‘Black Widow Pulsar’ Spotted 6,500 Light-Years From Earth Could Offer More Clues On Fast Radio Bursts

Mark A. GarlickDunlap Institute for Astronomy & Astrophysics/University of Toronto

A study just published in the journal Nature hails several new and exciting discoveries which could be used in the future to unlock the secrets of one of the most mysterious phenomena in the universe, namely Fast Radio Bursts, or FRBs.

It all started with a distant pulsar, a fast-spinning superdense neutron star residing in a binary star system 6,500 light-years away from our planet. This pulsar, dubbed PSR B1957+20, is believed to be one of the most massive ever discovered and, according to Science Alert, was identified 30 years ago.

The neutron star is about 20 kilometers (about 12.5 miles) wide, which makes it roughly the size of a large town, and spins at dizzying speeds, completing more than 600 rotations per second. As it does so, the pulsar emits powerful beams of radiation traced back to two cones of incredibly intense radio waves discovered on the star’ surface.

The reason we know all of this is because Canadian astronomers at the University of Toronto have managed to do something never before achieved in the entire astronomical history.

In a mind-blowing feat, the Canadian team succeeded in mapping the pulsar in unprecedented detail, performing one of the highest resolution observations ever accomplished.

In a news release by the Dunlap Institute for Astronomy and Astrophysics, the university commented on this spectacular achievement.

“The observation is equivalent to using a telescope on Earth to see a flea on the surface of Pluto.”

Here’s how they pulled it off.

The pulsar dwells in a double star system, which means it has a stellar companion — in this case, a brown dwarf that stretches for about a third of our sun’s width. This star orbits the pulsar about every nine hours, at a distance of nearly two million kilometers (about 1.2 million miles), or roughly five lunar distances.

The brown dwarf star is tidally locked to its pulsar neighbor, meaning that only one side ever faces the neutron star. Because of the relatively short distance between them (at least, in cosmic terms), that side is continuously blasted by the pulsar’s powerful radiation beams, which nuke the brown dwarf star and heat up its surface at temperatures comparable to those of the sun.

This makes the brown dwarf shoot a cloud of gas into space, which ended up helping the astronomers see the pulsar more clearly.

Black widow pulsar PSR B1957+20 and its brown dwarf companion.
The ‘black widow pulsar’ seen in the background, through the gas cloud enveloping its brown dwarf star companion.Featured image credit: Mark A. GarlickDunlap Institute for Astronomy & Astrophysics/University of Toronto

“The gas is acting like a magnifying glass right in front of the pulsar,” said study lead author Robert Main.

“We are essentially looking at the pulsar through a naturally occurring magnifier which periodically allows us to see the two regions separately,” he explained.

This amazing breakthrough allowed the astronomers to examine the pulsar’s emission spectrum, as seen through the cloud of plasma ejected by the brown dwarf star.

What they uncovered was that the pulsar’s emissions have a similar structure to that of a repeating Fast Radio Burst known as FRB 121102. Although this particular neutron star is not a known source of FRBs, this discovery could bring scientists one step closer to finally understanding this strange natural phenomenon.

“Many observed properties of FRBs could be explained if they are being amplified by plasma lenses,” Main points out.

As he explains, these observations could help reveal more details on the nature of FRBs.

“The properties of the amplified pulses we detected in our study show a remarkable similarity to the bursts from the repeating FRB, suggesting that the repeating FRB may be lensed by plasma in its host galaxy.”

Although a fortuitous circumstance for astronomical studies, the same phenomenon that helped the team map the pulsar will inevitably spell doom for its stellar companion, reports the university. The gas cloud is slowly being eroded by the pulsar’s powerful radiation, which is gradually consuming the brown dwarf in an act of stellar cannibalism.

This monstrous act has labeled PSR B1957+20 as a “black widow pulsar,” a new class of binary neutron stars that chew away at their companion.