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Artist concept of black hole pulling a blue star

Flickering black hole observed by astronomers in great detail

Astronomers have observed a flickering black hole in the Milky Way in an amazing detail with the help of a high frame-rate method that has helped to understand the dynamics of these cosmic objects. MAXI J1820+070, the black hole was discovered in 2018. It is nearly 7 times the weight of Sun and is at a distance of 10000 light years from Earth. The findings appear in the Monthly Notices of the Royal Astronomical Society journal. 

In comparison to other black holes, it ways much lesser as the “lightest” black hole has a mass of 5 Suns. Besides this, it is flickering and emits X-rays and visible radiation as it consumes matter from a surrounding star. 

Small black holes are normally very hard to observe. The supermassive black hole at the centre of the Universe, Sagittarius A*, although quiet is easier to view since we can observe the orbits of the objects around it. Sgr A* weighs nearly 4 million times that of Sun, acting as the centre of a huge system. But a black hole that weighs only 7 times that of Sun would not have many orbiters. Several stars are in a binary system, where the black hole can consume material from their companions. 

Astronomers think that this is occurring with MAXI J1820+070 where it is consuming matter from its companion star, the material forming an accretion disc around it in which frictional and magnetic forces compress it producing a high amount of heat. This process results in flickering electromagnetic radiation which has been captured by researchers at a frame rate of 300 fps in optical light with the help of HiPERCAM on Gran Telescopio Canarias and X-rays from NICER observatory, NASA on the International Space Station. 

John Paice, astronomer at the University of Southampton said that the movie was created using real data, although slowing the speed by 10 times so that the rapid flares can be differentiated by the human eye. He added that the material surrounding the black hole can be observed to be bright enough to outshine the star which is being consumed. The fastest flickers last only few milliseconds which is more than the rays from hundred Suns emitted in a blink. 

This approach helped to track both radiation types where rise in one meant a rise in another. However a time gap was observed as the X-ray flashes preceded the optical light flashes by a split second which according to the researchers is an indication of plasma, very close to the black hole. This delay was also observed accreting black holes in 2017 and 2018 clearly indicating a pattern. 

Poshak Gandhi, astronomer at the University of Southampton said that the observation in three systems indicates that it is a characteristic of such black holes. It would help in understanding the flow of plasmas around black holes. This is very important data as these are extreme physical conditions which cannot be replicated in Earth. 

Mars Image

Researcher claims we might have already detected the presence of life on Mars

NASA had sent two Viking landers to Mars in the 1970s. This mission gave some very important insights about Mars along with some very intriguing results. One of the experiments hinted about the detection of life on the Red Planet. The evidence at that time was not found to be fully conclusive however Dr Gilbert Levin, one of the experimenters says that he is highly convinced that we had found extraterrestrial life at that time. His findings are reported in the Scientific American journal. 

The experiment named Labeled Release (LR) had a simple setup. A drop of diluted nutrients was added to the Martian soil sample which was tagged with a radioactive carbon isotope. If there were lifeforms emitting carbon dioxide on the surface of Mars, the radioactive tag would have been released hence getting detected by the experiment. 

The experiment was conducted by both of the Viking landers. One collected a sample exposed to sunlight and the other collected one from beneath a rock. Both of these experiments reported detection. This was again repeated after a week by using the same sample however there was no detection at that point. Hence the results were deemed inconclusive by Levin and partner Dr Patricia Ann Straat. 

Since the Viking Experiments failed to detect life, NASA concluded that the detection by LR was nothing but a result of chemical reactions. However the results of the experiment have been under assessment over the last few years and scientists have argued that this might be the first detection of alien life. This along with the results of several other experiments have made Mars a strong candidate for sustaining life. 

Levin mentions in his paper that there is no evidence against the possibility of life on the Red Planet. Studies have also shown that few terrestrial microbes could grow on Mars. 

