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Category: physics – Page 200

About five years ago, Areg Danagoulian, associate professor in the MIT Department of Nuclear Science and Engineering (NSE), became intrigued by a technique developed by researchers at Los Alamos National Laboratory that uses a neutron beam to identify unknown materials.

“They could look into a black box containing uranium and say what kind and how much,” says Danagoulian, who directs MIT’s Laboratory of Applied Nuclear Physics (LANPh). “I was thinking about the problem of verifying in warheads, and it just dawned on me, this amazing technology could be applied to what we’re working on.”

But there was a problem: This method, called resonance transmission analysis (NRTA), requires an enormous, expensive apparatus, limiting its utility for the kind of on-site nuclear material applications Danagoulian and his research colleagues focus on. To leapfrog this obstacle, they determined to make NRTA technology portable.

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At the heart of almost every sufficiently massive galaxy there is a black hole whose gravitational field, although very intense, affects only a small region around the center of the galaxy. Even though these objects are thousands of millions of times smaller than their host galaxies, our current view is that the Universe can be understood only if the evolution of galaxies is regulated by the activity of these black holes, because without them the observed properties of the galaxies cannot be explained.

Theoretical predictions suggest that as these black holes grow they generate sufficient energy to heat up and drive out the gas within to great distances. Observing and describing the mechanism by which this energy interacts with galaxies and modifies their is therefore a basic question in present day Astrophysics.

With this aim in mind, a study led by Ignacio Martín Navarro, a researcher at the Instituto de Astrofísica de Canarias (IAC), has gone a step further and has tried to see whether the matter and energy emitted from around these black holes can alter the evolution, not only of the host galaxy, but also of the satellite galaxies around it, at even greater distances. To do this, the team has used the Sloan Digital Sky Survey, which allowed them to analyze the properties of the galaxies in thousands of groups and clusters. The conclusions of this study, started during Navarro’s stay at the Max Planck Institute for Astrophysics, are published today in Nature magazine.

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A Penn State scientist studying crystal structures has developed a new mathematical formula that may solve a decades-old problem in understanding spacetime, the fabric of the universe proposed in Einstein’s theories of relativity.

“Relativity tells us space and time can mix to form a single entity called spacetime, which is four-dimensional: three space-axes and one time-axis,” said Venkatraman Gopalan, professor of materials science and engineering and physics at Penn State. “However, something about the time-axis sticks out like sore thumb.”

For calculations to work within relativity, scientists must insert a negative sign on time values that they do not have to place on space values. Physicists have learned to work with the negative values, but it means that spacetime cannot be dealt with using traditional Euclidean geometry and instead must be viewed with the more complex hyperbolic geometry.

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A ball of gas around the Milky Way’s black hole has sparked a new debate. Could it be a massive puff of dark matter?

The orbit of S2 and its stellar companions indicated that they were circling around a massive object, about 4 million times the mass of the Sun. Although astronomers could not directly see the object, they knew it could only be one thing.

By 1974, the object, eventually dubbed Sagittarius A*, was more or less solidified as your own local supermassive black hole. Since then, scientists have made several follow-up observations to reestablish the existence of this dark, lurking beast in the Milky Way — even turning one of the largest virtual telescopes in the world on it.

But not everyone seems to agree on the true nature of Sagittarius A*. A recent study claims that the black hole of our galaxy is not a black hole at all. Instead, it gives a more exotic take on physics that isn’t yet proven: that Sagittarius A* is an imposter, not a black hole but a massive, fluffy ball of fermionic dark matter.

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When a massive star dies, first there is a supernova explosion. Then, what’s left over becomes either a black hole or a neutron star.

That neutron star is the densest celestial body that astronomers can observe, with a mass about 1.4 times the size of the sun. However, there is still little known about these impressive objects. Now, a Florida State University researcher has published a piece[1] in Physical Review Letters arguing that new measurements related to the neutron skin of a lead nucleus may require scientists to rethink theories regarding the overall size of neutron stars.

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A team of Leiden astronomers has managed to calculate the first 100 million years of the history of the Oort cloud in its entirety. Until now, only parts of the history had been studied separately. The cloud, with roughly 100 billion comet-like objects, forms an enormous shell at the edge of our solar system. The astronomers will soon publish their comprehensive simulation and its consequences in the journal Astronomy & Astrophysics.

The Oort cloud was discovered in 1950 by the Dutch Jan Hendrik Oort to explain why there continue to be new comets with elongated orbits in our solar system. The cloud, which starts at more than 3000 times the distance between the Earth and the Sun, should not be confused with the Kuiper belt. This is the rim of rock, grains and ice in which the dwarf planet Pluto is located and which orbits relatively close to the Sun at about 30 to 50 times the Earth-Sun distance.

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Like all metals, silver, copper, and gold are conductors. Electrons flow across them, carrying heat and electricity. While gold is a good conductor under any conditions, some materials have the property of behaving like metal conductors only if temperatures are high enough; at low temperatures, they act like insulators and do not do a good job of carrying electricity. In other words, these unusual materials go from acting like a chunk of gold to acting like a piece of wood as temperatures are lowered. Physicists have developed theories to explain this so-called metal-insulator transition, but the mechanisms behind the transitions are not always clear.

“In some cases, it is not easy to predict whether a material is a or an insulator,” explains Caltech visiting associate Yejun Feng of the Okinawa Institute for Science and Technology Graduate University. “Metals are always good conductors no matter what, but some other so-called apparent metals are insulators for reasons that are not well understood.” Feng has puzzled over this question for at least five years; others on his team, such as collaborator David Mandrus at the University of Tennessee, have thought about the problem for more than two decades.

Now, a new study from Feng and colleagues, published in Nature Communications, offers the cleanest experimental proof yet of a theory proposed 70 years ago by physicist John Slater. According to that theory, magnetism, which results when the so-called “spins” of electrons in a material are organized in an orderly fashion, can solely drive the metal-insulator transition; in other previous experiments, changes in the lattice structure of a material or based on their charges have been deemed responsible.

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China has announced a milestone in the development of clean, sustainable energy by setting a new world record for the longest duration of temperatures needed for fusion to occur.

The Experimental Advanced Superconducting Tokamak (EAST) located in Hefei, Anhui Province, is the successor to HT-7, China’s first superconducting tokamak, which retired in 2013. The Hefei Institutes of Physical Science (HIPS) is conducting the experiment for the Chinese Academy of Sciences (CAS).

Professor Gong Xianzu, a researcher at the CAS Institute of Plasma Physics (IPP) who is leading the project, announced the breakthrough. The reactor achieved not one but two milestones. Firstly it reached a plasma temperature of 120 million degrees Celsius for 101 seconds. This is 20% hotter and five times longer than last year, when EAST managed 100 million degrees Celsius for 20 seconds. Secondly, it reached an even higher peak temperature of 160 million degrees Celsius, lasting for 20 seconds.

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New research is helping to explain one of the big questions that has perplexed astrophysicists for the past 30 years — what causes the changing brightness of distant stars called magnetars.

Magnetars were formed from stellar explosions or supernova e and they have extremely strong magnetic field s, estimated to be around 100 million, million times greater than the magnetic field found on earth.

The magnetic field on each magnetar generates intense heat and x-rays. It is so strong it affects the physical properties of matter, most notably the way that heat is co nducted through the crust of the star and across its surface, creating the variations in brightness which has puzzled astrophysicists and astronomers.

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