The NuSTAR telescope is sensitive to the high-energy X-rays that would provide stronger evidence for the existence of axions.
NASA/JPL-Caltech

Jonathan O'Callaghan  -  October 19, 2021

Approximately 85% of the mass in the universe is missing — we can infer its existence, we just can’t see it. Over the years, a number of different explanations for this “dark matter” have been proposed, from undiscovered particles to black holes. One idea in particular, however, is drawing renewed attention: the axion. And researchers are turning to the skies to track it down.

Axions are hypothetical lightweight particles whose existence would resolve two major problems. The first, fussed over since the 1960s, is the strong charge-parity (CP) problem, which asks why the quarks and gluons that make up protons and neutrons obey a certain symmetry. Axions would show that an unseen field is responsible.

The second is dark matter. Axions “are excellent dark matter candidates,” said Asimina Arvanitaki, a theoretical physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada. Axions would clump together in exactly the ways we expect dark matter to, and they have just the right properties to explain why they’re so hard to find — namely, they’re extremely light and reluctant to interact with regular matter.

Earlier this year, a group of scientists reported that they might have spotted evidence of axions being produced by neutron stars — collapsed stars that are so dense, a tiny sample little bigger than a grain of sand would weigh as much as an aircraft carrier. Ever since the 1980s, physicists have thought that if axions do exist, they should be produced inside the hot cores of neutron stars, where neutrons and protons smash together at high energies.

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The Molten Ring. (Saurabh Jha/Rutgers, The State University of New Jersey)

MICHELLE STARR

24 SEPTEMBER 2021

One of the most spectacular Einstein rings ever seen in space is enabling us to see what's happening in a galaxy almost at the dawn of time.

The smears of light called the Molten Ring, stretched out and warped by gravitational fields, are magnifications and duplications of a galaxy whose light has traveled a whopping 9.4 billion light-years. This magnification has given us a rare insight into the stellar 'baby boom' when the Universe was still in its infancy.

The early evolution of the Universe is a difficult time to understand. It blinked into existence as we understand it roughly 13.8 billion years ago, with the first light emerging (we think) around 1 billion years later. Light traveling for that amount of time is faint, the sources of it small, and dust obscures much of it.

Even the most intrinsically luminous objects are extraordinarily hard to see across that gulf of space-time, so there are large gaps in our understanding of how the Universe assembled itself from primordial soup.

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October 30, 2020• Physics 13, 164

The BICEP Array radio telescope, which searches for signatures of gravitational waves in the early Universe, has started an observing run that will break new ground in detection sensitivity.

In 2020, the raging pandemic halted many scientific endeavors around the globe. But after the last flights of the season left the Amundsen-Scott South Pole Station in February, the complex remained “frozen” in a pre-COVID era. There, a few dozen researchers can still mingle without face masks while managing physics, astronomy, and geoscience experiments that run during the six-month-long winter night. The latest experiment to kick off at the South Pole is the BICEP Array telescope, an instrument designed to probe the faint microwave light coming from the infant Universe. After a team assembled the new telescope in the brief austral summer, a lone engineer stayed to tend to the instrument (see Q&A: Searching for Light in the Darkness of Winter).

Focusing on a small patch of the South Pole’s dark winter sky, the BICEP Array will characterize with unprecedented accuracy the polarization of the cosmic microwave background (CMB). From these measurements, cosmologists hope to learn about inflation, the Universe’s extremely rapid expansion that occurred in the first 10−32
seconds after the big bang, before a more leisurely expansion began. They will examine subtle polarization patterns, called B modes, that theorists predict were produced by gravitational waves that arose during the inflation epoch.

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Daniel Meerburg  October 4, 2021• Physics 14, 135

An updated search for primordial gravitational waves has not found a signal, which implies that some popular early Universe models are becoming less viable.

Remarkably, the large-scale Universe can be adequately described by a model involving only a handful of parameters. This lambda cold dark matter (LCDM) model postulates that the expansion of the Universe is driven by the presence of two dark components—dark energy and dark matter—and that the galactic structure we observe today was sourced by small density variations in the very early Universe. However, cosmologists expect that these primordial density fluctuations were accompanied by fluctuations in the fabric of spacetime itself. These gravitational waves could be observed through a predicted signal in the cosmic microwave background (CMB). The BICEP/Keck Collaboration, which has been a frontrunner in the search for this illustrious signal, reports on its latest data set, finding no evidence of gravitational waves [1]. The resulting limits push up against model predictions, which suggests that we are either quickly closing in on a detection or that we may soon witness a paradigm shift. In addition, the analysis shows that researchers properly understand the astrophysical contaminants that obscure the search for this relic signature. By reducing uncertainties about this contamination, we should have greater confidence in any future claims of a detection.

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The Andromeda nebula, photographed at the Yerkes Observatory around 1900. To modern eyes, this object is clearly a galaxy. At the time, though, it was described as "a mass of glowing gas," its true identity unknown. (From the book Astronomy of To-Day, 1909)

Thanks to Edwin Hubble, we now can better comprehend the true scale of the universe.

