Thursday, December 21, 2017

Radio waves from neutron star merger detected


PUNE: The Giant Metrewave Radio Telescope (GMRT) in Khodad, about 80 km from Pune, has detected radio waves from the neutron star merger on August 17, this year. The radio waves, originally detected by GMRT 16 days after the event, are still measurable and increasing in strength as of December 2.

It is among the biggest achievements for GMRT. The observatory, for the first time, grasped radio waves from the collision of two neutron stars and photons (or radiation) at the lowest-ever frequency.

The findings, made at the lowest sub-GHz frequencies by GMRT in Pune, and corroborated by Karl G. Janksy Very Large Array in New Mexico, and the Australia Telescope Compact Array, were reported in a new paper in the December 20 online issue of Nature, an acclaimed scientific journal. The lead author is Kunal Mooley, formerly of the University of Oxford, and now a Jansky Fellow at Caltech.

Neutron stars are huge objects in the universe consisting of highly compressed matter. Their mergers are violent. Advanced LIGO and advanced Virgo instruments detected the gravitational waves from two neutron stars spiraling inward and merging, followed by a burst of gamma rays on August 17.

It was the second big discovery for Laser Interferometer Gravitational-Wave Observatory (LIGO) after the 2015 detection of gravitational waves, ripples in space and time, generated when black holes merged.

Dean of GMRT observatory Yashwant Gupta said, "The neutron merger gave rise to an explosion. The initial signals that came from the explosion were gravitational waves, followed by radiations like X-ray and Gamma ray among others. As the event progresses, radio waves are also emitted but always spotted last."

Even so, the radio waves are the most important since they help know the nature of the explosion and what happened during the event, Gupta added. Poonam Chandra, astronomer at National Centre for Radio Astrophysics, who is part of the team, told, "GMRT's is the lowest frequency detection of the gravitational wave event. Low frequencies are crucial to extract information on the environments of such exotic events."

Two teams of scientists have been following this event at GMRT. Gupta said, "The upgraded facility had very good sensitivity and hence it could pick up the radio waves. The detection portrays GMRT in good light in world astronomy."

Researchers said future observations with LIGO, Virgo, and other telescopes will clarify the origins and mechanisms of such extreme events. The observatories should be able to detect more neutron-star mergers, and eventually, mergers of neutron stars and black holes, they added. 


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