Release date: Jul 12, 2018 10:00 AM (EDT)

Most precise measurement yet adds to debate over universe’s expansion rate

Using the powerful Hubble and Gaia space telescopes, astronomers just took a big step toward finding the answer to the Hubble constant, one of the most important and long-sought numbers in all of cosmology. This number measures the rate at which the universe is expanding since the big bang, 13.8 billion years ago. The constant is named for astronomer Edwin Hubble, who nearly a century ago discovered that the universe was uniformly expanding in all directions. Now, researchers have calculated this number with unprecedented accuracy.

Intriguingly, the new results further intensify the discrepancy between measurements for the expansion rate of the nearby universe, and those of the distant, primeval universe — before stars and galaxies even existed. Because the universe is expanding uniformly, these measurements should be the same. The so-called “tension” implies that there could be new physics underlying the foundations of the universe.

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The Einstein Telescope, the European vision for a third-generation gravitational-wave detector, would consist of three interferometers formed into a triangle, with 10-kilometer-long arms. To minimize noise, it would be underground and cooled to around 10 K.

PHYSICS TODAY  - 01 OCTOBER 2018

Physics Today 71, 10, 25 (2018); https://doi.org/10.1063/PT.3.4041

Toni Feder

The promise of multimessenger astronomy drives the field, brings together scientific communities.

Word traveled fast when gravitational-wave detectors in the US and Europe announced the detection of a binary black hole merger on 14 September 2015. Then on 17 August 2017 the detection of merging neutron stars marked the beginning of multimessenger cosmic science with gravitational waves. (See Physics Today, April 2016, page 14, and December 2017, page 19.) Once that alert went out, dozens of telescopes were pointed toward the merger; radio astronomers are still watching it. Hundreds of papers followed, including one with more than 3500 authors. The excitement created by those detections has the gravitational-wave community chomping at the bit to lay plans for more powerful observatories.

Scientists in Europe put forward a design for the Einstein Telescope in 2011. (See Physics Today, September 2015, page 20.) Their US counterparts held off because NSF, which funded the bulk of the Laser Interferometer Gravitational-Wave Observatory (LIGO), encouraged them to score a detection before focusing on future observatories. So the US Cosmic Explorer design is less far along. But both future facilities would seek to increase sensitivity by at least a factor of 10.

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CASEY REED/PENN STATE UNIVERSITY, WIKIMEDIA COMMONS

TOUGH STUFF An exotic substance thought to exist within a type of collapsed star called a neutron star (illustrated) may be stronger than any other known material.

A strand of spaghetti snaps easily, but an exotic substance known as nuclear pasta is an entirely different story.

Predicted to exist in ultradense dead stars called neutron stars, nuclear pasta may be the strongest material in the universe. Breaking the stuff requires 10 billion times the force needed to crack steel, for example, researchers report in a study accepted in Physical Review Letters.

“This is a crazy-big figure, but the material is also very, very dense, so that helps make it stronger,” says study coauthor and physicist Charles Horowitz of Indiana University Bloomington.

Neutron stars form when a dying star explodes, leaving behind a neutron-rich remnant that is squished to extreme pressures by powerful gravitational forces, resulting in materials with bizarre properties (SN: 12/23/17, p. 7).

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MASSIVE MACHINES A researcher stands in the cavernous spectrometer of KATRIN, an experiment in Germany to measure the mass of particles called neutrinos.

Physicists build giant machines to study tiny particles
BY EMILY CONOVER 9:30AM, SEPTEMBER 19, 2018

Diana Parno’s head swam when she first stepped inside the enormous, metallic vessel of the experiment KATRIN. Within the house-sized, oblong structure, everything was symmetrical, clean and blindingly shiny, says Parno, a physicist at Carnegie Mellon University in Pittsburgh. “It was incredibly disorienting.”

Now, electrons — thankfully immune to bouts of dizziness — traverse the inside of this zeppelin-shaped monstrosity located in Karlsruhe, Germany. Building the experiment took years and tens of millions of dollars. Why create such an extreme apparatus? It’s all part of a bid to measure the mass of itty-bitty subatomic particles known as neutrinos.