By Corey S. Powell  January 2, 2017 

What’s in a date? Strictly speaking, New Year’s Day is just an arbitrary flip of the calendar, but it can also be a cathartic time of reflection and renewal. So it is with one of the most extraordinary dates in the history of science, January 1, 1925. You could describe it as a day when nothing remarkable happened, just the routine reading of a paper at a scientific conference. Or you could recognize it as the birthday of modern cosmology–the moment when humankind discovered the universe as it truly is.

Until then, astronomers had a myopic and blinkered view of reality. As happens so often to even the most brilliant minds, they could see great things but they could not comprehend what they were looking at. The crucial piece of evidence was staring them right in the face. All across the sky, observers had documented intriguing spiral nebulae, swirls of light that resembled ghostly pinwheels in space. The most famous one, the Andromeda nebula, was so prominent that it was easily visible to the naked eye on a dark night. The significance of those ubiquitous objects was a mystery, however.

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Samuel Velasco/Quanta Magazine

The Gaia telescope gauges the distances to stars by measuring their parallax, or apparent shift over the course of a year. Closer stars have a larger parallax.

Natalie Wolchover - December 17, 2020

On December 3, humanity suddenly had information at its fingertips that people have wanted for, well, forever: the precise distances to the stars.

“You type in the name of a star or its position, and in less than a second you will have the answer,” Barry Madore, a cosmologist at the University of Chicago and Carnegie Observatories, said on a Zoom call last week. “I mean …” He trailed off.

“We’re drinking from a firehose right now,” said Wendy Freedman, also a cosmologist at Chicago and Carnegie and Madore’s wife and collaborator.

“I can’t overstate how excited I am,” Adam Riess of Johns Hopkins University, who won the 2011 Nobel Prize in Physics for co-discovering dark energy, said in a phone call. “Can I show you visually what I’m so excited about?” We switched to Zoom so he could screen-share pretty plots of the new star data.

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See also a recent article on the debate about the Hubble constant

A view of the center of the Milky Way galaxy. Theories of modified gravity have had a hard time describing the universe from relatively small scales like this all the way up to the scale of the universe as a whole. NASA/JPL-Caltech/ESA/CXC/STScI

Modified gravity theories have never been able to describe the universe’s first light. A new formulation does.

Charlie Wood July 28, 2020

For decades, a band of rebel theorists has waged war with one of cosmology’s core concepts — the idea that an invisible, intangible form of matter forms the universe’s primary structure. This dark matter, which seems to outweigh the stuff we’re made of 5-to-1, accounts for a host of observations: the tight cohesion of galaxies and packs of galaxies, the way light from faraway galaxies will bend on its way to terrestrial telescopes, and the mottled structure of the early universe, to name a few.

The would-be revolutionaries seek an alternative cosmic recipe. In place of dark matter, they substitute a subtly modified force of gravity. But attempts to translate their rough idea into precise mathematical language have always run afoul of at least one key observation. Some formulations get galaxies right, some get the contortion of light rays right, but none have pierced dark matter’s most bulletproof piece of evidence: precise maps of ancient light, known as the cosmic microwave background (CMB). “A theory must do really well to agree with this data,” said Ruth Durrer, a cosmologist at the University of Geneva. “This is the bottleneck.”

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Observations of 11 galaxy clusters, such as MACSJ1206.2-0847 (shown), reveal that some globs of dark matter in these clusters are denser than expected. HUBBLE/ESA AND NASA

Not only is the mysterious substance invisible, but it’s also not all where we thought it was

By Maria Temming  September 10, 2020

Dark matter just got even more puzzling.

This unidentified stuff, which makes up most of the mass in the cosmos, is invisible but detectable by the way it gravitationally tugs on objects like stars. (SN: 11/25/19). Dark matter’s gravity can also bend light traveling from distant galaxies to Earth — but now some of this mysterious substance appears to be bending light more than it’s supposed to. A surprising number of dark matter clumps in distant clusters of galaxies severely warp background light from other objects, researchers report in the Sept. 11 Science.

This finding suggests that these clumps of dark matter, in which individual galaxies are embedded, are denser than expected. And that could mean one of two things: Either the computer simulations that researchers use to predict galaxy cluster behavior are wrong, or cosmologists’ understanding of dark matter is.

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Sakkmesterke/Science Photo Library

Massive objects can distort light from distant galaxies, as seen in this illustration.

Charlie Wood  September 8, 2020

The cosmos is starting to look a bit weird. For a few years now, cosmologists have been troubled by a discrepancy in how fast the universe is expanding. They know how fast it should be going, based on ancient light from the early universe, but apparently the modern universe has picked up too much speed — a clue that scientists might have overlooked one of the universe’s fundamental ingredients, or some aspect of how those ingredients stir together.

