Black holes in these environments could combine repeatedly to form objects bigger than anything a single star could produce.

Jennifer Chu | MIT News Office
April 10, 2018

When LIGO’s twin detectors first picked up faint wobbles in their respective, identical mirrors, the signal didn’t just provide first direct detection of gravitational waves — it also confirmed the existence of stellar binary black holes, which gave rise to the signal in the first place.
Stellar binary black holes are formed when two black holes, created out of the remnants of massive stars, begin to orbit each other. Eventually, the black holes merge in a spectacular collision that, according to Einstein’s theory of general relativity, should release a huge amount of energy in the form of gravitational waves.

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Artist’s illustration of two merging neutron stars. Astronomers witnessed such a merger in August 2017, and we're now trying to interpret these observations. [University of Warwick/Mark Garlick]

By Susanna Kohler on 13 April 2018

Now that the hubbub of GW170817 — the first coincident detection of gravitational waves and an electromagnetic signature — has died down, scientists are left with the task of taking the spectrum-spanning observations and piecing them together into a coherent picture. Researcher Iair Arcavi examines one particular question: what caused the blue color in the early hours of the neutron-star merger?

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The center of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*), located in the middle.
PHOTOGRAPH BY NASA/UMASS/D.WANG ET AL., STSCI

By Sarah Gibbens
PUBLISHED APRIL 4, 2018

A gaggle of black holes has been found clustered around the center of our home galaxy, the Milky Way—and the discovery hints at a much larger population of black holes hidden across the galaxy. The discover offers a new test bed for understanding the ripples in space-time known as gravitational waves.

For years, scientists have known that a monster black hole sits in the middle of the galaxy. Called Sagittarius A* (Sgr A*), the compact object is more than four million times as massive as our sun, but it's packed into a region of space no bigger than the distance between Earth and our star.

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March 22, 2018

Sabine Hossenfelder

We all dream the same dream, here in theoretical physics. We dream of the day when one of our equations will be plotted against data and fit spot on. It’s rare for this dream to come true. Even if it does, some don’t live to see it.

Take, for example, Albert Einstein, who passed away in 1955, 60 years before his equations’ most stunning consequence was confirmed: Space-time has periodic ripples — gravitational waves — that can carry energy across billions of light-years.

Since that September 2015 black hole collision, the Laser Interferometer Gravitational-Wave Observatory (LIGO) team has reported five more events (a sixth fell just short of the standard of significance). But the LIGO data is still virgin territory. It is an entirely new way of decoding the universe, and physicists must develop methods of data analysis along with the measurements.

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A neutrino passing through the Super-Kamiokande experiment creates a telltale light pattern on the detector walls.

Katia Moskvitch -- December 12, 2017

Updated results from a Japanese neutrino experiment continue to reveal an inconsistency in the way that matter and antimatter behave

From above, you might mistake the hole in the ground for a gigantic elevator shaft. Instead, it leads to an experiment that might reveal why matter didn’t disappear in a puff of radiation shortly after the Big Bang.

I’m at the Japan Proton Accelerator Research Complex, or J-PARC — a remote and well-guarded government facility in Tokai, about an hour’s train ride north of Tokyo. The experiment here, called T2K (for Tokai-to-Kamioka) produces a beam of the subatomic particles called neutrinos. The beam travels through 295 kilometers of rock to the Super-Kamiokande (Super-K) detector, a gigantic pit buried 1 kilometer underground and filled with 50,000 tons (about 13 million gallons) of ultrapure water. During the journey, some of the neutrinos will morph from one “flavor” into another.

In this ongoing experiment, the first results of which were reported last year, scientists at T2K are studying the way these neutrinos flip in an effort to explain the predominance of matter over antimatter in the universe. During my visit, physicists explained to me that an additional year’s worth of data was in, and that the results are encouraging.

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Credit: NASA / GSFC

The history of the Universe and the arrow of time, which always flows forward in the same direction and at the same rate for any observer.

Ethan Siegel , Contributor  

MAR 9, 2018 

Every moment that passes finds us traveling from the past to the present and into the future, with time always flowing in the same direction. At no point does it ever appear to either stand still or reverse; the “arrow of time” always points forwards for us. But if we look at the laws of physics — from Newton to Einstein, from Maxwell to Bohr, from Dirac to Feynman — they appear to be time-symmetric. In other words, the equations that govern reality don’t have a preference for which way time flows. The solutions that describe the behavior of any system obeying the laws of physics, as we understand them, are just as valid for time flowing into the past as they are for time flowing into the future. Yet we know from experience that time only flows one way: forwards. So where does the arrow of time come from?

