and luminous events in the uni-
verse. But few are easy to find, and
even fewer emit the radio waves
crucial to understanding them.
Each new discovery is precious.
And in just a few more minutes,
I will be the only person on Earth
to know whether, for this source, a
radio signal exists. I drum my fin-
gers faster.To r n a p a r t
The story of a TDE begins at the
heart of a galaxy, near the edge of
a supermassive black hole millions
or billions of times the mass of the
Sun. Astronomers now think that
practically every large galaxy has
one such black hole at its center.
These gravitational monstrosities
play a key role in the formation of
their host galaxies and wield huge
inf luence on their surroundings.
Black holes are famously so
dense that even light cannot
escape their gravity. But despite
popular conceptions, they don’tactually suck material in any more
than the Sun sucks in the planets
that orbit it. For example, if the
Sun were to suddenly compress
into a black hole, it would shrink
to just 4 miles (6 kilometers)
across, yet the planets would con-
tinue to orbit as they currently do
because its mass wouldn’t change.The gravity of a black hole
works the same way. When astron-
omers look to the center of our
own Milky Way Galaxy, we see
over a dozen stars orbiting a com-
mon point where our galaxy’s
supermassive black hole, called
S a g it t a r iu s A* (S g r A*), r e s i d e s.
In fact, astronomers have been
observing Sgr A* for so long thatthey have seen the innermost star,
S2, complete one full orbit, which
takes 16 years. After establishing
S2’s orbital parameters, researchers
applied Kepler’s third law of plan-
etary motion to calculate the mass
of Sgr A*, which clocks in at a
whopping 4 million solar masses.
While the final calculation wassimple, the work to get the data
over so many years was not — in
fact, it won astronomers Andrea
Ghez and Reinhard Genzel the
2020 Nobel Prize in physics.
S2 looks like it’s on a stable
orbit for now, but researchers esti-
mate that thousands of stars,
including stellar remnants like
neutron stars and white dwarfs,26 ASTRONOMY • DECEMBER 2021
The star deforms from its usual sphere
into an oval, and then into a long,
thin stream. This process is called
spaghettification.
The 64-dish array of
the MeerKAT radio
telescope lies in
South Africa’s Karoo
region, in the
Northern Cape
province. SOUTH AFRICAN
RADIO ASTRONOMY
OBSERVATORY (SARAO)