News

Black holes of ‘all shapes and sizes’ in new gravitational wave catalogue

LIGO image

The largest catalogue of gravitational wave events ever assembled has been released, with dozens of ripples in space time captured by a global network of detectors.

The aftershocks of huge astronomical events were picked up by a world-wide team of scientists, with leadership from the UK. 

The team has detected a further 35 gravitational wave events, bringing the total number of observed events since detection began to 90.

International detectors

The catalogue updates the list of all gravitational-wave events observed to date with events observed between November 2019 and March 2020, using international detectors based in Louisiana and Washington state in the US and in Italy. 

Scientists from 12 different universities across the UK, including Strathclyde, are involved in the LIGO Scientific Collaboration, with many taking leading roles from detector calibration to data analysis.

The UK’s contribution to the collaborations is funded by the Science and Technology Facilities Council (STFC).

Professor Stuart Reid from the Department of Biomedical Engineering at Strathclyde and elected Co-chair of the Optics Working Group of the LIGO Scientific Collaboration, said:

This third observing run has revealed more about the diversity of black holes and neutron stars that exist, answering some longstanding questions about how stars evolve, and opening up some new ones.

The continued improvement of these ultra-sensitive detectors will shed more light on the nature of our Universe, in addition to increasing our chances of observing yet undiscovered sources and potentially new surprises.”

Of the 35 events detected, 32 were most likely to be black hole mergers – two black holes spiralling around each other and finally joining together, an event which emits a burst of gravitational waves.

Black holes

Several of the black holes formed from these mergers exceed 100 times the mass of our Sun, and are classed as intermediate-mass black holes. This type of black hole has long been theorised by astrophysicists, and has now been proven to exist thanks to gravitational wave observations.

Two of the 35 events spotted were likely to be neutron stars and black holes merging – a much rarer event, and one that was only discovered in the most recent observing run of LIGO and Virgo.

Of these rare neutron star and black hole mergers, one event seems to show a massive black hole (about 33 times the mass of our Sun) with a very low-mass neutron star (about 1.17 times the mass of our Sun). This one of the lowest-mass neutron stars ever detected, either using gravitational waves or electromagnetic observations.

Key clues

The masses of black holes and neutron stars are key clues to how massive stars live their lives and die in supernova explosions.

The final gravitational wave event came from either a black hole and a neutron star or a black hole and another black hole. The mass of the lighter object crosses the expected divide between the two, a region where previously no black holes or neutron stars were expected to be formed, and which remains a mystery.

Since the first gravitational wave detection in 2015, the frequency of detections has dramatically increased. In a matter of years, gravitational wave scientists have gone from observing these vibrations in the fabric of the universe for the first time, to now observing many events every month, and even multiple events on the same day.

Pioneering instruments

To achieve this monumental progress, the pioneering instruments have been getting more sensitive thanks to a programme of constant upgrades and maintenance. In the third observing run, the gravitational wave detectors reached their best ever performance, as the lasers were tuned to even higher power.

Scientists have also improved their analytical techniques to ensure the high accuracy of results. The growing catalogue of observations will enable astrophysicists to study the properties of black holes and neutron stars with unprecedented precision.