For the first time, astronomers using a new instrument on the European Southern Observatory’s Very Large Telescope (VLT) have conducted observations of the supermassive black hole at the center of the Milky Way, officials from the facility announced early Thursday morning.
The instrument in question is known as GRAVITY. It is part of the VLT Interferometer, and it combines light from all four of the array’s telescopes so that it can achieve the same spatial resolution and precision in measuring positions as a telescope 130 meters in diameter – a 15-fold increase over the individual telescopes’ capabilities, according to ESO officials.
“These results provide a taste of the groundbreaking science that GRAVITY will produce as it probes the extremely strong gravitational fields close to the central supermassive black hole and tests Einstein’s general relativity,” the Observatory explained. “Even from early test results, it is already clear that it will soon be producing world-class science.”
One of the primary goals of the new instrument, they added, is to conduct detailed observations of the four million solar mass black hole at the heart of the Milky Way. While experts have known the black hole’s position and mass for more than a decade, using GRAVITY to precisely measure the movement of stars orbiting the black hole will allow scientists to better analyze the gravitational field surrounding it and test the general theory of relativity.
Breakthrough comes just in the nick of time
With that ultimate goal in mind, the ESO scientists are calling these first observations of the Milky Way’s black hole, which is located in the constellation of Sagittarius (The Archer) some 25,000 light years from Earth, “very exciting.” They have already used GRAVITY to monitor a star known as S2 as it orbits the black hole over a period of just 16 years.
These observations have demonstrated the instrument’s sensitivity, as it was able to detect this relatively faint star after just a few minutes time, and indicates that they should soon be able to use the device to gather extremely precise positions of S2 equivalent to measuring an object’s position on the Moon within a few centimeters. By doing so, they can determine whether or not the object travels around the black hole in the manner predicted by Einstein’s theory.
“It was a fantastic moment for the whole team when the light from the star interfered for the first time — after eight years of hard work,” GRAVITY’s lead scientist, Frank Eisenhauer of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said in a statement. “First, we actively stabilized the interference on a bright nearby star, and then only a few minutes later we could really see the interference from the faint star – to a lot of high-fives.”
The timing of this breakthrough is ideal, the ESO said. In 2018, S2 will be at its closest distance from the black hole – only 17 light-hours away and moving at a velocity of nearly 30 million km per hour. At this distance, the influence of general relativity will be at its greatest and GRAVITY scientists will be able to obtain their best results at the attempt to measure two relativistic effects (the gravitational redshift and the precession of the pericentre) of the star orbiting the black hole. It will be another 16 years before a similar opportunity presents itself, the Observatory said.
Image credit: ESO