While someone’s online gaming session times out and someone else’s 87 new Facebook notifications are being ignored, millions of idle home computers sort through galaxies of data in the relentless search for gravitational waves. Online science brain Einstein@Home uses the power of computers that would otherwise be daydreaming to detect these ripples in spacetime. Now this unexpected network has discovered something massive.
Einstein@Home has upgraded since starting out as a program that exclusively searched data from LIGO (Laser Interferometer Gravitational-Wave Observatory). After seeing no sparks in the LIGO data, the app expanded to other projects, including the Arecibo PALFA pulsar survey. While investigating incoming data from the Arecibo 305m telescope, it discovered a rare binary pulsar, aka a duo of dead stars orbiting each other with at least one still emitting electromagnetic radiation. PSR J1913+1102 is something of a unicorn in that it is one of only 14 pulsars ever to have been discovered in binary neutron star pairs. It may also be the most massive binary pulsar known. So much for Facebook updates.
Binary pulsars are so sought after because they are valuable sources of information on gravitational waves—in fact, from their discovery in 1974 up until 2015, the only sources. These elusive star corpses are still some of the best subjects floating out there for physicists studying Einstein’s theory of general relativity. Einstein predicted that gravitational waves would be emitted by a pair of neutron stars as they orbited the same center of mass, which would gradually pull the stars closer and closer together. This leads to orbital decay, or to sound less morbid, the gradual decrease of orbit distance and time. Science has one of the most outstanding opportunities in (literally) the entire universe to further understand gravitational waves: measurements taken from the first binary pulsar ever discovered were nearly a perfect match for these predictions.
"[The system] shows an exponential decay after the main pulse, as if the signal is affected by interstellar scattering,” said Patrick Lazarus of the Max Planck Institute of Radio Astromony, in his recently published study of PSR J1913+1102 in the Astrophysical Journal. “This is confirmed by the fact that the exponential decay timescale becomes much longer at lower frequencies.”
PSR J1913+1102 was initially telescope-shy because the silence from its companion star could only tell astronomers they were looking at a pulsar with a mysterious orbit companion. Neutron stars are much quieter than black holes that crash and burn, which is why they are so difficult to bring to light. It took numerous pieces of data that Einstein@Home gleaned from the Acaibo telescope to reach the conclusion that millions of idling home computers had indeed found a binary pulsar. While many pulsars orbit white dwarves, the total mass of of the system gave away that this companion had to be at least as massive as the sun, which eliminated that possibility since no white dwarf could possibly be so huge. Orbiting in nearly a perfect circle was the star’s second glaring giveaway, evidence of some force interfering with the system after the pulsar had evolved. Scientists reasoned something so powerful could only have been the explosive supernova of another neutron star in its final death throes.
“[This discovery] speaks to the value of Einstein@Home, which can find clues other projects just don’t have the computing power or time to drill down to,” said Einstein@Home director Bruce Allen. “And the results all feed into the eventual goal: finding continuous gravitational waves from binary pulsars.”