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Science

Astronomers Have Found The First Evidence For Tectonic Activity on an Exoplanet

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You may not be all that familiar with planet LHS 3844b, but it now has its own particular distinction: It’s the first planet outside of our Solar System where astronomers think they might have evidence of tectonic activity.

 

That evidence is a set of advanced simulations based on observations of the rocky planet, which is slightly larger than Earth. Importantly for this particular piece of research, it doesn’t look as though the exoplanet has an atmosphere.

That leaves half of LHS 3844b permanently exposed to its sun and could mean temperatures of up to roughly 800 degrees Celsius (1,472 degrees Fahrenheit) on the ‘daytime’ side, and about minus 250 degrees Celsius (minus 418 degrees Fahrenheit) on the ‘night-time’ side.

“We thought that this severe temperature contrast might affect material flow in the planet’s interior,” says astronomer Tobias Meier, from the University of Bern in Switzerland.

Based on phase curve observations of the planet’s brightness and possible temperatures, and computer models simulating various possible tectonic materials and heat sources, Meier and his colleagues think a hemisphere-scale flow of subsurface material is happening.

Most of the simulations the researchers ran showed only upwards flow on one side of the planet and only downwards flow on the other, but in some scenarios that was reversed – a surprising find, and one that doesn’t match tectonic movement on Earth.

 

“Based on what we are used to from Earth, you would expect the material on the hot dayside to be lighter and therefore flow upwards and vice versa”, says geophysicist Dan Bower, from the University of Bern

The underlying reason is the changing temperature of the mantle material as it moves, with colder rock stiffening up and becoming less mobile, and warmer rock becoming much more liquid-like as it heats up. The scientists say that shifting surface and material could lead to some rather incredible tectonic activity.

“On whichever side of the planet the material flows upwards, one would expect a large amount of volcanism on that particular side,” says Bower.

As a result, scientists suggest that LHS 3844b could have one entire hemisphere covered in volcanoes, while the other side shows hardly any volcanic activity – all because of the intense temperature contrast around the planet.

The sort of upwelling that would cause these volcanoes does match what we see on Earth, but only in specific places, such as Hawaii and Iceland. In more general terms, the tectonic movement that these models suggest is unlike anything in our Solar System.

As more powerful space telescopes come online and our understanding of exoplanets improves, further observations and research should help confirm what’s happening across the surface of LHS 3844b – and whether it really is half covered in volcanoes.

“Our simulations show how such patterns could manifest, but it would require more detailed observations to verify,” says Meier.

“For example, with a higher-resolution map of surface temperature that could point to enhanced outgassing from volcanism, or detection of volcanic gases. This is something we hope future research will help us to understand.”

The research has been published in the Astrophysical Journal Letters.

 

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Entertainment

‘The Muppets’ Contains Offensive Material, Declares A Disney+ Disclaimer – Deadline

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“This program includes negative depictions and/or mistreatment of people or cultures. These stereotypes were wrong then and are wrong now,” the disclaimer states. “Rather than remove this content, we want to acknowledge its harmful impact, learn from it and spark conversation to create a more inclusive future together,” the disclaimer says.

“Disney is committed to creating stories with inspirational and aspirational themes that reflect the rich diversity of the human experience around the globe,” the statement concludes.

The Muppets was once celebrated for its depictions Native American, Middle Eastern, and Asian people.

But there are some moments that haven’t survived the change in attitudes since they first aired. For example, country singer Johnny Cash is seen performing in front of a Confederate flag in one episode. That former staple of southern country is now verboten, as seen by the recent apology from singer Luke Combs for his past use of it.



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Science

Swirling Vortex of Bathtub Water Reveals an Elusive Mechanism of Black Hole Physics

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When a black hole is active, we tend to focus on the effect it has on the material it’s slurping up. It makes sense to do so; black holes themselves are difficult to probe. But the interaction between the black hole and the material should have an effect on the black hole, too – as it gains material, it should also gain in mass.

 

Such small feedback responses – especially ones previously ignored as trivial – are known as backreactions, and scientists have just observed an analogue of one that’s specific to black holes, and which can be seen in water swirling down a drain.

It’s a detection that could help study black hole phenomena that are too subtle for our current instruments, such as the Hawking radiation that is thought to be emitted by black holes. This is a theoretical type of black-body radiation that would eventually – after a very, very long time – see a black hole completely evaporate, provided it was not growing at all.

In order to study cosmic objects in finer detail than we can across the vast distances of space, scaled-down versions, or analogues, can be created in a lab. Like, for instance, a recent experiment to replicate white dwarf core pressures.

Black hole analogues are an excellent way to find out more about these enigmatic objects, and different kinds can help reveal their secrets in multiple ways.

Optical fibre and Bose-Einstein condensates have both been used to learn more about Hawking radiation. But one of the simplest has to do with how black holes feed: the draining bathtub vortex.

 

Black hole accretion can be compared with water swirling down a drain. Treating matter as a ripple in a field, the water can stand in for spacetime itself, or a field rippling with quantum activity.

Measuring the ripples responses as the water vanishes down a swirling drain might have something to say about waves of energy disappearing into a black hole.

A bathtub vortex black hole analogue. (The University of Nottingham)

From such analogues, we’ve learnt a lot about the effect of black holes on the space and material around them. But with an external water pump keeping the background of the system steady, it was unclear whether a water black hole analogue would have the freedom to be able to react to waves.

