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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. 

Researchers have finally created a quantum X-Ray device

Researchers have finally created a quantum X-Ray device

A research team has demonstrated quantum enhancement in a real X-ray machine, thereby achieving the goal of elimination of background noise for precision detection. The relationship between photon pairs on quantum scales can be used to generate sharp, high-resolution images compared to classical optics. This field is called quantum imaging and has huge potential since optical light can be used to show objects that cannot be seen normally like bones and organs. Quantum correlation describes several relationships between photon pairs, among which entanglement is one and it is used in optical quantum imaging.

The technical challenges of generating entangled photons in X-ray wavelength are greater than optical light, so the team used a different approach. They used a method called quantum illumination to minimize background noise. Using parametric down-conversion (PDC), the researchers split a high energy photon into two low energy photons, signal photon, and idler photon. Researchers mentioned that the application of X-Ray PDC as a source of ghost imaging has been demonstrated recently.  In previous publications, the photon statistics were not measured with any experimental evidence to date, which is generated by X-Ray PDC. Similarly, the observations of quantum enhancement sensitivity were not reported at X-ray wavelengths. The work appears in Physical Review X.

The X-Ray PDC was achieved with the help of a diamond crystal. The non-linear structure of crystal splits X-Ray photons into signal and idler beams, each having half the energy of the pump beam. The team scaled up power by using SPring-8 synchrotron in Japan. They shot a 22 KeV beam of X-rays at their crystal, splitting into two beams, carrying the energy of 11 KeV. The signal beam is sent towards the object which has to be imaged. Here, it is a small metal piece with three slits and a detector on the other side. The idler beam is directly sent to another detector so that each beam hits its respective detector at the same place and time.

The researchers then compared the detections. They found 100 correlated photons per point in the image and 10,000 background photons. Researchers could match each idler to the signal and could trace back the photons which came from the beam, thereby eliminating the noise. They later compared the images to the images developed using non-correlated photons. The correlated photons produced a sharper image.

Quantum X-ray imaging could have many uses outside current X-ray technology with a benefit of lower X-ray radiation required for imaging. This means that samples which are easily damaged by X-Rays could be imaged along with the samples with lower temperature requirement. As quantum X-Ray requires particle accelerator, there are no medical applications currently. The researchers say that they have demonstrated the ability to utilize the strong time-energy correlations of photon pairs for quantum-enhanced photodetection. The procedure they have presented possesses great potential for improving the performances of X-ray measurements.

Journal Reference: Physical Review X.

galactic clusters plasma

Scientists use X-rays from faraway galaxy cluster to reveal secrets of plasma

Most visible matter in the universe doesn’t look like our textbook picture of a nucleus surrounded by tethered electrons. Out beyond our borders, inside massive clusters, galaxies swim in a sea of plasma—a form of matter in which electrons and nuclei wander unmoored.

Though it makes up the majority of the visible matter in the universe, this plasma remains poorly understood; scientists do not have a theory that fully describes its behavior, especially at small scales.

However, a University of Chicago astrophysicist led a study that provides a brand-new glimpse of the small-scale physics of such plasma. Using NASA’s Chandra X-ray Observatory, scientists took a detailed look at the plasma in a distant galaxy cluster and discovered the flow of plasma is much less viscous than expected and, therefore, turbulence occurs on relatively small scales—an important finding for our numerical models of the largest objects in the universe.

“High-resolution X-ray observations allowed us to learn some surprising truths about the viscosity of these plasmas,” said Irina Zhuravleva, an assistant professor of astrophysics and first author of the study, published June 17 in Nature Astronomy. “One might expect that variations in density that arise in the plasma are quickly erased by viscosity; however, we saw the opposite—the plasma finds ways to maintain them.”

Scattered around the universe are massive clusters of galaxies, some of them millions of light-years across containing thousands of galaxies. They sit in a type of plasma that we cannot recreate on Earth. It is extremely sparse—on the order of a sextillion times less dense than air on Earth—and has very weak magnetic fields, tens of thousands of times weaker than we experience on the Earth’s surface. To study this plasma, therefore, scientists must rely on cosmic laboratories such as clusters of galaxies.