Now a second crack in the so-called standard model of cosmology may be forming. In late July, scientists announced that the modern universe also looks unexpectedly thin. Galaxies and gas and other matter haven’t clumped together quite as much as they should have. A few earlier studies offered similar hints, but this new analysis of seven years of data represents the cleanest stand-alone indication of the anomaly yet.

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The Australian Square Kilometre Array Pathfinder helped detect the universe's missing matter.(Supplied: Kirsten Gottschalk, COMET)

28.05.2020

By science, technology and environment reporter Michael Slezak and the Specialist Reporting Team's Penny

After an intergalactic search lasting more than two decades, an Australian-led team of scientists say they have finally found the universe's "missing matter", solving a mystery that has long stumped astronomers.

Since the mid-90s, scientists have been trying to locate half of the universe's ordinary matter. They believed it was out there because of clues left over from the Big Bang, but it had never been seen.

"What we're talking about here is what scientists call baryonic matter, which is the normal stuff that you and I are made of," said Associate Professor Jean-Pierre Macquart, from the Curtin University node of the International Centre for Radio Astronomy Research.

Astronomy is full of missing stuff. Most of the universe is understood to be "dark matter" and "dark energy", which nobody has ever directly seen. But even more of a mystery for astronomers was that they couldn't find about half the ordinary matter in the universe.

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Do you understand enough about the Big Bang theory to challenge it? GETTY

Jamie Carter,  May 14, 2020

In cosmology, the Big Bang theory is king. It wasn’t always that way, but over the years the evidence has mounted and, for the most part, astronomers are convinced it’s the best we have.

So why do many people hate it? Black holes, invisible dark matter and the idea of the cosmos being born in a millisecond defy plain common sense.

Frustrated by people telling them how to do their job, two astronomers set-out to answer the questions and criticism they are so frequently sent. The result is The Cosmic Revolutionary’s Handbook (Or: How to Beat the Big Bang), which sets out exactly what any Big Bang theory-hater needs to explain before a new theory can even begin to take hold.

“As cosmologists, our job is to explain the Universe as a whole—it’s structure, constituents and evolution,” said Dr Luke A. Barnes is a postdoctoral researcher at Western Sydney University. “People email us with their ideas about how the Universe works, and while we love their enthusiasm, we found ourselves sending the same kind of reply over and over again.”

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Galaxy cluster glows with x-rays from hot gas (shown here in purple). Surveys of such clusters across the sky are revealing what may be curious anomalies in cosmic structure. Credit: ESA and XMM-Newton (x-rays); CFHTLS (optical); XXL Survey

Lee Billings on April 15, 2020

A new study of galaxy clusters suggests the cosmos may not be the same in all directions

If your life sometimes seems directionless, you might legitimately blame the universe.

According to the key tenets of modern physics, the cosmos is “isotropic” at multi-billion-light-year scales—meaning it should have the same look and behavior in every direction. Ever since the big bang nearly 14 billion years ago, the universe ought to have expanded identically everywhere. And that expectation matches what astronomers see when they observe the smooth uniformity of the big bang’s all-sky afterglow: the cosmic microwave background (CMB). Now, however, an x-ray survey of distances to galaxy clusters across the heavens suggests some are significantly closer or farther away than isotropy would predict. This finding could be a sign that the universe is actually “anisotropic”—expanding faster in some regions than it does in others. With apologies to anyone seeking a cosmic excuse for personal woes, maybe the universe is not so directionless after all.

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A map showing the rate of the expansion of the Universe in different directions across the sky based on data from ESA's XMM-Newton, NASA's Chandra and the German-led ROSAT X-ray observatories.

08/04/2020

Astronomers have assumed for decades that the Universe is expanding at the same rate in all directions. A new study based on data from ESA’s XMM-Newton, NASA’s Chandra and the German-led ROSAT X-ray observatories suggests this key premise of cosmology might be wrong.

Konstantinos Migkas, a PhD researcher in astronomy and astrophysics at the University of Bonn, Germany, and his supervisor Thomas Reiprich originally set out to verify a new method that would enable astronomers to test the so-called isotropy hypothesis. According to this assumption, the Universe has, despite some local differences, the same properties in each direction on the large scale.

Widely accepted as a consequence of well-established fundamental physics, the hypothesis has been supported by observations of the cosmic microwave background (CMB). A direct remnant of the Big Bang, the CMB reflects the state of the Universe as it was in its infancy, at only 380 000 years of age. The CMB’s uniform distribution in the sky suggests that in those early days the Universe must have been expanding rapidly and at the same rate in all directions.

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TheOskarKleinCentre

On December 13th, 2019, James Peebles, Nobel Prize in Physics 2019, visited the Oskar Klein Centre and the Department of Physics at Stockholm university to give an informal talk.

