Stephen Hawking Was Right: Black Holes Can Evaporate, Weird New Study Shows

https://www.space.com/sonic-black-hole-spews-hawking-radiation.html

In 1974, Stephen Hawking made one of his most famous predictions: that black holes eventually evaporate entirely.

According to Hawking’s theory, black holes are not perfectly “black” but instead actually emit particles. This radiation, Hawking believed, could eventually siphon enough energy and mass away from black holes to make them disappear. The theory is widely assumed to be true but was once thought nearly impossible to prove.

For the first time, however, physicists have shown this elusive Hawking radiation — at least in a lab. Though Hawking radiation is too faint to be detected in space by our current instruments, physicists have now seen this radiation in a black hole analog created using sound waves and some of the coldest, strangest matter in the universe. [9 Ideas About Black Holes That Will Blow Your Mind]

Pairs of particles

Black holes exert such an incredibly powerful gravitational force that even a photon, which travels at the speed of light, could not escape. While the vacuum of space is generally thought of as empty, the uncertainty of quantum mechanics dictates that a vacuum is instead teeming with virtual particles that flit in and out of existence in matter-antimatter pairs. (Antimatter particles have the same mass as their matter counterparts, but opposite electrical charge.)

Normally, after a pair of virtual particles appears, they immediately annihilate each other. Next to a black hole, however, the extreme forces of gravity instead pull the particles apart, with one particle absorbed by the black hole as the other shoots off into space. The absorbed particle has negative energy, which reduces the black hole’s energy and mass. Swallow enough of these virtual particles, and the black hole eventually evaporates. The escaping particle becomes known as Hawking radiation.

This radiation is weak enough that it’s impossible right now for us to observe it in space, but physicists have thought up very creative ways to measure it in a lab.

A waterfall event horizon

Physicist Jeff Steinhauer and his colleagues at the Technion – Israel Institute of Technology in Haifa used an extremely cold gas called a Bose-Einstein condensate to model the event horizon of a black hole, the invisible boundary beyond which nothing can escape. In a flowing stream of this gas, they placed a cliff, creating a “waterfall” of gas; when the gas flowed over the waterfall, it turned enough potential energy into kinetic energy to flow faster than the speed of sound.

Instead of matter and antimatter particles, the researchers used pairs of phonons, or quantum sound waves, in the gas flow. The phonon on the slow side could travel against the flow of the gas, away from the waterfall, while the phonon on the fast side could not, trapped by the “black hole” of supersonic gas.

“It’s like if you were trying to swim against a current that was going faster than you could swim,” Steinhauer told Live Science. “You’d feel like you were going forward, but you were really going back. And that’s analogous to a photon in a black hole trying to get out of the black hole but being pulled by gravity the wrong way.”

Hawking predicted that the radiation of emitted particles would be in a continuous spectrum of wavelengths and energies. He also said that it could be described by a single temperature that was dependent only on the mass of the black hole. The recent experiment confirmed both of these predictions in the sonic black hole.

“These experiments are a tour de force,” Renaud Parentani, a theoretical physicist at Laboratoire de Physique Théorique of Paris-Sud University, told Live Science. Parentani also studies analog black holes but from a theoretical angle; he was not involved in the new study. “It’s a very precise experiment. From the experimental side, Jeff [Steinhauer] is really, at the moment, the world-leading expert of using cold atoms to probe black hole physics.”

Parentani, however, emphasized that this study is “one step along a long process.” In particular, this study did not show the phonon pairs being correlated on the quantum level, which is another important aspect of Hawking’s predictions.

“The story will continue,” said Parentani. “It is not at all the end.”

