Artist’s impression of a gamma-ray burst, a powerful flash of gamma-rays that may be emitted from the merger of a neutron star with another compact object. [ESO/A. Roquette]

By Susanna Kohler on 9 October 2017

With the first detection of gravitational waves in 2015, scientists celebrated the opening of a new window to the universe. But multi-messenger astronomy — astronomy based on detections of not just photons, but other signals as well — was not a new idea at the time: we had already detected tiny, lightweight neutrinos emitted from astrophysical sources. Will we be able to combine observations of neutrinos and gravitational waves in the future to provide a deeper picture of astrophysical events?

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Discoveries seem to back up many of our ideas about how the universe got its large-scale structure
Andrey Kravtsov (The University of Chicago) and Anatoly Klypin (New Mexico State University). Visualisation by Andrey Kravtsov

By Leah Crane -- 9 October 2017

The missing links between galaxies have finally been found. This is the first detection of the roughly half of the normal matter in our universe – protons, neutrons and electrons – unaccounted for by previous observations of stars, galaxies and other bright objects in space.

You have probably heard about the hunt for dark matter, a mysterious substance thought to permeate the universe, the effects of which we can see through its gravitational pull. But our models of the universe also say there should be about twice as much ordinary matter out there, compared with what we have observed so far.

Two separate teams found the missing matter – made of particles called baryons rather than dark matter – linking galaxies together through filaments of hot, diffuse gas.

“The missing baryon problem is solved,” says Hideki Tanimura at the Institute of Space Astrophysics in Orsay, France, leader of one of the groups. The other team was led by Anna de Graaff at the University of Edinburgh, UK.

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Figure 1. John T. Tate, circa 1930. Tate edited the Physical Review at the University of Minnesota from 1926 until his death in 1950.

Daniel Kennefick Physics Today 58, 9, 43 (2005) [Comment by KK: it's worth reading]

Albert Einstein had two careers as a professional physicist, the first spent through 1933 entirely at German-speaking universities in central Europe, the second at the Institute for Advanced Studies in Princeton, New Jersey, from 1933 until his death in 1955. During the first period he generally published in German physics journals, most famously the Annalen der Physik, where all five of his celebrated papers of 1905 appeared.

After relocating to the US, Einstein began to publish frequently in North American journals. Of those, the Physical Review, then under the editorship of John Tate (pictured in figure 1), was rapidly assuming the mantle of the world’s premier journal of physics.  Einstein first published there in 1931 on the first of three winter visits to Caltech. With Nathan Rosen, his first American assistant, Einstein published two more papers in the Physical Review: the famous 1935 paper by Einstein, Boris Podolsky, and Rosen (EPR) and a 1936 paper that introduced the concept of the Einstein–Rosen bridge, nowadays better known as a wormhole. But except for a letter to the journal’s editor he wrote in 1952—in response to a paper critical of his unified field theory work—that 1936 paper was the last Einstein would ever publish there.

Einstein stopped submitting work to the Physical Review after receiving a negative critique from the journal in response to a paper he had written with Rosen on gravitational waves later in 1936. That much has long been known, at least to the editors of Einstein’s collected papers. But the story of Einstein’s subsequent interaction with the referee in that case is not well known to physicists outside of the gravitational-wave community. Last March, the journal’s current editor-in-chief, Martin Blume, and his colleagues uncovered the journal’s logbook records from the era, a find that has confirmed the suspicions about that referee’s identity.  Moreover, the story raises the possibility that Einstein’s gravitational-wave paper with Rosen may have been his only genuine encounter with anonymous peer review. Einstein, who reacted angrily to the referee report, would have been well advised to pay more attention to its criticisms, which proved to be valid.

DOUBTING GRAVITATIONAL WAVES

Einstein introduced gravitational waves into his theory of general relativity in 1916...

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Physicists have gathered evidence that space-time can behave like a fluid. Is space not as immaterial as we thought?

Tuesday 03rd October
Sabine Hossenfelder | Research fellow at the Frankfurt Institute for Advanced Studies and author of blog Backreaction

Physicists have gathered evidence that space-time can behave like a fluid. Mathematical evidence, that is, but still evidence. If this relation isn’t a coincidence, then space-time – like a fluid – may have a substructure.

We shouldn’t speak of space and time as if the two were distant cousins. We have known at least since Einstein that space and time are inseparable, two hemispheres of the same cosmic brain, joined to a single entity: space-time. Einstein also taught us that space-time isn’t flat, like paper, but bent and wiggly, like a rubber sheet. Space-time curves around mass and energy and this gives rise to the effect we call gravity.