Levin is correct in suggesting that the possibility of life cannot be ignored although we cannot take lack of proper evidence as proof for existence. He mentions that efforts should be made for life detection experiments in the next mission to Mars. An improved version of the LR experiment with an ability to detect chiral metabolism have been proposed by Levin and his partner scientist to be sent for confirming the existence of life. Living things can distinguish between left and right handed organic molecules which cannot be done by non-biological chemical reactions. 

Existence of life on Mars has been debated for several years now, there has been no concrete proof yet but we might be nearing towards some solid evidence.

Universe consisting of fuzzy dark matter galaxies visualized by researchers

Astronomers keen to understand the reasons for death of galaxies in the universe

Galaxies are getting killed in the extreme regions of the universe as their star formation is being closed and researchers are intrigued to know the reasons behind it. A new program termed as the Virgo Environment Traced in Carbon Monoxide survey (VERTICO) is investigating how the galaxies are being killed. 

Toby Brown, the principal investigator of VERTICO led a team of 30 experts using the Atacama Large Millimeter Array (ALMA) for mapping the molecular hydrogen gas, the fuel from which new stars are created, at a very high resolution in 51 galaxies in the Virgo Cluster, the nearest galaxy cluster. 

ALMA was commissioned in 2013 at a price of USD 1.4 billion. It is an array of connected radio dishes at a height of 5000 metres in Atacama Desert, Northern Chile. This is an international cooperation between the United States, Canada, Japan, Taiwan, Chile, South Korea and Europe. This is the largest astronomical project that is ground based and is the most advanced millimetre wavelength telescope to have been constructed. This is best suited to study cold gas clouds from which new stars are created that cannot be observed by visible light. Programs such as VERTICO are designed to address the issues leading to a major breakthrough in this domain. 

The location of galaxies in the universe and their interaction with surroundings are major influences in their ability to form stars. But it is unknown how this environment rules on the life and death of the galaxies. 

The galaxy clusters are the most massive environments in universe which contain many hundreds of galaxies. The presence of high gravitational forces results in high acceleration of the galaxies, superheating the plasma to extreme temperatures. In these dense interiors, galaxies interact with their surroundings that can kill their star formation. The main focus of VERTICO is to understand the mechanisms that remove star formation. 

When galaxies fall through clusters, the intergalactic plasma can remove the gas in a very violent process known as ram pressure stripping. Clearing the fuel for star formation can result in killing the galaxy where no new stars are formed. The high temperature in clusters can stop the cooling and condensing of hot gas onto galaxies. Here the gas is slowly consumed as stars are formed leading to a gradual shut down in formation of stars known as strangulation. 

These processes vary a lot but each leaves behind a unique imprint on the star forming gas of the galaxy. VERTICO aims to bring together a complete picture from each of these processes building on the previous work to understand the impact of environment on evolution of galaxy. 

As Virgo Cluster is the nearest massive cluster, we can capture snapshots of the different stages of the galaxies. As a result, a complete picture of how star formation is shut in the cluster galaxies can be built. Virgo Cluster galaxies have been observed at nearly all wavelengths of the spectrum the observations of the star forming gas along with the required sensitivity do not exist as of now. 

VERTICO aims to generate high resolution maps of the molecular hydrogen gas and understand the exact quenching mechanisms, ram pressure stripping responsible for killing the galaxies. This will improve the understanding of the evolution of galaxies in the densest places of the universe. 

 

Google contributes large sums to climate change denying organisations

Google contributes large sums to climate change denying organizations

As per the online documents released by The Guardian, internet giant Google has made large donations to some of the most influential and powerful groups which are connected to the denial of climate change. A transparency document from Google reveals that the tech giant has contributed to several organizations, think tanks, lobby groups that deny climate change and campaign against laws to stop climate change. However, the exact figure donated to these organizations was not revealed. 

