Power Behind Mysterious Gamma-Ray Source Revealed Thanks To Thousands Of Volunteers

Artist's impression of PSR J2039−5617 and its companion. Image credit: Knispel/Clark/Max Planck Institute for Gravitational Physics/NASA GSFC

For years gamma-ray source PSR J2039−5617 has been a cosmic mystery. Astronomers had an inkling of what may be behind it but were struggling to find the evidence needed to confirm it. Now, using the computing power of 500,000 volunteers in the citizen science Einstein@Home program, they've been able to confirm that a rapidly rotating neutron star is responsible.

The Einstein@Home app uses your computer when you are not. With half a million users, the computational power is incredible and can be used to go through huge catalogs of data to recognize faint signals, something that would take a long time otherwise. In the case of PSR J2039−5617, this approach delivered the long-sought evidence of an incredible cosmic object.

As reported in the Monthly Notices of the Royal Astronomical Society, the gamma-ray source is a binary system consisting of a pulsating neutron star, called a pulsar, and a smaller companion. The team discovered the pulsar rotates on its axis 377 times each second.

The Einstein@Home side of the project was able to characterize the pulsar’s behavior by analyzing 11 years of data from using data from NASA’s Fermi Space Telescope. A single computer would have taken 500 years to find the rotational period. With the app, they were able to find it in just two months.

"It had been suspected for years that there is a pulsar, a rapidly rotating neutron star, at the heart of the source we now know as PSR J2039−5617," co-author Lars Nieder, a graduate researcher at the Max Planck Institute for Gravitational Physics, said in a statement. "But it was only possible to lift the veil and discover the gamma-ray pulsations with the computing power donated by tens of thousands of volunteers to Einstein@Home."

The true understanding of the system also comes from new observations in optical wavelength. The pulsar is slowly evaporating its companion, something that was inferred by how different the companion stars look in its 5.5-hour orbit around the pulsar.

"For J2039-5617, there are two main processes at work," explained lead author Dr Colin Clark from Jodrell Bank Centre for Astrophysics. "The pulsar heats up one side of the light-weight companion, which appears brighter and more bluish. Additionally, the companion is distorted by the pulsar's gravitational pull causing the apparent size of the star to vary over the orbit."

The fantastic precision in the data from Einstein@Home has also demonstrated that there some really unique dynamics happening in the system.

"We found that the companion's orbital period varies slightly and unpredictably over the 11 years. It only changes by up to about 10 milliseconds, but since we know the arrival time of every single gamma photon from the pulsar to microsecond precision, even this little is a lot!" said Nieder.

More cosmic mysteries such as this are just waiting to be discovered in the data. If you want to get involved, you can download the Einstein@Home app and be part of some amazing citizen science yourself.

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