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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.

Researchers observe stationary Hawking radiation in an analogue black hole
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

© 2021 Science X Network

Citation:
Researchers observe stationary Hawking radiation in an analog black hole (2021, February 19)
retrieved 19 February 2021
from https://phys.org/news/2021-02-stationary-hawking-analog-black-hole.html

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Perseverance saw its own descent stage crash – EarthSky

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The Mars rover Perseverance captured a photo on February 18, 2021, of its own descent stage crashing onto Mars’ surface and triggering a plume of smoke. Image via NASA.

One of the coolest shots we’ve seen from Perseverance on Mars so far came from the day of its successful landing, February 18, 2021. Minutes after landing, Perseverance managed to look off into the distance and capture an image of its own descent stage crash landing on Mars’ surface.

What’s the descent stage? Its role in Perseverance’s landing was brief, but vital. The descent stage is the rocket-powered section that deployed after the parachute. It was needed in part because Mars’ atmosphere is so thin that parachutes alone can’t guarantee a soft-enough landing. The descent stage kept the rover steady just above Mars’ surface, as the rover was deployed to Mars’ surface via cables. The descent stage wasn’t designed to land safely. After deploying the rover, it flew some distance off and crashed itself. That’s what Perseverance captured in this image.

Perseverance is busy on Mars examining its environs and recording all that it sees. It reports its findings with an anthropomorphized – and adorable – Twitter account @NASAPersevere. Its tweet about the descent stage crash landing was one of its first.

Diagram of stages of rover's descent through Mars' atmosphere to the surface.

Artist’s concept illustrating Perseverance’s landing on Mars, via NASA.

As you may have heard by now – or realized yourself – Mars is the only planet we know that’s populated by robots! A total of 18 spacecraft have been put in orbit around Mars, eight of which are still operating. Of the Mars’ rovers sent to Mars’s surface, five are still operational: Sojourner, Spirit and Opportunity, Curiosity, and Perseverance.

One Mars orbiter, the European Space Agency’s ExoMars Trace Gas Orbiter, also captured Perseverance on Mars’ surface, at its landing spot. It managed to find the rover and the pieces shed on descent, then tweeted an image:

The rover is near the bottom center of the image, with the heat shield a dark circular spot in the upper right, the descent stage to the left (and in the plume photo above), and the white parachute and back shell bright on the surface at far left. You can see from the overhead view the large ridge between the rover and the descent stage that the rover is looking toward in the top image.

Since 1960, nine countries have sent missions either to orbit Mars or attempt to land on its surface, and many of them have crashed and burned, quite literally.

February 2021 saw three missions successfully make it to Mars, both in orbit and on the surface. Perseverance was one. The other two were the UAE’s Hope mission and China’s Tianwen-1.

Graphic showing Mars and over 20 missions with successes and failures.

Many spacecraft have tried to land on Mars but few have succeeded. Image via Al Jazeera.

Bottom line: NASA’s Mars rover Perseverance tweeted a photo of the resulting plume of smoke from the impact of the descent stage.

Kelly Kizer Whitt

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BlackburnNews.com – Fireball flies over Chatham-Kent sky – BlackburnNews.com

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Fireball flies over Chatham-Kent sky

February 26, 2021 fireball (Screen capture via fireballs.ndc.nasa.gov)


If you witnessed a bright light flash across the sky Friday night in Chatham-Kent, you weren’t imagining things.

A fireball passed over the region around 10:07 p.m.

Peter Brown, a Western University professor, meteor scientist and planetary astronomer tweeted a video of the event. Brown described it as being “as bright as [the] full Moon.”

According to the NASA All Sky Fireball Network, observers in Ontario, Michigan, New York, Ohio and Pennsylvania reported seeing a bright fireball in the sky on Friday evening. The event was captured by several all-sky meteor cameras belonging to the NASA All Sky Fireball Network and the Southern Ontario Meteor Network operated by Western University.

According to NASA, an initial analysis of the video shows that the meteor appears 90 km above Erieau on the northern shore of Lake Erie. It moved northwest at a speed of 105,800 km per hour as it crossed the Canada-U.S. border before ending 32 km above Fair Haven, MI.

“At its brightest, the fireball rivalled the quarter Moon in intensity,” read a statement on the NASA All Sky Fireball Network. “Combining this with the speed gives the fragment a mass of at least 2 kilograms and a diameter of approximately 12 centimetres.”

It’s believed that the meteor was caused by a fragment of a Jupiter family comet although an asteroidal origin is also possible.

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Fireball flies over Chatham-Kent sky – BlackburnNews.com

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Fireball flies over Chatham-Kent sky

February 26, 2021 fireball (Screen capture via fireballs.ndc.nasa.gov)


If you witnessed a bright light flash across the sky Friday night in Chatham-Kent, you weren’t imagining things.

A fireball passed over the region around 10:07 p.m.

Peter Brown, a Western University professor, meteor scientist and planetary astronomer tweeted a video of the event. Brown described it as being “as bright as [the] full Moon.”

According to the NASA All Sky Fireball Network, observers in Ontario, Michigan, New York, Ohio and Pennsylvania reported seeing a bright fireball in the sky on Friday evening. The event was captured by several all-sky meteor cameras belonging to the NASA All Sky Fireball Network and the Southern Ontario Meteor Network operated by Western University.

According to NASA, an initial analysis of the video shows that the meteor appears 90 km above Erieau on the northern shore of Lake Erie. It moved northwest at a speed of 105,800 km per hour as it crossed the Canada-U.S. border before ending 32 km above Fair Haven, MI.

“At its brightest, the fireball rivalled the quarter Moon in intensity,” read a statement on the NASA All Sky Fireball Network. “Combining this with the speed gives the fragment a mass of at least 2 kilograms and a diameter of approximately 12 centimetres.”

It’s believed that the meteor was caused by a fragment of a Jupiter family comet although an asteroidal origin is also possible.

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