KATRIN, which is short for Karlsruhe Tritium Neutrino Experiment, started test runs in May. The experiment is part of a multipronged approach to the study of particle physics, one of dozens of detectors built in an assortment of odd-looking shapes and sizes. Their mission: dive deep into the standard model, particle physicists’ theory of the subatomic building blocks of matter — and maybe overthrow it.

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Artist's impression of a neutron-star merger (Courtesy: NASA)

Physics World

05 Sep 2018

A jet of charged particles moving at nearly the speed of light smashed its way out of debris left behind in the aftermath of the neutron-star merger that produced the gravitational waves detected by the LIGO–Virgo collaboration on 17 August 2017.

The event, catalogued as GW170817, has been a Rosetta Stone for astronomers because it allowed them for to observe the same event using gravitational waves and electromagnetic radiation ranging from a gamma ray burst (GRB) to a radio afterglow. This was a first for the new and exciting field of multimessenger astronomy.

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[Credit: NSF/LIGO/Sonoma State University/A. Simonnet]

B. F. Schutz
Posted on August 20, 2018

Last Friday we celebrated the one-year anniversary of an event that those of us who were involved will never forget. The Virgo gravitational-wave detector had joined the two LIGO instruments on August 1, 2017, and the three detectors had since then been patiently listening out together for gravitational wave sounds coming from anywhere in the Universe. On August 17, the deep quiet was interrupted by a squeal, a chirp lasting much longer and going to a much higher pitch than the GW150914 chirp that had launched the field of gravitational wave observational astronomy two years earlier. We named it, prosaically, GW170817.

This one-minute-long squeal was followed by an incredible explosion that radiated intense gamma-rays, X-rays, light, radio waves — right across the whole electromagnetic spectrum. What came first was a burst of gamma-rays, just 2 seconds after the end of the squeal. Then it began brightening up at other wavelengths. The explosion itself did not register in LIGO and Virgo, because as it rushed out in all directions it was too smooth to generate gravitational waves. But astronomers at their telescopes saw it: a kilonova, a new type of cosmic explosion.

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In this artistic rendering, a blazar emits both neutrinos and gamma rays that could be detected by the IceCube Neutrino Observatory as well as by other telescopes on Earth and in space. Credit: IceCube/NASA

By the IceCube Collaboration, 12 Jul 2018 10:00 AM

An international team of scientists has found the first evidence of a source of high-energy cosmic neutrinos, ghostly subatomic particles that can travel unhindered for billions of light years from the most extreme environments in the universe to Earth.
The observations, made by the IceCube Neutrino Observatory at the Amundsen–Scott South Pole Station and confirmed by telescopes around the globe and in Earth’s orbit, help resolve a more than a century-old riddle about what sends subatomic particles such as neutrinos and cosmic rays speeding through the universe.

Since they were first detected over one hundred years ago, cosmic rays—highly energetic particles that continuously rain down on Earth from space—have posed an enduring mystery: What creates and launches these particles across such vast distances? Where do they come from?
Because cosmic rays are charged particles, their paths cannot be traced directly back to their sources due to the powerful magnetic fields that fill space and warp their trajectories. But the powerful cosmic accelerators that produce them will also produce neutrinos. Neutrinos are uncharged particles, unaffected by even the most powerful magnetic field. Because they rarely interact with matter and have almost no mass—hence their sobriquet “ghost particle”—neutrinos travel nearly undisturbed from their accelerators, giving scientists an almost direct pointer to their source.

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Multi-national study challenges long-held assumptions about efficiency.

23 May 2018

Smriti Mallapaty

Scientists are more efficient at producing high-quality research when they have more academic freedom, according to a recent study of 18 economically advanced countries. Researchers in the Netherlands are the most efficient of all.

The existence of a national evaluation system that is not tied to funding was also associated with efficiency, the study finds.

The analysis challenges the prevailing view that competition for funding and strong university management drive efficiency. “For both variables we find the opposite,” says Peter Van den Besselaar, an informatics researcher at VU University Amsterdam, the Netherlands, who co-authored the paper with Ulf Sandström at KTH Royal Institute of Technology, Sweden.

