Many stars are found in binary systems where two-star orbit one another. Recently, astronomers have discovered two unique stars that revolve around each other at a neck-break speed, meaning they complete an orbit in every 38 minutes. This is about the time it takes to stream a TV drama.
The binary star is named IGR J17062–6143 or J17062 for short and it consists of a rapidly spinning, a super-dense star called a pulsar and a white dwarf with a mass around 1.5 percent of our Sun. Data from NASA’s Neutron star Interior Composition Explorer (NICER) mission show that these stars are only 186,000 miles apart, which is less than the distance between Earth and the moon. The stellar pair now holds the record for the shortest-known orbital period for a certain class of pulsar binary system.
The binary star system was first observed in 2008 by the Rossi X-ray Timing Explorer (RXTE). But that 20-minute observation could not determine the exact orbital speed of the binary star. With NICER installed aboard the International Space Station, researchers were able to observe the system for much longer periods of time and confirmed the record-setting orbital period for a binary system with an accreting millisecond X-ray pulsar (AMXP). X-ray pulsar is a rapidly spinning neutron star that displays variations in X-ray intensity. These variations or pulses mark the locations of hot spots around the pulsar’s magnetic poles, which allow astronomers to determine how fast it is spinning. Observations reveal that J17062’s pulsar is rotating at about 9,800 revolutions per minute.
“Neutron stars turn out to be truly unique nuclear physics laboratories, from a terrestrial standpoint,” said lead researcher Zaven Arzoumanian, a Goddard astrophysicist for NICER. “We can’t recreate the conditions on neutron stars anywhere within our solar system. One of NICER’s key objectives is to study subatomic physics that isn’t accessible anywhere else.”
Hot spots are caused by long-lasting mass transfer from a low-mass companion star (in J17062, from the white dwarf) through an accretion disc onto a slow-rotating neutron star. As a neutron star continues to pull the material away from a stellar companion through its intense gravitational field, it spins more rapidly and makes hot spots visible for X-ray instruments like NICER, which record the fluctuations. NICER’s high-precision measurements could be used to further study the behavior of neutron stars.
“The distance between us and the pulsar is not constant,” said Tod Strohmayer an astrophysicist at Goddard. “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.”