Competitive Enterprise Institute(CEI) is one of the organizations to receive donations from Google. It is a libertarian think tank that questions the alarmism surrounding global warming. It has played a role in many campaigns which doubt the consensus of the scientific community around global warming, downplaying climate change. Besides this, they have also been instrumental in convincing the American President Donald Trump to cancel the Paris agreement. 

Google has also contributed to the Cato Institute, a think tank opposing legislation related to climate change and American Conservative Union, a conservative think tank having several climate change deniers on the board. 

Google has always promoted itself as an environment-friendly company that takes climate change and global warming very seriously. Since 2007, the company has been carbon-neutral and supports several initiatives related to climate change. It has also recently made the largest corporate purchaser of renewable energy in history. 

Along with some other organizations, Google has also pledged to support the Paris Agreement abiding by the goals of the climate pact, irrespective of the decision taken by President Trump to cancel the support of the United States from the agreement. 

Responding to the accusations, a spokesperson from Google said that they are not the only major company that contributes to the organisations although disagreeing with them on their policies related to climate change. It has also made clear that collaboration or sponsoring a third-party organization does not mean in any way that it supports their entire agenda, events nor does it advocate the views of its leadership or members. Google sponsors several organizations across the entire spectrum which advocates for better policies related to technology. 

Sheldon Whitehouse, a Democratic Senator criticized Google’s action as he mentioned that corporate America should not support any trade organization or lobby group that interferes with climate. 

CEI has not answered any questions related to Google as it respects the privacy of donors. A spokesperson of the organization said that the core value of the organization is to make energy accessible to the most vulnerable sections of the society. 

Reference: The Guardian

Researchers fabricate all-perovskite tandem solar cells with improved efficiency

Researchers fabricate all-perovskite tandem solar cells with improved efficiency

A kind of solar cell having an important perovskite structured element known as Perovskite tandem solar cells (PSCs) has been fabricated by a group of scientists from Nanjing University, China and the University of Toronto, Canada. Hairen Tan, the lead researcher told that instead of making single-junction perovskite solar cells, the primary idea was to make more efficient all-perovskite tandem solar cells. The findings are reported in Nature Energy journal.

Perovskites are a group of minerals having the same crystal structure as perovskite which is yellow, black or brown mineral comprising mostly of calcium titanate. Many researchers over the past few years have been attempting to build solar cells using this material, either wide-bandgap (~1.8 eV) or narrow-bandgap (~1.2 eV) perovskites.

Merging wide and narrow bandgap perovskites together could enhance power conversion efficiency (PCEs) than that achieved by single-junction cells without any increase in fabrication costs. Scientists need to find a method to strengthen the efficiency of individual subcells, while also integrating the wide and narrow-bandgap cells synergistically for building this type of cell.

Tan said that low efficiencies (PCE~18-20 percent) and low short-circuit current densities (Jsc~28-30 mA/cm2) have been demonstrated by the mixed Pb-Sn narrow-bandgap perovskite solar cells which fall under their capacity, and under the performance of the best Pb-based single-junction perovskite cells. One of their vital components, Sn2+, readily oxidizes into Sn4+ is responsible for the weak performance in narrow-bandgap perovskite solar cells. Tan and his team wanted to determine solutions that could overcome the high trap densities and short carrier diffusion lengths exhibited by the resultant cells.

He also added that their main purpose is to extend the diffusion of narrow-bandgap perovskite solar cells thus to achieve better-performed tandem solar cells. Also, they took a perspective to stop the oxidation of Sn2+ to Sn4+ in the precursor solution to enhance charge carrier diffusion length and whose inclusion in the mixed Pb-Sn perovskites causes Sn vacancies. A new chemical method was used by Tan’s team that is based on a comproportionation reaction and leads to significant improvements in the charge carrier diffusion lengths of mixed Pb-Sn narrow-bandgap perovskites. This could eventually increase the performance of PSCs.

