Space

Astronomers have detected a star careening through the Milky Way at 2.5 million mph

Many stars sedately tread the measure of the galaxies they inhabit, slowly orbiting the galactic core. Not a star called PSR J0002+6216, though. PSR J0002+6216, astronomers have discovered, is rocketing through the Milky Way at absolutely breakneck speeds.

To be precise, it’s travelling at 1,130 kilometres per second (700 miles per second). That could take it from Earth to the Moon in 6 minutes. It’s one of the fastest stars we’ve ever seen.

And boy, is it spectacular – zooming away from the expanding cloud of a recent supernova explosion, leaving a trail behind after it punched through the explosion’s outer shell of debris.

PSR J0002+6216 (J0002 for short, although we prefer ‘Zoomy’) is a type of neutron star called a pulsar. A neutron star is the collapsed core of a star below a certain mass after it has gone supernova.

In turn, pulsars are highly magnetised neutron stars with an extraordinarily fast spin rate, which emit jets of electromagnetic radiation as they spin. If these jets are lined up correctly, spinning so the radiation flashes at Earth, we can see it – like a cosmic lighthouse.

“Thanks to its narrow dart-like tail and a fortuitous viewing angle, we can trace this pulsar straight back to its birthplace,” said astronomer Frank Schinzel of the National Radio Astronomy Observatory.

“Further study of this object will help us better understand how these explosions are able to ‘kick’ neutron stars to such high speed.”

Zoomy, which is about 6,500 light-years (1,992 parsecs) away in the constellation of Cassiopeia, is about 53 light-years from the centre of a bubble-shaped supernova remnant called CTB 1. The tail, observed in the radio spectrum, trails for 13 light-years between the outer shell of the supernova debris, and the star.

This acts as a cosmic arrow of sorts, pointing directly to the pulsar’s birthplace.

“Measuring the pulsar’s motion and tracing it backwards shows that it was born at the centre of the remnant, where the supernova explosion occurred,” said astrophysicist Matthew Kerr of the Naval Research Laboratory.

The researchers think that the supernova explosion that produced CTB 1 could have been asymmetrical, which somehow kicked the pulsar into high speed, sending it careening off into space.

The explosion, the team was able to ascertain, took place around 10,000 years ago. Zoomy caught up with the edge of the supernova bubble around 5,000 years ago.

“The explosion debris in the supernova remnant originally expanded faster than the pulsar’s motion,” said astronomer Dale Frail of the National Radio Astronomy Observatory. “However, the debris was slowed by its encounter with the tenuous material in interstellar space, so the pulsar was able to catch up and overtake it.”

It’s moving so fast that it will eventually be able to escape the Milky Way and continue speeding through intergalactic space.

Other neutron stars have been observed at these incredible speeds, too – the fastest being RX J0822-4300, travelling at an absolutely jaw-dropping 1,500 kilometres per second.

Our friend Zoomy is still one of the fastest, though, with the average pulsar only travelling at about 240 kilometres per second. And it has the clearest signpost to its point of origin. This is an amazing discovery, because it could help astronomers understand the dynamics that launch these stars into space at such tremendous speeds.

One hypothesis is that instabilities in the collapsing star could create a region of slow-moving matter that gravitationally pulls the neutron star towards it, creating the acceleration. So far, Zoomy seems to be consistent with this – although, naturally, more observation is needed.

“We have more work to do to fully understand what’s going on with this pulsar, and it’s providing an excellent opportunity to improve our knowledge of supernova explosions and pulsars,” Schinzel said.

The team’s paper has been submitted to The Astrophysical Journal Letters.

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