On 8 November 2017, a spinning neutron star inside one of the most studied objects in the sky “glitched” more than it had ever glitched before.
Back in the year 1054, Chinese astronomers spotted what looked like a new star, which soon dimmed. They’d actually seen a supernova: a star exploding, ejecting gas and dust and perhaps collapsing. Today, all that’s left of the supernova is a cloud inside the constellation Taurus with a central, rapidly spinning neutron star called a pulsar. Pulsars are extreme objects that have about the mass of our sun but are mere kilometres across. They typically rotate at a constant rate and emit a beam of radiation that appears to us like the regular flashing of a lighthouse. Recently, that pulsar hiccuped.
Assuming the Crab pulsar is really the remnant of the 1054 supernova, it’s pretty young, astronomically. Younger pulsars can glitch, meaning they suddenly rotate faster before relaxing to their original rotation rate.
The Jodrell Bank Observatory’s 42-foot telescope devoted to observing the Crab pulsar. (Photo: Benjamin Shaw/Wikimedia Commons)
There are plenty of things astronomers can learn from these glitches. “The physics of neutron stars embodies tremendous extremes, not just of density but of gravity and magnetic field,” McGill University astrophysicist Victoria Kaspi, who was not involved in the new study of the pulsar, told Gizmodo. “Glitches are possibly a rare probe of the inside of these incredible objects.”
Scientists at the Jodrell Bank Observatory at the University of Manchester have been observing the Crab pulsar daily since 1984. The star, which typically spins at a rate of 30 rotations per second, has had smaller glitches 24 times since then. These were increases of around a millionth of rotation more per second.
This glitch, an increase of around 15 millionths of a rotation per second, was the Crab pulsar’s largest, according to the paper published on the arXiv physics preprint server. This was surprising, as scientists have long thought that the Crab pulsar only experienced small glitches, unlike other pulsars, such as the Vela pulsar, which experience larger ones.
The Crab Nebula with the pulsar inside. (Image: X-ray: NASA/CXC/SAO/F Seward; Optical: NASA/ESA/ASU/J Hester & A Loll; Infrared: NASA/JPL-Caltech/Univ. Minn./R Gehrz)
It’s still unknown what causes these glitches, scientist Benjamin Shaw explained in a Twitter thread. Some think it could be momentum exchanged between the star’s interior and its crust, in which the fluid interior slows and the crust speeds up, but that’s not the only possibility.
Some extreme glitches are thought to relate to these stars’ magnetic fields, and glitches can be associated with changes to x-ray energies or even an explosion, said Kaspi. But despite its extremity, this most recent glitch from the Crab pulsar didn’t come with a noticeable change to the pulsar’s emitted energy.
The scientists will continue to observe the Crab pulsar and watch as it slows back to normal following the glitch. Being that it is a neutron star, turning it off and back on again will not prevent further glitches. [arXiv]