BrainStuff Classics: How Can a Black Hole Help Prove General Relativity?

Astronomers detected hints of Einstein's theory of general relativity in the Milky Way's supermassive black hole. Learn more in this classic episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeart Radio. Hi brain Stuff.
I'm Lauren Bogelbaum, and today's episode is a classic from
our erstwhile host, Christian Sager. This one is about one
of the many amazing observations that researchers have made about
black holes over the past few years, and how it
proves Einstein's theory of relativity to be correct once again.

(00:25):
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 in Chile. Astronomers there have been studying
the stars at orbit dangerously close to the supermassive black

(00:48):
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
gravitate sational field in our galaxy. Most galaxies are known
to have super massive black holes lurking in their cores.

(01:08):
In our galaxy, the Milky Way is no different. Located
approximately twenties six thousand light years from Earth, our black
hole behemoth is called Sagittarius A, and it has a
mass four million times that of our Sun. Astrophysicists are
hugely interested in black holes, as they're the most compact,

(01:32):
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 other telescopes using a new

(01:55):
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 inside the black hole's gravitational well,

(02:19):
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 orbit deviated from Newtonian predictions

(02:43):
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 space time,
like the famous example of the bowling ball suspended it
on a rubber sheet. If another object travels past the

(03:04):
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 Very Large Telescope are preparing a new

(03:25):
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 even more precise gauge on Einstein's

(03:47):
general relativity, it might even detect deviations away from relativity,
possibly hinting at new physics beyond relativity. An update the
research that came out in eighteen was also groundbreaking. It

(04:08):
was the best evidence would record it yet, but Sagittarius.
A star is indeed a black hole and not a
different kind of phenomenon. Today's episode was written by Ian
O'Neill and produced by Dylan Fagan and Tyler Clang. For
more and listen lots of other massive topics, visit houstof
works dot com. Brain Stuff is production of iHeart Radio
or more podcasts my heart Radio visit the iHeart Radio app,

(04:29):
Apple Podcasts, or wherever you listen to your favorite shows.