanced optical space observatories in the world. It consists of four main telescopes, each 8.2 meters in diameter, and four auxiliary telescopes, 1.8 meters in diameter. It can detect stellar objects four billion times fainter than what can be seen with the naked eye.
In his ongoing exploration of our galaxy’s deepest interior, he detected dancing stars near the mysterious Sagittarius A*. The measurements and images obtained were made possible by GRAVITY, an instrument of ESO’s VLTI. GRAVITY combines light from the four telescopes using a technique called interferometry. This technique is complex, “but in the end you get images 20 times sharper than individual VLT telescopes, revealing the secrets of the Galactic Center,” said Frank Eisenhauer of the MPE, principal investigator at the GRAVITY. And that’s how they’ve been able to observe the movement of stars very close to the black hole at the center of our galaxy.
The new research were published in two articles published in the journal Astronomy & Astrophysics