Uncontrolled rockets pose unnecessary risk, study finds - The Verge

What are the odds a free-falling rocket will kill one person somewhere in the world? There’s about a 10 percent chance over the next decade if current practices in the space industry stay the same, according to the authors of a new paper published in the journal Nature Astronomy.

While that’s not a huge risk, the threat is significantly bigger in some parts of the world than in others. In particular, many countries in theGlobal South are likely to deal with a larger share of space trash even though they’re not responsible for it, according to the analysis. And it could become a bigger issue as rockets launch into space more frequently to ferry up a growing number of satellites.

“It’s a statistically low risk, but it’s not negligible, and it’s increasing — and it’s totally avoidable,” says Michael Byers, lead author of the analysis and a professor in the Department of Political Science at the University of British Columbia. “So, should we take available measures to eliminate casualty risks? I think the answer should be yes,” he says.

As rockets propel themselves into space, they typically drop dead weight — shedding “stages” or rocket bodies that contain empty fuel tanks and engines that are no longer useful for launch. Some rockets drop boosters before reaching orbit and can usually aim for the ocean with some precision (it helps that oceans cover most of the Earth’s surface).

If a rocket has already made it into orbit, it’s possible to guide that equipment back down to Earth safely, again into the ocean, using engines that can reignite. SpaceX has also become famous for landing parts of its Falcon 9 rocket so that they can be reused again, and the company also performs controlled deorbits of the parts it cannot save.

Some rocket stages are still left abandoned in orbit after launch — which are the focus of this new paper.

To date, there hasn’t been a documented death from an uncontrolled rocket reentering the atmosphere. But in 2020, a 12-meter-long pipe and other debris from China’s Long March 5B rocket crash-landed into two villages in Ivory Coast.

There was another nail-biter last year when a 100-foot-tall Chinese rocket stage weighing in at around 20 metric tons plummeted back down to Earth. It finally dropped down in the Indian Ocean after scaring cities like New York and Madrid under its path. That was the spark for the research Byers led, with help from his son, an undergraduate at the University of Victoria who is another author on the paper.

Looking back at the last 30 years of rocket launches, Byers and his colleagues found that Jakarta, Indonesia, Mexico City, Mexico, and Lagos, Nigeria are at least three times as likely to see an uncontrolled rocket body reenter the atmosphere above them as Washington, DC and New York City in the US.

“The risk at an individual level is really, really small ... [but] if you’re living in a densely populated city at 30 degrees north latitude, then it should be of more concern to you,” Byers said. That’s because a lot of the debris from uncontrolled reentries comes from rockets launching payloads to geosynchronous orbit, which roughly follows the Earth’s equator and allows a satellite to match the Earth’s rotation.There’s also “significantly increased risk” about 30 degrees north of the equator because of the population density at that latitude, according to Byers.

If governments mandate changes and the space industry is willing to take on the additional costs, that risk can disappear. The newly published paper points to international agreements that could serve as an example, like the 1987 Montreal Protocol that’s phased out much of the ozone-depleting substances previously used as refrigerants in air conditioners and refrigerators. It might mean carrying smaller payloads so there’s enough fuel left to guide a discarded rocket stage back down to Earth safely. Luckily, it looks like industry is already starting to adapt.

“Current common practice is still to go, ‘Oh, well, that’s too bad. We’ll leave the rocket stage in geotransfer orbit and have it reenter uncontrolled.’ And that’s starting to change, particularly in the US,” says Jonathan McDowell, an astrophysicist at Harvard. The Space Force, for example, nowrequires that their launch providers deorbit rocket stages. And SpaceX is designing a next-generation rocket called Starship that is supposed to be completely reusable.

“The general practice with regards to aviation is to maximize safety. And we believe that same approach should be taken to space launches,” Byers says. So while it’s still pretty unlikely that pieces of a free-falling rocket will land on anyone’s head, Byers thinks there’s more that can be done to make spaceflight as safe as can be.