Pros and cons of competition

Until recently, studies into research efficiency usually looked at the attributes of countries that scored highly when measuring their inputs (funding) against their outputs (publications) in absolute terms. Van den Besselaar and Sandström looked instead at relative changes, to gauge a system’s efficiency at converting additional funding to additional publications.

Specifically, they assessed how a change in spending on higher education between 2000 and 2009 contributed to a change in authorship in the top 10% of highly cited papers in the Web of Science database. In this assessment, the Netherlands scored the highest, with a funding-to-publication ratio of 2.67, followed by Belgium.

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The full article can be downloaded from here

Artist conception of a tidal disruption event (TDE) that happens when a star passes fatally close to a supermassive black hole, which reacts by launching a relativistic jet. (Sophia Dagnello, NRAO/AUI/NSF; NASA, STScI )

Andrew Griffin  15.06.2018

The huge, violent event sees a blast of matter shot across the universe

Scientists have seen the vast blast thrown out by a black hole eating a star for the first ever time.

Researchers have finally watched the formation and expansion of the fast-moving jet of material that is thrown out when a supermassive black hole's gravity grabs a star and tears it apart.

Scientists watched the dramatic event using highly specialised telescopes, which are trained on a pair of colliding galaxies called Arp 299, nearly 150 million light-years from Earth. At the centre of one of those galaxies, a star twice the size of the Sun came too close to a black hole that is more than 20 million times big as our Sun – and was shredded apart, throwing a blast across the universe.

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Inside the MiniBooNE tank, photodetectors capture the light created when a neutrino interacts with an atomic nucleus. (Reidar Hahn / Fermilab)

Natalie Wolchover  1.6.2018

Physicists are both thrilled and baffled by a new report from a neutrino experiment at Fermi National Accelerator Laboratory near Chicago. The MiniBooNE experiment has detected far more neutrinos of a particular type than expected, a finding that is most easily explained by the existence of a new elementary particle: a “sterile” neutrino that’s even stranger and more reclusive than the three known neutrino types. The result appears to confirm the anomalous results of a decades-old experiment that MiniBooNE was built specifically to double-check.

The persistence of the neutrino anomaly is extremely exciting, said the physicist Scott Dodelson of Carnegie Mellon University. It “would indicate that something is indeed going on,” added Anže Slosar of Brookhaven National Laboratory.

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In the Bullet Cluster, light seems to bend in what should be empty space. Researchers now believe those areas contain dark matter. Image: X-ray: NASA/CXC/CfA/ M. Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.

Ryan F. Mandelbaum  7.6.2018

Five-sixths of the universe’s stuff seems to be missing, and we just can’t find it. It’s called “dark matter,” and scientists have gone looking for it with some of the world’s largest, most expensive experiments.

Time and time again, these experiments come up empty handed. Most recently, the scientists at the XENON1T experiment, a literal ton of super-sensitive liquid xenon, didn’t find the signal they were looking for after a nine-month search. Nor has the Large Hadron Collider, the world’s largest particle accelerator in Geneva, Switzerland, managed to turn up anything. So, you might wonder, what are we looking for and why? And why are the world’s physicists so deeply divided about what “dark matter” could be?

Big, strange somethings

As early as the late 19th century, scientific observations were telling us that the universe was more massive than it appeared. Scientists now consider Swiss physicist Fritz Zwicky to be the father of dark matter. Zwicky realized that galaxies in the Coma Cluster seemed to move much too quickly. He thought there should perhaps 400 times more mass in the cluster than he could see, a bit of an overshoot, and called the missing stuff dunkle Materie, or “dark matter.”

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A 1998 illustration of a spacecraft using negative energy to warp space-time and travel faster than light (digital art by Les Bossinas (Cortez III Service Corp.), 1998)

Dave Mosher May 24, 2018

• The US Department of Defense funded a series of studies on advanced aerospace technologies, including warp drives.
• The studies came out of a program that also funded research into UFO sightings.
• One report describes the possibility of using dark energy to warp space and effectively travel faster than light.
• However, a theoretical physicist says there's "zero chance that anyone within our lifetimes or the next 1,000 years" will see it happen.

