Two electrons and two holes, created by light quanta, held together by a chessboard-like background.
In physics, there are very different types of particles: Elementary particles are the fundamental building blocks of matter. Other particles, such as atoms, are bound states consisting of several smaller constituents. And then there are so-called “quasi-particles”—excitations in a system that consists of many particles, which in many ways behave just like a particle themselves.
Such a quasiparticle has now been discovered in computer simulations at TU Wien (Vienna) and named pi-ton. It consists of two electrons and two holes. The new particle is presented in the journal Physical Review Letters, the article also describes how the pi-ton can be detected experimentally.
A hole is almost a particle
“The simplest quasi-particle is a hole”, explains professor Karsten Held from the Institute for Solid State Physics at Vienna University of Technology (TU Wien). “Let us imagine, for example, that many atoms are arranged in a regular pattern in a crystal and that there is a moving electron at each atom. Only at one particular atom the electron is missing—this is called a hole.” Now an electron can move up from the neighboring atom. The original hole is closed, a new hole opens.
Instead of describing the motion of constantly moving electrons, it is easier to study the motion of the hole. If the electrons move to the right, the hole moves to the left—and this movement follows certain physical rules, just like the movement of an ordinary particle. However, unlike an electron, which can also be observed outside the crystal, the hole only exists in conjunction with the other particles. In this case we speak of a “quasi-particle.”
“However, the dividing line between particles and quasi-particles is not as clear as one might think,” says Held. “Strictly speaking, even ordinary particles can only be understood in the context of their environment. Even in a vacuum, particle-hole excitations occur constantly, albeit for a very short time. Without them, the mass of an electron for example would be completely different. In this sense, even in experiments with ordinary electrons, what we see is really a quasi-particle electron.”
More complicated bonds
But there are also more complex quasi-particles: The exciton, for example, which plays an important role in semiconductor physics. It is a bound state consisting of an electron and a hole, which is created by light. The electron is negatively charged, the hole is the absence of a negative charge – and thus positively charged. Both attract each other and can form a bond.
“We actually wanted to investigate such excitons,” report Dr. Anna Kauch and Dr. Petra Pudleiner, the first authors of the paper. “We developed computer simulations to calculate quantum physical effects in solids.” But soon Kauch, Pudleiner, and their colleague Katharina Astleithner realized that they had come across something totally different in their calculations—a completely new type of quasi-particle. It consists of two electrons and two holes that couple to the outside world via photons.
The team gave this previously unknown object the name “pi-ton.”
“The name pi-ton comes from the fact that the two electrons and two holes are held together by charge density fluctuations or spin fluctuations that always reverse their character by 180 degrees from one lattice point of the crystal to the next—i.e. by an angle of pi, measured in radians,” explains Kauch.
“This constant change from plus to minus can perhaps be imagined like a change from black to white on a chessboard,” says Pudleiner. The pi-ton is created spontaneously by absorbing a photon. When it disappears, a photon is emitted again.
The particle that came out of the computer
So far, the pi-ton has been discovered and verified by computer simulations. For the research team, there is no doubt about the existence of the pi-ton: “We have now investigated the phenomenon of the pi-ton using various models—it shows up again and again. Therefore, it should definitely be detectable in a variety of different materials, ” Held says. “Some experimental data obtained with the material samarium titanate already seem to point to the pi-ton. Additional experiments with photons and neutrons should soon provide clarity.”
Even though we are constantly surrounded by countless quasiparticles—the discovery of a new quasiparticle species is something very special. Besides the exciton, there is now also the pi-ton. In any case, this contributes to a better understanding of the coupling between light and solids, a topic that plays an important role not only in basic research but also in many technical applications—from semiconductor technology to photovoltaics.
– This press release was originally published on the TU Wien website
NASA’s Hubble Space Telescope captured two festive-looking nebulas – Tech Explorist
The image shows NGC 248, about 60 light-years long and 20 light-years wide. They are two nebulas, situated to appear as one. The nebulas, together, are called NGC 248.
Initially discovered in 1834 by the astronomer Sir John Herschel, NGC 248 resides in the Small Magellanic Cloud, located approximately 200,000 light-years away in the southern constellation Tucana.
Small Magellanic Cloud is a dwarf galaxy that is a satellite of our Milky Way galaxy. The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE).
The dwarf satellite galaxy contains several brilliant hydrogen nebulas, including NGC 248. Intense radiation from the brilliant central stars is heating hydrogen in each nebula, causing them to glow red.
