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Category: cosmology – Page 297

Fast spinning black holes could have features different from those predicted by general relativity.

General relativity is a profoundly complex mathematical theory, but its description of black holes is amazingly simple. A stable black hole can be described by just three properties: its mass, its electric charge, and its rotation or spin. Since black holes aren’t likely to have much charge, it really takes just two properties. If you know a black hole’s mass and spin, you know all there is to know about the black hole.

This property is often summarized by the no-hair theorem. Specifically, the theorem asserts that once matter falls into a black hole, the only characteristic that remains is mass. You could make a black hole out of a Sun’s worth of hydrogen, chairs, or those old copies of National Geographic from Grandma’s attic, and there would be no difference. Mass is mass as far as general relativity is concerned. In every case the event horizon of a black hole is perfectly smooth, with no extra features. As Jacob Bekenstein said, black holes have no hair.

But with all its predictive power, general relativity has a problem with quantum theory. This is particularly true with black holes. If the no-hair theorem is correct, the information held within an object is destroyed when it crosses the event horizon. Quantum theory says that information can never be destroyed. So the valid theory of gravity is contradicted by the valid theory of the quanta. This leads to problems such as the firewall paradox, which can’t decide whether an event horizon should be hot or cold.

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When a black hole is actively feeding, something strange can be observed: enormously powerful jets of plasma shoot from its poles, at velocities approaching light speed.

Given the intense gravitational interactions at play, exactly how those jets form is a mystery. But now, using computer simulations, a team of physicists has hit upon an answer — particles seeming to have “negative energy” extract energy from the black hole and redirect it to the jets.

And this theory has, for the first time, united two different and seemingly irreconcilable theories about how energy can be extracted from a black hole.

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Circa 2014

We propose the new dark matter particle candidate—the “black hole atom,” which is an atom with the charged black hole as an atomic nucleus and electrons in the bound internal quantum states. As a simplified model we consider the central Reissner-Nordström black hole with the electric charge neutralized by the internal electrons in bound quantum states. For the external observers these objects would look like the electrically neutral Schwarzschild black holes. We suppose the prolific production of black hole atoms under specific conditions in the early universe.

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Michigan State University researchers have discovered that one of the most important reactions in the universe can get a huge and unexpected boost inside exploding stars known as supernovae.

This finding also challenges ideas behind how some of the Earth’s heavy elements are made. In particular, it upends a theory explaining the planet’s unusually high amounts of some forms, or isotopes, of the elements ruthenium and molybdenum.

“It’s surprising,” said Luke Roberts, an assistant professor at the Facility for Rare Isotope Beams and the Department of Physics and Astronomy, at MSU. Roberts implemented the computer code that the team used to model the environment inside a supernova. “We certainly spent a lot of time making sure the results were correct.”

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MIT grad student Chiara Salemi and Professor Lindley Winslow use the ABRACADABRA instrument to reveal insights into dark matter.

On the first floor of MIT’s Laboratory for Nuclear Science hangs an instrument called “A Broadband/Resonant Approach to Cosmic Axion Detection with an Amplifying B-field Ring Apparatus,” or ABRACADABRA for short. As the name states, ABRACADABRA’s goal is to detect axions, a hypothetical particle that may be the primary constituent of dark matter, the unseen and as-of-yet unexplained material that makes up the bulk of the universe.

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Extremely light and weakly interacting particles may play a crucial role in cosmology and in the ongoing search for dark matter. Unfortunately, however, these particles have so far proved very difficult to detect using existing high-energy colliders. Researchers worldwide have thus been trying to develop alternative technologies and methods that could enable the detection of these particles.

Over the past few years, collaborations between particle and atomic physicists working at different institutes worldwide have led to the development of a new technique that could be used to detect interactions between very light bosons and neutrons or electrons. Light bosons, in fact, should change the energy levels of electrons in atoms and ions, a change that could be detectable using the technique proposed by these teams of researchers.

Using this method, two different research groups (one at Aarhus University in Denmark and the other at Massachusetts Institute of Technology) recently performed experiments aimed at gathering hints of the existence of dark bosons, elusive particles that are among the most promising dark matter candidates or mediators to a dark sector. Their findings, published in Physical Review Letters, could have important implications for future dark matter experiments.

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An antimatter laser can turn matter in the black hole into energy.

Invisible object has two companion stars visible to the naked eye.

A team of astronomers from the European Southern Observatory (ESO) and other institutes has discovered a black hole lying just 1000 light-years from Earth. The black hole is closer to our Solar System than any other found to date and forms part of a triple system that can be seen with the naked eye. The team found evidence for the invisible object by tracking its two companion stars using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. They say this system could just be the tip of the iceberg, as many more similar black holes could be found in the future.

“We were totally surprised when we realized that this is the first stellar system with a black hole that can be seen with the unaided eye,” says Petr Hadrava, Emeritus Scientist at the Academy of Sciences of the Czech Republic in Prague and co-author of the research. Located in the constellation of Telescopium, the system is so close to us that its stars can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope. “This system contains the nearest black hole to Earth that we know of,” says ESO scientist Thomas Rivinius, who led the study published today (May 6, 2020) in Astronomy & Astrophysics.

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Images from the Survey of the MAgellanic Stellar History (SMASH) reveal a striking family portrait of our galactic neighbors—the Large and Small Magellanic Clouds. The images represent a portion of the second data release from the deepest, most extensive survey of the Magellanic Clouds. The observations consist of roughly 4 billion measurements of 360 million objects.

A sprawling portrait of two astronomical galactic neighbors presents a new perspective on the swirls of stars, gas, and dust making up the nearby dwarf known as the Large and Small Magellanic Clouds—a pair of dwarf satellite galaxies to our Milky Way. While this isn’t the first survey to map these nearby cosmic siblings—the Survey of the MAgellanic Stellar History (SMASH) is the most extensive survey yet.

The international team of astronomers responsible for the observations used the 520-megapixel high-performance Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile. These data are now available to astronomers worldwide through Astro Data Lab at NOIRLab’s Community Science and Data Center (CSDC). CTIO and CSDC are both Programs of NSF’s NOIRLab.

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