When black holes and other enormously massive, dense objects whirl around one another, they send out ripples in space and time called gravitational waves. These waves are one of the few ways we have to study the enigmatic cosmic giants that create them.
Astronomers have observed the high-frequency “chirps” of colliding black holes, but the ultra-low-frequency rumble of supermassive black holes orbiting one another has proven harder to detect. For decades, we have been observing pulsars, a type of star that pulses like a lighthouse, in search of the faint rippling of these waves.
In 1915, German-born physicist Albert Einstein presented a breakthrough insight into the nature of gravity: the general theory of relativity.
The theory describes the universe as a four-dimensional “fabric” called spacetime that can stretch, squeeze, bend and twist. Massive objects distort this fabric to give rise to gravity.
A curious consequence of the theory is that the motion of massive objects should produce ripples in this fabric, called gravitational waves, which spread at the speed of light.
It takes an enormous amount of energy to create the tiniest of these ripples. For this reason, Einstein was convinced gravitational waves would never be directly observed.
A century later, researchers from the LIGO and Virgo collaborations witnessed the collision of two black holes, which sent a burst of gravitational waves chirping throughout the universe.
Now, seven years after this discovery, radio astronomers from Australia, China, Europe, India, and North America have found evidence for ultra-low-frequency gravitational waves.
A slow rumbling of gravitational waves
Unlike the sudden burst of gravitational waves reported in 2016, these ultra-low-frequency gravitational waves take years or even decades to oscillate.
They are expected to be produced by pairs of supermassive black holes, orbiting at the cores of distant galaxies throughout the universe. To find these gravitational waves, scientists would need to construct a detector the size of a galaxy.
Or we can use pulsars, which are already spread across the galaxy, and whose pulses arrive at our telescopes with the regularity of precise clocks.
CSIRO’s Parkes radio telescope, Murriyang, has been observing an array of these pulsars for almost two decades. Our Parkes Pulsar Timing Array team is one of several collaborations around the world that have today announced hints of gravitational waves in their latest data sets.
Other collaborations in China (CPTA), Europe and India (EPTA and InPTA), and North America (NANOGrav) see similar signals.
As gravitational waves warp spacetime around Earth, they distort the arrival times of radio waves from distant pulsars. Credit: OzGrav / Swinburne / Carl Knox
The signal we are searching for is a random “ocean” of gravitational waves produced by all the pairs of supermassive black holes in the universe.
Observing these waves is not only another triumph of Einstein’s theory, but has important consequences for our understanding of the history of galaxies in the universe. Supermassive black holes are the engines at the heart of galaxies that feed on gas and regulate star formation.
The signal appears as a low-frequency rumble, common to all pulsars in the array. As the gravitational waves wash over Earth, they affect the apparent rotation rates of the pulsars.
The stretching and squeezing of our galaxy by these waves ultimately changes the distances to the pulsars by just tens of meters. That’s not much when the pulsars are typically about 1,000 light-years away (that’s about 10,000,000,000,000,000,000 meters).
Remarkably, we can observe these shifts in spacetime as nanosecond delays to the pulses, which radio astronomers can track with relative ease because pulsars are such stable natural clocks.
What has been announced?
Because the ultra-low-frequency gravitational waves take years to oscillate, the signal is expected to emerge slowly.
First, radio astronomers observed a common rumble in the pulsars, but its origin was unknown.
Now, the unique fingerprint of gravitational waves is beginning to appear as an attribute of this signal, observed by each of the pulsar timing array collaborations around the world.
This fingerprint describes a particular relationship between the similarity of pulse delays and the separation angle between pulsar pairs on the sky.
The relationship arises because spacetime at Earth is stretched, changing the distances to pulsars in a way that depends on their direction. Pulsars close together in the sky show a more similar signal than pulsars separated at right angles, for example.
The breakthrough has been enabled by improved technology at our observatories. The Parkes Pulsar Timing Array has the longest high-quality data set, thanks to the advanced receiver and signal processing technology installed on Murriyang. This technology has enabled the telescope to discover many of the best pulsars used by collaborations around the globe for the gravitational wave searches.
Earlier results from our collaboration and others showed the signal expected from gravitational waves was missing from pulsar observations.
Now, we seem to be seeing the signal with relative clarity. By segmenting our long data set into shorter “time-slices,” we show the signal appears to be growing with time. The underlying cause of this observation is unknown, but it may be that the gravitational waves are behaving unexpectedly.
The new evidence for ultra-low-frequency gravitational waves is exciting for astronomers. To confirm these signatures, the global collaborations will need to combine their data sets, which increases their sensitivity to gravitational waves many-fold.
Efforts to produce this combined data set are now in progress under the International Pulsar Timing Array project, whose members met in Port Douglas in Far North Queensland last week. Future observatories, like the Square Kilometre Array under construction in Australia and South Africa, will turn these studies into a rich source of knowledge about the history of our universe.
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Using a detector the size of a galaxy, astronomers detect gravitational waves from supermassive black hole pairs (2023, July 1)
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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.
