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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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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