This set of experiments is the first time a draining bathtub vortex has demonstrated an effect on the black hole itself.

“We have demonstrated that analogue black holes, like their gravitational counterparts, are intrinsically backreacting systems,” said physicist Sam Patrick of the University of Nottingham in the UK.

“We showed that waves moving in a draining bathtub push water down the plug hole, modifying significantly the drain speed and consequently changing the effective gravitational pull of the analogue black hole.”

 

When waves were sent rippling into the system towards the drain, they pushed extra water in, accelerating the “accretion” process so significantly that the water levels in the tub dropped noticeably, even while a pump maintained the same level of water going in.

This change in the water level corresponds to a change in the properties of the black hole, the researchers said.

This could be extremely useful information, partially because an increase in mass changes the gravitational strength of a black hole – it changes the way the black hole warps its surrounding spacetime, as well as the effect the black hole has on the accretion disc. In addition, it offers a new way to study how waves can affect black hole dynamics.

“What was really striking for us is that the backreaction is large enough that it causes the water height across the entire system to drop so much that you can see it by eye! This was really unexpected,” Patrick said.

“Our study paves the way to experimentally probing interactions between waves and the spacetimes they move through. For example, this type of interaction will be crucial for investigating black hole evaporation in the laboratory.”

The team’s research has been published in Physical Review Letters.

 

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Science

Squeezing a rock-star material could make it stable enough for solar cells

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Scientists at SLAC National Accelerator Laboratory and Stanford University discovered that squeezing a promising lead halide material in a diamond anvil cell (left) produces a so-called “black perovskite” (right) that’s stable enough for solar power applications. Credit: Greg Stewart/ SLAC National Accelerator Laboratory

Among the materials known as perovskites, one of the most exciting is a material that can convert sunlight to electricity as efficiently as today’s commercial silicon solar cells and has the potential for being much cheaper and easier to manufacture.

There’s just one problem: Of the four possible atomic configurations, or phases, this material can take, three are efficient but unstable at room temperature and in ordinary environments, and they quickly revert to the fourth phase, which is completely useless for solar applications.

Now scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have found a novel solution: Simply place the useless version of the material in a diamond anvil cell and squeeze it at high temperature. This treatment nudges its atomic structure into an efficient configuration and keeps it that way, even at room temperature and in relatively moist air.

The researchers described their results in Nature Communications.

“This is the first study to use pressure to control this stability, and it really opens up a lot of possibilities,” said Yu Lin, a SLAC staff scientist and investigator with the Stanford Institute for Materials and Energy Sciences (SIMES).

“Now that we’ve found this optimal way to prepare the material,” she said, “there’s potential for scaling it up for industrial production, and for using this same approach to manipulate other perovskite phases.”

A search for stability

Perovskites get their name from a natural mineral with the same atomic structure. In this case the scientists studied a lead halide perovskite that’s a combination of iodine, lead and cesium.

One phase of this material, known as the yellow phase, does not have a true perovskite structure and can’t be used in solar cells. However, scientists discovered a while back that if you process it in certain ways, it changes to a black perovskite phase that’s extremely efficient at converting sunlight to electricity. “This has made it highly sought after and the focus of a lot of research,” said Stanford Professor and study co-author Wendy Mao.

Unfortunately, these black phases are also structurally unstable and tend to quickly slump back into the useless configuration. Plus, they only operate with high efficiency at high temperatures, Mao said, and researchers will have to overcome both of those problems before they can be used in practical devices.

There had been previous attempts to stabilize the black phases with chemistry, strain or temperature, but only in a moisture-free environment that doesn’t reflect the real-world conditions that solar cells operate in. This study combined both pressure and temperature in a more realistic working environment.

Pressure and heat do the trick

Working with colleagues in the Stanford research groups of Mao and Professor Hemamala Karunadasa, Lin and postdoctoral researcher Feng Ke designed a setup where yellow phase crystals were squeezed between the tips of diamonds in what’s known as a diamond anvil cell. With the pressure still on, the crystals were heated to 450 degrees Celsius and then cooled down.

Under the right combination of pressure and temperature, the crystals turned from yellow to black and stayed in the black phase after the pressure was released, the scientists said. They were resistant to deterioration from moist air and remained stable and efficient at room temperature for 10 to 30 days or more.

Examination with X-rays and other techniques confirmed the shift in the material’s crystal structure, and calculations by SIMES theorists Chunjing Jia and Thomas Devereaux provided insight into how the pressure changed the structure and preserved the black phase.

The pressure needed to turn the crystals black and keep them that way was roughly 1,000 to 6,000 times atmospheric pressure, Lin said—about a tenth of the pressures routinely used in the synthetic diamond industry. So one of the goals for further research will be to transfer what the researchers have learned from their diamond anvil cell experiments to industry and scale up the process to bring it within the realm of manufacturing.

First glimpse of polarons forming in a promising next-gen energy material

More information:
Feng Ke et al, Preserving a robust CsPbI3 perovskite phase via pressure-directed octahedral tilt, Nature Communications (2021). DOI: 10.1038/s41467-020-20745-5
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SLAC National Accelerator Laboratory

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Squeezing a rock-star material could make it stable enough for solar cells (2021, January 21)
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