NGC1052-DF2 is a large, but very diffuse galaxy located some 60 million light-years away. This image of the galaxy, which is thought to contain a negligible amount of dark matter, was captured by the Advanced Camera for Surveys on the Hubble Space Telescope. NASA/ESA/P. van Dokkum (Yale University

Ironically, by finding two galaxies severely lacking in dark matter, researchers have made a compelling case for the existence of the mysterious material.

By Jake Parks | Published: Friday, March 29, 2019

One year ago, astronomers were flabbergasted when they discovered a galaxy almost entirely devoid of dark matter. As the first galaxy ever found lacking the elusive substance — which is thought to account for 85 percent of the universe's mass — the news rippled through the astronomical community. This left some researchers delightfully intrigued, and others understandably skeptical.

"If there's [only] one object, you always have a little voice in the back of your mind saying, 'but what if you're wrong?'" astronomer Pieter van Dokkum of Yale University, who led last year's ground-breaking study, said in a press release. "Even though we did all the checks we could think of, we were worried that nature had thrown us for a loop and had conspired to make something look really special whereas it was really something more mundane."

Now, a new study published in The Astrophysical Journal Letters on March 27 shows van Dokkum and his team had it right all along.

According to the work, they've confirmed a ghostly galaxy located some 60 million light-years away named NGC 1052-DF2 (DF2 for short) has virtually no discernible dark matter. Furthermore, a second study published March 20 in the same journal announced the discovery of yet another dim and diffuse galaxy with a dearth of dark matter, nicknamed DF4.

See full text

1 April 2019

The European Commission, European Research Council, and the Event Horizon Telescope (EHT) project will hold a press conference to present a groundbreaking result from the EHT.

When: On 10 April 2019 at 15:00 CEST

Where: The press conference will be held at the Berlaymont Building, Rue de la Loi (Wetstraat) 200, B-1049 Brussels, Belgium. The event will be introduced by European Commissioner for Research, Science and Innovation, Carlos Moedas, and will feature presentations by the researchers behind this result.

What: A press conference to present a groundbreaking result from the EHT.

Who: The European Commissioner for Research, Science and Innovation, Carlos Moedas, will deliver remarks. Anton Zensus, Chair of the EHT Collaboration Board will also make remarks and introduce a panel of EHT researchers who will explain the result and answer questions:
        Heino Falcke, Radboud University, Nijmegen, The Netherlands (Chair of the EHT Science Council)
        Monika Mościbrodzka, Radboud University, Nijmegen, The Netherlands (EHT Working Group Coordinator)
        Luciano Rezzolla, Goethe Universität, Frankfurt, Germany (EHT Board Member)
        Eduardo Ros, Max-Planck-Institut für Radioastronomie, Bonn, Germany, (EHT Board Secretary)

RSVP: This invitation is addressed to media representatives. To participate in the conference, members of the media must register by completing an online form before April 7 23:59 CEST. Please indicate whether you wish to attend in person or if you will participate online only. On-site journalists will have a question-and-answer session with panellists during the conference. In-person individual interviews immediately after the conference will also be possible.
The conference will be streamed online on the ESO website, by the ERC, and on social media. We will take a few questions from social media using the hashtag #AskEHTeu.

See full text

The Virgo gravitational-wave detector near Pisa, Italy, has roughly doubled its sensitivity since 2017.Credit: Cappello/Ropi via ZUMA

Detailed data on space-time ripples are set to pour in from LIGO and Virgo’s upgraded detectors.

Davide Castelvecchi  --  02 APRIL 2019

The hunt for gravitational waves is on again — this time assisted by the quirks of quantum mechanics.

Three massive detectors — the two in the United States called LIGO and one in Italy known as Virgo — officially resumed collecting data on 1 April, after a 19-month shutdown for upgrades. Thanks in part to a quantum phenomenon known as light squeezing, the machines promise not only to spot more gravitational waves — ripples in space-time that can reveal a wealth of information about the cosmos — but also to make more detailed detections. Researchers hope to observe as-yet undetected events, such as a supernova or the merging of a black hole with a neutron star.

The run, which will last until next March, also marks a major change in how gravitational-wave astronomy is done. For the first time, LIGO and Virgo will send out public, real-time alerts on wave detections to tip off other observatories — and anyone with a telescope — on how to find the events, so that they can be studied with traditional techniques, from radio- to space-based X-ray telescopes. The alerts will also be available through a smartphone app. “Astronomers are really hungry,” says David Reitze, a physicist at the California Institute of Technology in Pasadena and director of the Laser Interferometer Gravitational-wave Observatory (LIGO), which made the first historic detection of gravitational waves in 2015.