The study’s principal investigator, Dr. Karin Sandstrom of the University of California, San Diego, said, “The Small Magellanic Cloud has between a fifth and a tenth of the amount of heavy elements that the Milky Way does. Because it is so close, astronomers can study its dust in great detail and learn about what dust was like earlier in the history of the universe.”
“It is important for understanding the history of our galaxy, too. Most of the star formation happened earlier in the universe, at a time when there was a much lower percentage of heavy elements than there is now. Dust is a critical part of how a galaxy works, how it forms stars.”
The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE). The data used in this image were taken with Hubble’s Advanced Camera for Surveys in September 2015.
When To See An ‘Earth-Grazer’ This Weekend: Don’t Write-Off The Perseid Meteor Shower, Says Expert – Forbes
If you’ve ever laid down a blanket or set up a lawn chair to watch a meteor shower there’s a good chance it was to watch the Perseids.
Due to peak at 01:00 UT on Saturday, August 13, 2022, normal advice would be to be outside at that time (in Europe) or just as soon as its gets dark on Friday, August 12 (North America).
As I’ve already reported, this year the Perseids coincides with a full Moon, so all but the brightest meteors and “fireballs” (larger, brighter meteors) will be visible. So from the 50-75-or-so “shooting stars” you might normally see during the peak of the Perseids only a few—albeit bright—meteors will be visible.
It’s almost not worth the bother, I said, advising you to go watch this instead next weekend.
However, there is another opinion. In an article published on the American Meteor Society’s website, fireball coordinator Robert Lunsford says that despite the bright full Moon visible meteor rates during the peak of the Perseid meteor shower will be better than 95% of all other nights this year.
When to see the Perseid meteor shower
“Most of the Perseid meteors are faint and bright moonlight will make it difficult to view,” he writes. “Despite the glare of moonlight, the Perseids produce many bright meteors that can still be easily seen despite the bright moonlight.”
He also advises two great times to watch for shooting stars—just after sunset on Friday, August 12 and just before dawn on Saturday, August 13.
Perseids: ‘Earth-grazers’ just after sunset
You’ll need patience, but to see an “Earth-grazer” is unforgettable.
Just after sunset is actually thee worst time in terms of numbers of shooting stars you might see, but the few that do come your way this time of night are special.” The reason is that they just skim the upper regions of the atmosphere and will last much longer than Perseids seen during the morning hours,” writes Lunsford. “Most of these “earth-grazing” Perseids will be seen low in the east or west, traveling north to south.”
Perseids: ‘shooting stars’ before dawn
The activity from the Perseid meteor shower will peak where you are as the radiant—the constellation of Perseus—rises higher into the night sky. “Theoretically, the best time to watch the Perseids is just before the break of dawn when the radiant lies highest in a dark sky,” writes Lunsford. That’s about 04:00 local time, though he also reveals that experienced observers often say the hour between 03:00 and 04:00 is usually the best.
Perseids: ‘shooting stars’ in a moonless sky
If you want to look for Perseids in a dark, moonless sky then you’re mostly out of luck this year. By the time the full Moon is rising long after midnight the meteor rates will have vastly reduced, though it may be worth shooting star-gazing after August 19, 2022.
When is the Perseid meteor shower in 2023?
The Perseid meteor shower will next year peak—in thankfully moonless skies—at around 07:00 UT on August 13, 2023 (so 03:00 EST and midnight PST), which will be ideal for North America.
Wishing you clear skies and wide eyes.
Meet Qikiqtania, a fossil fish who stayed in the water while others ventured onto land – Big Think
Approximately 365 million years ago, one group of fishes left the water to live on land. These animals were early tetrapods, a lineage that would radiate to include many thousands of species including amphibians, birds, lizards and mammals. Human beings are descendants of those early tetrapods, and we share the legacy of their water-to-land transition.
But what if, instead of venturing onto the shores, they had turned back? What if these animals, just at the cusp of leaving the water, had receded to live again in more open waters?
A new fossil suggests that one fish, in fact, did just that. In contrast to other closely related animals, which were using their fins to prop their bodies up on the bottom of the water and perhaps occasionally venturing out onto land, this newly discovered creature had fins that were built for swimming.
In March 2020, I was at The University of Chicago and a member of biologist Neil Shubin’s lab. I was working with Justin Lemberg, another researcher in our group, to process a fossil that was collected back in 2004 during an expedition to the Canadian Arctic.