Youtube Link

"My thesis advisor and professor of continuing education, Bob Dicke, suggested I look into cosmology. That was 1964. I was uneasy because the empirical basis seemed so slight, but I could think of a few things to analyze after which I imagined I would return to something more substantial. But one thought led to another and then another through my career as the theory and practice of cosmology grew. I will offer thoughts about my experience and the broader lessons to drawn from the establishment of this considerable extension of the reach of natural science. The lessons can be drawn from other branches of science, but I think they are particularly clear in cosmology because this is a conceptually simple subject involving relatively few people up to its transition to Big Science."

Rather than being a beginning, the Big Bang could have been a moment of transition from one period of space and time to another – more of a bounce (Credit: Alamy)

By Patchen Barss 20th January 2020 - BBC Future

The Big Bang is widely accepted as being the beginning of everything we see around us, but other theories that are gathering support among scientists are suggesting otherwise.

The usual story of the Universe has a beginning, middle, and an end.

It began with the Big Bang 13.8 billion years ago when the Universe was tiny, hot, and dense. In less than a billionth of a billionth of a second, that pinpoint of a universe expanded to more than a billion, billion times its original size through a process called “cosmological inflation”.

Next came “the graceful exit”, when inflation stopped. The universe carried on expanding and cooling, but at a fraction of the initial rate. For the next 380,000 years, the Universe was so dense that not even light could move through it – the cosmos was an opaque, superhot plasma of scattered particles. When things finally cooled enough for the first hydrogen atoms to form, the Universe swiftly became transparent. Radiation burst out in every direction, and the Universe was on its way to becoming the lumpy entity we see today, with vast swaths of empty space punctuated by clumps of particles, dust, stars, black holes, galaxies, radiation, and other forms of matter and energy.

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This new and incredibly deep image from Hubble shows the dim and diffuse galaxy NGC 1052-DF4. New research presents the strongest evidence yet that this strange galaxy is basically devoid of dark matter.  NASA/ESA/STScI/S. Danieli et al.

The new research may have dramatic implications for galaxy formation.
By Jake Parks | Published: Friday, October 18, 2019

Astronomers have all but confirmed the universe has at least one galaxy that's woefully deficient in dark matter. The new finding not only indicates that galaxies really can exist without dark matter, but also raises fundamental questions about how such oddball galaxies form in the first place.

The research, posted October 16 on the preprint site arXiv, used Hubble's keen eye to take new, deep images of the ghostly galaxy NGC 1052-DF4 (or DF4 for short). Equipped with fresh observations, the researchers identified the bizarre galaxy's brightest red giant stars (called the Tip of the Red Giant Branch, or TRGB). Because TRGB stars all shine with the same true brightness when viewed in infrared, the only thing that should affect how bright they appear is their distance.

So, by identifying the galaxy's TRGB and using that to determine DF4's distance, the new data essentially confirms the galaxy is located some 61 million light-years away. And according to the researchers, this essentially debunks other studies that claim DF4 is much closer and therefore contains a normal amount of dark matter.

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Red giant stars—such as those speckling the Messier 79 globular cluster in this Hubble Space Telescope image—are providing new constraints on the expansion rate of the universe. Credit: NASA, ESA, STScI, F. Ferraro University of Bologna and S. Djorgovski California Institute of Technology

Researchers hoped new data would resolve the most contentious question in cosmology. They were wrong
By Leila Sloman on July 29, 2019

How fast is the universe expanding?

One might assume scientists long ago settled this basic question, first explored nearly a century ago by Edwin Hubble. But right now the answer depends on who you ask. Cosmologists using the Planck satellite to study the cosmic microwave background—light from the “early” universe, only about 380,000 years after the big bang—have arrived at a high-precision value of the expansion rate, known as the Hubble constant (H0). Astronomers observing stars and galaxies closer to home—in the “late” universe—have also measured H0 with extreme precision. The two numbers, however, disagree. According to Planck, H0 should be about 67—shorthand for the universe expanding some 67 kilometers per second faster every 3.26 million light-years. The most influential measurements of the late universe, coming from a project called Supernova H0 for the Equation of State (SH0ES), peg the Hubble constant at about 74.

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                      Mike Zeng for Quanta Magazine

Natalie Wolchover - June 6, 2019

A recent challenge to Stephen Hawking’s biggest idea — about how the universe might have come from nothing — has cosmologists choosing sides.

In 1981, many of the world’s leading cosmologists gathered at the Pontifical Academy of Sciences, a vestige of the coupled lineages of science and theology located in an elegant villa in the gardens of the Vatican. Stephen Hawking chose the august setting to present what he would later regard as his most important idea: a proposal about how the universe could have arisen from nothing.

Before Hawking’s talk, all cosmological origin stories, scientific or theological, had invited the rejoinder, “What happened before that?” The Big Bang theory, for instance — pioneered 50 years before Hawking’s lecture by the Belgian physicist and Catholic priest Georges Lemaître, who later served as president of the Vatican’s academy of sciences — rewinds the expansion of the universe back to a hot, dense bundle of energy. But where did the initial energy come from?

