A gravitational wave isn’t a ripple through objects in spacetime; it passes through spacetime itself. Gravitational waves make the Universe itself vibrate, says Brian Clegg, author of Gravitational Waves: How Einstein’s Spacetime Ripples Reveal the Secrets of the Universe.
A team of international scientists have unveiled the largest number of gravitational waves ever detected. The discoveries will help solve some of the most complex mysteries of the Universe, including the building blocks of matter and the workings of space and time.
90 Detections to Date
The global team’s study includes 35 new detections of gravitational waves caused by pairs of black holes merging or neutron stars and black holes smashing together based on LIGO and Virgo observatories between November 2019 and March 2020. This brings the total number of detections to 90 after three observing runs between 2015 and 2020. Most of the compact object mergers are located billions of light years away, hurling ripples of gravitational waves through space-time across extreme cosmic distances.
The Australia National University (ANU) is one of the key players in the international team making the observations and developing the sophisticated technology to hunt down elusive gravitational waves across the vast expanse of the Universe.
Unlock the Secrets of the Universe’s Evolution
Distinguished Professor Susan Scott, from the ANU Center for Gravitational Astrophysics, said the latest discoveries represented “a tsunami” and were a “major leap forward in our quest to unlock the secrets of the Universe’s evolution. These discoveries represent a tenfold increase in the number of gravitational waves detected by LIGO and Virgo since they started observing,” Scott said.
“We’ve detected 35 events. That’s massive. In contrast, we made three detections in our first observing run, which lasted four months in 2015–16. This really is a new era for gravitational wave detections and the growing population of discoveries is revealing so much information about the life and death of stars throughout the Universe.”
Raises Fascinating Questions
“Looking at the masses and spins of the black holes in these binary systems indicates how these systems got together in the first place. It also raises some really fascinating questions. For example, did the system originally form with two stars that went through their life cycles together and eventually became black holes? Or were the two black holes thrust together in a very dense dynamical environment such as at the center of a galaxy?” Black hole pairs that formed via binary evolution are expected to have aligned spins, while black hole pairs that dynamically evolved in dense globular clusters or centers of galaxies may have misaligned spin-orbit orientations.
The observed population of compact stellar remnants in our Milky Way and nearby galaxies suggest a gap in masses between neutron stars and black holes. The most massive neutron star discovered to date is about 2.2 times the mass of the sun, whereas the least massive black hole sits just above 3 solar masses. However, distant sources of gravitational waves that formed earlier in the Universe may have a different mass distribution, possibly filling in the mass gap. There is also a second mass gap: normal stellar evolution can produce black holes up to about 100 solar masses while the centers of galaxies host supermassive black holes exceeding 100,000 times the mass of the sun. LIGO and Virgo are searching for the elusive intermediate-mass black holes between these two limits.
Unveiling the Nature of Dark Matter
Scott, who is also a Chief Investigator of the ARC Center of Excellence for Gravitational Wave Discovery (OzGrav), said the continual improvement of gravitational wave detector sensitivity was helping drive an increase in detections. “This new technology is allowing us to observe more gravitational waves than ever before,” she said. “We are also probing the two black hole mass gap regions and providing more tests of Einstein’s theory of general relativity.”
In an email to The Daily Galaxy, Scott wrote, “With increasing sensitivity of the instruments, we hope to detect a continuous stream of gravitational waves from isolated, misshapen neutron stars. These enigmatic objects are made up of the densest material in the Universe, and we want to unlock the mystery of their structure, composition, mass and size. Detecting gravitational waves from a supernova will enable us to better understand the powerful processes happening in these factories of the Universe.”
“We hope,” she adds, “in the future, to shed light on the nature of dark matter with gravitational waves. It is also entirely possible that we could receive a gravitational wave signal which we cannot classify from one of our known or expected sources. It would be truly amazing to be presented with such a mystery.”
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