Fri 2018-08-03 09:39:47 -0400
Observations have been made of a star S2 apparently orbiting the black hole at the center of the Milky Way Galaxy Sgr A* using positional and spectroscopic observations at the Very Large Telescope on Cerro Paranal in Chile.
The VLT consists of four 8.2-meter telescopes and operates at visible and infrared wavelengths.
From the announcement at ESO,
New infrared observations from the exquisitely sensitive GRAVITY ,
SINFONI and NACO instruments on ESO’s Very Large Telescope (VLT) have
now allowed astronomers to follow one of these stars, called S2, as it
passed very close to the black hole during May 2018. At the closest
point this star was at a distance of less than 20 billion kilometres
from the black hole and moving at a speed in excess of 25 million
kilometres per hour — almost three percent of the speed of light.
The new measurements clearly reveal an effect called gravitational
redshift. Light from the star is stretched to longer wavelengths by
the very strong gravitational field of the black hole. And the change
in the wavelength of light from S2 agrees precisely with that
predicted by Einstein’s theory of general relativity. This is the
first time that this deviation from the predictions of the simpler
Newtonian theory of gravity has been observed in the motion of a star
around a supermassive black hole.
Continuing observations are expected to reveal another relativistic
effect very soon — a small rotation of the star’s orbit, known as
Schwarzschild precession — as S2 moves away from the black hole.
There’s an amazing video from observations over a period of 20 years clearly showing S2 passing periapsis.