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Category: cosmology – Page 311

Black holes born with magnetic fields quickly shed them

Like a shaggy dog in springtime, some black holes have to shed. New computer simulations reveal how black holes might discard their magnetic fields.

Unlike dogs with their varied fur coats, isolated black holes are mostly identical. They are characterized by only their mass, spin and electric charge. According to a rule known as the no-hair theorem, any other distinguishing characteristics, or “hair,” are quickly cast off. That includes magnetic fields.

The rule applies to black holes in a vacuum, where magnetic fields can simply slip away. But, says astrophysicist Ashley Bransgrove of Columbia University, “what we were thinking about is what happens in a more realistic scenario.” A magnetized black hole would typically be surrounded by electrically charged matter called plasma, and scientists didn’t know how — or even if — such black holes would undergo hair loss.

Astronomers Discover a “Changing-Look” Blazar – A Powerful Active Galactic Nucleus

A University of Oklahoma doctoral student, graduate and undergraduate research assistants, and an associate professor in the Homer L. Dodge Department of Physics and Astronomy in the University of Oklahoma College of Arts and Sciences are lead authors on a paper describing a “changing-look” blazar — a powerful active galactic nucleus powered by a supermassive black hole at the center of a galaxy. The paper is published in The Astrophysical Journal.

Hora D. Mishra, a Ph.D. student, and faculty member Xinyu Dai are lead authors of the paper, along with Christopher Kochanek and Kris Stanek at the Ohio State University and Ben Shappee at the University of Hawaii. The paper represents the findings of researchers from 12 different institutions who participated in a two-year collaborative project involving the collection of spectra or imaging data in different electromagnetic bands. The OU team led the effort in analyzing all the data collected from the collaboration and contributed primarily on the interpretation of the analysis results, assisted by OU graduate student Saloni Bhatiani and undergraduate students Cora DeFrancesco and John Cox who performed ancillary analyses to the project.

Axion dark matter detection

O,.o circa 2017.

We present a detection scheme to search for QCD axion dark matter, that is based on a direct interaction between axions and electrons explicitly predicted by DFSZ axion models. The local axion dark matter field shall drive transitions between Zeeman-split atomic levels separated by the axion rest mass energy m a.

C.
2. Axion-related excitations are then detected with an upconversion scheme involving a pump laser that converts the absorbed axion energy (~hundreds of μeV) to visible or infrared photons, where single photon detection is an established technique. The proposed scheme involves rare-earth ions doped into solid-state crystalline materials, and the optical transitions take place between energy levels of 4f.

N
electron configuration.

Laser pincers generate antimatter

Some of the greatest mysteries in cosmology revolve around antimatter, and it’s hard to study because it’s rare and hard to produce in the lab. Now a team of physicists has outlined a relatively simple new way to create antimatter, by firing two lasers at each other to reproduce the conditions near a neutron star, converting light into matter and antimatter.

In principle, antimatter sounds simple – it’s just like regular matter, except its particles have the opposite charge. That basic difference has some major implications though: if matter and antimatter should ever meet, they will annihilate each other in a burst of energy. In fact, that should have destroyed the universe billions of years ago, but obviously that didn’t happen. So how did matter come to dominate? What tipped the scales in its favor? Or, where did all the antimatter go?

Unfortunately, antimatter’s scarcity and instability make it difficult to study to help answer those questions. It’s naturally produced under extreme conditions, such as lightning strikes, or near black holes and neutron stars, and artificially in huge facilities like the Large Hadron Collider.

Antimatter from laser pincers

In the depths of space, there are celestial bodies where extreme conditions prevail: Rapidly rotating neutron stars generate super-strong magnetic fields. And black holes, with their enormous gravitational pull, can cause huge, energetic jets of matter to shoot out into space. An international physics team with the participation of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now proposed a new concept that could allow some of these extreme processes to be studied in the laboratory in the future: A special setup of two high-intensity laser beams could create conditions similar to those found near neutron stars. In the discovered process, an antimatter jet is generated and accelerated very efficiently. The experts present their concept in the journal Communications Physics.

The basis of the new concept is a tiny block of plastic, crisscrossed by micrometer-fine channels. It acts as a target for two lasers. These simultaneously fire ultra-strong pulses at the block, one from the right, the other from the left — the block is literally taken by laser pincers. “When the laser pulses penetrate the sample, each of them accelerates a cloud of extremely fast electrons,” explains HZDR physicist Toma Toncian. “These two electron clouds then race toward each other with full force, interacting with the laser propagating in the opposite direction.” The following collision is so violent that it produces an extremely large number of gamma quanta — light particles with an energy even higher than that of X-rays.

The swarm of gamma quanta is so dense that the light particles inevitably collide with each other. And then something crazy happens: According to Einstein’s famous formula E=mc2, light energy can transform into matter. In this case, mainly electron-positron pairs should be created. Positrons are the antiparticles of electrons. What makes this process special is that “very strong magnetic fields accompany it,” describes project leader Alexey Arefiev, a physicist at the University of California at San Diego. “These magnetic fields can focus the positrons into a beam and accelerate them strongly.” In numbers: Over a distance of just 50 micrometers, the particles should reach an energy of one gigaelectronvolt (GeV) — a size that usually requires a full-grown particle accelerator.

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