Chalk up yet another win for Einstein.
A twist in the fabric of spacetime — predicted by the
physicist’s theory of general relativity (SN: 10/7/15) — is causing
the orbit of one stellar corpse to teeter around another stellar corpse,
researchers report. And the relativistic corkscrew is helping astronomers
reconstruct the final days of these two long-dead stars.
According to general relativity, any spinning mass drags
spacetime around with it, like a hand mixer in molasses. One way to see this
“frame dragging” is to keep a careful eye on anything circling the spinning
object on a tilted orbit — the spacetime maelstrom will make the orbit wobble,
For the last 20 years, researchers have been using radio
telescopes to track the motion of a pulsar, the dense remains of a massive star
that went supernova, as it orbits a spinning white dwarf, the core of a lighter
star that died less violently. The pulsar, dubbed PSR J1141–6545, emits a
steady beat of radio waves as it spins, and by recording the arrival times of
those pulses, researchers can tell when the pulsar is moving toward and away
Over those two decades, the orbit
of the pulsar has been slowly precessing, astronomers report. The
precession isn’t much — the orbit’s tilt drifts by just 0.0004 degrees per year.
But it matches what researchers expect if the neighboring white dwarf whips up
spacetime as it spins. Vivek Venkatraman Krishnan, an astrophysicist at the Max
Planck Institute for Radio Astronomy in Bonn, Germany, and colleagues report the
results in the Jan. 31 Science.
This finding isn’t the first time that researchers have
observed frame dragging. Satellites in Earth’s orbit have captured the
relatively puny effect around our planet (SN: 11/24/15). And
astronomers also have observed fluctuations
in the frequency of X-ray light coming from a black hole, where frame
dragging should be quite intense, suggesting that gas may be precessing around it (SN: 12/17/15).
The new observation “is much more direct than mine,” says Adam
Ingram, an astrophysicist at the University of Oxford who studied the black
hole. “I can only infer that something is precessing in black hole systems,
whereas the precision radio observations presented here leave little room for
The pulsar precession helps researchers piece together the
final moments in the lives of both stars. Relativistic wobbling occurs only if
the orbit of the pulsar and the spin of the white dwarf are misaligned, something
which is usually smoothed over by an exchange of mass between the dying stars. “This
immediately tells us that the orbit was tilted due to the supernova explosion
that produced the pulsar,” Venkatraman Krishnan says.
Normally, the supernova would go off and then the progenitor
of the white dwarf would dump gas on the pulsar after the explosion, aligning
spin to orbit. But in this case, the opposite happened: The pulsar’s progenitor
dumped gas on the white dwarf and then the supernova occurred.