May 25 2018
One of the highest resolution observations in astronomical history was performed by a group of astronomers observing two intense regions of radiation, at a distance of 20 km from each other, around a star 6500 light-years away.
The pulsar PSR B1957+20 is seen in the background through the cloud of gas enveloping its brown dwarf star companion. (Image credit: Dr. Mark A. Garlick; Dunlap Institute for Astronomy & Astrophysics, University of Toronto)
The observation can be compared to using a telescope on Earth to view a flea on Pluto’s surface.
The amazing observation was achievable due to the unusual geometry and features of a pair of stars orbiting each other. One is a cool, lightweight star known as a brown dwarf, which has a “wake” or comet-like tail of gas. The other is an unusual, rapidly spinning star known as a pulsar.
“The gas is acting like a magnifying glass right in front of the pulsar,” says Robert Main the paper’s lead author describing the observation being published May 24 in the journal Nature. “We are essentially looking at the pulsar through a naturally occurring magnifier which periodically allows us to see the two regions separately.”
Main is a PhD astronomy student in the Department of Astronomy & Astrophysics at the University of Toronto, partnering with colleagues at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics and Canadian Institute for Theoretical Astrophysics, and the Perimeter Institute.
The pulsar is a neutron star that spins rapidly - more than 600 times per second. As the pulsar spins, it releases beams of radiation from the two hotspots on its surface. The intense regions of radiation being witnessed are related to the beams.
The brown dwarf star is nearly a third the diameter of the Sun. It is approximately two million kilometers from the pulsar - or five times the distance between the moon and the Earth - and orbits around it in little over nine hours. The dwarf companion star is tidally secured to the pulsar so that one side permanently faces its pulsating companion, similar to the way the moon is tidally secured to the Earth.
As it is so near the pulsar, the brown dwarf star is blasted by the intense radiation emanating from its smaller companion. The pulsar’s strong radiation heats one side of the comparatively cool dwarf star to the temperature of the Sun, or about 6000 °C.
The pulsar’s blast could eventually cause its companion’s demise. Pulsars in these types of binary systems are referred to as “black widow” pulsars. Like a black widow spider eating its mate, it is thought the pulsar, given the precise conditions, could progressively erode gas from the dwarf star until the latter is consumed.
Besides being an observation of extraordinarily high resolution, the result could be a clue to the nature of mysterious occurrences known as Fast Radio Bursts, or FRBs.
“Many observed properties of FRBs could be explained if they are being amplified by plasma lenses. 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.
Robert Main, Lead Author