On Wednesday evening, an international consortium of research collaborations revealed compelling evidence for the existence of a low-pitch hum of gravitational waves reverberating across the universe.
The scientists strongly suspect that these gravitational waves are the collective echo of pairs of supermassive black holes — thousands of them, some as massive as a billion suns, sitting at the hearts of ancient galaxies up to 10 billion light-years away — as they slowly merge and generate ripples in space-time.
“I like to think of it as a choir, or an orchestra,” said Xavier Siemens, a physicist at Oregon State University who is part of the North American Nanohertz Observatory for Gravitational Waves, or NANOGrav, collaboration, which led the effort. Each pair of supermassive black holes is generating a different note, Siemens said, “and what we’re receiving is the sum of all those signals at once.”
The findings were highly anticipated, coming more than 15 years after NANOGrav began taking data. Scientists said that, so far, the results were consistent with Albert Einstein’s theory of general relativity, which describes how matter and energy warp space-time to create what we call gravity. As more data is gathered, this cosmic hum could help researchers understand how the universe achieved its current structure and perhaps reveal exotic types of matter that may have existed shortly after the Big Bang 13.7 billion years ago.
“The gravitational-wave background was always going to be the loudest, most obvious thing to find,” said Chiara Mingarelli, an astrophysicist at Yale University and a member of NANOGrav, which is funded by the National Science Foundation. “This is really just the beginning of a whole new way to observe the universe.”
On Thursday, the NANOGrav collaboration streamed a public news briefing to officially announce their results. “Today’s announcement shatters the perception of a static universe,” said Sean Jones, assistant director for the Directorate of Mathematical and Physical Sciences at the National Science Foundation. “These observations reveal a rolling, noisy universe alive with the cosmic symphony of gravitational waves.”
Gravitational waves are created by any object that spins, such as the rotating remnants of stellar corpses, orbiting black holes or even two people “doing a do-si-do,” Mingarelli said. But unlike other types of waves, these ripples stretch and squeeze the very fabric of space-time, warping the distances between any celestial objects they pass by.
“It sounds very sci-fi,” Mingarelli said. “But it’s for real.”
The discovery of gravitational waves was first announced in 2016 by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, collaboration; the breakthrough solidified Einstein’s theory of general relativity as an accurate model of the universe and earned the project’s founders the Nobel Prize in physics in 2017. But LIGO’s signals were mostly in the frequency range of a few hundred hertz, and were created by individual pairs of black holes or neutron stars that were 10 to 100 times as massive as our sun.
In contrast, the researchers involved in this work were looking for a collective hum at much lower frequencies — one-billionth of one hertz, far below the audible range — emanating from everywhere all at once.
At the lowest frequencies, that hum is so loud “that it could be coming from hundreds of thousands, or possibly a million, overlapping signals from the cosmic merger history of supermassive black hole binaries,” Mingarelli said.
The signal was discovered by studying the behavior of rapidly spinning stars called pulsars, using a method that in 1993 earned two scientists the Nobel Prize in physics for indirectly measuring the effects of gravitational waves.
The NANOGrav team simultaneously published four studies in The Astrophysical Journal Letters, as well as two papers on the preprint server arXiv.org, detailing the collection and analysis of the data and the different interpretations of the result.
If the signal does arise from orbiting pairs of supermassive black holes, studying the gravitational-wave background will shed light on the evolutionary history of these systems and the galaxies surrounding them. But the gravitational-wave background could also be coming from something else, like hypothetical cracks in space-time known as cosmic strings.
Or it could be a relic of the Big Bang, akin to the cosmic microwave background, which led to fundamental discoveries about the structure of the universe to within 400,000 years of its beginning. The gravitational-wave background would be an even better primordial probe, Mingarelli said, because it would have been emitted almost instantaneously.