See full text

A worker inspects quartz fibers that suspend a mirror inside the Virgo gravitational-wave observatory. EGO/Virgo Collaboration/Perciballi

Business Insider

Dave Mosher Mar. 28, 2019

One of the most remarkable experiments in history — a pair of giant machines that listen for ripples in spacetime called gravitational waves— will wake up from a half-year nap on Monday. And it will be about 40% stronger than before.

That experiment is called the Laser Interferometer Gravitational-Wave Observatory (LIGO); it consists of two giant, L-shaped detectors that together solved a 100-year-old mystery posed by Albert Einstein.

In 1915, Einstein predicted the existence of ripples in the fabric of space However, he didn't think these gravitational waves would ever be detected — they seemed too weak to pick up amid all the noise and vibrations on Earth. For 100 years, it seemed Einstein was right.

See full text

Any distant gravitational source can emit gravitational waves and send out a signal that deforms the fabric of space, which manifests as gravitational attraction. But while gravitational forces fall off as the distance squared, the gravitational wave signal only falls off proportionally to the distance.

EUROPEAN GRAVITATIONAL OBSERVATORY, LIONEL BRET/EUROLIOS

Ethan Siegel - Senior Contributor
Mar 2, 2019

One of the things we often just accept about the world is that physical effects get weaker the farther away we get from them. Light sources appear dimmer, the gravitational force gets weaker, magnets deflect by smaller amounts, etc. The most common way this arises is through an inverse-square law, meaning that if you double the distance between you and the source that creates the effect you're measuring, the effect will be one quarter of what it was previously. But this isn't true for gravitational waves, and that puzzles reader Jack Dectis, who asks:

You have stated:
1) The strength of gravity varies with the square of the distance.
2) The strength of gravity waves, as detected by LIGO, varies directly with the distance.
So the question is, how can those two be the same thing?

This is a real surprise to almost everyone when they hear about it, even professional physicists. But it's true! Here's the science of why.

See full text

LHCb. Maximilien Brice et al./CERN

March 21, 2019

Author: Marco Gersabeck
Lecturer in Physics, University of Manchester

Why do we exist? This is arguably the most profound question there is and one that may seem completely outside the scope of particle physics. But our new experiment at CERN’s Large Hadron Collider has taken us a step closer to figuring it out.

To understand why, let’s go back in time some 13.8 billion years to the Big Bang. This event produced equal amounts of the matter you are made of and something called antimatter. It is believed that every particle has an antimatter companion that is virtually identical to itself, but with the opposite charge. When a particle and its antiparticle meet, they annihilate each other – disappearing in a burst of light.

Why the universe we see today is made entirely out of matter is one of the greatest mysteries of modern physics. Had there ever been an equal amount of antimatter, everything in the universe would have been annihilated. Our research has unveiled a new source of this asymmetry between matter and antimatter.

See full text

The Cepheid variable star RS Puppis, as seen by the Hubble Space Telescope. Such stars are crucial rungs on the “cosmic distance ladder,” a method for measuring vast intergalactic distances and the universe’s rate of expansion. Credit: NASA, ESA, and the Hubble Heritage Team. Processing by Stephen Byrne

The latest disagreement over the universe’s expansion rate suggests researchers may be on the threshold of revolutionary discoveries

By Anil Ananthaswamy on March 22, 2019

A long-running dispute about how fast our universe is expanding just became even more entrenched. New and more precise measurements of stars in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, have only strengthened the differences between two independent methods of calculating the expansion rate.
This impasse may soon force cosmologists to reexamine the “standard model” of cosmology, which tells us about the composition of the universe (radiation, normal matter, dark matter and dark energy) and how it has evolved over time.
For about five years now, two projects have been at odds over the value of the Hubble constant (H0), the rate at which the universe is expanding. One relies on studies of the cosmic microwave background (CMB), the relic afterglow from the hot, dense plasma that suffused the universe shortly after the big bang. The other project uses a potpourri of more “local” measurements, which constitute the so-called cosmic distance ladder.

See full text

Massive sound. A small amount of mass is transported along with all sound waves, according to a new theory.

March 1, 2019• Physics 12, 23
Even if you ignore general relativity, sound waves transport a small amount of mass, according to theory.

Ordinary sound waves carry a small amount of mass with them as they travel, according to a new theoretical study. The theory assumes Newtonian conditions, so the effect is unrelated to either quantum theory or the equivalence of energy and mass known from relativity. The researchers do not yet have a clear physical explanation of their mathematical results, but they say that the idea should be testable in experiments with ultracold atoms, or possibly in observations of earthquakes.

