GRAVITY reveals the most detailed and deepest images of the Milky Way’s Supermassive Black Hole
The European Southern Observatory’s Very Large Telescope Interferometer (VLTI) has captured the most detailed and crisp images to date of the region surrounding our galaxy’s supermassive black hole.
The new images provide a 20-fold increase in magnification above what was previously achievable before the VLTI and have enabled scientists to discover a previously unseen star near the black hole.
The scientists made the most precise assessment of the black hole’s mass to date by following the orbits of stars at the center of our Milky Way.
“We want to learn more about the black hole at the centre of the Milky Way, Sagittarius A*: How massive is it exactly? Does it rotate? Do stars around it behave exactly as we expect from Einstein’s general theory of relativity? The best way to answer these questions is to follow stars on orbits close to the supermassive black hole. And here we demonstrate that we can do that to a higher precision than ever before,” said Reinhard Genzel, who was awarded a Nobel Prize in 2020 for Sagittarius A* research.
The latest findings by Genzel and his team, which build on a three-decade study of stars around the Milky Way’s supermassive black hole, were published today in two papers in Astronomy & Astrophysics.
The GRAVITY collaboration created a new analysis technique that allowed them to collect the deepest and sharpest photos of our Galactic Centre yet, in order to identify even more stars near to the black hole.
“The VLTI gives us this incredible spatial resolution and with the new images we reach deeper than ever before. We are stunned by their amount of detail, and by the action and number of stars they reveal around the black hole,” added Julia Stadler, who led the team’s imaging efforts during her time at MPE.
Surprisingly, they discovered a star called S300 that had never been spotted before, demonstrating how effective this method is for detecting dim objects near Sagittarius A*.
The scientists concentrated their most recent observations, which took place between March and July 2021, on taking exact measurements of stars as they approached the black hole. This covers the world’s closest approach to the black hole, which occurred in late May 2021. It passed it at an astounding speed of 8740 kilometers per second at a distance of just 13 billion kilometers, roughly 90 times the Sun-Earth distance. No other star has ever been seen passing so near to the black hole or traveling so quickly around it.
GRAVITY uses interferometry to integrate the light from all four 8.2-metre telescopes of ESO’s Very Large Telescope (VLT).
This technique is complex, “but in the end you arrive at images 20 times sharper than those from the individual VLT telescopes alone, revealing the secrets of the Galactic Centre,” said Frank Eisenhauer from MPE, principal investigator of GRAVITY.
“Following stars on close orbits around Sagittarius A* allows us to precisely probe the gravitational field around the closest massive black hole to Earth, to test General Relativity, and to determine the properties of the black hole,” explained Genzel.
The new observations, when paired with prior data from the team, demonstrate that the stars move in the exact path predicted by General Relativity for objects orbiting around a black hole with a mass 4.30 million times that of the Sun. This is the most precise estimate of the Milky Way’s center black hole’s mass to date. The researchers were also able to fine-tune the distance to Sagittarius A*, which they discovered to be 27 000 light-years away.
The scientists utilized a machine-learning technique known as Information Field Theory to capture the new images. They created a model of how real sources may appear, simulated how GRAVITY would see them, and compared it to GRAVITY observations.
This enabled them to discover and track stars in the vicinity of Sagittarius A* with unprecedented depth and accuracy. In addition to the GRAVITY observations, the researchers used data from two former VLT instruments, NACO and SINFONI, as well as measurements from the Keck Observatory and NOIRLab’s Gemini Observatory in the United States.
GRAVITY will be upgraded to GRAVITY+ later this decade, which will also be put on ESO’s VLTI and will increase sensitivity to show fainter stars even closer to the black hole. The team hopes to eventually identify stars that are so close to the black hole that their orbits are affected by the gravitational effects induced by its revolution. ESO’s forthcoming Extremely Large Telescope (ELT), which is now under construction in Chile’s Atacama Desert, will allow the scientists to determine the velocity of these stars with much greater precision.
“With GRAVITY+’s and the ELT’s powers combined, we will be able to find out how fast the black hole spins,” added Eisenhauer.
“Nobody has been able to do that so far.”
Source: 10.1051/0004-6361/202142465 and doi:10.1051/0004-6361/202142459
Image Credit: ESO/GRAVITY collaboration
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