The team obtained an extraordinary 3 μm diffusion length that allows performance-record-breaking Pb-Sn cells and all-perovskite tandem cells unlike the earlier intended method characterized by sub-micrometer diffusion lengths, that can reduce the efficiency of the cell. He also explained that a tin-reduced precursor solution was developed to obtain this by restoring the Sn4+ (an oxidization product of Sn2+) back to Sn2+ through comproportionation reaction in the precursor solution.

The major challenge for the advancement of solar cells with a perovskite element is the oxidation of tin-containing perovskites as it adversely affects their efficiency and hampers their utilities. A substitute path for fabricating tandem solar cells using tin-containing narrow-bandgap perovskite is given by the new chemical method introduced by Tan and his co-workers making cells more stable and efficient.

Tan added that the electronic quality of tin-containing perovskites is comparable to that of lead halide perovskites that have shown efficiency similar to crystalline silicon cells. This approach will eventually provide them a way to very inexpensive and highly efficient solar devices.

The performance of monolithic all-perovskite tandem cells was tested using the chemical approach after fabrication. Remarkable independently approved PCEs of 24.8 percent for small-area devices (0.049 cm2) and 22.1 percent for large-area devices (1.05 cm2) was obtained by their cells. Additionally, after functioning for over 400 hours at their highest power point under full one sun illumination, the cells retained 90 percent of their performance. The method introduced by this team of scientists could lead to the development of more efficient and cost-effective solar-powered devices in the future.

Tan said that they are now planning to further enhance the power conversion efficiency of all-perovskite tandem solar cells above 28 percent. Minimizing the photovoltage loss in the wide-bandgap perovskite solar cell will be the primary feasible method to attain this while minimizing the optical losses in the tunneling recombination junction is another possibility.

Journal Reference: Nature Energy

NASA detects organic compounds suitable for life in an ocean on Enceladus

NASA detects organic compounds suitable for life in an ocean on Enceladus

Scientists have detected the basic ingredients for life from an ocean on Enceladus, one of Saturn’s moons. Analysis of NASA data shows the presence of organic compounds in plumes of liquid water shooting into space from the ocean. The findings appear in Monthly Notices of the Royal Astronomical Society journal. 

These compounds contain nitrogen, oxygen and play a major role in creating amino acids, the building blocks of protein. Researchers previously detected organic molecules from the moon but this is the first time molecules were found to be dissolved in water. This indicates that compounds could take part in chemical reactions under the sea leading to amino acids. 

Frank Postberg, one of the study’s authors said that this work reveals the building blocks that are abundant in the ocean of Enceladus. This is a positive indication to carry out research for the habitability of the moon. Jets of ocean water and ice shoot out into space regularly through the cracks in the crust of the moon. 

The compounds were dissolved in the ocean water which then evaporated with surface water finally getting condensed and frozen into the crust of the moon. They were carried into space by the plumes and detected by Cassini spacecraft of NASA. This is an indication that Enceladus might have its own method of generation of life. 

In the oceans of Earth, seawater combines with magma which comes out through the cracks in the ocean floor. This results in the production of hydrothermal vents whose temperature can rise till 370 degrees Celsius. The water from these vents is rich in hydrogen, catalyzing chemical reactions of organic compounds into amino acids. These then combine to form proteins, one of the main components of life. This method works without sunlight and this is significant in the case of Enceladus where the sunlight is reflected back to space in its entirety. So life has to develop in the dark. 

Nozair Khawaja, the research team leader said that the molecules might follow the same pathway in oceans of Enceladus as that of Earth. The discovery of molecules forming amino acids is quite significant. The compounds discovered by the team last were not soluble in water hence researchers were not sure if the organic molecules on Enceladus were capable of life formation. 

Cassini was launched in 1997 and it spent 13 years in the exploration of Saturn and its moons. Scientists purposefully crashed the spacecraft into Saturn thereby ending its mission as they did not want to contaminate Enceladus or Titan in any manner.