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The ultimate fate of a star shredded by a black hole - Phys.org

If a star (red trail) wanders too close to a black hole (left), it can be shredded, or spaghettified, by the intense gravity. Some of the star’s matter swirls around the black hole, like water down a drain, emitting copious X-rays (blue). Recent studies of these so-called tidal disruption events suggest that a significant fraction of the star’s gas is also blown outward by intense winds from the black hole, in some cases creating a cloud that obscures the accretion disk and the high-energy events happening within. Credit: NASA/CXC/M. Weiss

In 2019, astronomers observed the nearest example to date of a star that was shredded, or "spaghettified," after approaching too close to a massive black hole.

That tidal disruption of a sun-like star by a black hole 1 million times more massive than itself took place 215 million light years from Earth. Luckily, this was the first such event bright enough that astronomers from the University of California, Berkeley, could study the optical light from the stellar death, specifically the light's polarization, to learn more about what happened after the star was torn apart.

Their observations on Oct. 8, 2019, suggest that a lot of the star's material was blown away at high speed—up to 10,000 kilometers per second—and formed a spherical cloud of gas that blocked most of the high-energy emissions produced as the black hole gobbled up the remainder of the star.

Earlier, other observations of optical light from the blast, called AT2019qiz, revealed that much of the star's matter was launched outward in a powerful wind. But the new data on the light's polarization, which was essentially zero at visible or optical wavelengths when the event was at its brightest, tells astronomers that the cloud was likely spherically symmetric.

"This is the first time anyone has deduced the shape of the gas cloud around a tidally spaghetiffied star," said Alex Filippenko, UC Berkeley professor of astronomy and a member of the research team.

The results support one answer to why astronomers don't see high-energy radiation, such as X-rays, from many of the dozens of tidal disruption events observed to date: The X-rays, which are produced by material ripped from the star and dragged into an accretion disk around the black hole before falling inward, are obscured from view by the gas blown outward by powerful winds from the black hole.

"This observation rules out a class of solutions that have been proposed theoretically and gives us a stronger constraint on what happens to gas around a black hole," said UC Berkeley graduate student Kishore Patra, lead author of the study. "People have been seeing other evidence of wind coming out of these events, and I think this polarization study definitely makes that evidence stronger, in the sense that you wouldn't get a spherical geometry without having a sufficient amount of wind. The interesting fact here is that a significant fraction of the material in the star that is spiraling inward doesn't eventually fall into the black hole—it's blown away from the black hole."

Polarization reveals symmetry

Many theorists have hypothesized that the stellar debris forms an eccentric, asymmetric disk after disruption, but an eccentric disk is expected to show a relatively high degree of polarization, which would mean that perhaps several percent of the total light is polarized. This was not observed for this tidal disruption event.

"One of the craziest things a supermassive black hole can do is to shred a star by its enormous tidal forces," said team member Wenbin Lu, UC Berkeley assistant professor of astronomy. "These stellar tidal disruption events are one of very few ways astronomers know the existence of supermassive black holes at the centers of galaxies and measure their properties. However, due to the extreme computational cost in numerically simulating such events, astronomers still do not understand the complicated processes after a tidal disruption."

A second set of observations on Nov. 6, 29 days after the October observation, revealed that the light was very slightly polarized, about 1%, suggesting that the cloud had thinned enough to reveal the asymmetric gas structure around the black hole. Both observations came from the 3-meter Shane telescope at Lick Observatory near San Jose, California, that is fitted with the Kast spectrograph, an instrument that can determine the polarization of light over the full optical spectrum. The light becomes polarized—its electrical field vibrates primarily in one direction—when it scatters off electrons in the gas cloud.

"The accretion disk itself is hot enough to emit most of its light in X-rays, but that light has to come through this cloud, and there are many scatterings, absorptions and reemissions of light before it can escape out of this cloud," Patra said. "With each of these processes, the light loses some of its photon energy, going all the way down to ultraviolet and optical energies. The final scatter then determines the polarization state of the photon. So, by measuring polarization, we can deduce the geometry of the surface where the final scatter happens."

Patra noted that this deathbed scenario may apply only to normal tidal disruptions—not "oddballs," in which relativistic jets of material are expelled out the poles of the black hole. Only more measurements of the polarization of light from these events will answer that question.

"Polarization studies are very challenging, and very few people are well-versed enough in the technique around the world to utilize this," he said. "So, this is uncharted territory for tidal disruption events."

