Deepest images yet of Milky Way's supermassive black hole

Date:
December 14, 2021
Source:
ESO
Summary:
Astronomers have obtained the deepest and sharpest images to date
of the region around the supermassive black hole at the center of
our galaxy.

The new images zoom in 20 times more than what was possible before
the VLTI and have helped astronomers find a never-before-seen
star close to the black hole. By tracking the orbits of stars at
the centre of our Milky Way, the team has made the most precise
measurement yet of the black hole's mass.



FULL STORY ==========================================================================
The European Southern Observatory's Very Large Telescope Interferometer
(ESO's VLTI) has obtained the deepest and sharpest images to date of the
region around the supermassive black hole at the centre of our galaxy. The
new images zoom in 20 times more than what was possible before the VLTI
and have helped astronomers find a never-before-seen star close to the
black hole. By tracking the orbits of stars at the centre of our Milky
Way, the team has made the most precise measurement yet of the black
hole's mass.


==========================================================================
"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," explains Reinhard Genzel, a director at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany who was awarded a
Nobel Prize in 2020 for Sagittarius A* research. Genzel and his team's
latest results, which expand on their three-decade-long study of stars
orbiting the Milky Way's supermassive black hole, are published today
in two papers in Astronomy & Astrophysics.

On a quest to find even more stars close to the black hole, the team,
known as the GRAVITY collaboration, developed a new analysis technique
that has allowed them to obtain the deepest and sharpest images yet of
our Galactic Centre. "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," explains Julia Stadler, a researcher at
the Max Planck Institute for Astrophysics in Garching who led the team's imaging efforts during her time at MPE. Remarkably, they found a star,
called S300, which had not been seen previously, showing how powerful
this method is when it comes to spotting very faint objects close to Sagittarius A*.

With their latest observations, conducted between March and July 2021,
the team focused on making precise measurements of stars as they
approached the black hole. This includes the record-holder star S29,
which made its nearest approach to the black hole in late May 2021. It
passed it at a distance of just 13 billion kilometres, about 90 times
the Sun-Earth distance, at the stunning speed of 8740 kilometres per
second. No other star has ever been observed to pass that close to,
or travel that fast around, the black hole.

The team's measurements and images were made possible thanks to GRAVITY,
a unique instrument that the collaboration developed for ESO's VLTI,
located in Chile. GRAVITY combines the light of all four 8.2-metre
telescopes of ESO's Very Large Telescope (VLT) using a technique
called interferometry. 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," says
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," explains Genzel. The new observations,
combined with the team's previous data, confirm that the stars follow
paths exactly as predicted by General Relativity for objects moving
around a black hole of mass 4.30 million times that of the Sun. This is
the most precise estimate of the mass of the Milky Way's central black
hole to date. The researchers also managed to fine-tune the distance to Sagittarius A*, finding it to be 27,000 light-years away.

To obtain the new images, the astronomers used a machine-learning
technique, called Information Field Theory. They made a model of how the
real sources may look, simulated how GRAVITY would see them, and compared
this simulation with GRAVITY observations. This allowed them to find and
track stars around Sagittarius A* with unparalleled depth and accuracy. In addition to the GRAVITY observations, the team also used data from NACO
and SINFONI, two former VLT instruments, as well as measurements from
the Keck Observatory and NOIRLab's Gemini Observatory in the US.

GRAVITY will be updated later this decade to GRAVITY+, which will
also be installed on ESO's VLTI and will push the sensitivity further
to reveal fainter stars even closer to the black hole. The team aims
to eventually find stars so close that their orbits would feel the gravitational effects caused by the black hole's rotation. ESO's
upcoming Extremely Large Telescope (ELT), under construction in the
Chilean Atacama Desert, will further allow the team to measure the
velocity of these stars with very high precision. "With GRAVITY+'s and
the ELT's powers combined, we will be able to find out how fast the black
hole spins," says Eisenhauer. "Nobody has been able to do that so far." ========================================================================== Story Source: Materials provided by ESO. Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
*
ESO's_VLTI_images_of_stars_at_the_centre_of_the_Milky_Way:_Images,_video,
and_animation ========================================================================== Journal References:
1. R. Abuter, N. Aimar, A. Amorim, J. Ball, M. Baubo"ck, S. Gillessen,
F.

Widmann, G. Heissel. Mass distribution in the Galactic Center based
on interferometric astrometry of multiple stellar orbits. Astronomy
& Astrophysics, 2021; DOI: 10.1051/0004-6361/202142465
2. J. Stadler, A. Drescher. Deep images of the Galactic center with
GRAVITY.

Astronomy & Astrophysics, 2021; DOI: 10.1051/0004-6361/202142459 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211214104235.htm

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