Cassini found a global ocean containing liquid saltwater below the surface of Enceladus and captured images of water jets shooting to space. The data about their composition was collected in 2008. Scientists will continue studying the data collected by Cassini as NASA also plans of sending a probe to Titan, another moon of Saturn which also contains organic compounds. Dragonfly, a nuclear-powered helicopter will start for Titan in 2026 and arrive in 2034.

Reference: Monthly Notices of the Royal Astronomical Society journal.  

Virtual Reality for Scientists

Virtual Reality for Scientists

When you think of virtual reality, or VR, you might conjure up images of action-packed video games or immersive tours of deep ocean waters and other exotic locale. But, in recent years, scientists have started to don VR goggles too—not for entertainment, but for analyzing and comprehending their data.

At Caltech, efforts to design VR tools for the future are underway, with prototypes in development for studying everything from worms to ocean waters to biomolecules and more.

“We are thinking about what doing science will look like 10 to 15 years from now,” says Santiago Lombeyda, a computational scientist at the Center for Data-Driven Discovery (CD3), the group behind the virtual reality research, as well as other data science projects. CD3 is a joint partnership between Caltech and JPL, which is managed by Caltech for NASA. “In the future, a scientist might be working on their desktop, and then they could just grab a pair of virtual reality glasses, or they may even be already wearing regular glasses that enable VR, and then start manipulating their data in the same shared visual context of their actual work area.”

“Billions of dollars have been poured into VR in the gaming industry. We can leverage their software and ask what it can do for science and scholarship,” says George Djorgovski, director of CD3 and a professor of astronomy at Caltech. Djorgovski has been working on developing VR tools for data analylsis for more than a decade and, in 2015, developed a related startup company called Virtualitics, which combines VR with machine learning.

The CD3 group’s latest project, in collaboration with the National Cancer Institute, is to develop better tools for finding tumors in diagnostic imaging scans. To that end, they have developed a virtual reality environment, using a Vive VR headset, where a user can visualize computed tomography (CT) scans from patients and identify possible tumors. According to the Caltech and JPL researchers, the 3-D virtual environment allows radiologists to better visualize and identify potential tumors than with the standard 2-D imaging methods available now.

“The 3-D environment can really have an impact in understanding three-dimensional structures,” says Lombeyda. “And that’s why it applies so well to looking for tumors. By walking around the data and seeing it from all sides, you might find things you wouldn’t otherwise see by just looking at 2-D slices of tissues.”

The group has begun working with several radiologists to identify possible tumors in patients. The idea is to then take this VR training data and feed it into machine-learning, or artificial intelligence (AI), programs, an effort being managed by Caltech’s Ashish Mahabal, lead computational and data scientist for CD3. Once those programs have learned how to better identify tumors, they could be used in the future to help medical professionals find candidate tumors for follow-up. “The better the training data, the better the machine-learning program,” says Djorgovski.

“There is a synergy with machine learning and virtual reality,” says Dan Crichton, director of the Center for Data Science and Technology at JPL, a partner organization to CD3. “We are training AI to see things, such as tumors, that otherwise might have gone missing. This can be a useful aid to medical practitioners.”

Crichton says that components of the software they are using for their VR programs were developed originally for astronomy and planetary imaging. “Anytime you look at data in three or more dimensions, it’s challenging,” he says. “When we study planetary surfaces, for example, we want to see more than just a one-dimensional slice. We want to see the depth and how other variables change. The principles we’ve learned from this kind of imaging apply to our VR programs.”

According to the scientists, the virtual reality environment offers scientists a more instinctive way to understand their data, whether it signifies an object such as a tumor or a molecule, or is represented in the form of a graph, with many variables plotted out.

“In a 3-D virtual environment, scientists have a more intuitive and longer-lasting grasp of the spatial relations of objects. In today’s world, more and more multidimensional data are becoming available, and these tools are improving the ability of humans to comprehend them,” says Djorgovski. “In the same way that we went from black-and-white photography to color photography, or from phone calls to Skype chats, people will not want to go back from virtual reality.”

