The types of black hole mergers predicted
by Einstein's general relativity have been accurately simulated
in a computer model for the first time.
The new
three-dimensional model provides a direct test of Einstein's theory
and could guide the hunt for gravitational waves, one of the most
elusive and sought-after forms of energy in the universe. "In the
past, we've always shown animations or artists' conceptions of
gravitational waves, but now we have Einstein's conception," said
Joan Centralla, head of NASA
Goddard's Gravitational Astrophysics Laboratory and a member of the
team that created the model.
The model was announced in a media
teleconference today.
Blinded by the waves
Black holes are regions of space where matter
is packed so tightly that the resulting gravity ensnares matter and
even light.
Einstein's general relativity predicts that
when black holes merge, they will emit gravitational waves that
distort the fabric of space-time like ripples spreading across a
pond. "These mergers are by far the most powerful events occurring
in the universe, with each one generating more energy than all of
the stars combined," Centralla said. "If our brains could detect
gravitational waves like light waves, we'd be blinded by black hole
mergers."
Even though gravitational waves are thought to
be ubiquitous throughout the universe, they have yet to be detected
directly because even the strongest gravitational waves would
interact with matter only very weakly.
Interpreting Einstein
Previous simulations of
black hole mergers
were plagued by crashes because they used translations of Einstein's
general relativity equations too complex for even the most
sophisticated computers.
Einstein's theory of general relativity uses
tensor calculus, a type of mathematics that can't be programmed
directly into computer code. The equations must be translated, but
as in the translation of a book from one language to another, the
process leaves some room for interpretation.
Just as some translations of Tolstoy's "Anna
Karenina" read better than others, certain renditions of Einstein's
equations are easier for computers to understand.
The new model, developed by scientists at
NASA's Goddard Space Flight Center in Maryland, is one such
translation. The simulation, shown
here in a
video animation, follows two non-spinning black holes of equal mass
spiraling around each other before colliding and then merging.
Stable result
Another reason the researchers think their
model is true to Einstein's equations, aside from not triggering
crashes, is that it shows black holes orbiting stably and producing
identical waveforms, called "ringdown," during the infall, collision
and aftermath—a first in these types of simulations.
"We're throwing down the gauntlet for
Einstein's theory of general relativity," said Paul Hertz, head
scientists of NASA's Science Mission Directorate, who was not
involved in the modeling. "When LIGO and LISA detect gravitational
waves from merging black holes, we'll know whether Einstein's theory
is right or wrong," Hertz said. LIGO, short for Laser Interferometer
Gravitational-Wave Observatory, is a currently operational
ground-based detector designed to detect these subtle waves. The
Laser Interferometer Space Antenna (LISA) is a planned NASA-ESA
mission with similar goals. The new work, led by John Baker of NASA
Goddard, is detailed in the March 26 issue of the journal Physical
Review Letters and an upcoming issue of Physical Review D.
