Einstein's Right Again

Astronomers have detected hints of Einstein's general relativity in the Milky Way's supermassive black hole.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff from how stuff Works. Hey, brain stuff,
it's Christian Sager. Scientists always seem to be finding new
evidence of Albert Einstein being right. The latest example comes
from astronomers using the European Southern Observatories very large telescope

(00:22):
in Chile. Astronomers there have been studying the stars that
orbit dangerously close to the supermassive black hole in the
center of our galaxy. To find that you guessed it.
Einstein's landmark theory of general relativity is holding strong even
at the doorstep of the most extreme gravitational field in
our galaxy. Most galaxies are known to have super massive

(00:46):
black holes lurking in their cores. In our galaxy, the
Milky Way is no different. Located approximately twenties six thousand
light years from Earth, our black hole behemoth is called
Agittarius A, and it has a mass four million times
that of our Sun. Astrophysicists are hugely interested in black holes,

(01:10):
as they're the most compact, gravitationally dominant objects known in
the universe, and therefore an extreme test for relativity. By
tracking the motion of stars orbiting close to Sagittarius A,
a team of German and Czech astronomers have analyzed twenty
years of observations made by the Very Large Telescope and

(01:34):
other telescopes using a new technique that pinpoints the positions
of these stars. One of the stars, called S two
orbits Sagittarius A every sixteen years and zooms very close
to the black hole, around four times the distance between
Neptune and our Sun. Because of its racetrack orbit deep

(01:57):
inside the black holes gravitational well S two is treated
as a natural relativity probe into this mysterious strong gravity environment.
By precisely measuring its motion around the black hole, the
researchers could compare its orbit with predictions laid out by
classical Newtonian dynamics, and they found that the star's actual

(02:21):
orbit deviated from Newtonian predictions exactly as predicted by Einstein's
general relativity, although the effect was slight. Here's a quick
example of Einsteinian gravity at work. If you have a
massive object, it will bend spacetime, like the famous example
of the bowling ball suspended on a rubber sheet. If

(02:42):
another object travels past the massive object, the curvature of
space time will deflect its direction of motion like a
marble rolling past the bowling ball. Now in two thousand
and eighteen, S two will swoop to its closest point
in its orbit around Sagittarius A, and astronomers using the

(03:03):
Very Large Telescope are preparing a new instrument to get
an even more precise view of the extreme environment surrounding
the black hole, called gravity and that's gravity in all caps.
The instrument is installed on the Very Large Telescopes Interferometer,
and astronomers not only predict that it will get an

(03:25):
even more precise gauge on Einstein's general relativity, it might
even detect deviations away from relativity, possibly hinting at new
physics beyond relativity. Today's episode was written by Ian O'Neill,

(03:45):
produced by Dylan Fagan, and for more on this and
other topics, don't forget to visit how Stuff Works dot com.