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The expanding Universe, full of galaxies and the complex structure we observe today, arose from a smaller, hotter, denser, more uniform state. It took thousands of scientists working for hundreds of years for us to arrive at this picture, and yet the lack of a consensus on what the expansion rate actually is tells us that either something is dreadfully wrong, we have an unidentified error somewhere, or there’s a new scientific revolution just on the horizon. (C. FAUCHER-GIGUÈRE, A. LIDZ, AND L. HERNQUIST, SCIENCE 319, 5859 (47))

How fast is the Universe expanding? The results might be pointing to something incredible.

Ethan Siegel  May 10, 2019

If you want to know how something in the Universe works, all you need to do is figure out how some measurable quantity will give you the necessary information, go out and measure it, and draw your conclusions. Sure, there will be biases and errors, along with other confounding factors, and they might lead you astray if you’re not careful. The antidote for that? Make as many independent measurements as you can, using as many different techniques as you can, to determine those natural properties as robustly as possible.
If you’re doing everything right, every one of your methods will converge on the same answer, and there will be no ambiguity. If one measurement or technique is off, the others will point you in the right direction. But when we try to apply this technique to the expanding Universe, a puzzle arises: we get one of two answers, and they’re not compatible with each other. It’s cosmology’s biggest conundrum, and it might be just the clue we need to unlock the biggest mysteries about our existence.

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Credit: (agsandrew/iStock)

MIKE MCRAE 31 MAR 2019

Today our middle-aged Universe looks eerily smooth. Too smooth, in fact.

While a rapid growth spurt in space-time would explain what we see, science needs more than nice ideas. It needs evidence that whittles away contending arguments. We might finally know where to look for some.

A team of physicists from the Centre for Astrophysics | Harvard & Smithsonian (CfA) and Harvard University went back to the drawing board on the early Universe's evolution to give us a way to help those inflation models stand out from the crowd.

"The current situation for inflation is that it's such a flexible idea, it cannot be falsified experimentally," says theoretical physicist Avi Loeb from the CfA.

"No matter what value people measure for some observable attribute, there are always some models of inflation that can explain it."

We've been convinced for some time that our Universe is expanding – its fabric slowly stretching out under the influence of some kind of strange 'dark' energy.

If we press rewind on the Universe until it was barely 10^-43 seconds old, we arrive at the limit of what our knowledge of physics can handle. Before that moment? Geometry is so nuts, we just don't know where to start.

Running the calculations backward, we also find the Universe would have had a radius of 10^-10 metres at this crucial moment. That sounds tiny, sure, but it's not tiny enough.

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Credit: Kavli IPMU

MICHELLE STARR 4 APR 2019

We still don't know what dark matter is, but we can strike a line through one option. It is not, as per a theory proposed by the brilliant Stephen Hawking, a bunch of teeny-tiny microscopic black holes.

In the most rigorous test of the theory to date, an international team led by researchers from the Kavli Institute for the Physics and Mathematics of the Universe (IPMU) in Japan has searched for the telltale sign of such minuscule black holes, and the result was pretty damning.

The scientists were hunting for a particular flicker of stars in a nearby galaxy - the way the light would appear to us if a black hole less than a tenth of a millimetre were passing in front of it.

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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.

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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.

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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.

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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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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 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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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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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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Recent observations of a neutron star merger 130 million light years away found that gravitational waves and light from the event arrived at Earth within 2 s of one another. This indicates that the two fundamentally different types of wave travel at the same speed to within 1 part in 1015
. The finding constrains several theories that explain the accelerated expansion of the Universe using a modified version of general relativity in which gravity couples to a time-dependent scalar field, 𝜑(t)
. In such theories, the value of the scalar field needed to explain acceleration would lead to gravitational waves (orange) that travel at significantly different speeds from that of light (light blue) [2–5]. Show less

Fabian Schmidt, Max Planck Institute for Astrophysics, Karl-Schwarzschild-Straße 1, Garching, 85748, Germany

December 18, 2017• Physics 10, 134

Theorists have tightly constrained alternative theories of gravity using the recent joint detection of gravitational waves and light from a neutron star merger.

Our current theory of gravity, general relativity (GR), has been spectacularly successful. It accurately describes the dynamics of astronomical objects over a vast range of sizes from planets and stars, to black holes, all the way to galaxies. GR also predicts the expansion of the Universe as a whole.

But the theory has fallen short in one respect: explaining the finding that the Universe is expanding at an accelerating rate. According to GR, the sum of all known radiation, visible matter, and dark matter should exert an inward “tug” on the Universe, slowing down its rate of expansion over time. So to account for acceleration, physicists have been forced to consider three possibilities [1], all of which are often loosely referred to as “dark energy.” The first option—and also the simplest and most favored—is the existence of a cosmological constant, or vacuum energy, which counteracts gravity by exerting a constant negative effective pressure. The second imagines that the cosmological constant is actually dynamical. Finally, the third possibility is that gravity behaves differently on large distance scales, requiring a modification of GR. Using the recent detection of a gravitational wave and light from a distant binary neutron merger, four research groups have now placed some of the tightest constraints to date on this third scenario [2–5].

