Lightest known pair of neutron stars passes another test of Einstein's theory
Astronomers have found the lightest known pair of neutron stars, Live Science and Phys.org reported. The two dead stars circle each other every 2 hours and 22 minutes. Timing radio pulses from one of the stars showed that their motion matches Einstein's theory of gravity to within about 1%.
Astronomers have discovered the lightest known pair of neutron stars, and its motion matches Albert Einstein's general theory of relativity to within about 1%, according to Live Science. Phys.org also reported the find.
Neutron stars are the collapsed cores of huge stars that exploded. Each holds more mass than the sun in a ball about 12 miles (20 kilometers) across. Some, called pulsars, spin fast and send out beams of radio waves that work like very precise clocks.
The new system, called PSR J1856-0039, lies about 4,200 to 6,500 light-years from Earth, Live Science reported. China's FAST radio telescope, the world's largest single-dish radio telescope, found it in 2020. The two stars circle each other every 2 hours and 22 minutes.
The pulsar weighs about 1.3 times as much as the sun, and its partner about 1.19 times, Live Science reported. The partner is one of the lightest neutron stars known.
The team watched the pair 17 times between 2020 and 2025. By timing radio pulses, the researchers found three effects that Einstein's theory predicts. The orbit is shrinking by about 9 feet (2.7 meters) a year as the stars give off gravitational waves. The oval orbit also slowly turns, and the pulsar's clock speeds up and slows down along its path.
"We found that general relativity is needed to explain the data, and the consistency is about 1%," said study co-author JinLin Han of the National Astronomical Observatories of the Chinese Academy of Sciences, according to Live Science.
The stars are expected to merge in about 82 million years. The merger would probably leave a heavier neutron star, though it could instead collapse into a black hole, the researchers estimate.
The findings were published Sept. 15 in the journal Physical Review Letters. The team hopes to keep watching the pulsar for decades to measure how its spin twists space-time.
What we know: The pair is the lightest known double neutron star system, and it fits Einstein's theory to within about 1%.
What we don't: Whether decades of more data will reveal any cracks in the theory.
Where outlets agree Live Science and Phys.org report that PSR J1856-0039 is the lightest known double neutron star system, with a 2.36-hour orbit that fits Einstein's general relativity.
Where they differ The cited reports agree on the key facts so far.