Last year, high-energy physicists Alberto Nicolis of Columbia University in New York and Riccardo Penco, now at Carnegie Mellon University (CMU) in Pittsburgh, used quantum field theory to analyze the behavior of sound waves moving through superfluid helium [1]. To their surprise, they found that the waves carry a small amount of mass, not only by virtue of Einstein’s famous formula equating energy with mass. The duo found that phonons, the quantum units of sound waves, interact with a gravitational field in a way that requires them to transport mass as they move.

See full text

WATCHING THE CLOCK Scientists monitored two atomic clocks for six months in order to test a tenet of Einstein’s special theory of relativity. Each clock, like the one shown, contained a single ion of ytterbium.

An experiment tested a foundational principle of physics known as Lorentz symmetry
BY EMILY CONOVER 2:00PM, MARCH 13, 2019

The ticktock of two ultraprecise clocks has proven Einstein right, once again.

A pair of atomic clocks made of single ions of ytterbium kept pace with one another over six months, scientists report March 13 in Nature. The timepieces’ reliability supports a principle known as Lorentz symmetry. That principle was the foundation for Einstein’s special theory of relativity, which describes the physics of voyagers dashing along at nearly the speed of light.

See full text

Katia Moskvitch - Contributing Writer : April 30, 2018

New observations of extreme astrophysical systems have “brutally and pitilessly murdered” attempts to replace Einstein’s general theory of relativity.

Two white dwarfs and a pulsar orbit one another in a system that reveals how gravity behaves in extreme environments.

Miguel Zumalacárregui knows what it feels like when theories die. In September 2017, he was at the Institute for Theoretical Physics in Saclay, near Paris, to speak at a meeting about dark energy and modified gravity. The official news had not yet broken about an epochal astronomical measurement — the detection, by gravitational wave detectors as well as many other telescopes, of a collision between two neutron stars — but a controversial tweet had lit a firestorm of rumor in the astronomical community, and excited researchers were discussing the discovery in hushed tones.

Zumalacárregui, a theoretical physicist at the Berkeley Center for Cosmological Physics, had been studying how the discovery of a neutron-star collision would affect so-called “alternative” theories of gravity. These theories attempt to overcome what many researchers consider to be two enormous problems with our understanding of the universe. Observations going back decades have shown that the universe appears to be filled with unseen particles — dark matter — as well as an anti-gravitational force called dark energy. Alternative theories of gravity attempt to eliminate the need for these phantasms by modifying the force of gravity in such a way that it properly describes all known observations — no dark stuff required.

See full text

The observatories are also releasing their first catalog of gravitational-wave events

On Saturday, December 1, scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from the National Science Foundation's LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European- based VIRGO gravitational-wave detector regarding their searches for coalescing cosmic objects, such as pairs of black holes and pairs of neutron stars. The LIGO and Virgo collaborations have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Six of the black hole merger events had been reported before, while four are newly announced.

From September 12, 2015, to January 19, 2016, during the first LIGO observing run since undergoing upgrades in a program called Advanced LIGO, gravitational waves from three binary black hole mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational-wave events being reported now. The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.

All of the events are included in a new catalog, also released Saturday, with some of the events breaking records. For instance, the new event GW170729, detected in the second observing run on July 29, 2017, is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were ever observed from the merger of a binary neutron star system. What's more, this collision was seen in gravitational waves and light, marking an exciting new chapter in multi-messenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

One of the new events, GW170818, which was detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

See full text

A still image of a visualization of the merging black holes that LIGO and Virgo have observed so far. As the horizons of the black holes spiral together and merge, the emitted gravitational waves become louder (larger amplitude) and higher pitched (higher in frequency). The black holes that merge range from 7.6 solar masses up to 50.6 solar masses, with about 5% of the total mass lost during each merger.TERESITA RAMIREZ/GEOFFREY LOVELACE/SXS COLLABORATION/LIGO-VIRGO COLLABORATION

Dec 4, 2018,
Ethan Siegel Senior Contributor
Science

On September 14th, 2015, just days after LIGO first turned on at its new-and-improved sensitivity, a gravitational wave passed through Earth. Like the billions of similar waves that had passed through Earth over the course of its history, this one was generated by an inspiral, merger, and collision of two massive, ultra-distant objects from far beyond our own galaxy. From over a billion light years away, two massive black holes had coalesced, and the signal — moving at the speed of light — finally reached Earth.

