Wednesday, December 28, 2016

Crowdsourcing Discovery: Meet the Massive Binary System Detected by Einstein@Home

As fingertips and keyboards cool off from the flurry of online shopping and term papers, it’s time to relax and let device processors do the work. Did you know that while you binge on TV shows and holiday leftovers, your laptop and smart phone could help discover an exotic astrophysical system? Just ask the Einstein@Home volunteers whose otherwise idle devices discovered two neutron stars locked in a tight orbit. The massive binary system could inform the search for gravitational waves and may turn out to be a unique cosmic laboratory.

An artist’s conception of binary pulsar PSR J0737-3039, shown not-to-scale.
Image Credit: Michael Kramer (Jodrell Bank Observatory, University of Manchester).
The binary system featured in this story (PSR J1913+1102) may be a binary pulsar, but only one of the neutron stars in the system has been confirmed as a pulsar to-date.

Started in 2005 as part of the World Year of Physics program, Einstein@Home is a distributed computing project supported by the American Physical Society (which runs PhysicsCentral and Physics Buzz), along with the National Science Foundation and the Max Planck Society, among others. The idea is this: our observatories generate more data than scientists have the resources to comb through, even with the help of supercomputers. That's where you come in. Regular people can donate the idle time from their computer (or phone) to searching data from the LIGO gravitational-wave detectors, the Arecibo radio telescope, and the Fermi gamma-ray satellite for evidence of pulsars—fast-spinning neutron stars. Interesting objects are flagged for follow-up by project scientists. The ultimate goal? To directly detect gravitational waves emitted by pulsars.

A pulsar is a strange, extremely dense, highly magnetized object that forms when a large star violently explodes. The outer layers of the star shoot off into space, leaving behind a collapsing, spinning core that isn’t quite massive enough to become a black hole. Many neutron stars have a strong charge, so they emit beams of electromagnetic waves as they move. Since they are spinning, we detect these signals as eerily regular pulses. In fact, on discovering a pulsar signal in 1967, the first one ever detected, then-graduate student Jocelyn Bell Burnell and her advisor Antony Hewish nicknamed the signal “LGM” for “little green men.”

What’s the gravitational wave connection? When two neutron stars orbit one another, general relativity predicts that the orbit will slowly contract because gravitational waves are emitted, depleting the system's energy. By precisely tracking the signals from binary pulsar systems, we can look for these predicted changes in the orbit. An experimental observation of this earned Russell Huse and Joseph Taylor Jr. the 1993 Nobel Prize in Physics. The more we know about pulsars, their distribution, and how often they appear in binary systems, the better equipped we are to directly detect the gravitational waves they emit with LIGO and future gravitational wave detectors.

In a recent issue of The Astrophysical Journal, a team using the world's largest radio telescope at Arecibo Observatory in Puerto Rico to search for radio pulsars, known as the PALFA survey, published a paper introducing the most massive double neutron star system ever seen. The system was detected by Einstein@Home in 2012 from the pulsing signal emitted by of one of the stars. Follow-up observations at Arecibo Observatory led to the discovery of the second neutron star. The two stars orbit each other in less than five hours, and are each much smaller in diameter but much larger in mass than the sun. This is the fourteenth double neutron star system observed, and the most massive yet.

The system is most likely the result of two separate supernovae. The pulsar detected by Einstein@Home computers appears to have formed first. The companion neutron star may also be a pulsar, but PALFA scientists haven’t seen any evidence of a signal in the available data. Right now it’s impossible to determine the mass of each of the stars individually, but it seems that the mass of the pulsar may be larger than the mass of the companion star. If that’s the case, scientists could have the chance to test some previously impossible-to-verify predictions related to general relativity and the composition of our galaxy, in addition to gathering more information for the gravitational wave search.

With eleven years under its belt, Einstein@Home has put idle time to good use. The project has discovered more than 70 pulsars and you can see publications resulting from several discoveries on the Einstein@Home website. The project includes more than 500,000 volunteers contributing about 1.7 petaflops (1015) of computing power, making it one of the largest computing clusters in the world! If you’d like to contribute, check out the Einstein@Home website for the quick and easy directions. It doesn’t take long to download the software and once you’re done, you can pick up the remote guilt free. Thanks to Einstein@Home, you can be dozing on the couch and on the cutting edge of gravitational wave detection at the same time.

Kendra Redmond

1 comment:

  1. > An experimental observation of this earned Russell Huse and
    > Joseph Taylor Jr. the 1993 Nobel Prize in Physics.

    It is "Hulse", and actually they got the Nobel Prize for the discovery of the system, not for the observation of the orbit changes due to gravitational wave emission implied here (which were actually done by Taylor and Weisberg, when Hulse had already turned to different research fields AFAIK, e.g see http://adsabs.harvard.edu/doi/10.1086/159690 ).

    Also this was the 13th double NS system known, not the 14th (but there are 14 pulsars in double-NS systems because there is one double pulsar system known).

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