An important breakthrough in how we can understand dead star collisions and the expansion of the universe has been made by an international team that includes researchers with the Center for Gravitational Waves and Cosmology at West Virginia University.
They have discovered an unusual pulsar – one of deep space’s magnetized spinning neutron-star ‘lighthouses’ that emits highly focused radio waves from its magnetic poles.
The newly discovered pulsar (known as PSR J1913+1102) is part of a binary system – which means that it is locked in a fiercely tight orbit with another neutron star. The research has been published in Nature.
“Binaries with two neutron stars orbiting each other are relatively rare, representing less than one percent the known radio pulsar population,” said Maura McLaughlin, Eberly Distinguished Professor of Physics and Astronomy and one of the study’s authors. “The neutron stars in these binaries are gradually getting closer and closer together, as they lose energy due to the emission of gravitational waves, and eventually they will merge in a cataclysmic explosion and form a black hole.”
Neutron stars are the dead stellar remnants of a supernova. They are made up of the most dense matter known – packing hundreds of thousands of times the Earth’s mass into a sphere the size of a city.
In around half a billion years the two neutron stars will collide, releasing astonishing amounts of energy in the form of gravitational waves and light.
But the newly discovered pulsar is unusual because the masses of its two neutron stars are quite different – with one far larger than the other.
“Just a few years ago, both gravitational waves and electromagnetic light were detected from a merger of two neutron stars,” McLaughlin said. “This revolutionized our view of neutron star mergers. In order to search for more of these events, astronomers must use templates that assume some neutron star properties, and so far these templates assume that the two merging neutron stars have equal masses. However, our discovery shows that the neutron stars in one of these systems can have very unequal masses. This should be taken into account in the way these objects are searched for and also provides information on the way these binaries form.”
Also involved in the discovery was student Nihan Pol, who is slated to graduate this summer with a Ph.D. in astrophysics.
Pol served as co-lead on the population synthesis part of this discovery with Ben Perera, a former WVU student. Pol helped develop the software used for the analysis. The result of this analysis is that about one in 10 of observed mergers between two neutron stars will be from a system like J1913+1102.
“I think being at WVU, which has the largest neutron star/pulsar research group in the U.S., and maybe even the world, has been really great for my professional development,” Pol said. “It is very exciting to be involved in this kind of research where we find new and exotic systems which have implications not just for the study of stellar evolution and binary neutron star systems, but also for the relatively new field of gravitational wave astrophysics. These large, international projects afford me the opportunity to learn how to communicate and collaborate with colleagues from around the world and work together to produce amazing science.”
This asymmetric system gives scientists confidence that double neutron star mergers will provide vital clues about unsolved mysteries in astrophysics – including a more accurate determination of the expansion rate of the universe, known as the Hubble constant.
The discovery was made using the Arecibo radio telescope in Puerto Rico.
The research was led by the University of East Anglia, in collaboration with scientists at Max Planck Institute for Radio Astronomy in Bonn, the Arecibo Observatory in Puerto Rico, Columbia University, Cornell University, Franklin and Marshall College, the University of Amsterdam, McGill University, WVU, the University of British Columbia, the South African Radio Astronomy Observatory and the Netherlands Institute for Radio Astronomy (ASTRON).