Rare Double Neutron Star Discovered Thanks To Einstein@Home Project

Artist’s impression of a double neutron star system. John Rowe Animations

Many astronomical discoveries are slowed down by limited resources. There’s an infinite universe out there and we only have the time, money, and effort to study a small part of it.

To help ease the load on the gravitational waves hunters, a group of scientists has started the Einstein@Home project, which uses the downtime of volunteers' personal computers to discover sources of gravitational waves.

The project has already borne fruit as it has discovered a double neutron star system, one which will help astronomers test important predictions of Einstein’s general relativity and how stars evolve. These systems are rare to observe, needles in the cosmic haystack. Out of about 2,500 known pulsars (pulsating neutron stars), there are only 14 paired up systems.

The international team of researchers led by Patrick Lazarus from the Max Planck Institute for Radio Astronomy followed up the detection from the automated program and confirmed the properties of such an unusual stellar system, located almost 25,000 light-years from us. The results are published in the Astrophysical Journal.

The main object in the double neutron star system is known as PSR J1913+1102, a pulsar that spins on itself every 27.3 milliseconds. The pulsar is in a pretty circular orbit with a dense companion, most likely another neutron star, which orbits around PSR J1913+1102.

The team believed that the pulsar went supernova first, and its spin was accelerated by interactions with the companion. When the companion exploded as well, the system received a kick that made the orbit more circular.

Such orbits are not stable and that instability is actually what makes these systems crucial to testing general relativity. As these two dense objects spin around each other, they lose energy in the form of gravitational waves. This energy loss produces an orbital decay, and the theory of general relativity has very fine predictions for what it should look like.

The team is now collecting more measurements to estimate the decaying time and see if the system is changing according to the theory. The gravitational waves produced by the system are way beyond what we can currently measure, even with the newly upgraded LIGO. But if the stars were to collide, our instruments would catch them. Unfortunately, based on current estimates, that won’t happen for at least another 500 million years.

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