That’s what Einstein said. But turns out if you write down the equations for small wiggles in a medium – such as soundwaves in a fluid – then the equations look exactly like those of waves in a curved background.

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Rainer Weiss                                                       Kip Thorne                                       Barry Barish

A model of the universe that takes into account the irregular distribution of galaxies may make dark energy disappear.
NASA, H. FORD (JHU), G. ILLINGWORTH (UCSC/LO), M. CLAMPIN (STSCI), G. HARTIG (STSCI), THE ACS SCIENCE TEAM AND ESA

Research finds a possible explanation for accelerating cosmic expansion that challenges standard cosmological models.

Stuart Gary reports.

The accelerating expansion of the universe due to a mysterious quantity called “dark energy” may not be real, according to research claiming it might simply be an artefact caused by the physical structure of the cosmos.

The findings, reported in the Monthly Notices of the Royal Astronomical Society, claims the fit of Type Ia supernovae to a model universe with no dark energy appears to be slightly better than the fit using the standard dark energy model.

The study’s lead author David Wiltshire, from the University of Canterbury in New Zealand, says existing dark energy models are based on a homogenous universe in which matter is evenly distributed.

“The real universe has a far more complicated structure, comprising galaxies, galaxy clusters, and superclusters arranged in a cosmic web of giant sheets and filaments surrounding vast near-empty voids”, says Wiltshire.

Current models of the universe require dark energy to explain the observed acceleration in the rate at which the universe is expanding.

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A recent study provides a renewed look at whether the universe's dark matter could be primordial black holes — and, if so, whether LIGO could detect them. [dark matter. [SXS Lensing]

By Susanna Kohler on 27 September 2017 

Today promises to be an exciting day in the world of gravitational-wave detections. To keep with the theme, we thought we’d use this opportunity to take a renewed look at an interesting question about the Laser Interferometer Gravitational-Wave Observatory (LIGO) and dark matter: if dark matter is made up of primordial black holes, will LIGO be able to detect them?

Black Holes in the Early Universe

The black holes we generally think about in the context of gravitational-wave detections are black holes formed by the collapse of massive stars. Indeed, LIGO’s detections have thus far been of merging black holes weighing between 7 and 35 solar masses — the perfect sizes to have formed from massive-star collapses.

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News Release • September 27, 2017

The LIGO Scientific Collaboration and the Virgo collaboration report the first joint detection of gravitational waves with both the LIGO and Virgo detectors. This is the fourth announced detection of a binary black hole system and the first significant gravitational-wave signal recorded by the Virgo detector, and highlights the scientific potential of a three-detector network of gravitational-wave detectors.

The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, and funded by the National Science Foundation (NSF), and the Virgo detector, located near Pisa, Italy, detected a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes.

A paper about the event, known as GW170814, has been accepted for publication in the journal Physical Review Letters.

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LYING IN WAIT Huge tubs of water (one shown) at the Pierre Auger Observatory in Argentina reveal the tracks left as cosmic particles zip through them.

Huge experiment is trying to track the particles back to their sources
BY LISA GROSSMAN 2:00PM, SEPTEMBER 21, 2017

The largest study yet of the most energetic particles to slam into Earth provides the first solid clues to where the particles come from. Using a giant array of tubs of water, scientists found that these ultrahigh energy cosmic rays mostly originate outside the Milky Way.

An international team analyzed about 12 years of data to show that particles with energies above 8 billion billion electron volts generally come from a particular direction in the sky, and it’s not the galaxy’s center. The researchers report their findings in the Sept. 22 Science.

“It’s the first clear experimental indication that the sources of these high-energy particles are located outside of our own galaxy, probably somewhere in the nearby universe,” says Karl-Heinz Kampert of the University of Wuppertal in Germany, a spokesperson for the Pierre Auger Collaboration, which made the discovery.

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The two compact radio sources separated by less than a light year at the center of the galaxyNGC7674. The two sources correspond to the location of the two active supermassive blackholes which form a binary and orbit around each other. Credit: TIFR-NCRA and RIT, USA

September 18, 2017 by Susan Gawlowicz

A study using multiple radio telescopes confirms that supermassive black holes found in the centers of galaxies can form gravitationally bound pairs when galaxies merge.