Originally published on Live Science.

via Space.com http://bit.ly/2WPkkGi

June 11, 2019 at 02:30PM

Astronomers Think They’ve Finally Found the Lost Lunar Module From Apollo 10

https://gizmodo.com/astronomers-think-they-ve-finally-found-the-lost-lunar-1835422156

NASA’s Apollo 10 lunar module, or “Snoopy,” above the Moon on May 22, 1969.
Image: NASA

A discarded Apollo 10 lunar module known as “Snoopy” has been drifting in space for the past 50 years, its location a complete mystery. Now, after a meticulous eight-year search, a team of astronomers suspect they’ve finally found it.

On May 22, 1969, just two months before Neil Armstrong and Buzz Aldrin made their famous walk, NASA’s Apollo 10 mission performed an important preparatory exercise some 47,400 feet above the Moon.

During this dress rehearsal for the Moon landing, astronauts Thomas Stafford and Eugene Cernan spent some time in a lunar module, nicknamed Snoopy, as fellow astronaut John Young waited in the command module, appropriately dubbed Charlie Brown. The lunar module got its name because it was going to “snoop” around the future lunar landing site.

Prior to launch, NASA astronaut Thomas Stafford touches Snoopy’s nose for good luck.
Image: NASA

After the docking maneuver, the astronauts re-joined Young in the command module and headed back to Earth, but Snoopy never made it home, or to the lunar surface for that matter. Instead, the lunar lander was flung into an orbit around the Sun, never to be heard of again—until now. Possibly.

As reported in Sky News, a team of astronomers say they’re “98% certain” they’ve located Snoopy’s position in space. The news was disclosed by Nick Howes, a fellow of the Royal Astronomical Society, to an audience attending the recent Cheltenham Science Festival in the United Kingdom.

Howes began the search for Snoopy back in 2011. Over the past eight years, his team has sifted through radar data gathered by multiple observatories. Howes told Gizmodo in a Twitter direct message that his team “trawled through lots of data” with help from Asteroid Zoo members. Back in 2015, the team thought they had detected Snoopy, but object Wt1190f, as it was called, re-entered Earth’s atmosphere, at which time it was identified as the trans-lunar injection stage of the 1998 Lunar Prospector mission.

The object-in-question was finally picked up by the Mount Lemmon Sky Survey team in January 2018. It “quickly became obvious that the size and orbit were very much like the calculations we made in 2011 and 2012 for Snoopy,” Howes told Gizmodo. To make the discovery, Howes said his team used online orbital calculators such as AGI’s Systems Tool Kit (STK) to determine the object’s orbit.

Speaking to Sky News, Howes said “we can’t be 100% sure” this object is Snoopy. For that, we’ll need to get “really close to it and get a detailed radar profile.” As to when that might happen, Howe told Gizmodo that it won’t be any time soon.

“Right now [it’s] heading away from us” and it’s “due to come back around 18 years from now,” he said. The object is currently at magnitude 29.5 in terms of its brightness, which means it’s impossible to image with most telescopes, he added.

Should the object eventually be confirmed as Snoopy, Howes said we should try to intercept and image it. He thought SpaceX CEO Elon Musk might be a good candidate for such a mission. As to whether we should scoop up Snoopy, “that’s an interesting question,” he said, “as the cost would be high versus the science return,” adding that “it’s a similar argument I guess to the one Bob Ballard faced in the 80s when looking for the Titanic.”

Howes is right to say it’s an “interesting question” as to whether we should retrieve Snoopy, if that’s what the object really is. But to be fair, this historical relic is doing nothing for nobody out there in the depths of space. My preference is that we go get it and put it in a museum for all to see. It would be an expensive proposition, no doubt, but also pretty cool.

via Gizmodo https://gizmodo.com

June 11, 2019 at 04:06PM

Scientists found these old photographs contain metallic nanoparticles

https://arstechnica.com/?p=1519385

The earliest reliably dated photograph of people, taken by Louis Daguerre one spring morning in 1838.
Enlarge /

The earliest reliably dated photograph of people, taken by Louis Daguerre one spring morning in 1838.