To detect the gravitational-wave background, researchers took advantage of the lighthouse-like nature of pulsars spread across the Milky Way. “Our detector isn’t something you can build in a lab or even launch into space,” Thankful Cromartie, an astronomer at Cornell University, said during Thursday’s news conference. “It’s closer to the size of the galaxy.”
Pulsars act like cosmic clocks, emitting beams of radio waves that can be periodically measured on Earth. Einstein’s theory of general relativity predicts that as gravitational waves sweep past pulsars, they should expand and shrink the distance between these objects and Earth, changing the time it takes for the radio signals to arrive at observers. And if the gravitational-wave background is indeed everywhere, pulsars across the universe should be affected in a correlated way.
Rather than build a dedicated instrument, the NANOGrav team took advantage of existing radio telescopes around the world: the Very Large Array in New Mexico, the Green Bank Telescope in West Virginia and Arecibo Observatory in Puerto Rico (before its fateful collapse three years ago).
In 2020, after more than 12 years of gathering data, the NANOGrav team released results from monitoring the timing of 45 pulsars. Even then, Siemens said, the researchers saw tantalizing hints of a gravitational-wave background, but they needed to track more pulsars for longer amounts of time to confirm that they were indeed correlated, and to claim a discovery. So the NANOGrav team approached colleagues through the International Pulsar Timing Array — an umbrella organization that includes collaborations based in India, Europe, China and Australia — and coordinated an effort to uncover the gravitational-wave background together.
Fast-forward to Wednesday: Each collaboration is now publishing results from independently collected data, all of which support the existence of a gravitational-wave background. The NANOGrav team has the largest data set, with 15 years of measurements from 67 pulsars, each monitored for at least three years.
The findings carry a confidence level in the range of 3.5- to 4-sigma, just shy of the 5-sigma standard generally expected by physicists to claim a smoking-gun discovery. That means the odds of seeing a result like this randomly are about 1 in 1,000 years, Mingarelli said. “That’s good enough for me, but other people want once in a million years,” she said. “We’ll get there eventually.”
Marcelle Soares-Santos, an astrophysicist at the University of Michigan who was not involved in the work, acknowledged that while this was early evidence, the results were enticing. “This is something that the community has been anticipating for quite a while,” she said, adding that independent measurements from other pulsar timing collaborations strengthened the findings.
Still, Soares-Santos said, it was too soon to tell what impact a gravitational-wave background might have on future research. If the signal really was from the slow, inward spiraling of supermassive black holes, as many NANOGrav collaborators believe, it would augment what scientists understand about the way early galaxies merged, forming ever-larger systems of stars and dust that eventually settled into the complex structures observed today.
But if the ripples originated with the Big Bang, they might instead provide insight into the expansion of the cosmos or the nature of dark matter — the invisible glue scientists think holds the universe together — and perhaps even reveal new particles or forces that once existed. (Experts noted that the gravitational-wave background could also originate from multiple sources, in which case the challenge would be to disentangle how much comes from where.)
The NANOGrav team is already working on analyzing all the data from gravitational-wave collaborations around the world, equaling around 25 years’ worth of measurements from 115 pulsars. These results will be unveiled in a year or so, Siemens said, adding that he expected them to exceed the 5-sigma discovery level.
But a few more years may be needed to confirm the source of the gravitational-wave background. Researchers have already begun using their data to piece together maps of the universe and to look for intense, nearby regions of gravitational-wave signals indicative of an individual supermassive black hole binary. That’s where the fun starts, said Mingarelli, who is looking forward to analyzing those maps and searching for even more exotic phenomena, like galactic jets, cosmic strings or wormholes.
“This could lead to something really groundbreaking,” Soares-Santos said, comparing it to the discovery of the cosmic microwave background in the 1960s, which has since transformed physicists’ knowledge about the early universe.
At Thursday’s news conference Maura McLaughlin, a NANOGrav collaborator at West Virginia University, was enthusiastic about the next phase of research. “We are certainly expecting the unexpected,” she said. “All we have to do is keep listening.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