Patra, Filippenko, Lu and UC Berkeley researcher Thomas Brink, graduate student Sergiy Vasylyev and postdoctoral fellow Yi Yang reported their observations in a paper that has been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.

A cloud 100 times larger than Earth's orbit

The UC Berkeley researchers calculated that the polarized light was emitted from the surface of a spherical cloud with a radius of about 100 astronomical units (au), 100 times farther from the star than Earth is from the sun. An optical glow from hot gas emanated from a region at about 30 au.

The 2019 spectropolarimetric observations—a technique that measures polarization across many wavelengths of light—were of AT2019qiz, a tidal disruption event located in a spiral galaxy in the constellation of Eridanus. The zero polarization of the entire spectrum in October indicates a spherically symmetric cloud of gas—all the polarized photons balance one another. The slight polarization of the November measurements indicates a small asymmetry. Because these tidal disruptions occur so far away, in the centers of distant galaxies, they appear as only a point of light, and polarization is one of few indications of the shapes of objects.

"These disruption events are so far away that you can't really resolve them, so you can't study the geometry of the event or the structure of these explosions," Filippenko said. "But studying polarized light actually helps us to deduce some information about the distribution of the matter in that explosion or, in this case, how the gas—and possibly the accretion disk—around this black hole is shaped."

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Death by spaghettification: Scientists record last moments of star devoured by black hole

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More information: Kishore C Patra et al, Spectropolarimetry of the tidal disruption event AT 2019qiz: a quasispherical reprocessing layer, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac1727

Provided by University of California - Berkeley

Citation: The ultimate fate of a star shredded by a black hole (2022, July 11) retrieved 11 July 2022 from https://ift.tt/m9HrEOq

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After Years of Searching, Physicists Observe Electrons Flow Into Fluid-Like Whirlpools - ScienceAlert

For the first time, physicists have witnessed something incredibly exciting: electrons forming whirlpools just like a fluid.

This behavior is one that scientists have long predicted, but never observed before. And it could be the key to developing more efficient and faster next-generation electronics.

"Electron vortices are expected in theory, but there's been no direct proof, and seeing is believing," says one of the researchers behind the new study, physicist Leonid Levitov from MIT. 

"Now we've seen it, and it's a clear signature of being in this new regime, where electrons behave as a fluid, not as individual particles."

While electrons flowing in a vortex may not sound that groundbreaking, this a big deal because flowing like a fluid results in more energy being delivered to the end point, instead of being lost en route while electrons are jostled around by things such as impurities in the material or vibrations in atoms.

"We know when electrons go in a fluid state, [energy] dissipation drops, and that's of interest in trying to design low-power electronics," says Levitov. "This new observation is another step in that direction."

The work was a joint experiment between MIT, the Weizmann Institute for Science in Israel, and the University of Colorado at Denver.

Of course, we already know that electrons can bounce off each other and flow without resistance in superconductors, but this is the result of the formation of something known as 'Cooper pairs', and isn't a true example of electrons collectively flowing like a fluid.

Take water, for example. Water molecules are individual particles, but they travel as one according to the principles of fluid dynamics, carrying each other across a surface, making streams and whirlpools as they go.

An electric current should essentially be able to do the same, but any collective behavior of electrons is usually overridden by impurities and vibrations in normal metals and even semiconductors. These 'distractions' knock electrons around as it travels and stops them from exhibiting fluid-like behavior. 

It's long been predicted that within special materials at near-zero temperatures, these interferences should disappear allowing the electrons to move like a fluid… but the problem was no one had actually been able to prove this was the case, until now.

There are two fundamental features of a fluid: linear flow, where separate particles all flow in parallel as one; and the formation of vortices and eddies.

The first was observed by Levitov and colleagues at the University of Manchester back in 2017 using graphene. In atom-thin sheets of carbon, Levitov and his team showed that an electrical current could flow through a pinch point like fluid, rather than like grains of sand.

But no one had seen the second feature. "The most striking and ubiquitous feature in the flow of regular fluids, the formation of vortices and turbulence, has not yet been observed in electron fluids despite numerous theoretical predictions," the researchers write.

To figure this out, the team took pure, single crystals of an ultra-clean material known as tungsten ditelluride (WTe₂) and sliced off single-atom-thin flakes. 