In another application of the VR program developed by the CD3 group, in collaboration with Paul Sternberg, Bren Professor of Biology, a user has the ability to manipulate a model of a tiny transparent worm called Caenorhabditis elegans (C. elegans) using a tool that seemingly grasps the worm like a pair of tongs. When the program turns on, the worm first appears on a desk surface in a virtual office environment, at a fairly small scale. The user can then enlarge the worm by throwing it on the floor. And if the user wants to see a huge model of the worm, they can toss it out of a virtual window, where it blows up to a scale bigger than a human.

“We want researchers to come to us with data that we can then quickly prep for viewing in a VR space,” says Lombeyda. “Whatever they are studying can be seen at desktop scale, or they can drop it on the floor and walk around it.”

One of the challenges of developing VR tools that scientists will actually use lies in making the experience smooth, without jerky motions. VR programs can leave people feeling dizzy, and avoiding this is something that the CD3 group continues to work on. Lombeyda says that their overall goal is to make the experience as natural and seamless as possible for a scientist working at an office desk, so that they might be checking email and then could pop on a pair of VR glasses to quickly examine new data.

“Most of the time, scientists work at desks, so we want to optimize that experience,” says Lombeyda, adding that augmented reality, or AR, glasses, in which a viewer is only partially immersed in a virtual environment, may also become a common tool for scientists. But, he says, they are focusing on VR now in this early phase of development.

The group is also working on building VR classrooms, and last year they taught a course in a virtual space. VR classrooms can bring together students in different locations, and even across the globe, to understand and manipulate data in 3-D. According to Djorgovski, this kind of setup could also be used to improve teaching skills. For example, students in a VR classroom could anonymously hit a button if they were not comprehending a certain topic. “If the teacher were to get a few alerts, they would know at that point the students were confused and they needed to backtrack.This is something that can be done more easily and more quickly in VR versus traditional classrooms.”

Recently, the scientists presented their VR tumor program at a computer graphics conference, called SIGGRAPH, to favorable reviews. “Some of the comments we kept hearing were how people were excited to see VR for something other than gaming, and also how natural the experience was in our VR setup,” says Lombeyda.

Though the technology may still be in its early phases, the researchers are excited to press on. The future of VR, they say, is not just for fun and games but for collectively making sense of our world. “All sciences are undergoing the same transformations of having to deal with larger and larger data sets, and traditional tools won’t work,” says Djorgovski. “Instead of reinventing the wheel everywhere, scientific groups are developing new methodologies for big and complex data sets. Everybody faces the same problems so we have a great opportunity for sharing solutions and ideas.”

Hacker claims access to 218 million accounts of one of the most popular games

Hacker claims access to 218 million accounts of one of the most popular games

A hacker going by the name Gnosticplayers has claimed to obtain access records of 218 million players of Words with Friends which includes names, email and login IDs, hashed passwords, Facebook IDs and phone numbers. If a user has signed up for Words with Friends as recent as last month, then it is best to change the password as soon as possible since there lies a possibility of the data being stolen and misused. 

Cracking a hashed password can be very simple if it is a commonly used term or a simple word or if the original encryption is weak. Thus it is considered a best practice to change the passwords on remaining social accounts where the same email address and password are used. More damage can be caused in these sites than just attacking a simple game like Words with Friends. Security experts thus advice to use different passwords and login details for various social media applications and websites. Any breach of data on one application does not affect any of the remaining ones. 

Zynga, the developer of Words with Friends said that they discovered some player account information to be accessed by external hackers. They initiated immediate investigation along with the assistance of leading forensic firms and the support of law enforcement. 

As the world goes more and more digital, the threat of such attacks increases and the users are often left vulnerable since it is their data which is being tampered with. Millions of user credentials are being leaked out every year even with big giants such as Facebook. 

