Scientists have detected gravitational waves from the collision of a stellar-mass black hole with another undefined, compact object 800 million years ago. The findings were published in The Astrophysical Journal Letters on Tuesday.
The gravitational signal from this merger event travelled for 800 million years through the universe and arrived at the network of two advanced-LIGO detectors – at Hanford, Washington and Livingston, Louisiana, USA and the advanced-Virgo detector in Cascina, Italy, in the wee hours of August 15 2019, just past 2.40 am IST. This new event was very “loud” and has been named GW190814.
An official statement by the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, said the LIGO-Virgo detectors were in the middle of their third observing run when they observed this “extremely loud event”. Scientists said GW190814 is the third loudest event that has been seen to date, after the binary neutron star system GW170817 and the first binary black hole system GW150914 observed by the LIGO detectors.
The IUCAA said GW190814 has two outstanding features that make it unique: Before the two objects merged, their masses differed by a factor of 9, making this the most extreme mass ratio known for a gravitational-wave event. In comparison, the recent LIGO-Virgo event GW190412 had a mass ratio of about 4:1. From the measured mass of the lighter compact object, scientists believe it is either the lightest black hole or ‘most massive neutron star’ ever discovered in a compact binary system.
According to the LIGO and Virgo scientists, electromagnetic counterparts of the GW190814 event were not seen for a few possible reasons. First, this event was six times farther away than the merger observed in 2017, making it harder to pick up any light signals. Second, if the collision involved two black holes, it likely would not have shone with light. Third, if the object was, in fact, a neutron star, its 9-fold more massive black-hole partner might have swallowed it whole – a neutron star consumed whole by a black hole would not give off any light.
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