Astronomers using NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) have found the most luminous pulsar ever discovered. Located 12 million light-years away in the galaxy Messier 82 (M82), a pulsar exists that is 10 million times brighter than the sun. The research was led by Matteo Bachetti of the University of Toulouse and the paper was published in Nature.
As with many incredible discoveries, this one came by chance as the team was looking for something else entirely. While using NuSTAR to image a supernova in M82, they noticed two incredibly bright X-ray signatures. One of these sources was a medium-sized black hole, but the other signal was pulsing, indicating that they were looking at a pulsar.
Pulsars are neutron stars that spin rapidly and are magnetized. As gas and dust are pulled inward, they are heated up and become illuminated. Electromagnetic radiation spanning from radio all the way up to high-energy gamma rays appears to burst out as the pulsar rotates. Just like a lighthouse beacon, this light can only be viewed when spotted head on. As such, they are identified by the pulsing effect they produce.
This particular star creates a pulse once every 1.37 seconds that is brighter than any pulsar previously discovered, at around 10 million times brighter than our sun. This is far more luminous than anything astronomers predicted.
"You might think of this pulsar as the 'Mighty Mouse' of stellar remnants," Fiona Harrison of CalTech and NuSTAR’s principal investigator said in a press release. "It has all the power of a black hole, but with much less mass."
This pulsar is much brighter than any pulsar that has ever been detected. It has been classified as an ultraluminous X-ray source (ULX), as it is much brighter than radiation detected in typical stellar activity. Because of the amount of radiation required to produce that much light, most ULXs are black holes and not ordinary stellar objects like pulsars.
"We took it for granted that the powerful ULXs must be massive black holes," Bachetti added. "When we first saw the pulsations in the data, we thought they must be from another source."
What hasn’t been made immediately clear is how this pulsar is able to produce that much light. The pulsar, which is about the size of a city yet as massive as our sun, must be consuming much more than what has ever been deemed theoretically possible.
"The pulsar appears to be eating the equivalent of a black hole diet," she continued. "This result will help us understand how black holes gorge and grow so quickly, which is an important event in the formation of galaxies and structures in the universe."
Earlier this week, astronomers with the International Centre for Radio Astronomy Research announced they have discovered a ULX as well, also from an unexpected source. P13 is a small black hole that eats ten times faster than what was believed to be possible for its size. This black hole as well as the discoveries made by Bachetti’s team are pushing the boundaries of what astronomers believe to be true about ULXs.