Public domain

Daguerreotypes are one of the earliest forms of photography, producing images on silver plates that look subtly different, depending on viewing angle. For instance they can appear positive or negative, or the colors can shift from bluish to brownish-red tones. Now an interdisciplinary team of scientists has discovered that these unusual optical effects are due to the presence of metallic nanoparticles in the plates. They described their findings in a new paper in the Proceedings of the National Academy of Sciences.

Co-author Alejandro Manjavacas—now at the University of New Mexico in Albuquerque—was a postdoc at Rice University, which boasts one of the top nanophotonics research groups in the US. That’s where he met his co-author, Andrea Schlather, who ended up in the scientific research department at the Metropolitan Museum of New York. The Met has a valuable collection of daguerreotypes, and her new colleagues were keen to find better methods for preserving these valuable artifacts.

Schlather contacted Manjavacas and suggested this might be a great place to apply their combined expertise in nanoplasmonics—a field dedicated to detailing how nanoparticles interact with light. Think of it this way: light is an optical oscillation made up of photons. Sound is a mechanical oscillation made up of quasiparticles known as phonons. And plasma (ionized gas, the fourth fundamental state of matter) oscillations consist of plasmons. Surface plasmons play a critical role in determining the optical properties of metals in particular.

All photography dates back to an ancient optical effect known as the camera obscura, in which inverted images of external scenes or objects form on a white surface within a darkened chamber. A pinhole camera works much the same way. But nobody could figure out how to fix those ephemeral images for posterity, although 18th-century novelist Charles-Francois Tiphaigne de la Roche envisioned a world in his novel, Giphantie, where it was possible to do so by coating a canvas with a wet, sticky substance, and then letting it dry in the dark to preserve the captured image. He wasn’t that far off the mark. By the end of the 1700s, scientists had realized that silver chloride and silver nitrate would darken when exposed to light, a photochemical effect that would soon make photography possible.

Examples of a gilded (left) and unglued (right) daguerreotype created in 1844 by Joseph-Philabert Girault de Prangey.
Enlarge /

Examples of a gilded (left) and unglued (right) daguerreotype created in 1844 by Joseph-Philabert Girault de Prangey.

A. Schlather et al.

Nicephore Niepce is now widely credited with taking the first still photograph in July of 1827, using a material that hardened when exposed to light to capture the image. But it took a full eight hours of exposure, and the image was temporary. Louis Daguerre built on Niepce’s work, figuring out how to reduce exposure times and fix the images by immersing the photographic plates in a salt solution. Introduced in 1839, his daguerreotypes” were all the rage for several decades—Abraham Lincoln and Emily Dickinson were among the luminaries whose portraits were captured this way, along with the transit of Venus and the horrors of the American Civil War.

The basic process involved polishing a silver-plated copper substrate until it shone like a mirror and then treating it with fumes to make it light sensitive. The plate would be inserted into the camera and exposed for however long was necessary to capture the desired latent image. Fumes of mercury vapor would reveal the image, and the plate would be rinsed and dried to reverse the light sensitivity before placing it under glass to preserve it for posterity.

For their experiments, Manjavacas and Schlather figured a good place to start was to gain a better understanding of what is going on microscopically at the nanoscale with this process. Of course, 19th-century daguerreotypes are very fragile and highly valuable, so it wasn’t possible to conduct the kind of experiments required on the originals. “We needed something where we could literally break pieces apart,” said Manjavacas.

“Daguerreotypes rely on light scattering by metallic nanoparticles to create an image that projects off a reflective silver substrate.”

So they brought in co-author Michael Robinson, one of the top daguerreotype artists in the world, who wrote his PhD thesis on the techniques and aesthetics of this type of photography. Robinson was able to fabricate original daguerreotypes in strict accordance with 19th-century techniques, so experiments could be done without worrying about damaging period photographs. They tested their experimental findings with computer simulations of the electromagnetic effects.