The paper published in the Sept. 18 issue of Nature Astronomy sheds light on a class of black holes having a mass upwards of one million times the mass of the sun. Supermassive black holes are expected to form tightly bound pairs following the merger of two galaxies.
"The dual black hole we found has the smallest separation of any so far detected through direct imaging," said David Merritt, professor of physics at Rochester Institute of Technology, a co-author on the paper.

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A good peer review requires disciplinary expertise, a keen and critical eye, and a diplomatic and constructive approach.
Credit: dmark/iStockphoto

By Elisabeth Pain

Sep. 22, 2016 

As junior scientists develop their expertise and make names for themselves, they are increasingly likely to receive invitations to review research manuscripts. It’s an important skill and service to the scientific community, but the learning curve can be particularly steep. Writing a good review requires expertise in the field, an intimate knowledge of research methods, a critical mind, the ability to give fair and constructive feedback, and sensitivity to the feelings of authors on the receiving end. As a range of institutions and organizations around the world celebrate the essential role of peer review in upholding the quality of published research this week, Science Careers shares collected insights and advice about how to review papers from researchers across the spectrum. The responses have been edited for clarity and brevity.

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Are we about to make a breakthrough to go beyond black holes? Here’s what it means if we do!

If there’s one major difference between General Relativity and Newtonian gravity, it’s this: in Einstein’s theory, nothing lasts forever. Even if you had two perfectly stable masses in orbit around one another — masses that never burned out, lost material, or otherwise changed — their orbits would eventually decay. Whereas in Newtonian gravity, two masses would orbit their mutual center of gravity for an eternity, relativity tells us that a tiny amount of energy gets lost with every moment that one mass is accelerated by the gravitational field it passes through. That energy doesn’t disappear, but gets carried away in the form of gravitational waves. Over long enough time periods, enough energy is radiated away that those two orbiting masses will touch and merge together. Three times, now, LIGO has seen this happen for black holes. But it may be about to take the next step, and see neutron stars merge for the first time.

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Sept. 5, 2017

By following up on mysterious high-energy sources mapped out by NASA's Fermi Gamma-ray Space Telescope, the Netherlands-based Low Frequency Array (LOFAR) radio telescope has identified a pulsar spinning at more than 42,000 revolutions per minute, making it the second-fastest known.

A pulsar is the core of a massive star that exploded as a supernova. In this stellar remnant, also called a neutron star, the equivalent mass of half a million Earths is crushed into a magnetized, spinning ball no larger than Washington, D.C. The rotating magnetic field powers beams of radio waves, visible light, X-rays and gamma rays. If a beam happens to sweep across Earth, astronomers observe regular pulses of emission and classify the object as a pulsar.

"Roughly a third of the gamma-ray sources found by Fermi have not been detected at other wavelengths," said Elizabeth Ferrara, a member of the discovery team at NASA's Goddard Space Center in Greenbelt, Maryland. "Many of these unassociated sources may be pulsars, but we often need follow-up from radio observatories to detect the pulses and prove it. There's a real synergy across the extreme ends of the electromagnetic spectrum in hunting for them."

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A still from a computer simulation of merging neutron stars, which are thought to power short gamma-ray bursts. Rumors are swirling that gravitational-wave observatories as well as electromagnetic ground- and space-based telescopes have all spied such a merger in the distant galaxy NGC 4993. Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla

Astrophysicists may have detected gravitational waves last week from the collision of two neutron stars in a distant galaxy—and telescopes trained on the same region might also have spotted the event.

Rumours to that effect are spreading fast online, much to researchers’ excitement. Such a detection could mark a new era of astronomy: one in which phenomena are both seen by traditional telescopes and ‘heard’ as vibrations in the fabric of space-time. “It would be an incredible advance in our understanding,” says Stuart Shapiro, an astrophysicist at the University of Illinois at Urbana-Champaign.

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11 Jul 2017

The Nobel laureate discusses his dissatisfaction with the state of quantum physics and suggests a new way to move forward.
Melinda Baldwin

The laws of quantum mechanics seem to tell us that there is a fundamental random component to the universe. But Gerard ’t Hooft, who received the Nobel Prize in 1999 for his work on gauge theories in particle physics, is not convinced that physicists have to abandon determinism.

In his new book, The Cellular Automaton Interpretation of Quantum Mechanics (Springer, 2016), ’t Hooft suggests that we may simply be lacking the data that would turn quantum probability distributions into specific predictions. Reviewer Stefano Forte praises it as a “beautifully written, entertaining, and provocative book” that “will dwarf all other contributions ’t Hooft has given to science” if correct. The book is also open access, available as a free e-book on Springer’s website.

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NOTE: You can freely download his book