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Article written: 10 Feb , 2016 Updated: 11 Feb , 2016

by Markus Pössel

It’s official: this Thursday, February 11, at 10:30 EST, there will be parallel press conferences at the National Press Club in Washington, D.C., in Hannover, Germany, and near Pisa in Italy. Not officially confirmed, but highly probable, is that people running the LIGO gravitational wave detectors will announce the first direct detection of a gravitational wave. The first direct detection of minute distortions of spacetime, travelling at the speed of light, first postulated by Albert Einstein almost exactly 100 years ago. Nobel prize time.

Time to brush up on your gravitational wave basics, if you haven’t done so! In Gravitational waves and how they distort space, I had a look at what gravitational waves do. Now, on to the next step: How can we measure what they do? How do gravitational wave detectors such as LIGO work?

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X-ray image of the Perseus galaxy cluster, approximately 240 million light-years away from Earth. The x-ray radiation emitted by galaxies and galaxy clusters still poses numerous puzzles to astrophysicists. In particular, it may provide clues to the nature of the mysterious dark matter. Credit: Photo courtesy of NASA

February 8, 2018, Universitaet Mainz

Dark matter is increasingly puzzling. Around the world, physicists have been trying for decades to determine the nature of these matter particles, which do not emit light and are therefore invisible to the human eye. Their existence was postulated in the 1930s to explain certain astronomical observations. As visible matter, like the one that makes up the stars and the Earth, constitutes just 5 percent of the universe, it has been proposed that dark matter must represent 23 percent of what is out there. But to date and despite intensive research, it has proved impossible to actually identify the particles involved. Researchers at Johannes Gutenberg University Mainz (JGU) have now presented a novel theory of dark matter, which implies that dark matter particles may be very different from what is normally assumed. In particular, their theory involves dark matter particles which are extremely light—almost one hundred times lighter than electrons, in stark contrast to many conventional models that involve very heavy dark matter particles instead.

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NASA, ESA, AND D. COE, J. ANDERSON, AND R. VAN DER MAREL (STSCI)

The most prestigious journal in physics highlights dozens of its most famous papers
BY TOM SIEGFRIED 11:00AM, FEBRUARY 8, 2018

No anniversary list is ever complete. Just last month, for instance, my Top 10 scientific anniversaries of 2018 omitted the publication two centuries ago of Mary Shelley’s Frankenstein. It should have at least received honorable mention.

Perhaps more egregious, though, was overlooking the 125th anniversary of the physics journal Physical Review. Since 1893, the Physical Review has published hundreds of thousands of papers and has been long regarded as the premier repository for reports of advances in humankind’s knowledge of the physical world. In recent decades it has split itself into subjournals (A through E, plus L — for Letters — and also X) to prevent excessive muscle building by librarians and also better organize papers by physics subfield. (You don’t want to know what sorts of things get published in X.)

To celebrate the Physical Review anniversary, the American Physical Society (which itself is younger, forming in 1899 and taking charge of the journal in 1913), has released a list, selected by the journals’ editors, of noteworthy papers from Physical Review history.

The list comprises more than four dozen papers, oblivious to the concerns of journalists composing Top 10 lists. If you prefer the full list without a selective, arbitrary and idiosyncratic Top 10 filter, you can go straight to the Physical Review journals’ own list. But if you want to know which two papers the journal editors missed, you’ll have to read on.

10. ....

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LISA Pathfinder performance analysis

5 February 2018

Imagine a packed party: music is blaring and you can feel the bass vibrate in your chest, lights are flashing, balloons are falling from the ceiling and the air is filled with hundreds of separate conversations. At the same time your cell phone is vibrating in your pocket and your drink is fizzing in the glass. Now imagine you can block out this assault on your senses to create a perfectly quiet bubble around you, only letting in the unmistakable voice of your best friend who’s trying to get your attention from the other side of the room.

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Photo Archive VISTA

Donald Lynden-Bell CBE FRS (5 April 1935 - 5 February 2018) was an English astrophysicist, best known for his theories that galaxies contain massive black holes at their centre, and that such black holes are the principal source of energy in quasars. He was a co-recipient, with Maarten Schmidt, of the inaugural Kavli Prize for Astrophysics in 2008. Lynden-Bell was the president of the Royal Astronomical Society. He worked at the Institute of Astronomy in Cambridge; he was the Institute's first director.