However, there are certain tips to prevent these damages. One of them includes using unique and long passwords for every account. Using password managers can also help so that you need not remember every password. It is also advised to use the advantage of two-factor authentication wherever provided. Most major accounts including Google, Facebook, Apple support this. Besides the password, this method requires entering the unique code sent to the user’s mobile number in every login attempt. 

Users should also delete their old accounts which they decide not to use anymore. People often uninstall the application and forget but it does not end there. The user should delete their entire account information from the application or contact the developer if such an option is not provided. If all of these practices are followed, then it is highly unlikely for a user to have his/her information compromised. We should learn to protect our data and keep ourselves safe. 

Time reversibility might be the reason why gamma rays seem to travel backwards

Time reversibility might be the reason why gamma-rays seem to travel backward

It is known that time can move in only one direction. However, last year scientists detected some events in which the gamma-ray bursts seemed to repeat as if they were moving backward in time. 

New research suggests the potential answer to the cause of this time reversibility effect. If the waves in the relativistic jets producing gamma-ray bursts propagate faster than light at what is known as “superluminal speeds”, then one of its possible effects could be time reversibility. The work appears in The Astrophysical Journal. 

When light travels through a medium, the phase velocity is lesser than the light’s speed in a vacuum, which is the ultimate speed barrier in the Universe. Hence a wave could move through gamma-ray burst jet at superluminal speeds without violating relativity. The most energetic explosions in the Universe are gamma-ray bursts. While they can last a time span ranging milliseconds to hours, they are very bright and till now no concrete reason for their cause is found.

From 2017 observations of colliding neutron stars, it is known that gamma-ray bursts can be created from these collisions. When a huge, violently spinning star collapses to black hole resulting in the ejection of material in a colossal hypernova then these bursts can be produced. Then the black hole is surrounded by the accretion material around the equator. With quick rotation, the exploded material falls back resulting in relativistic jets from the polar regions. It blasts through the outer envelope of the star resulting in gamma-ray bursts. 

Particles can move faster than light when traveling through a medium. This causes Cherenkov radiation which is viewed as a blue glow, also known as a luminal boom. When particles such as electrons travel faster than the phase velocity of light in the medium then the glow is produced. 

Scientists Jon Hakkila, College of Charleston and Robert Nemiroff, Michigan Technological University think that the same effect is responsible for gamma-ray burst jets. They have created mathematical modeling to demonstrate it. They mention in their model that an impactor wave in a gamma-ray burst either propagates from subluminal to superluminal velocities or decelerates vice-versa. This impactor wave interacts with the medium resulting in Cherenkov radiation when moving faster than light’s speed in the medium or creates a synchrotron shock radiation when moving slower than the light’s speed. 

A time-forward and time-reversed set of light curve features are created by the transitions by relativistic image doubling. When a charged particle enters the water near to light’s speed, it moves faster than Cherenkov radiation resulting in the illusion of appearing at two places simultaneously, one seems to travel ahead in time and one backward. 

This has not yet been observed experimentally. If verified it might be responsible for the time-reversibility in gamma-ray burst light curves. 

Researchers made an assumption that impactor creating gamma-ray burst would be a wave of a large scale produced by changes of the magnetic field. More analysis is needed in this direction. Since the model includes time-reversibility it explains gamma-ray bursts much better than those which don’t. 

Reference: The Astrophysical Journal.

Discovery in gallium nitride a key enabler of energy efficient electronics

Discovery in gallium nitride a key enabler of energy efficient electronics

Gallium nitride, a semiconductor that revolutionized energy-efficient LED lighting, could also transform electronics and wireless communication, thanks to a discovery made by Cornell researchers.

Their paper, “A Polarization-Induced 2D Hole Gas in Undoped Gallium Nitride Quantum Wells,” was published Sept. 26 in Science.

Silicon has long been the king of semiconductors, but it has had a little help. The pure material is often augmented, or “doped,” with impurities like phosphorus or boron to enhance current flow by providing negative charges (electrons) or positive charges (“holes,” the absence of electrons) as needed.