Scientists used NASA’s Chandra X-ray Observatory to take a detailed look at the plasma in a distant galaxy cluster. (Courtesy of NASA/CXC/SAO)

Zhuravleva and the team chose a relatively nearby galaxy cluster called the Coma Cluster, a gigantic, bright cluster made up of more than 1,000 galaxies. They chose a less dense region away from the cluster center, where they hoped to be able to capture the average distance that particles travel between interactions with NASA’s Chandra X-ray Observatory. In order to build a high-quality map of the plasma, they observed the Coma cluster for almost 12 days—much longer than a typical observing run.

One thing that jumped out was how viscous the plasma was—how easily it’s stirred. “One could expect to see the viscosity resisting chaotic motions of plasma as we zoom in to smaller and smaller scales,” Zhuravleva said. But that didn’t happen; the plasma was clearly turbulent even on such small scales.

“It turned out that plasma behavior is more similar to the swirling motions of milk stirred in a coffee mug than the smoother ones that honey makes,” she said.

Such low viscosity means that microscopic processes in plasma cause small irregularities in the magnetic field, causing particles to collide more frequently and making the plasma less viscous. Alternately, Zhuravleva said, viscosity could be different along and perpendicular to magnetic field lines.

Understanding the physics of such plasmas is essential for improving our models of how galaxies and galaxy clusters form and evolve with time.

“Plasma behavior is more similar to the swirling motions of milk stirred in a coffee mug than the smoother ones that honey makes.”—Asst. Prof. Irina Zhuravleva Click To Tweet

“It is exciting that we were able to use observations of clusters of galaxies to understand fundamental properties of intergalactic plasmas,” said Zhuravleva. “Our observations confirm that clusters are great laboratories that can sharpen theoretical views on plasmas.”

Materials provided by the University of Chicago

lcls SLAC National Accelerator Laboratory

Researchers produce the loudest possible sound in water

For human beings, sound is a perception of waves in the brain. However, physically it is the propagation of vibration as an audible pressure wave which requires a medium for its transmission. The medium need not be air always as loud sounds can also propagate through water.

A group of scientists of SLAC National Accelerator Laboratory, Department of Energy took an X-Ray laser to generate a very loud sound in water. The team reported that the loudness was such that it was almost at the edge of being the loudest sound which could be produced through water. The results of the experiment were reported in Physical Review Fluids. 

Physicist Claudiu Stan of Rutgers University Newark said that the produced sound was slightly below the threshold that would be enough for boiling the water. To achieve this result, scientists used an equipment known as Linac Coherent Light Source (LCLS). This is a very powerful X-ray laser which is capable of creating molecular black holes and also raise the temperature of water to 100,000 degrees celsius in a time period which is lesser than millionth of a millionth of second. The X-rays produced by the laser have very high brightness and is considered to be the most powerful X-ray source in the world.

LCLS was used by scientists to understand how the high-intensity sound waves that generate very loud sounds impact materials. For the experiment, researchers blasted very small liquid water microjets with a thickness less than hair strand in a vacuum chamber having X-ray pulses.

As the water stream was intercepted by the laser, very rapid ionisation occurred in the microjet due to heating of the water leading to its vapourisation which in turn produced shock waves.

The researchers found out that these shock waves had peak pressures which match with high sound intensity and sound pressures above 270 decibels. This is louder than a rocket launch or a jet plane taking off. It has been found that it is not possible to reach an intensity louder than this as it would result in the break down of water.

Researchers explained that the magnitudes of the sound intensity were restricted since the wave would destroy the medium of propagation though cavitation. This makes the ultrasonic waves in jets as one of the most intense sounds possible to be generated in water. Scientists also estimate these sound waves to be the highest intensity sound waves produced in water till date.