They then etched a pattern into a central channel with a circular chamber on either side, creating a 'maze' for an electrical current to run through. They etched the same pattern on flakes of gold, which doesn't have the same ultra-clean properties as the tungsten ditelluride and therefore acted as a control. 

(Aharon-Steinberg et al., Nature, 2022)

Above: The diagram on the left shows how electrons flowed in the experiment in gold (Au) flakes. The image on the right shows a simulation of how they'd expect fluid-like electrons to behave.

After cooling the material to around -269 degrees Celsius (4.5 Kelvin or -451.57 Fahrenheit) they ran an electrical current through it and measured the flow at specific points throughout the material, to map how the electrons were flowing.

In the gold flakes, the electrons flowed through the maze without changing direction, even when the current had passed through each side chamber before coming back to the main current.

In contrast, within the tungsten ditelluride, the electrons flowed through the channel and then swirled into each side chamber creating whirlpools, before flowing back into the main channel – like you'd expect a fluid to do.

"We observed a change in the flow direction in the chambers, where the flow direction reversed the direction as compared to that in the central strip," says Levitov.

"That is a very striking thing, and it is the same physics as that in ordinary fluids, but happening with electrons on the nanoscale. That's a clear signature of electrons being in a fluid-like regime."

(Aharon-Steinberg et al., Nature, 2022)

Above: The column on the left shows how the electrons flowed through tungsten ditelluride (WTe₂) compared to the hydrodynamic simulations in the left column. 

Of course, this experiment was done at ultra-cold temperatures with a specialized material – it's not something that'll be happening in your home gadgets any time soon. There were also size constraints on the chambers and the middle channel.

But this is the "first direct visualization of swirling vortices in an electric current" as the press release explains. Not only is this confirmation that electrons can behave as a fluid, the advance could also help engineers to better understand how to harness this potential in their devices. 

The research has been published in Nature.

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500-million-year-old fossilized brains of Stanleycaris prompt a rethink of the evolution of insects and spiders - Phys.org

Reconstruction of a pair of Stanleycaris hirpex; upper individual has transparency of the exterior increased to show internal organs. Nervous system is shown in light beige, digestive system in dark red. Credit: Sabrina Cappelli, © Royal Ontario Museum

Royal Ontario Museum revealed new research based on a cache of fossils that contains the brain and nervous system of a half-billion-year-old marine predator from the Burgess Shale called Stanleycaris. Stanleycaris belonged to an ancient, extinct offshoot of the arthropod evolutionary tree called Radiodonta, distantly related to modern insects and spiders. These findings shed light on the evolution of the arthropod brain, vision, and head structure. The results were announced in the paper, "A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation," published in the journal Current Biology.

It's what's inside Stanleycaris' head that has the researchers most excited. In 84 of the fossils, the remains of the brain and nerves are still preserved after 506 million years.

"While fossilized brains from the Cambrian Period aren't new, this discovery stands out for the astonishing quality of preservation and the large number of specimens," said Joseph Moysiuk, lead author of the research and a University of Toronto (U of T) Ph.D. Candidate in Ecology and Evolutionary Biology, based at the Royal Ontario Museum. "We can even make out fine details such as visual processing centers serving the large eyes and traces of nerves entering the appendages. The details are so clear it's as if we were looking at an animal that died yesterday."

Turntable animation of Stanleycaris hirpex, including transparency to show internal organs. Credit: Animation by Sabrina Cappelli © Royal Ontario Museum

The new fossils show that the brain of Stanleycaris was composed of two segments, the protocerebrum and deutocerebrum, connected with the eyes and frontal claws, respectively. "We conclude that a two-segmented head and brain has deep roots in the arthropod lineage and that its evolution likely preceded the three-segmented brain that characterizes all living members of this diverse animal phylum," added Moysiuk.

In present day arthropods like insects, the brain consists of protocerebrum, deutocerebrum, and tritocerebrum. While the difference of a segment may not sound game-changing, it in fact has radical scientific implications. Since repeated copies of many arthropod organs can be found in their segmented bodies, figuring out how segments line up between different species is key to understanding how these structures diversified across the group. "These fossils are like a Rosetta Stone, helping to link traits in radiodonts and other early fossil arthropods with their counterparts in surviving groups."

