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Giant gravitational waves: why scientists are so excited

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The collision of two supermassive block holes emits gravitational waves in this artist’s illustration.Credit: Aurore Simonnet for the NANOGrav Collaboration

On 29 June, four separate teams of scientists made an announcement14 that promises to shake up astrophysics: they had seen strong hints of very long gravitational waves warping the Galaxy.

Gravitational waves are ripples in the fabric of space-time that are generated when large masses accelerate. They were first detected in 2015, but the latest evidence hints at ‘monster’ ripples with wavelengths of 0.3 parsecs (1 light year) or more; the waves detected until now have wavelengths of tens to hundreds of kilometres.

Here Nature reports what these monster gravitational waves could mean for our understanding of the cosmos, and how the field could evolve.

How do the newly announced gravitational waves differ from those astronomers had already found?

Gravitational waves were first spotted by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington State. They sensed the ripples produced by two black holes spiralling into each other and merging. LIGO and its counterpart Virgo in Europe have since reported dozens of similar events.

For the latest results, the authors relied on special beacon stars called millisecond pulsars. The teams tracked changes over more than a decade in the distances between Earth and millisecond pulsars in the Milky Way, comparing the signals from arrays of dozens of the beacon stars. These pulsar timing arrays (PTAs) are sensitive to waves that are 0.3 parsecs long or more.

And whereas LIGO and Virgo spot evidence of the last stages of individual merger events — regularly spaced waves coming from one definite direction in the sky — the four PTA collaborations have so far found only a ‘stochastic background’, a constant jostling in random directions. This is comparable to the random sloshing of water on the surface of a pond caused by the rain.

What is the origin of the waves?

The most likely explanation for the stochastic background seen by PTAs is that it is produced by many pairs of supermassive black holes orbiting each other in the hearts of distant galaxies, says Sarah Burke-Spolaor, an astrophysicist at West Virginia University in Morgantown.

Most galaxies are thought to harbour one such monster black hole, with a mass millions or billions of times that of the Sun. And astronomers know that throughout the Universe’s history, many galaxies have merged. So, some galaxies must have ended up with two supermassive black holes, known as a black-hole binary.

Researchers also have calculated that in the crowded centre of such a galactic merger, each black hole would transfer some of its momentum to surrounding stars, slinging them out at high speed or simply dragging them around. As a result, the two black holes would eventually slow down and end up orbiting each other at distances of around 1 parsec, explains Chiara Mingarelli, a gravitational-wave astrophysicist at Yale University in New Haven, Connecticut.

Only paired black holes that got much closer to each other than 1 parsec would contribute to the PTA signal, however. “They need to be separated by a milliparsec to emit detectable gravitational waves,” says Mingarelli. Theories that explain how this would happen are speculative, however, and whether the binaries can do this has been an open question, known as the final-parsec problem. “If you don’t overcome the final-parsec problem, then you don’t get any gravitational waves,” says Mingarelli.

Scientists will now seek to verify that the PTA signal does indeed come from binary supermassive black holes. If that could be confirmed, it would be evidence that supermassive black holes can come very close to each other in nature.

That result would be of fundamental importance, says Monica Colpi, an astrophysicist at the University of Milan-Bicocca in Italy — showing that thousands of black-hole binaries across the Universe have somehow ‘solved’ the final-parsec problem. “It would be the discovery that such a population exists.”

What would such binary black holes mean for LISA, Europe’s planned space-based detector?

Supermassive-black-hole pairs that got close enough to emit gravitational waves would eventually collide and merge. That’s because the gravitational waves themselves would carry energy and momentum away from the black holes, turning their orbits into spirals. In hundreds to tens of thousands of years, each of the pairs would end up colliding.

Colpi says this could be good news for the Laser Interferometer Space Antenna (LISA), a trio of probes the European Space Agency plans to launch in the mid-2030s.

As the black holes spiral inwards, the frequencies of their gravitational waves will increase and, in some cases, enter LISA’s spectrum of sensitivity. LISA will be sensitive to wavelengths of between 3 million km and 3 billion km — shorter than the wavelengths that can be detected by the PTAs, although still much longer than those seen by ground-based detectors. So LISA could see several of these mergers during its mission.

Black-hole mergers could also help to explain how some of the black holes have grown so large: they are themselves the result of earlier mergers.

Could something other than binary black holes be producing the stochastic background?

There is a plethora of exotic-physics theories that predict a similar omnidirectional background of waves coming from all directions in space. These sources could constitute part or even most of the signal. The possibilities include certain types of dark matter and even cosmic strings, hypothetical infinitesimally thin defects in the curvature of space-time. Cosmic strings could develop kinks, which could eventually snap, producing gravitational waves.

One of the most exciting alternative explanations is a cosmic gravitational-wave background originating from the early Universe, says Burke-Spolaor. Telescopes that see across the electromagnetic spectrum — from radio waves to γ-rays — are limited in how far away they can peek, and thus in how far into the past they can see. This is because, long before galaxies and stars existed, an opaque ionized gas filled the cosmos. This blocks astronomers’ view of what happened in the Universe during its first 400,000 years or so.

But gravitational waves can travel across any medium. As a result, any such waves created since the first instant after the Big Bang could still be around and be detectable as part of a stochastic background, providing a window into the extreme physics of the Big Bang. “That is just amazing to me,” says Burke-Spolaor. “Who knows what’s back there.”

 

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Here’s how Helene and other storms dumped a whopping 40 trillion gallons of rain on the South

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More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.

That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.

“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”

The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.

Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.

Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.

Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.

Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.

Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.

“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”

The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.

North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.

Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”

Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.

Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.

For Dello, the “fingerprints of climate change” were clear.

“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”

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Follow AP’s climate coverage at https://apnews.com/hub/climate

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Follow Seth Borenstein on Twitter at @borenbears

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Associated Press climate and environmental coverage receives support from several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.

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‘Big Sam’: Paleontologists unearth giant skull of Pachyrhinosaurus in Alberta

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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.

On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.

They call it “Big Sam.”

The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.

It didn’t die alone.

“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.

She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”

“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.

The head alone, she said, is about the size of a baby elephant.

The discovery was a long time coming.

The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.

“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.

When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”

“It contains about 100 to 300 bones per square metre,” she said.

Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.

About a year ago, they found the second adult: Big Sam.

Bamforth said both dinosaurs are believed to have been the elders in the herd.

“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.

“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”

The genders of the two adults are unknown.

Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.

The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.

She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.

“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.

“It’s pretty exciting.”

This report by The Canadian Press was first published Sept. 25, 2024.

The Canadian Press. All rights reserved.

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The ancient jar smashed by a 4-year-old is back on display at an Israeli museum after repair

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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.”

The Canadian Press. All rights reserved.

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