Sometime after August 2008, the US Department of Defense contracted dozens of researchers to look into some very, very out-there aerospace technologies, including never-before-seen methods of propulsion, lift, and stealth.

Two researchers came back with a 34-page report for the propulsion category, titled "Warp Drive, Dark Energy, and the Manipulation of Extra Dimensions."

The document is dated April 2, 2010, though it was only recently released by the Defense Intelligence Agency. (Business Insider first learned about in a post by Paul Szoldra at Task & Purpose.)

The authors suggest we may not be too far away from cracking the mysteries of higher, unseen dimensions and negative or "dark energy," a repulsive force that physicists believe is pushing the universe apart at ever-faster speeds.

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Mathematicians have disproved the strong cosmic censorship conjecture. Their work answers one of the most important questions in the study of general relativity and changes the way we think about space-time.

Kevin Hartnet   May 17, 2018

Nearly 60 years after it was proposed, mathematicians have settled one of the most profound questions in the study of general relativity. In a paper posted online last fall, mathematicians Mihalis Dafermos and Jonathan Luk have proven that the strong cosmic censorship conjecture, which concerns the strange inner workings of black holes, is false.

“I personally view this work as a tremendous achievement — a qualitative jump in our understanding of general relativity,” emailed Igor Rodnianski, a mathematician at Princeton University.

The strong cosmic censorship conjecture was proposed in 1979 by the influential physicist Roger Penrose. It was meant as a way out of a trap. For decades, Albert Einstein’s theory of general relativity had reigned as the best scientific description of large-scale phenomena in the universe. Yet mathematical advances in the 1960s showed that Einstein’s equations lapsed into troubling inconsistencies when applied to black holes. Penrose believed that if his strong cosmic censorship conjecture were true, this lack of predictability could be disregarded as a mathematical novelty rather than as a sincere statement about the physical world.

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Physicists believe that at the tiniest scales, space emerges from quanta. What might these building blocks look like?

George Musser  09 MAY 2018

People have always taken space for granted. It is just emptiness, after all—a backdrop to everything else. Time, likewise, simply ticks on incessantly. But if physicists have learned anything from the long slog to unify their theories, it is that space and time form a system of such staggering complexity that it may defy our most ardent efforts to understand.

Albert Einstein saw what was coming as early as November 1916. A year earlier he had formulated his general theory of relativity, which postulates that gravity is not a force that propagates through space but a feature of spacetime itself. When you throw a ball high into the air, it arcs back to the ground because Earth distorts the spacetime around it, so that the paths of the ball and the ground intersect again. In a letter to a friend, Einstein contemplated the challenge of merging general relativity with his other brainchild, the nascent theory of quantum mechanics. That would not merely distort space but dismantle it. Mathematically, he hardly knew where to begin. “How much have I already plagued myself in this way!” he wrote.

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With the first detections behind them, researchers have set their sights on ambitious scientific quarry.

Davide Castelvecchi

In the mid-1980s, Bernard Schutz came up with a new solution to one of astronomy’s oldest problems: how to measure the distance from Earth to other objects in the cosmos. For generations, researchers have relied on an object’s brightness as a rough gauge for its distance. But this approach carries endless complications. Dim, nearby stars, for example, can masquerade as bright ones that are farther away.

Schutz, a physicist at the University of Cardiff, UK, realized that gravitational waves could provide the answer. If detectors could measure these ripples in space-time, emanating from interacting pairs of distant objects, scientists would have all the information needed to calculate how strong the signal was to start with — and so how far the waves must have travelled to reach Earth. Thus, he predicted, gravitational waves could be unambiguous markers of how quickly the Universe is expanding.

His idea was elegant but impractical: nobody at the time could detect gravitational waves. But, last August, Schutz finally got the opportunity to test this concept when the reverberations of a 130-million-year-old merger between two neutron stars passed through gravitational-wave detectors on Earth. As luck would have it, the event occurred in a relatively nearby galaxy, producing a much cleaner first measure than Schutz had dreamed. With that one data point, Schutz was able to show that his technique could become one of the most reliable for measuring distance. “It was hard to believe,” Schutz says. “But there it was.”

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