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Researchers observe stationary Hawking radiation in an analog black hole – Phys.org

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Black holes are regions in space where gravity is very strong—so strong that nothing that enters them can escape, including light. Theoretical predictions suggest that there is a radius surrounding black holes known as the event horizon. Once something passes the event horizon, it can no longer escape a black hole, as gravity becomes stronger as it approaches its center.

Theoretical physicist Stephen Hawking predicted that while nothing can escape from within them, black holes spontaneously emit a limited amount of light, which is known as Hawking . According to his predictions, this radiation is spontaneous (i.e., it arises from nothing) and stationary (i.e., its intensity does not change much over time).

Researchers at Technion- Israel Institute of Technology have recently carried out a study aimed at testing Hawking’s . More specifically, they examined whether the equivalent of Hawking radiation in an “artificial black hole” created in a laboratory setting was stationary.

“If you go inside the , there’s no way to get out, even for light,” Jeff Steinhauer, one of the researchers who carried out the study, told Phys.org. “Hawking radiation starts just outside the event , where light can barely escape. That is really weird because there’s nothing there; it’s empty space. Yet this radiation starts from nothing, comes out, and goes towards Earth.”

The artificial black hole created by Steinhauer and his colleagues was approximately 0.1 millimeters long and was made of a gas composed of 8000 rubidium atoms, which is a relatively low number of atoms. Every time the researchers took a picture of it, the black hole was destroyed. To observe its evolution over time, they thus had to produce the black hole, take a picture of it and then create another one. This process was repeated many times, for months.

The analog black hole created by the researchers. Credit: Kolobov et al.

The Hawking radiation emitted by this analog black hole is made of sound waves, rather than light waves. The rubidium atoms flow faster than the speed of sound, so sound waves cannot reach the event horizon and escape from the black hole. Outside of the event horizon, however, the gas flows slowly, so sound waves can move freely.

“The rubidium is flowing fast, faster than the speed of sound, and that means that sound cannot go against the flow,” Steinhauer explained. “Let’s say you were trying to swim against the current. If this current is going faster than you can swim, then you can’t move forward, you are pushed back because the flow is moving too fast and in the opposite direction, so you’re stuck. That’s what being stuck in a black hole and trying to reach the event horizon from inside would be like.”

According to Hawking’s predictions, the radiation emitted by black holes is spontaneous. In one of their previous studies, Steinhauer and his colleagues were able to confirm this prediction in their artificial black hole. In their new study, they set out to investigate whether the radiation emitted by their black hole is also stationary (i.e., if it remains constant over time).

“A black hole is supposed to radiate like a black body, which is essentially a warm object that emits a constant infrared radiation (i.e., black body radiation),” Steinhauer said. “Hawking suggested that black holes are just like regular stars, which radiate a certain type of radiation all the time, constantly. That’s what we wanted to confirm in our study, and we did.”

Hawking radiation is composed of pairs of photons (i.e., light particles): one emerging from a black hole and another falling back into it. When trying to identify the Hawking radiation emitted by the analog black hole they created, Steinhauer and his colleagues thus looked for similar pairs of sound waves, one coming out of the black hole and one moving into it. Once they identified these pairs of , the researchers tried to determine whether there were so-called correlations between them.

“We had to collect a lot of data to see these correlations,” Steinhauer said. “We thus took 97,000 repetitions of the experiment; a total of 124 days of continuous measurement.”

Overall, the findings appear to confirm that the radiation emitted by black holes is stationary, as predicted by Hawking. While these findings apply primarily to the analog black hole they created, could help to confirm if they can also be applied to real black holes.

“Our study also raises important questions, because we observed the entire lifetime of the analog black hole, which means that we also saw how the Hawking radiation started,” Steinhauer said. “In future studies, one could try to compare our results with predictions of what would happen in a real black hole, to see if ‘real’ Hawking radiation starts from nothing and then builds up, as we observed.”

At some point during the researchers’ experiments, the radiation surrounding their analog black hole became very strong, as the black hole formed what is known as an ‘inner horizon.” In addition to the event horizon, Einstein’s theory of general relativity predicts the existence of an inner horizon, a radius inside that delineates a further region closer to its center.

In the region inside the inner horizon the gravitational pull is far lower, thus objects are able to move around freely and are no longer pulled towards the center of the black hole. Yet they are still unable to leave the black hole, as they cannot pass through the inner horizon in the opposite direction (i.e., heading toward the event horizon).

“Essentially, the event horizon is a black hole’s outer sphere, and inside it, there’s a small sphere called the inner horizon,” Steinhauer said. “If you fall through the inner horizon, then you’re still stuck in the black hole, but at least you don’t feel the weird physics of being in a black hole. You’d be in a more ‘normal’ environment, as the pull of gravity would be lower, so you wouldn’t feel it anymore.”

Some physicists have predicted that when an analog black hole forms an inner horizon, the radiation it emits becomes stronger. Interestingly, this is exactly what happened in the analog black hole created by the researchers at Technion. This study could thus inspire other physicists to investigate the effect of the formation of an inner horizon on the intensity of a black hole’s Hawking radiation.


Explore further

Researcher devises a new way to mimic Hawking radiation in a lab


More information:
Observation of stationary spontaneous Hawking radiation and the time evolution of an analog black hole. Nature Physics(2021). DOI: 10.1038/s41567-020-01076-0

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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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‘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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