Ripples in space-time: First Detection - A Neutron star merger
- phys1500.astronomy
- Aug 17, 2018
- 2 min read
Editor's Note: This 3-part blog post is being published early to mark one year from the ground-breaking discovery of this event! The related quiz questions for the PHYS1500 course will be in the tutorial 7 pre-work Quiz (released Friday 14th Sept).
by Dougal Dobie
One year ago, on August 17 2017, thousands of astronomers across the world received an alert that the Advanced LIGO-Virgo interferometer had detected a gravitational wave event, now named GW170817.
LIGO had detected gravitational waves from black hole mergers in the past, but this event was exciting because it was the first time a neutron star merger had been detected. Neutron star mergers are expected to produce electromagnetic radiation (gamma-rays, X-rays, visible light, radio waves) and within minutes of receiving the alert, telescopes on every continent on earth and in space were slewing towards the target region hoping to make a detection.
LIGO was only able to localise the location of the merger to an area of about 150 times the full Moon, but detecting electromagnetic radiation would allow us to pinpoint the host galaxy of the merger. 11 hours after the merger the detection of an optical counterpart was announced, with ultra-violet and infra-red detections in the following few hours, determining that the merger had taken place on the outskirts of the galaxy NGC 4993.
Our team at the University of Sydney was granted special observing time to follow up the event with the Australia Telescope Compact Array (ATCA), a radio telescope in Narrabri, NSW operated by the CSIRO. The next few days were frantic as we observed this event, searching for radio emission that was yet to be detected while we sent and received updates from other astronomers observing the event.
Eventually on September 3 our collaborators from the United States made a detection with the Very Large Array in New Mexico. The emission was extremely faint - comparable to the radio signals sent by your mobile phone if it was placed 40 times further away than the moon.
The discovery was announced two months later on October 16, with press conferences across the globe and 80 scientific papers published simultaneously. A year later we are still observing GW170817 with the ATCA and nearly 300 papers have been published about the event.
Further reading:
https://theconversation.com/after-the-alert-radio-eyes-hunt-the-source-of-the-gravitational-waves-85106
https://arxiv.org/abs/1710.05435
http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9
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