'Orphan Memory' Could Broaden Gravitational Wave Hunt

Gravitational waves
Artist's illustration showing two merging black holes creating ripples in the fabric of space-time, also known as gravitational waves. (Image credit: NASA)

There may be a new way to study gravitational waves.

These ripples in the fabric of space-time were first predicted by Albert Einstein a century ago, and first detected directly in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO) consortium. 

Twice in that year, the LIGO team spotted gravitational waves spawned by black-hole mergers: once in September and once in December (though both detections were announced in 2016). 

But the LIGO gear can "hear" gravitational waves only if they occur at certain frequencies. A new study by researchers at Monash University in Australia proposes a way to broaden the search by using something called "orphan memory."

Gravitational waves are a manifestation of the stretching of space-time, by black-hole collisions or other dramatic cosmic events. Once stretched, space-time doesn't return to normal, the scientists explained. It may therefore be possible to infer the presence of "parent" gravitational waves by studying the signatures such stretching leaves behind, according to the new study. (Hence the term "orphan memory," which refers to the notion that the parent is not around to observe.)

Orphan memory remains a speculative term at this point. But if the phenomenon can be observed, the researchers argue, scientists would be able to observe a broader range of gravitational waves. 

"If there are exotic sources of gravitational waves out there — for example, from micro black holes — LIGO would not hear them because they are too high-frequency," study lead author Lucy McNeill, an astrophysicist at Monash, said in a statement. "But this study shows LIGO can be used to probe the universe for gravitational waves that were once thought to be invisible to it."

The new study was published earlier this month in the journal Physical Review Letters.

Follow Elizabeth Howell @howellspace, or Space.com @Spacedotcom. We're also on Facebook and Google+. Original article on Space.com.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.

Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for Space.com for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: https://qoto.org/@howellspace