Rapidly-spinning pulsar is devouring brown dwarf companion

Gas trailing brown dwarf acts as a natural magnifier, enabling detailed observations of the pulsar.
By Laurel Kornfeld | Oct 05, 2018
A team of researchers conducted the highest-resolution astronomical observation in history with the Arecibo Observatory in Puerto Rico, looking at two regions of intense radiation on the rapidly spinning pulsar PSR B1957+20, also known as the Black Widow pulsar.

PSR B1957+20 is classed as a millisecond pulsar because it spins more than 600 times per second. While spinning, it emits beams of intense radiation from two surface hot spots.

Pulsars are spinning neutron stars, stellar remnants left behind when massive stars die in supernova explosions.

By observing the pulsar, located 6,500 light years away, in high resolution, the scientists successfully pointed out its two radiation regions, which are separated by just 12 miles (20 km), a feat compared to using a telescope on Earth to see a flea on the surface of Pluto.

Scientists can see this pulsar in such detail because it is part of a binary system and has a brown dwarf companion. The two objects orbit each other every nine hours. By chance, they are aligned with Earth in a configuration that causes an eclipse to occur for 20 seconds during each orbit.

Because the brown dwarf is speeding through space at 620,000 miles per hour (one million kilometers per hour), it has a comet-like tail of gas that acts as a naturally occurring magnifying glass, enabling astronomers to see the pulsar and its two separate radiation areas up close.

"The extraordinary observation was made possible by the rare geometry and characteristics of a pair of stars orbiting each other. One is a cool, lightweight star called a brown dwarf, which features a 'wake,' or comet-like tail of gas. The other is an exotic, rapidly spinning star called a pulsar," explained study leader Robert Main of the University of Toronto.

"The gas is acting like a magnifying glass right in front of the pulsar. We are essentially looking at the pulsar through a naturally occurring magnifier, which periodically allows us to see the two regions [of radiation] separately."

With a diameter of about one-third that of our Sun, the brown dwarf orbits the pulsar at a distance of just 1.2 million miles (about two million kilometers), in contrast with the Earth, which orbits the Sun at a distance of about 93 million miles (150 million kilometers).

In such a close orbit, the brown dwarf is tidally locked to the pulsar, meaning one side of it always faces the pulsar while the other side always faces away from it.

Bombarded by intense radiation from the pulsar, the side facing it is heated up to a temperature as high as 10,000 degrees Fahrenheit (6,000 degrees Celsius)

Eventually, the pulsar will destroy the brown dwarf by pulling away all its gas.

A paper on the observations, which were conducted before Arecibo was damaged by Hurricane Maria last September, has been published in the journal Nature.

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