In recent years, a newer, sturdier family of lab-grown compound semiconductor materials has emerged: group III-nitrides. Gallium nitride (GaN) and aluminum nitride (AlN) and their alloys have a wider bandgap, allowing them to withstand greater voltages and higher frequencies for faster, more efficient energy transmission.

“Silicon is very good at switching off and on and controlling electrical energy flow, but when you take it to high voltages it doesn’t operate very well because silicon has a weak electric strength, whereas GaN can sustain much higher electric fields,” said co-senior author Debdeep Jena, the David E. Burr Professorin Electrical and Computer Engineering and in Materials Science and Engineering. “If you’re doing very large amounts of energy conversion, then wide-bandgap semiconductors such as GaN and silicon carbide are the solutions.”

Since the 1990s, researchers have doped GaN by adding magnesium impurities to create holes, but the process is highly inefficient. For every hundred magnesium atoms introduced into the crystal, only three or four holes might appear at room temperature, and even fewer at low temperatures.

Rather than using impurities, Ph.D. student Reet Chaudhuri stacked a thin GaN crystal layer – called a quantum well – atop an AlN crystal, and the difference in their crystal structures was found to generate a high density of mobile holes. Compared with magnesium-doping, the researchers discovered that the resulting 2D hole gas makes the GaN structures almost 10 times more conductive.

“In 1992, researchers discovered that when aluminum nitride is deposited on top of gallium nitride, you get free electrons at the interface. Having electrons conduct inside GaN makes what we call n-type electronic devices,” said Chaudhuri, the paper’s lead author. “The polarization theory that explains why we get mobile electrons in this structure, which in fact was conceptualized and validated by Cornell researchers in late ’90s, also predicts that we should expect holes when the structure is flipped. But to date, there had not been any report of holes in an undoped III-nitride semiconductor structure. And that’s what we have found in this work.”

Using the new material structure created by Reet, co-author and Ph.D. student Samuel James Bader recently demonstrated some of the most efficient p-type GaN transistors in a collaborative project with Intel. Now that the team has the capability to make hole-channel transistors – which are called p-type – they plan to pair them with n-type transistors to form more complex circuits, opening up new possibilities in high-power switching, 5G cellular technology and energy efficient electronics, including phone and laptop chargers.

“It’s very difficult to simultaneously achieve n-type and p-type in a wide bandgap semiconductor. Right now, silicon carbide is the only other one that has both besides GaN. But the mobile electrons in silicon carbide are more sluggish than those in GaN,” said co-senior author Huili Grace Xing, the William L. Quackenbush Professor in electrical and computer engineering and in materials science and engineering. “Using these complementary operations enabled by both n-type and p-type devices, much more energy efficient architecture can be built.”

Another advantage of the 2D hole gas is that its conductivity improves as the temperature is lowered, meaning that researchers will now be able to study fundamental GaN properties in ways that haven’t been previously possible. Equally important is its ability to retain energy that would otherwise be lost in less efficient power systems.

“Gallium nitride caused a revolution in the lighting industry,” Jena said. “It enabled the white lighting that is in our cellphones, laptops, and LED bulbs that are replacing the incandescent bulbs in our homes. With a regular 100W incandescent light bulb, which is about 4% energy efficient, you might get 4 watts of light and the rest is heat. You know this very well if you touch the bulb when it is on. LEDs on the other hand can be almost 80% efficient, and only 20% is heat. A similar change in energy-efficiency of electronics has not yet happened. And maybe this finding is a step in that direction.”

A patent application has been filed through the Center for Technology Licensing for the discovery. Other contributors included David Muller, the Samuel B. Eckert Professor in Applied and Engineering physics; and Zhen Chen, a postdoctoral researcher in Muller’s lab.

The research was supported in part by Intel, the Air Force Office of Scientific Research, the National Science Foundation and the Cornell Center for Materials Research.

Materials provided by Cornell University