material it was plowing through.
Finally, optical observations con-
firmed the location of the source
itself: smack in the center of the
host galaxy, where a supermassive
black hole lurks.
Then, after about a year and
a half of this activity, the X-ray
signal suddenly dropped off pre-
cipitously, to the point where
Swift could no longer detect it.
Astronomers realized they’d justwitnessed another
incredible event — the jet
turning off. Normally, relativ-
istic jets from black holes last for
thousands of years, at least. The
fact that this one lasted for less
time than it takes Mars to orbit
the Sun was unprecedented, and
a boon for astronomers working
to unravel their mysteries.
Once the jet turned off, the
shock wave from Swift J1644+57slowly faded in energy. The
X-ray emission is now long gone,
but the blast still has enough
power to send out radio waves
that the Very Large Array (VLA)
in New Mexico can study for
100 years. I know this because
I did the analysis myself.3
Eventually, the tidal forces become stronger than the star’s self-gravity,
ripping the star apart. Some of the disassembled stellar material forms an
accretion disk around the black hole, and some of it is flung into space.
4
As matter swirls around the black hole, magnetic fields focus some of the
material into a powerful jet, whose particles travel at close to the speed of
light. This creates shock waves inside the jet that produce intense beams of X-rays
and radio waves.Accretion diskDisrupted
starRelativistic jetWWW.ASTRONOMY.COM 29
A thin stream of
material from a
tidally disrupted
star is pulled into
an accretion disk
around a black hole
in this illustration.
DESY, SCIENCE
COMMUNICATION LABIn this close-up view,
the remnants of the
star are visible on
the right side of the
black hole. The ring
of light that appears
to surround the
black hole is due to
gravitational lensing
— the gravity of the
black hole bending
light around it. DESY,
SCIENCE COMMUNICATION LABAL
L^ ILL
USTRAT
IO
NS:^ AST
RONOMY:^ R
OEN^
KELLY