Asymmetrical Double Neutron Stars Could Help Understand Expansion of Universe

The Arecibo Observatory belonging to the National Science Foundation and located in Puerto Rico has achieved another major astronomical discovery.

A finding made using instruments at the Arecibo Observatory indicates asymmetrical double neutron star systems may be the key to understanding dead star collisions and the expansion of the universe. Image Credit: Arecibo Observatory/UCF William Gonzalez.

An international team of researchers, headed by the University of East Anglia in the United Kingdom, has discovered an asymmetrical double neutron star system with the help of the powerful radio telescope of the facility.

It is considered that a star system of this kind is a precursor to merging double neutron star systems such as the one discovered by LIGO (the Laser Interferometer Gravitational-Wave Observatory in the United States) in 2017. The LIGO observation was crucial as it confirmed the emission of gravitational waves from merging neutron stars.

The study reported by the researchers recently in the Nature journal suggests these particular types of double neutron star systems could be crucial to gain insights into dead star collisions as well as the expansion of the universe.

Back in 2017, scientists at LIGO first detected the merger of two neutron stars. The event caused gravitational-wave ripples through the fabric of space time, as predicted by Albert Einstein over a century ago. It confirmed that the phenomenon of short gamma-ray bursts was due to the merger of two neutron stars.

Robert Ferdman, Study Lead and Physicist, University of East Anglia

What was special about the 2017 discovery and the new one was that the observed double neutron systems are formed of stars with very different masses. Existing theories about the 2017 discovery are founded on the masses of stars being very close in size or equal.

The double neutron star system we observed shows the most asymmetric masses amongst the known merging systems within the age of the universe. Based on what we know from LIGO and our study, understanding and characterizing of the asymmetric mass double neutron star population is vital to gravitational wave astronomy.

Benetge Perera, UCF Scientist, Arecibo Observatory

Research by Perera, who was the co-author of the study, focused on pulsars and gravitational waves. He collaborated with the NSF-funded Arecibo Observatory in June 2019. The facility, managed by the University of Central Florida through a cooperative agreement with the NSF, provides researchers worldwide exclusive insights into space with its specialized instruments and its location near the equator.

The Discovery

The researchers found an unusual pulsar—a magnetized spinning neutron-star “lighthouse” in deep space that discharges highly focused radio waves from its magnetic poles.

The newfound pulsar (named PSR J1913+1102) forms part of a binary system—i.e., it is locked with another neutron star in an intensely tight orbit.

The Arecibo Observatory has a long legacy of important pulsar discoveries. This exciting result shows how incredibly relevant the facility’s unique sensitivity remains for scientific investigations in the new era of multi-messenger astrophysics.

Ashley Zauderer, Program Officer, National Science Foundation

Neutron stars, which are the dead stellar remnants of a supernova explosion, are formed of the densest known matter, where mass equal to hundreds of thousands of times that of the Earth is packed into a sphere measuring the size of a city, such as New York.

The two neutron stars will collide with each other in about half a billion years and discharge enormous amounts of energy as light and gravitational waves.

The LIGO team observed such a collision in 2017. Although the event itself was not astonishing, the huge amount of matter released from the merger and its brightness were stupendous, stated Ferdman.

Most theories about this event assumed that neutron stars locked in binary systems are very similar in mass,” Ferdman added. “But this newly discovered binary is unusual because the masses of its two neutron stars are quite different—with one far larger than the other. Our discovery changes these assumptions.”

With the observation of such an asymmetric system, researchers believe that double neutron star mergers will offer crucial insights about unsolved mysteries in astrophysics—such as a more accurate determination of the rate at which the universe expands, also called the Hubble constant.

Journal Reference:

Ferdman, R. D., et al. (2020) Asymmetric mass ratios for bright double neutron-star mergers. Nature. doi.org/10.1038/s41586-020-2439-x.

Source: https://www.ucf.edu/

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