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Until recently, simulations of the universe haven’t given its lumps their due

BY EMILY CONOVER 3:30PM, NOVEMBER 14, 2017

Magazine issue: Vol. 192 No. 9, November 25, 2017, p. 22

If the universe were a soup, it would be more of a chunky minestrone than a silky-smooth tomato bisque.

Sprinkled with matter that clumps together due to the insatiable pull of gravity, the universe is a network of dense galaxy clusters and filaments — the hearty beans and vegetables of the cosmic stew. Meanwhile, relatively desolate pockets of the cosmos, known as voids, make up a thin, watery broth in between.

Until recently, simulations of the cosmos’s history haven’t given the lumps their due. The physics of those lumps is described by general relativity, Albert Einstein’s theory of gravity. But that theory’s equations are devilishly complicated to solve. To simulate how the universe’s clumps grow and change, scientists have fallen back on approximations, such as the simpler but less accurate theory of gravity devised by Isaac Newton.

Relying on such approximations, some physicists suggest, could be mucking with measurements, resulting in a not-quite-right inventory of the cosmos’s contents. A rogue band of physicists suggests that a proper accounting of the universe’s clumps could explain one of the deepest mysteries in physics: Why is the universe expanding at an increasingly rapid rate?

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Natalie Wolchoverm --  October 25, 2017 

Newly discovered “standard sirens” provide an independent, clean way to measure how fast the universe is expanding.

To many cosmologists, the best thing about neutron-star mergers is that these events scream into space an otherwise close-kept secret of the universe. Scientists combined the gravitational and electromagnetic signals from the recently detected collision of two of these stars to determine, in a cleaner way than with other approaches, how fast the fabric of the universe is expanding — a much-contested number called the Hubble constant.

In the days since the neutron-star collision was announced, Hubble experts have been surprised to find themselves discussing not whether events like it could settle the controversy, but how soon they might do so.

Scientists have hotly debated the cosmic expansion rate ever since 1929, when the American astronomer Edwin Hubble first established that the universe is expanding - and that it therefore had a beginning. How fast it expands reflects what’s in it (since matter, dark energy and radiation push and pull in different ways) and how old it is, making the value of the Hubble constant crucial for understanding the rest of cosmology.

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NSF/Steffen Richter/Harvard Univ./SPL : Telescopes in Antarctica track the cosmic microwave background radiation left over from the Big Bang.

Multi-telescope project has ambitious goals and a big price tag.

Edwin Cartlidge - 30 October 2017

US researchers have drafted plans to study the faint afterglow of the Big Bang using a new facility. They hope it will be sensitive enough to confirm whether or not the infant Universe underwent a brief period of explosive expansion known as inflation.

The Cosmic Microwave Background Stage-4 experiment (CMB-S4) would comprise three 6-metre and 14 half-metre telescopes distributed across two sites in Antarctica and Chile, according to a preliminary design due to be made public this week. Potentially up and running within a decade, the facility would be nearly 100 times as sensitive as existing ground-based CMB experiments.

It won’t be cheap, however. Construction will cost a little over US$400 million, according to the expert task force commissioned by the US Department of Energy (DOE) and National Science Foundation (NSF) to produce the design. That is at least twice as much as envisioned in a less-detailed review 3 years ago, and 30 times the cost of existing experiments.

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BANG, FLASH Light waves and gravitational waves from a pair of colliding neutron stars reached Earth at almost the same time, ruling out theories about the universe based on predictions that the two kinds of waves might travel at different speeds

Speed of spacetime ripples rules out some alternatives to dark energy
BY LISA GROSSMAN 5:34PM, OCTOBER 24, 2017

Ripples in spacetime travel at the speed of light. That fact, confirmed by the recent detection of a pair of colliding stellar corpses, kills a whole category of theories that mess with the laws of gravity to explain why the universe is expanding as fast as it is.

On October 16, physicists announced that the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, had detected gravitational waves from a neutron star merger (SN Online: 10/16/17). Also, the neutron stars emitted high-energy light shortly after merging. The Fermi space telescope spotted that light coming from the same region of the sky 1.7 seconds after the gravitational wave detection. That observation showed for the first time that gravitational waves, the shivers in spacetime set off when massive bodies move, travel at the speed of light to within a tenth of a trillionth of a percent.

Within a day, five papers were posted at arXiv.org mourning hundreds of expanding universe theories that predicted gravitational waves should travel faster than light — an impossibility without changes to Einstein’s laws of gravity. These theories “are very, very dead,” says the coauthor of one of the papers, cosmologist Miguel Zumalacárregui of the Nordic Institute for Theoretical Physics, or NORDITA, in Stockholm. “We need to go back to our blackboards and start thinking of other alternatives.”