From the surface of the rock it was embedded in, we could see fragments of the jaws, about 2 inches long (5 cm) and with pointed teeth. There were also patches of white scales with bumpy texture. The anatomy gave us subtle hints that the fossil was an early tetrapod. But we wanted to see inside the rock.
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So we used a technology called CT scanning, which shoots X-rays through the specimen, to look for anything that might be hidden within, out of view. On March 13, we scanned an unassuming piece of rock that had a few scales on top and discovered it contained a complete fin buried inside. Our jaws dropped. A few days later, the lab and campus shut down, and COVID-19 sent us into lockdown.
The fin revealed
A fin like this is extremely precious. It can give scientists clues into how early tetrapods were evolving and how they were living hundreds of millions of years ago. For example, based on the shape of certain bones in the skeleton, we can make predictions about whether an animal was swimming or walking.
Although that first scan of the fin was promising, we needed to see the skeleton in high resolution. As soon as we were allowed back on campus, a professor in the university’s department of the geophysical sciences helped us to trim down the block using a rock saw. This made the block more fin, less rock, allowing for a better scan and a closer view of the fin.
When the dust had cleared and we’d finished analyzing data on the jaws, scales and fin, we realized that this animal was a new species. Not only that, it turns out that this is one of the closest known relatives to limbed vertebrates – those creatures with fingers and toes.
We named it Qikiqtania wakei. Its genus name, pronounced “kick-kiq-tani-ahh,” refers to the Inuktitut words Qikiqtaaluk or Qikiqtani, the traditional name for the region where the fossil was found. When this fish was alive, many hundreds of millions of years ago, this was a warm environment with rivers and streams. Its species name honors the late David Wake, a scientist and mentor who inspired so many of us in the field of evolutionary and developmental biology.
Skeletons tell how an animal lived
Qikiqtania reveals a lot about a critical period in our lineage’s history. Its scales tell researchers unambiguously that it was living underwater. They show sensory canals that would have allowed the animal to detect the flow of water around its body. Its jaws tell us that it was foraging as a predator, biting and holding onto prey with a series of fangs and drawing food into its mouth by suction.
But it is Qikiqtania’s pectoral fin that is most surprising. It has a humerus bone, just as our upper arm does. But Qikiqtania’s has a very peculiar shape.
Early tetrapods, like Tiktaalik, have humeri that possess a prominent ridge on the underside and a characteristic set of bumps, where muscles attach. These bony bumps tell us that early tetrapods were living on the bottom of lakes and streams, using their fins or arms to prop themselves up, first on the ground underwater and later on land.
Qikiqtania’s humerus is different. It lacks those trademark ridges and processes. Instead, its humerus is thin and boomerang-shaped, and the rest of the fin is large and paddle-like. This fin was built for swimming.
Whereas other early tetrapods were playing at the water’s edge, learning what land had to offer, Qikiqtania was doing something different. Its humerus is truly unlike any others known. My colleagues and I think it shows that Qikiqtania had turned back from the water’s edge and evolved to live, once again, off the ground and in open water.
Evolution isn’t a march in one direction
Evolution isn’t a simple, linear process. Although it might seem like early tetrapods were trending inevitably toward life on land, Qikiqtania shows exactly the limitations of such a directional perspective. Evolution didn’t build a ladder towards humans. It’s a complex set of processes that together grow the tangled tree of life. New species form and they diversify. Branches can head off in any number of directions.
This fossil is special for so many reasons. It’s not just miraculous that this fish was preserved in rock for hundreds of millions of years before being discovered by scientists in the Arctic, on Ellesmere Island. It’s not just that it’s remarkably complete, with its full anatomy revealed by serendipity at the cusp of a global pandemic. It also provides, for the first time, a glimpse of the broader diversity and range of lifestyles of fishes at the water-to-land transition. It helps researchers see more than a ladder and understand that fascinating, tangled tree.
Discoveries depend on community
Qikiqtania was found on Inuit land, and it belongs to that community. My colleagues and I were only able to conduct this research because of the generosity and support of individuals in the hamlets of Resolute Bay and Grise Fiord, the Iviq Hunters and Trappers of Grise Fiord, and the Department of Heritage and Culture, Nunavut. To them, on behalf of our entire research team, “nakurmiik.” Thank you. Paleontological expeditions onto their land have truly changed how we understand the history of life on Earth.
COVID-19 kept many paleontologists from traveling and visiting field sites across the world these last few years. We’re eager to return, to visit with old friends and to search again. Who knows what other animals lie hidden, waiting to be discovered inside blocks of unassuming stone.
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