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Astronomers have discovered the source of a mysterious gamma-ray emission. The culrpit is a peculiar binary star system whose oddity has set new records. The discovery is reported in The Astrophysical Journal Letters.
The system, known as PSR J1653-0158, is made of a heavy neutron star and a dwarf star remnant. The neutron star is the end-product of a supernova and pulsates, emitting bursts of gamma radiation. However, it has a surprisingly weak magnetic field.
“We have found a very tight binary system. In its center is the pulsar, which is about 20 kilometers in size and has twice the mass of our Sun. The remnant of a dwarf star orbits the pulsar at just 1.3 times the Earth-Moon distance in only 75 minutes at a speed of more than 700 kilometers per second,” lead author Lars Nieder, from the Albert Einstein Institute, Hanover, said in a statement.
Its companion has a mass of just 1 percent of the Sun. This extraordinary difference in mass between the two is another record-breaking feature.
Their difference in mass has a dark origin. The system is believed to be a Black Widow Pulsar system. This when a neutron star constantly steals material from its companion, eventually absorbing it. The team believes that we are seeing the end result of such dramatic theft.
“This unusual duo might have originated from an extremely close binary system, in which matter originally flowed from the companion star onto the neutron star, increasing its mass and causing it to rotate faster and faster while simultaneously dampening its magnetic field,” Nieder added.
Pulsars are usually observed in gamma rays or other wavelengths of light. Surprisingly though, the star system is completely invisible in radio waves. The discovery was possible thanks to the Einstein@Home app. Volunteers install the app on their computers, and when they are idle, it helps search archival data from NASA's Fermi Gamma-ray Space Telescope. It took just two weeks to find this system.
“In the catalog of gamma-ray sources found by the Fermi satellite, there are dozens more that I would bet have binary pulsars in them,” says Professor Bruce Allen, director at the Max Planck Institute for Gravitational Physics in Hannover and director and founder of Einstein@Home. “But so far no one has been able to detect the characteristic pulsation of their gamma rays. With Einstein@Home, we hope to do just that – who knows what other surprises await us.”