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A cloud of debris ejected into space as two neutron stars merge. (Credit: NASA Goddard Space Flight Center/CI Lab)

By Nathaniel Scharping | October 16, 2017

The first gravitational wave observed from a neutron star merger offers the potential for a whole raft of new discoveries. Among them is a more precise measurement of the Hubble constant, which captures how fast our universe is expanding.

Ever since the Big Bang, everything in the universe has been spreading apart. It also turns out that this is happening faster and faster — the rate of expansion is increasing.

We’ve known this for a century, but astronomers haven’t been able to get precise measurements of the increase in rate, due mostly to the fact that they’ve had to cobble together a range of data to estimate how far away things in the universe are. Gravitational wave observations offer a direct means of measuring distances in the universe. The LIGO collaboration is constantly monitoring the universe for the subtle stretching of space-time that huge astronomical collisions can create, and measurements of the amplitude and frequency of the waves it catches hold valuable information for astronomers.

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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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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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By Don Lincoln
Updated 1504 GMT (2304 HKT) May 14, 2017

(CNN)A recent astronomical observation of a "cold spot" in the universe is stirring the interest of scientists who are intrigued with an exciting and highly speculative theory that there may be more than one universe.

Now before you get incredibly excited about that prospect, I should caution that this particular explanation is a huge long shot and there are more prosaic possible explanations. The idea of multiple universes, or multiverses, is a highly speculative and contentious one, and many experts view it with a very jaundiced eye. (This includes me.)

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Ethan Siegel, Contributor

MAY 11, 2017

All scientific ideas, no matter how accepted or widespread they are, are susceptible to being overturned. For all the successes any idea may have, it only takes one experiment or observation to falsify it, invalidate it, or necessitate that it be revised. Beyond that, every scientific idea or model has a limitation to its range of validity: Newtonian mechanics breaks down close to the speed of light; General Relativity breaks down at singularities; evolution breaks down when you reach the origin of life. Even the Big Bang has its limitations, as there's only so far back we can extrapolate the hot, dense, expanding state that gave rise to what we see today. Since 1980, the leading idea for describing what came before it has been cosmic inflation, for many compelling reasons. But recently, a spate of public statements has shown a deeper controversy:

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Professor Andrei Linde is among the physicists responding to a recent media story taking aim at inflationary theory. Credit: L.A. Cicero

May 11, 2017 by Amy Adams

From the earliest human civilizations, people have looked to the heavens and pondered the origins of the stars and constellations above. Once, those stories involved gods and magical beings. Now, there's science, and a large research enterprise focused on understanding how the universe came to be.

Squarely in the center of this research enterprise is what's known as inflationary theory. It argues that the universe was born out of an unstable, energetic vacuum-like state then expanded dramatically, spinning off entire galaxies produced by quantum fluctuations. This theory was proposed in 1980 by Alan Guth, presently at MIT. A year later, this theory was improved and extended by Andrei Linde, Stanford professor of physics, who has spent a lifetime modifying and updating it as new data emerged.

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Figure 1: Both the LUX and PandaX-II experiments look for dark matter particles (𝜒) by sensing their interaction with xenon atoms. The detector in each experiment consists of a large tank of ultrapure liquid xenon (dark purple) topped with xenon gas (light purple). An interaction produces two light signals, one from photons, S1, and another, S2, from electrons when they drift into the gas. The signals are detected by photomultiplier tubes at the top and bottom of the tank (yellow cylinders). 

Jodi A. Cooley, Department of Physics, Southern Methodist University, 3215 Daniel Ave., Dallas, TX 75205, USA

January 11, 2017• Physics 10, 3

No dark matter particles have been observed by two of the world’s most sensitive direct-detection experiments, casting doubt on a favored dark matter model.

Over 80 years ago astronomers and astrophysicists began to inventory the amount of matter in the Universe. In doing so, they stumbled into an incredible discovery: the motion of stars within galaxies, and of galaxies within galaxy clusters, could not be explained by the gravitational tug of visible matter alone [1]. So to rectify the situation, they suggested the presence of a large amount of invisible, or “dark,” matter. We now know that dark matter makes up 84% of the matter in the Universe [2], but its composition—the type of particle or particles it’s made from—remains a mystery. Researchers have pursued a myriad of theoretical candidates, but none of these “suspects” have been apprehended. The lack of detection has helped better define the parameters, such as masses and interaction strengths, that could characterize the particles. For the most compelling dark matter candidate, WIMPs, the viable parameter space has recently become smaller with the announcement in September 2016 by the PandaX-II Collaboration [3] and now by the Large Underground Xenon (LUX) Collaboration [4] that a search for the particles has come up empty.

