Einstein@Home joins the Zooniverse

Citizen scientists can now also use their eyes and brains to help find new pulsars.

Since its launch in 2005, the Einstein@Home volunteer distributed computing project hosted at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Hannover, Germany, and at the University of Wisconsin-Milwaukee has been searching for and finding new neutron stars, compact remnants of exploded massive stars. Einstein@Home aggregates the otherwise idle computing power on the PCs of more than 15,000 active participants, making it one of the world’s largest projects of this kind. Since 2009, Einstein@Home has analyzed data from the Arecibo radio telescope and found 31 new radio pulsars, a special type of neutron star. Now Einstein@Home is teaming up with Zooniverse. On this successful citizen science web portal, volunteers will be able to classify graphical representations of Einstein@Home's computational results, with the goal of discovering more pulsars in the Arecibo data.

In brief: Since 2009, Einstein@Home volunteers have helped analyze observations from the large Arecibo telescope’s PALFA pulsar survey. The project’s science team has sifted through the results to find tens of thousands of promising pulsar candidates  and produced a small set of diagnostic plots for each. Now, the new “Pulsar Seekers” project is calling on volunteers from the Zooniverse citizen science platform to sort through these plots to find new pulsars.

Distributed computing augmented by distributed thinking

“Getting volunteers more directly involved in Einstein@Home and having them view and actively classify pulsar candidates has been our plan for a long time. It’s great to see this become a reality with this new Zooniverse project,” says Bruce Allen, director of Einstein@Home and director at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, AEI) in Hannover, Germany.

Neutron stars are compact remnants of supernova explosions and consist of extremely dense matter. They are about 25 kilometers across and weigh more than our Sun. Because of their strong magnetic fields and fast rotation, they emit beams of radio waves like a cosmic lighthouse. When these beams point toward Earth during the neutron star’s rotation, it becomes visible as a radio pulsar.

Pulsars are excellent astrophysical tools that enable research in several areas of astronomy, such as testing Einstein’s theory of general relativity, understanding the behavior of extremely dense matter, studying the thin gas between stars and our Galaxy’s magnetic field, and for searching low-frequency gravitational waves.

To date, Einstein@Home has discovered 31 radio pulsars in data from the Arecibo telescope, 24 radio pulsars in data from Parkes Observatory in Australia, and 39 gamma-ray emitting pulsars in data from NASA's Fermi Gamma-ray Space Observatory. The project’s long-term goal is the detection of continuous gravitational waves from neutron stars that have yet to be observed.

Hunting for treasures in Arecibo’s legacy

To search for new radio pulsars, telescopes like the iconic Arecibo radio telescope, which sadly collapsed in December 2020, observe hundreds of thousands of points in the sky, each for a few minutes. Each of these observations must then be checked for the regular pulsations expected from radio pulsars. Searches for pulsars alone in space can be done in a short time on a small number of computers. Finding pulsars in close orbits with stellar companions is much more computationally demanding, but potentially very rewarding. Astronomers estimate that there is at least one binary system of two neutron stars in a ten-minute orbit in our Galaxy, observations of which would allow some of the most rigorous tests of general relativity ever made.

Thanks to the Einstein@Home volunteers and the computing power they donate to the project, such searches become feasible. When the volunteers’ computers are finished analyzing an Arecibo observation, the end result of their combined efforts is a long list of nearly 400,000 candidates, or possible pulsar signals, each characterized by a handful of numbers. Typically, no more than one true pulsar is expected in an observation.

Separating the wheat from the chaff

“Einstein@Home has analyzed more than 150,000 observations made by the Arecibo radio telescope as part of the PALFA survey,” says Alexandra Botnariuc, a PhD student at AEI Hannover. “This gives us the gigantic number of 60 billion pulsar candidates! This is far too many to look at each one individually, and most of them aren’t real astrophysical signals anyway”. She developed and implemented an algorithm to reduce this number by detecting similar candidates that are likely caused by the same astrophysical signal, and by identifying the most pulsar-like among them.

To get the ball rolling, the research team prepared diagnostic plots for the 50,000 most promising Einstein@Home pulsar candidates and set up a new Zooniverse project called “Pulsar Seekers”. “The number of candidates is so large that it is impractical for one person to do the job. This makes the collective human effort of Zooniverse participants invaluable in identifying true pulsar candidates,” says Rahul Sengar, a postdoctoral researcher at the University of Wisconsin-Milwaukee who is leading the Pulsar Seekers project. “We can't wait to see what Zooniverse citizen scientists discover in our data!”

Citizen scientists will receive a short and simple tutorial on Zooniverse to teach them how to tell real pulsars from noise. “If all goes well, and several thousand Zooniverse volunteers participate in ‘Pulsar Seekers’, they will be able to sort through our first 50,000 pulsar candidates, separate the wheat from the chaff, and maybe find some exciting new pulsars, in just a few days," says Colin Clark, a research group leader at AEI Hannover. This could be just the beginning of a longer Einstein@Home Zooniverse collaboration. “We may have missed possible pulsars in our current pre-selection, but we can dig deeper and produce more plots for Zooniverse volunteers to look at,” adds Clark.