Daguerreotypes are made with polished silver plates, and the salt added in the latter stages of processing contains gold atoms. So perhaps it’s not surprising that the researchers found metallic nanoparticles. The size and shape of those nanoparticles influence the optical properties of the final product because they determine which wavelengths of light are scattered off the surface and which are absorbed, yielding different hues. Specifically, the scattering spectrum showed a narrow blue peak in the UV range, and a broader red peak. This is why a daguerreotype will have a bluish tone when viewed from above, and shift to brownish-red hues as the viewing angle increases. And no two daguerreotypes are exactly the same.

“Daguerreotypes, unlike other types of photograph, rely on light scattering by metallic nanoparticles to create an image that projects off a reflective silver substrate,” the authors wrote. “The balance between the light scattered by the nanostructure and the spectacular reflection on the substrate creates the bright and dark tones, respectively, with the behavior of the midtones depending on the density of the nanostructures.”

  • Scattering intensity diagrams for nanoparticles of varying size and shape.

    A. Schlather et al.

  • Viewing angle dependence of the daguerreotype image.

    A. Schlather et al.

It’s a similar phenomenon to the one responsible for the shifting colors of a famous Roman drinking goblet. Dating back to around 400 CE and made of dichroic glass, the Lycurgus Cup is notable for exhibiting different colors depending on the light. (It gets its name from the scene depicted on its surface, of King Lycurgus of Thrace.) Light it from the front, and the cup looks green; light it from behind, and the color changes to a deep red. Exactly why this occurred was a mystery until 2007, when a team of scientists discovered the color shifts were due to the presence of nanoparticles in the glass—the result of Roman artisans adding finely ground gold and silver into the mix. Those nanoparticles change how the electrons in the cup vibrate in response to light so that the color one sees shifts with the observer’s vantage point.

“The Romans knew that if they added salt when they melted the silicon (sand) to make the glass, those salts contain gold atoms,” said Manjavacas. “In the melting process, those atoms aggregate and produce nanoparticles, and that’s how they got the colors. That’s how any stained glass is made.” It’s similar to how the precise lattice-like structure of photonic crystals produces iridescent colors in nature, like the wings of butterflies, or opals.

Like the Lycurgus Cup, the unusual color properties of 19th-century daguerreotypes are the result of the scattering properties of nanoparticles, according to Manjavacas. There is a key difference, however: the nanoparticles are embedded into the glass of the cup, whereas with a daguerreotype, they are sitting on top of a substrate, adding some reflection that does not occur with an artifact like the Lycurgus Cup. “In our case, the scattering of the particles has a strong dependence on the substrate,” said Manjavacas.

The team also discovered that if they coated the surface of the daguerreotype with a layer of gold, the colors shifted more to the red side of the spectrum. That’s in keeping with a 19th-century trick called “gilding,” in which the photographer would apply a solution of gold salt to the image to achieve warmer tones and sharper contrast.

Plasmonic nanoparticles (gold, silver, and platinum, most notably) are “tunable,” because one can alter their size and shape to tweak the optical properties of the metallic material. That’s a highly desirable feature for all kinds of practical applications. Schlather’s interest, of course, lies in developing better preservation methods for 19th-century daguerreotypes. If, for instance, an analysis reveals the nanoparticles in a given artifact are growing larger, it might be because of the UV light used in the display. A museum can correct for that to ensure its collection doesn’t deteriorate further.

Manjavacas is also interested in developing novel color printing technologies, such as using the plasmonic properties of aluminum nanorods to make color filters for flat panel displays—or to create anti-counterfeit watermarks on currency, since the nano aspect makes it possible to create pixels as small as one micron. “In this sense, daguerreotypes can be considered the first realization of plasmonic color printing,” the authors wrote. “Indeed, novel proposals for the fabrication of these devices resemble daguerreotypes.”

DOI: PNAS, 2019. 10.1073/pnas.1904331116 (About DOIs).

via Ars Technica https://arstechnica.com

June 12, 2019 at 10:08AM