But this time, we were ready. The twin LIGO detectors saw their arms expand-and-contract by a subatomic amount, but that was enough for the laser light to shift and produce a telltale change in an interference pattern. For the first time, we had detected a gravitational wave. Three years later, we've detected 11 of them, with 10 coming from black holes. Here's what we've learned.

There have been two "runs" of LIGO data: a first one from September 12, 2015 to January 19, 2016 and then a second one, at somewhat improved sensitivity, from November 30, 2016 to August 25, 2017. That latter run was, partway through, joined by the VIRGO detector in Italy, which added not only a third detector, but significantly improved our ability to pinpoint the location of where these gravitational waves occurred. LIGO is currently shut down right now, as it's undergoing upgrades that will make it even more sensitive, as it prepares to begin a new data-taking observing run in the spring of 2019.

See full text

The relativistic eccentricity of Galileo satellites 5 and 6 reaches a peak amplitude of approximately 370 nanoseconds (billionths of a second), driven by the shifting altitude, and hence changing gravity levels, of their elliptical orbits around Earth. A periodic modulation of this size is clearly discernible, given the relative frequency stability of the Passive Hydrogen Maser atomic clocks aboard the satellites. Credit: European Space Agency

December 5, 2018, European Space Agency

Europe's Galileo satellite navigation system – already serving users globally – has now provided a historic service to the physics community worldwide, enabling the most accurate measurement ever made of how shifts in gravity alter the passing of time, a key element of Einstein's Theory of General Relativity.

Two European fundamental physics teams working in parallel have independently achieved about a fivefold improvement in measuring accuracy of the gravity-driven time dilation effect known as 'gravitational redshift.'
The prestigious Physical Review Letters journal has just published the independent results obtained from both consortiums, gathered from more than a thousand days of data obtained from the pair of Galileo satellites in elongated orbits.
"It is hugely satisfying for ESA to see that our original expectation that such results might be theoretically possible have now been borne out in practical terms, providing the first reported improvement of the gravitational redshift test for more than 40 years," comments Javier Ventura-Traveset, Head of ESA's Galileo Navigation Science Office.
"These extraordinary results have been made possible thanks to the unique features of the Galileo satellites, notably the very high stabilities of their onboard atomic clocks, the accuracies attainable in their orbit determination and the presence of laser-retroreflectors, which allow for the performance of independent and very precise orbit measurements from the ground, key to disentangle clock and orbit errors."

See full text

See also the 2015 announcement

Galileo satellites set for year-long Einstein experiment

Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole's accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results.GRMHD SIMULATIONS OF VISIBILITY AMPLITUDE VARIABILITY FOR EVENT HORIZON TELESCOPE IMAGES OF SGR A*, L. MEDEIROS ET AL., ARXIV:1601.06799

Oct 3, 2018

Ethan Siegel & Starts With A Bang

What does a black hole actually look like? For generations, scientists argued over whether black holes actually existed or not. Sure, there were mathematical solutions in General Relativity that indicated they were possible, but not every mathematical solution corresponds to our physical reality. It took observational evidence to settle that issue.

Owing to matter orbiting and infalling around black holes, both stellar-mass versions and the supermassive versions, we've detected the X-ray emissions characteristic of their existences. We found and measured the motions of individual stars that orbit suspected black holes, confirming the existence of massive objects at the centers of galaxies. If only we could directly image these objects that emit no light themselves, right? Amazingly, that time is here.

See full text

attempto online - Forum
17.10.2018

Die Erziehungswissenschaft an der Universität Tübingen kann erneut mit Bestnoten glänzen. Nach dem am Mittwoch veröffentlichten Times Higher Education Ranking nach akademischen Fächern landeten die Tübinger Pädagogen bundesweit auf Platz 2 sowie auf Platz 42 im weltweiten Vergleich. Bereits Ende Juli hatte sich die Tübinger Erziehungswissenschaft im diesjährigen Shanghai Ranking bundesweit auf Rang eins platzieren können.

Das Times Higher Education Ranking gilt als eines der angesehensten Systeme zur Klassifizierung von Universitäten weltweit. Das Ranking vergleicht mehr als 2.000 Hochschulen in 93 Ländern. Bewertet werden unter anderem die Leistungen einer Hochschule in Lehre und Forschung, die Zahl der wissenschaftlichen Veröffentlichungen, Drittmitteleinnahmen sowie die Reputation der Einrichtungen unter Wissenschaftlerinnen und Wissenschaftlern. Das Ranking wird seit 2010 vom britischen Magazin Times Higher Education organisiert und durchgeführt.

Karl G. Rijkhoek