Two doughnut-shaped vortexes ejected by a pulsating black hole. Also shown at the center are two red and two blue vortex lines attached to the hole, which will be ejected as a third doughnut-shaped vortex in the next pulsation. Credit: The Caltech/Cornell SXS Collaboration |
PASADENA,
Calif.—When black holes slam into each other, the surrounding space and
time surge and undulate like a heaving sea during a storm. This warping
of space and time is so complicated that physicists haven’t been able
to understand the details of what goes on—until now.
“We’ve
found ways to visualize warped space-time like never before,” says Kip
Thorne, Feynman Professor of Theoretical Physics, Emeritus, at the
California Institute of Technology (Caltech).
By
combining theory with computer simulations, Thorne and his colleagues
at Caltech, Cornell University, and the National Institute for
Theoretical Physics in South Africa have developed conceptual tools
they’ve dubbed tendex lines and vortex lines.
Using
these tools, they have discovered that black-hole collisions can
produce vortex lines that form a doughnut-shaped pattern, flying away
from the merged black hole like smoke rings. The researchers also found
that these bundles of vortex lines—called vortexes—can spiral out of the
black hole like water from a rotating sprinkler.
The
researchers explain tendex and vortex lines—and their implications for
black holes—in a paper that’s published online on April 11 in the
journal Physical Review Letters.
Tendex
and vortex lines describe the gravitational forces caused by warped
space-time. They are analogous to the electric and magnetic field lines
that describe electric and magnetic forces.
Tendex
lines describe the stretching force that warped space-time exerts on
everything it encounters. “Tendex lines sticking out of the moon raise
the tides on the earth’s oceans,” says David Nichols, the Caltech
graduate student who coined the term “tendex.” The stretching force of
these lines would rip apart an astronaut who falls into a black hole.
Vortex
lines, on the other hand, describe the twisting of space. If an
astronaut’s body is aligned with a vortex line, she gets wrung like a
wet towel.
These are two spiral-shaped vortexes (yellow) of whirling space sticking out of a black hole, and the vortex lines (red curves) that form the vortexes. Credit: The Caltech/Cornell SXS Collaboration |
When
many tendex lines are bunched together, they create a region of strong
stretching called a tendex. Similarly, a bundle of vortex lines creates a
whirling region of space called a vortex. “Anything that falls into a
vortex gets spun around and around,” says Dr. Robert Owen of Cornell
University, the lead author of the paper.
Tendex
and vortex lines provide a powerful new way to understand black holes,
gravity, and the nature of the universe. “Using these tools, we can now
make much better sense of the tremendous amount of data that’s produced
in our computer simulations,” says Dr. Mark Scheel, a senior researcher
at Caltech and leader of the team’s simulation work.
Using
computer simulations, the researchers have discovered that two spinning
black holes crashing into each other produce several vortexes and
several tendexes. If the collision is head-on, the merged hole ejects
vortexes as doughnut-shaped regions of whirling space, and it ejects
tendexes as doughnut-shaped regions of stretching. But if the black
holes spiral in toward each other before merging, their vortexes and
tendexes spiral out of the merged hole. In either case—doughnut or
spiral—the outward-moving vortexes and tendexes become gravitational
waves—the kinds of waves that the Caltech-led Laser Interferometer
Gravitational-Wave Observatory (LIGO) seeks to detect.
“With
these tendexes and vortexes, we may be able to much more easily predict
the waveforms of the gravitational waves that LIGO is searching for,”
says Yanbei Chen, associate professor of physics at Caltech and the
leader of the team’s theoretical efforts.
Additionally,
tendexes and vortexes have allowed the researchers to solve the mystery
behind the gravitational kick of a merged black hole at the center of a
galaxy. In 2007, a team at the University of Texas in Brownsville, led
by Professor Manuela Campanelli, used computer simulations to discover
that colliding black holes can produce a directed burst of gravitational
waves that causes the merged black hole to recoil—like a rifle firing a
bullet. The recoil is so strong that it can throw the merged hole out
of its galaxy. But nobody understood how this directed burst of
gravitational waves is produced.
Now,
equipped with their new tools, Thorne’s team has found the answer. On
one side of the black hole, the gravitational waves from the spiraling
vortexes add together with the waves from the spiraling tendexes. On the
other side, the vortex and tendex waves cancel each other out. The
result is a burst of waves in one direction, causing the merged hole to
recoil.
“Though
we’ve developed these tools for black-hole collisions, they can be
applied wherever space-time is warped,” says Dr. Geoffrey Lovelace, a
member of the team from Cornell. “For instance, I expect that people
will apply vortex and tendex lines to cosmology, to black holes ripping
stars apart, and to the singularities that live inside black holes.
They’ll become standard tools throughout general relativity.”
The
team is already preparing multiple follow-up papers with new results.
“I’ve never before coauthored a paper where essentially everything is
new,” says Thorne, who has authored hundreds of articles. “But that’s
the case here.”
The other authors on the Physical Review Letters
paper, “Frame-dragging vortexes and tidal tendexes attached to
colliding black holes: Visualizing the curvature of spacetime,” are Dr.
Jeandrew Brink at the National Institute for Theoretical Physics in
South Africa and Caltech graduate students Jeff Kaplan, Keith D.
Matthews, Fan Zhang, and Aaron Zimmerman.
This
research was supported by the National Science Foundation, the Sherman
Fairchild Foundation, the Brinson Foundation, NASA, and the David and
Barbara Groce Fund.