While we normally think about the sky as it appears to our eyes, the universe doesn’t limit itself to the narrow band of colors visible to humans. If you could see the sky in radio light, you might be able to make out the rapid pulses of fast rotating dead stars. 

When some massive stars die, their outer layers explode outward while their inner core collapses down to the diameter of Manhattan island. Like an ice skater drawing their arms inward and inward, these star cores spin ever faster and faster; some rotate as many a thousand times a second. These spinning tops have massive magnetic fields that aren’t aligned with their rotation, and every time the magnetic pole points toward us, radio telescopes see a flash. 

The largest radio telescope in the world is China’s Five-hundred-meter Aperture Spherical radio Telescope (FAST), and in a new study of pulsar PSR J0538+2817, a research team led by Jumei Yao has measured not just the pulsar’s rotation but also its three-dimensional motion through space. 

This pulsar lurks near the center of supernova remnant S147. We say near because the same supernova that formed that remnant formed the pulsar, and the pulsar has been on the move ever since. While astronomers have previously been able to measure the radial velocity of pulsars – their motion toward and away from us – we haven’t previously been able to measure their 3D motion. 

Using FAST and other powerful telescopes around the world, astronomers have now measured how this pulsar moves in the plane of the sky relative to the edges of the supernova remnant, and this has allowed them to see that the direction of the pulsar’s motion and its spin axis, and those two vectors are aligned to a small angle — the difference is just ten degrees. We don’t know if this means pulsar’s spin axis and motion are generally aligned or if just this one pulsar is aligned, but we now know this alignment can be measured, and I expect more publications like this to help us understand this alignment more in the future.

More Information

CAS press release

“Evidence for three-dimensional spin–velocity alignment in a pulsar,” Jumei Yao et al., 2021 May 6, Nature Astronomy