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http://www.kavliprize.org/prizes-and-laureates/laureates/donald-lynden-bell

Centaurus A, an elliptical galaxy 13 million light-years from Earth, hosts a group of dwarf satellite galaxies co-rotating in a narrow disk, a distribution not predicted by dark-matter-influenced cosmological models. Credit: Christian Wolf and the SkyMapper team / Australian National University

February 1, 2018, University of California, Irvine

An international team of astronomers has determined that Centaurus A, a massive elliptical galaxy 13 million light-years from Earth, is accompanied by a number of dwarf satellite galaxies orbiting the main body in a narrow disk. In a paper published today in Science, the researchers note that this is the first time such a galactic arrangement has been observed outside the Local Group, home to the Milky Way.

"The significance of this finding is that it calls into question the validity of certain cosmological models and simulations as explanations for the distribution of host and satellite galaxies in the universe," said co-author Marcel Pawlowski, a Hubble Fellow in the Department of Physics & Astronomy at the University of California, Irvine.
He said that under the lambda cold dark matter model, smaller systems of stars should be more or less randomly scattered around their anchoring galaxies and should move in all directions. Yet Centaurus A is the third documented example, behind the Milky Way and Andromeda, of a "vast polar structure" in which satellite dwarves co-rotate around a central galactic mass in what Pawlowski calls "preferentially oriented alignment."

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Visualization of the intensity of shock waves in the cosmic gas (blue) around collapsed dark matter structures (orange/white). Similar to a sonic boom, the gas in these shock waves is accelerated with a jolt when impacting on the cosmic filaments and galaxies. Credit: IllustrisTNG collaboration

February 1, 2018, Simons Foundation

Novel computational methods have helped create the most information-packed universe-scale simulation ever produced. The new tool provides fresh insights into how black holes influence the distribution of dark matter, how heavy elements are produced and distributed throughout the cosmos, and where magnetic fields originate.

Led by principal investigator Volker Springel at the Heidelberg Institute for Theoretical Studies, astrophysicists from the Max Planck Institutes for Astronomy (MPIA, Heidelberg) and Astrophysics (MPA, Garching), Harvard University, the Massachusetts Institute of Technology (MIT), and the Flatiron Institute's Center for Computational Astrophysics (CCA) developed and programmed the new universe simulation model, dubbed Illustris: The Next Generation, or IllustrisTNG.
The model is the most advanced universe simulation of its kind, says Shy Genel, an associate research scientist at CCA who helped develop and hone IllustrisTNG. The simulation's detail and scale enable Genel to study how galaxies form, evolve and grow in tandem with their star-formation activity. "When we observe galaxies using a telescope, we can only measure certain quantities," he says. "With the simulation, we can track all the properties for all these galaxies. And not just how the galaxy looks now, but its entire formation history." Mapping out the ways galaxies evolve in the simulation offers a glimpse of what our own Milky Way galaxy might have been like when the Earth formed and how our galaxy could change in the future, he says.

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Artist’s animation of a pair of neutron stars locked in a binary orbit. [NASA/Dana Berry, Sky Works Digital ]

 More than forty years after the first discovery of a double neutron star, we still haven’t found many others — but a new survey is working to change that.

The Hunt for Pairs

In 1974, Russell Hulse and Joseph Taylor discovered the first double neutron star: two compact objects locked in a close orbit about each other. Hulse and Taylor’s measurements of this binary’s decaying orbit over subsequent years led to a Nobel prize — and the first clear evidence of gravitational waves carrying energy and angular momentum away from massive binaries.
Forty years later, we have since confirmed the existence of gravitational waves directly with the Laser Interferometer Gravitational-Wave Observatory (LIGO). Nonetheless, finding and studying pre-merger neutron-star binaries remains a top priority. Observing such systems before they merge reveals crucial information about late-stage stellar evolution, binary interactions, and the types of gravitational-wave signals we expect to find with current and future observatories.

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Rapid-response program to explore a double neutron star merger

A simulation of a neutron star merger. NASA GODDARD SPACE FLIGHT CENTER

BY KATHERINE HIGNETT ON 1/19/18 AT 8:47 AM

Update | Last August, astronomers detected the massive collision of two neutron stars. This neutron star merger sent gravitational waves surging through space. It also unleashed a gamma ray burst—the world’s most powerful laser.

Normally gamma ray bursts glow brightly for a short time, then fizzle out and lose energy. New electromagnetic observations from NASA’s Chandra X-ray observatory show the burst brightening, baffling astronomers.

An exploding cocoon
A more complex explanation is needed for the bizarre brightening, the authors wrote. They propose that a "cocoon"-shaped explosion might do the job. In this model, a jet from the collision shock-heats the surrounding gas and debris, creating a boiling cocoon of matter.

The new X-ray observations support recent discoveries from radio emissions. Last month, another team of researchers reported the strengthening of radio emissions from the neutron star merger. They produced a digital reconstruction, seen in the video below, of a similar "cocoon" model.

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