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New research confirms the role Type Ia supernovae, like G299, play in measuring universe expansion. Credit: NASA

New research by cosmologists at the University of Chicago and Wayne State University confirms the accuracy of Type Ia supernovae in measuring the pace at which the universe expands. The findings support a widely held theory that the expansion of the universe is accelerating and such acceleration is attributable to a mysterious force known as dark energy. The findings counter recent headlines that Type Ia supernova cannot be relied upon to measure the expansion of the universe.

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December 7, 2016

This map of dark matter in the Universe was obtained from data from the KiDS survey, using the VLT Survey Telescope at ESO’s Paranal Observatory in Chile. It reveals an expansive web of dense (light) and empty (dark) regions. This image is one out of five patches of the sky observed by KiDS. Here the invisible dark matter is seen rendered in pink, covering an area of sky around 420 times the size of the full moon. This image reconstruction was made by analysing the light collected from over three million distant galaxies more than 6 billion light-years away. The observed galaxy images were warped by the gravitational pull of dark matter as the light travelled through the Universe. Some small dark regions, with sharp boundaries, appear in this image. They are the locations of bright stars and other nearby objects that get in the way of the observations of more distant galaxies and are hence masked out in these maps as no weak-lensing signal can be measured in these areas. Credit: Kilo-Degree Survey Collaboration/H. Hildebrandt & B. Giblin/ESO

Analysis of a giant new galaxy survey, made with ESO's VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team used data from the Kilo Degree Survey (KiDS) to study how the light from about 15 million distant galaxies was affected by the gravitational influence of matter on the largest scales in the Universe. The results appear to be in disagreement with earlier results from the Planck satellite.

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The newborn universe may have glowed with light beams moving much faster than they do today, according to a theory that overturns Einstein’s century-old claim that the speed of light is a constant.

João Magueijo, of Imperial College London, and Niayesh Afshordi, of the University of Waterloo in Canada, propose that light tore along at infinite speed at the birth of the universe when the temperature of the cosmos was a staggering ten thousand trillion trillion celsius.

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A new theory of gravity might explain the curious motions of stars in galaxies. Emergent gravity, as the new theory is called, predicts the exact same deviation of motions that is usually explained by invoking dark matter. Prof. Erik Verlinde, renowned expert in string theory at the University of Amsterdam and the Delta Institute for Theoretical Physics, published a new research paper today in which he expands his groundbreaking views on the nature of gravity.

In 2010, Erik Verlinde surprised the world with a completely new theory of gravity. According to Verlinde, gravity is not a fundamental force of nature, but an emergent phenomenon. In the same way that temperature arises from the movement of microscopic particles, gravity emerges from the changes of fundamental bits of information, stored in the very structure of spacetime.

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Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

The observable Universe contains about two trillion galaxies—more than ten times as many as previously estimated, according to the first significant revision of the count in two decades.

Since the mid-1990s, the working estimate for the number of galaxies in the Universe has been around 120 billion. That number was based largely on a 1996 study called Hubble Deep Field. Researchers pointed the Hubble Space Telescope at a small region of space for a total of ten days so that the long exposures would reveal extremely faint objects.

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The nonprofit Simons Foundation will fund a new observatory to search for signs of stretching in the very early universe
By Clara Moskowitz on May 12, 2016

How did it all begin? The origin of the cosmos is probably the biggest mystery in science—but amazingly, researchers do have some hard evidence to consult in their attempts to solve it. The cosmic microwave background (CMB), a microwave fog that pervades space, is the oldest light in existence—it was released about 13.7 billion years ago when the extremely hot and dense baby universe cooled enough to allow photons to travel freely for the first time. That was about 380,000 years after the big bang, and the light has been flying through space ever since. Although the light itself is already unimaginably ancient, it may preserve a record of things that happened even earlier—specifically, it might contain imprints from gravitational waves that may have ripped through the cosmos in the very first moments of space and time.

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X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/JPL-Caltech
Data from galaxies such as M101, seen here, allow scientists to gauge the speed at which the universe is expanding.

Davide Castelvecchi
11 April 2016

The most precise measurement ever made of the current rate of expansion of the Universe has produced a value that appears incompatible with measurements of radiation left over from the Big Bang1. If the findings are confirmed by independent techniques, the laws of cosmology might have to be rewritten.

This might even mean that dark energy — the unknown force that is thought to be responsible for the observed acceleration of the expansion of the Universe — has increased in strength since the dawn of time.

“I think that there is something in the standard cosmological model that we don't understand,” says astrophysicist Adam Riess, a physicist at Johns Hopkins University in Baltimore, Maryland, who co-discovered dark energy in 1998 and led the latest study.

Kevork Abazajian, a cosmologist at the University of California, Irvine, who was not involved in the study, says that the results have the potential of “becoming transformational in cosmology”.

Uncertainty limits
In the accepted model of cosmology, the Universe evolves mostly through the competing action of dark matter and dark energy. Dark matter’s gravity tends to slow cosmic expansion, while dark energy pushes in the opposite direction and makes it accelerate. Earlier observations made by Riess and others suggest that dark energy’s strength has been constant throughout the history of the Universe.

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