Astronomers find binary star system with x-ray pulsar in orbit
New Delhi : During the study of heavenly objects, astronomers have found a pair of stars orbiting one another at record speed. The duo revolves around each other once every 38 minutes, the shortest-known orbital period for its specific class of pulsar binary systems.
Strohmayer and his colleagues detailed their investigation and named the unusual pair as J17062 and they mentioned that the pair was discovered while interrogating the first batch of data recorded by the Neutron star Interior Composition Explorer mission, or NICER mission.
Researchers believe that the system is made up of a rapidly spinning, super dense neutron star called an accreting millisecond X-ray pulsar and a hydrogen-poor white dwarf.
"It's not possible for a hydrogen-rich star, like our sun, to be the pulsar's companion," Tod Strohmayer, an astrophysicist at NASA's Goddard Space Flight Center, said in a news release. "You can't fit a star like that into an orbit so small."
Experts explain that Neutron stars are the extremely hot, superdense stellar cores sometimes left over after supernovae. The stars are so hot, they emanate X-rays. Their violent spin and its accretion from its companion cause intense beams of X-rays to pulse from their poles.
NICER data showed J17062 pulses 163 times per second, which means the pulsar is spinning at a speed of 9,800 revolutions per minute. Though J17062 boasts a record orbit, its spin rate is average. Some pulsar spin some 700 revolutions per second, several orders of magnitude greater than J17062 spin rate.
The hotspots that create the neutron star's polar pulses are created by the accretion of material from its companion, the hydrogen-poor white dwarf. The material then is pulled into an accretion disk, much like a black hole. Because the pulsar has an intense magnetic field, the material in the accretion disk is pulled into the stellar core unevenly, creating hotspots.
Over time, the pulsar will accumulate more material than it can handle. The excess mass will finally trigger a thermonuclear reaction, a massive release of energy in the form of X-rays. NICER can detect such releases, but has yet to measure an outbreak from J17062.
While the pulsar's donor star is weak, it still has a minimal effect on the orbital path of J17062. That the slight perturbation can be measured is an evidence to the sensitivity of NICER's instruments.
"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 study of J17062 is being published this week in the Astrophysical Journal.