Pair of fossil specimens of Stanleycaris hirpex, specimen ROMIP 65674.1-2. Credit: Jean-Bernard Caron, © Royal Ontario Museum

In addition to its pair of stalked eyes, Stanleycaris possessed a large central eye at the front of its head, a feature never before noticed in a radiodont. "The presence of a huge third eye in Stanleycaris was unexpected. It emphasizes that these animals were even more bizarre-looking than we thought, but also shows us that the earliest arthropods had already evolved a variety of complex visual systems like many of their modern kin," said Dr. Jean-Bernard Caron, ROM's Richard Ivey Curator of Invertebrate Paleontology, and Moysiuk's Ph.D. supervisor. "Since most radiodonts are only known from scattered bits and pieces, this discovery is a crucial jump forward in understanding what they looked like and how they lived," added Caron, who is also an Associate Professor at the U of T, in Ecology & Evolution and Earth Sciences.

In the Cambrian Period, radiodonts included some of the biggest animals around, with the famous "weird wonder" Anomalocaris reaching up to at least 1 meter in length. At no more than 20 cm long, Stanleycaris was small for its group, but at a time when most animals grew no bigger than a human finger, it would have been an impressive predator. Stanleycaris' sophisticated sensory and nervous systems would have enabled it to efficiently pick out small prey in the gloom.

With large compound eyes, a formidable-looking circular mouth lined with teeth, frontal claws with an impressive array of spines, and a flexible, segmented body with a series of swimming flaps along its sides, Stanleycaris would have been the stuff of nightmares for any small bottom dweller unfortunate enough to cross its path.

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  Reconstruction of Stanleycaris hirpex. Credit: Art by Sabrina Cappelli © Royal Ontario Museum

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  Fossil specimen of Stanleycaris hirpex. Dark material inside the head is the remains of nervous tissue, specimen ROMIP 65674.2. Credit: Jean-Bernard Caron © Royal Ontario Museum

About the Burgess Shale

For this research, Moysiuk and Caron studied a previously unpublished collection of 268 specimens of Stanleycaris. The fossils were primarily collected in the 1980s and 90s from rock layers above the famous Walcott Quarry site of the Burgess Shale in Yoho National Park, B.C., Canada, and are part of the extensive collection of Burgess Shale fossils housed at ROM.

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  Paper summary, showing the interpretation of the nervous system from fossils of Stanleycaris and implications for understanding the evolution of the arthropod brain. The brain is represented in red and the nerve cords in purple. Credit: Jean-Bernard Caron © Royal Ontario Museum

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  Fossil specimen of Stanleycaris hirpex. Dark material inside the head is the remains of nervous tissue, specimen ROMIP 65674.1. Credit: Jean-Bernard Caron © Royal Ontario Museum

The Burgess Shale fossil sites are located within Yoho and Kootenay National Parks and are managed by Parks Canada. Parks Canada is proud to work with leading scientific researchers to expand knowledge and understanding of this key period of earth history and to share these sites with the world through award-winning guided hikes. The Burgess Shale was designated a UNESCO World Heritage Site in 1980 due to its outstanding universal value and is now part of the larger Canadian Rocky Mountain Parks World Heritage Site.

Fossils of Stanleycaris can be seen by the public in the new Burgess Shale fossil display in the Willner Madge Gallery, Dawn of Life at ROM.

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Massive new animal species discovered in half-billion-year-old Burgess Shale

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More information: Joseph Moysiuk, A three-eyed radiodont with fossilized neuroanatomy informs the origin of the arthropod head and segmentation, Current Biology (2022). DOI: 10.1016/j.cub.2022.06.027. www.cell.com/current-biology/f … 0960-9822(22)00986-1

Provided by Royal Ontario Museum

Citation: 500-million-year-old fossilized brains of Stanleycaris prompt a rethink of the evolution of insects and spiders (2022, July 8) retrieved 8 July 2022 from https://ift.tt/jDyQWve

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Scientists detect key building blocks for RNA in a cloud in Milky Way - Daily Mail

Scientists detect key building blocks for RNA in a cloud in Milky Way - Daily Mail

Asteroid Bennu's Surprising Surface Revealed by NASA Spacecraft - NASA Goddard

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