NASA’s NICER mission finds an X-ray pulsar in a record-fast orbit

The discovery bestows the stellar pair with the record for the shortest-known orbital period for a certain class of pulsar binary system.

By Jeanette Kazmierczak NASA’s Goddard Space Flight Center, Greenbelt, Md.
By Jeanette Kazmierczak NASA’s Goddard Space Flight Center, Greenbelt, Md.

Though Neutron star Interior Composition Explorer (NICER) mission, NASA scientists have found two stars that revolve around each other every 38 minutes — about the time it takes to stream a TV drama. The revelation offers the stellar match with the record for the briefest known orbital period for a specific class of pulsar binary system.

The explorer has detected that one of the stars named IGR J17062–6143 (J17062 for short), is a rapidly spinning. In view of the match’s very fast orbital period and division, researchers engaged in another investigation of the framework think the second star is a hydrogen-poor white dwarf.

Tod Strohmayer an astrophysicist at Goddard and lead author on the paper said, “It’s not possible for a hydrogen-rich star, like our Sun, to be the pulsar’s companion. You can’t fit a star like that into an orbit so small.”

In August, the instrument focused on J17062 for more than seven hours over 5.3 days. Combining additional observations in October and November, the science team was able to confirm the record-setting orbital period for a binary system containing what astronomers call an accreting millisecond X-ray pulsar (AMXP).

The researchers were able to determine that J17062’s stars revolve around each other in a circular orbit, which is common for AMXPs. The white dwarf donor star is a “lightweight,” only around 1.5 percent of our Sun’s mass. The pulsar is much heavier, around 1.4 solar masses, which means the stars orbit a point around 1,900 miles (3,000 km) from the pulsar.

Strohmayer said it’s almost as if the donor star orbits a stationary pulsar, but NICER is sensitive enough to detect a slight fluctuation in the pulsar’s X-ray emission due to the tug from the donor star.

“The distance between us and the pulsar is not constant,” Strohmayer said. “It’s varying by this orbital motion. When the pulsar is closer, the X-ray emission takes a little less time to reach us than when it’s further away. This time delay is small, only about 8 milliseconds for J17062’s orbit, but it’s well within the capabilities of a sensitive pulsar machine like NICER.”

The results of the study were published May 9 in The Astrophysical Journal Letters.

Other first-round results from the instrument have provided details about one object’s thermonuclear bursts and explored what happens to the accretion disk during these events.

NICER is an Astrophysics Mission of Opportunity within NASA’s Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined, and efficient management approaches within the heliophysics and astrophysics science areas. NASA’s Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.