Evidence that the Earth is enveloped in a slow-rolling sea of ​​gravitational waves

Scientists report the first evidence that our Earth, and the universe around us, is engulfed in a background of ripples in space-time called the Earth gravitational waves. The waves oscillate very slowly over years and even decades, and are thought to originate mainly from pairs of supermassive black holes slowly spiraling together before merging.

15 years of chasing

This groundbreaking discovery, is detailed in a series of papers in the Astrophysical Journal Letters, is the result of 15 years of careful observations by the North American Nanohertz Gravitational Wave Observatory (NANOGrav). As a physics frontiers center funded by the National Science Foundation (NSF), NANOGrav includes more than 190 scientists from the United States and Canada. They used radio telescopes at the Arecibo Observatory in Puerto Rico, the Green Bank Telescope in West Virginia, and the Very Large Array in New Mexico to observe 68 dead stars, called pulsars, in the sky. The pulsars acted like a network of buoys bobbing on a slowly flowing sea of ​​gravitational waves.

Build confidence in the results

says Katerina Chatzioannou, a NANOGrav team member and assistant professor of physics at Caltech. “In the future, we will continue to provide more observations and compare our results with those of international partners, which will allow us to learn more data.”

Katrina Chatziwanu. Credit: California Institute of Technology

detection of black holes

“We have a new way to explore what happens when monstrous black holes at the cores of galaxies begin a slow but relentless death spiral,” says NANOGrav team member Joseph Lazio, a principal scientist at JPL.Jet Propulsion Laboratory), and a visiting fellow in astronomy at the California Institute of Technology, who directs the Jet Propulsion Laboratory for NASA. “We think this process is standard for many galaxies, and we’ve seen many examples at different steps, but we’re finally starting to peek at one of the major final steps.”

Joseph Lazio. Credit: California Institute of Technology

Gravitational waves – Einstein’s concept

The concept of gravitational waves was first proposed by Albert Einstein in 1916. However, they were not directly discovered until nearly a century later by the National Science Foundation funded. lego (Laser Interferometer Gravitational-Wave Observatory). They discover waves from a pair of colliding black holes.

Unlike LIGO, which detects gravitational waves at a much higher frequency, NANOGrav, as the name suggests, focuses on lower-frequency gravitational waves in the nanohertz range, that is, one cycle every few years.

High-frequency gravitational waves come from pairs of smaller black holes that rapidly orbit each other in the last seconds before colliding, while lower-frequency waves are thought to be generated by massive black holes in the hearts of galaxies, which reach billions of times the mass of our sun, which They slowly scatter around each other and have millions of years before they merge.

The collective buzz of merging black holes

In the new studies, a nanograph is thought to have picked up the collective hum of gravitational waves from several pairs of merging supermassive black holes across the universe. “People compare that signal to more of a back puff than to the whoops that LIGO picks up,” explains Chatzioannou, who is also a member of the LIGO team and a William H. Hurt Scholar.

Patrick Myers. Credit: California Institute of Technology

“It’s like you’re at a cocktail party and you can’t pick out any individual sound. We only hear the background noise,” says Patrick Myers, a NANOGrav team member and postdoctoral researcher at Caltech who helped lead the statistical tests of the results.

Understanding cosmic buzz

The NANOGrav network of pulsars is also known as a pulsar– Set timing. Pulsars, formed from the explosions of massive stars, send out rapidly rotating beacons of light around very minute timescales. “These are like beacons of a beacon sweeping by at a regular rate. You can predict the timing at the level of tens of nanoseconds. They have the same level of accuracy as atomic clocks in some cases,” Myers says.

As gravitational waves travel through the universe, they stretch and compress the fabric of space-time a bit. This expansion and compression can cause a change in the distance between Earth and a particular pulsar, delaying or advancing the timing of the pulsar’s flashes of light. To look for the background hum of gravitational waves, the science team developed software to compare the timing of pairs of pulsars in their network. Gravitational waves will change this timing to different degrees depending on how close the pulsars are in the sky, a pattern first theoretically calculated by Ron Hellings and George Downes at the Jet Propulsion Laboratory in the early 1980s.

Michel Valesneri. Credit: California Institute of Technology

“Imagine a lot of ripples on the ocean from pairs of supermassive black holes scattered all over the place,” says Lazio. “Now, we’re sitting here on Earth, which acts like a buoy along with pulsars, and we’re trying to measure how the ripples change and cause other buoys to move toward and away from us.”

“To deduce the gravitational wave background, we had to identify many confounding influences, such as the motion of pulsars, disturbances caused by free electrons in our galaxy, the instability of reference clocks in radio observatories, and even the exact location of the center of the solar system, which we determined with the help of Juno and Cassini says NANOgrav team member Michele Valesneri, senior investigator at JPL and visiting fellow in theoretical astrophysics at Caltech.

Further conclusions and conclusions

Future NANOGrav results will include Canada’s CHIME telescope, which joined the project in 2019. Caltech’s Deep Synoptic Matrix-2000DSA-2000, or an array of 2,000 radio antennas slated to be built in the Nevada desert and start operating in 2027, will also join the search.

Scientists hope to answer mysteries about the nature of supermassive black hole mergers, such as how common they are, what holds them together, and other factors that contribute to their mergers.

“People have been trying to find supermassive black holes with telescopes for years,” says Chatzioannou. “They are getting closer and finding more candidates, but because the black holes are so close together, it is hard to tell them apart. Having gravitational waves as a new tool will help us better understand these mysterious monsters.”

“This was a beautiful and improbable experiment: assembling a galaxy-sized gravitational-wave detector that pulsates dead stars across our galaxy and brings together a multidisciplinary team of radio astronomers, experts in neutron stars and black holes, and experts in gravitational-wave scientists,” Vallesneri says.

For more information about this research:

Reference: “The 15-Year NANOGrav Data Set: Evidence for the Gravitational Wave Background” by Gabriela Agazi, Akash Anumarlabudi, Ann M Archibald, Zaven Arzumanian, Paul T. Brock, Sarah Burke-Spollor, Rand Burnett, Robin Case, Maria Charisi, Shami Chatterjee, Katerina Chatzioannou, Belinda DeChesiborough, Siwan Chen, Tyler Cohen, James M. Cordes, Neil G. Cornish, Fronfeld Crawford, H. Katherine Crotter, Curt J. Cutler, Megan E. Dessar, Dallas Deegan, Paul B. Demorest, Healing Ding, Timothy Dolch, Brendan Drachler, Justin A. Ellis, Elizabeth C. Ferrara, William Fury, Emanuel Fonseca, Gabriel E. Friedman, Nate Garver Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Judd, Kayhan Gultekin, Jeffrey S. Hazboun, Sophie Hourihane, Christina Islow, Ross J. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelly, Matthew Kerr, Joy SK, Tonya C. Klein, Nima Lal, Michael T. Lamm, William J. , Natalia Lewandowska, Tyson B. Littenberg, Tingting Liu, Andrea Lumen, Duncan R Lorimer, Jing Lu, Ryan S Lynch, Chong Pei Ma, Dustin R Madison, Margaret A. Mattson, Alexander McQueen, James W Mackey, Maura A. McLaughlin, Natasha McMahon, Bradley W. Myers, Patrick M. Myers, Chiara MF Mingarelli, Andrea Mithridat, Priyamvada Natarajan, Sherry Ng, David G. Ness, Stella Koch-Ocker, Ken D’Olum, Timothy T. Benucci, Benetge BP Perera, Polina Petrov, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, ​​Carl Schmiedekamp, ​​Kai Schmitz, Levi Schult, Brent J. Shapiro Albert, Xavier Siemens, Joseph Simon, Magdalena S Siwick, Ingrid H Steers, Daniel R. Steinbring, Kevin Stovall, Jerry B. Taylor, Jacob E. Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/acdac6

Other Caltech and JPL team members include Caltech postdoc Aaron Johnson, who led an effort to review and validate the key analysis code that produced all of the key findings; Curt Cutler, JPL senior research scientist, who helped craft statistical treatments of the data; and Caltech graduate student Sophie Hourihane, who developed a new method to speed up NANOGrav analyses.

A series of research papers detailing the new NANOGrav findings have been published in Astrophysical Journal Letters. The paper describing the evidence for gravitational waves, titled “The 15-Year NANOGrav Data Set: Evidence for the Background of Gravitational Waves,” was co-led by two former JPL/Caltech researchers Sarah Vigeland (now at the University of Wisconsin, Milwaukee) and Stephen Taylor (now at Vanderbilt University).