#rennan barkana

[the-garbanzo-annex-jr]

by Abigail Klein Leichman

Radio waves emitted from the hydrogen gas that filled the universe millions of years ago may contain clues about the cosmic “dark ages” before the formation of the first stars.

This study was led by Prof. Rennan Barkana’s research group, including the postdoctoral fellow Rajesh Mondal. Their novel conclusions have been published in Nature Astronomy.

The researchers explain that while every car has an antenna that detects radio waves, the specific waves from the early universe are blocked by the Earth’s atmosphere. They can only be studied from space, particularly the moon, which offers a stable environment, free of any interference from an atmosphere or from radio communications.

They say that putting a telescope on the moon isn’t an impossible dream, given that the United States, Europe, China and India are engaged in an international space race to return to the moon with space probes and, eventually, astronauts. Their research may intrigue one of these countries to try detecting radio waves from the cosmic dark ages.

Barkana explained: “NASA’s new James Webb space telescope discovered recently distant galaxies whose light we receive from the cosmic dawn, around 300 million years after the Big Bang. Our new research studies an even earlier and more mysterious era: the cosmic dark ages, only 50 million years after the Big Bang.”

Barkana said that conditions in the early universe were quite different from today and that using radio observations to determine the density and temperature of hydrogen gas at various times can reveal what is still to be discovered.

Furthermore, a radio telescope consisting of an array of antennas could accurately determine the amount of hydrogen and of helium in the universe. Hydrogen is the original form of ordinary matter in the universe, from which stars, planets, and eventually life began.

[jcmarchi]

History of universe can be determined using radio telescopes on the moon - Technology Org

New Post has been published on https://thedigitalinsider.com/history-of-universe-can-be-determined-using-radio-telescopes-on-the-moon-technology-org/

History of universe can be determined using radio telescopes on the moon - Technology Org

A new study from Tel Aviv University (TAU) has predicted for the first time the groundbreaking results that can be obtained from a lunar-based detection of radio waves. The study’s findings show that the radio signals can be used for a novel test of the standard cosmological model and to determine the composition of the universe as well as the weight of neutrino particles. They might also help scientists gain another clue to the mystery of dark matter.

Nebula and galaxies in space. Abstract cosmos background. Image credit: NASA

This study was led by Professor Rennan Barkana’s research group and his postdoctoral fellow Dr. Rajesh Mondal. Their novel conclusions were published in the journal Nature Astronomy.

The researchers say that the cosmic “dark ages” — the period just before the formation of the first stars — can be studied by detecting radio waves that were emitted from the hydrogen gas that filled the universe at that time. The Earth’s atmosphere blocks specific radio waves from the early universe. They can only be studied from space, particularly the moon, which offers a stable environment, free of any interference from an atmosphere or from radio communications. Space agencies in the US, Europe, China, and India are searching for worthy scientific goals for lunar development, and the new research highlights the prospects for detecting radio waves from the cosmic dark ages.

“NASA’s new James Webb space telescope discovered recently distant galaxies whose light we receive from the cosmic dawn, around 300 million years after the Big Bang, Professor Barkana explains. “Our new research studies an even earlier and more mysterious era: the cosmic dark ages, only 50 million years after the Big Bang.

“Conditions in the early Universe were quite different from today. The new study combines current knowledge of cosmic history with various options for radio observations, in order to reveal what can be discovered. Specifically, we computed the intensity of radio waves as determined by the density and temperature of the hydrogen gas at various times, and then showed how the signals can be analyzed in order to extract from them the desired results.”

The researchers believe that the findings may be very significant for the scientific understanding of our cosmic history, so that with a single lunar antenna, the standard model of cosmology can be tested to see if it can explain the cosmic dark ages or if instead there was, for example, an unexpected disturbance in the expansion of the universe that would point towards a new discovery. Furthermore, with a radio telescope consisting of an array of radio antennas, the composition of the universe (specifically, the amount of hydrogen and of helium within it) can be accurately determined. Hydrogen is the original form of ordinary matter in the Universe, from which formed the stars, planets, and eventually we ourselves.

A precise determination of the amount of helium is also of great importance. It would probe the ancient period, around a minute after the Big Bang, in which helium formed when the entire universe was essentially a giant nuclear reactor.

With an even larger array of lunar antennas, it will also be possible to measure the weight of cosmic neutrinos. These are tiny particles that are emitted in various nuclear reactions; their weight is a critical unknown parameter in developing physics beyond the established standard model of particle physics.

“When scientists open a new observational window, surprising discoveries usually result,” Professor Barkana concludes. “With lunar observations, it may be possible to discover various properties of dark matter, the mysterious substance that we know constitutes most of the matter in the universe, yet we do not know much about its nature and properties. Clearly, the cosmic dark ages are destined to shed new light on the universe.”

Source: AFTAU

You can offer your link to a page which is relevant to the topic of this post.

[spacenutspod]

In the coming decade, multiple space agencies and commercial space providers are determined to return astronauts to the Moon and build the necessary infrastructure for long-duration stays there. This includes the Lunar Gateway and the Artemis Base Camp, a collaborative effort led by NASA with support from the ESA, CSA, and JAXA, and the Russo-Chinese International Lunar Research Station (ILRS). In addition, several agencies are exploring the possibility of building a radio observatory on the far side of the Moon, where it could operate entirely free of radio interference. For years, researchers have advocated for such an observatory because of the research that such an observatory would enable. This includes the ability to study the Universe during the early “Cosmic Dark Ages,” even before the first stars and galaxies formed (about 50 million years after the Big Bang). While there have been many predictions about what kind of science a lunar-based radio observatory could perform, a new research study from Tel Aviv University has predicted (for the first time) what groundbreaking results this observatory could actually obtain. This study was led by Prof. Rennan Barkana and Dr. Rajesh Mondal, an astrophysics professor and a postdoctoral researcher (respectively) with the School of Physics and Astronomy at Tel Aviv University. The paper that describes their conclusions, “Prospects for precision cosmology with the 21 cm signal from the dark ages,” has been published in Nature Astronomy. As they argue, the study’s findings show that the measured radio signals can be used to test the Standard Model of Cosmology and determine the composition of the Universe. Artist’s impression of a radio telescope on the far side of the Moon. Credit: Made with DALLE The Cosmic Dark Ages, which occurred roughly 130,000 to 1 billion years after the Big Bang, has traditionally remained elusive to astronomers (hence the name). Essentially, light from this cosmological period is redshifted to the point where it is only visible in the radio spectrum. What’s more, the only sources of photons from this period are the remnant radiation from the Big Bang – which is visible today as the Cosmic Microwave Background (CMB) – or are visible as the 21 cm line (or hydrogen line) caused by the reionization of neutral hydrogen. These radio waves can only be studied from space, where they are free of atmospheric interference and other radio sources. On the far side of the Moon, a radio observatory would also be safe from radio interference caused by our Sun. Establishing an observatory there would still be a major challenge. As Prof. Barkana explained in a recent Tel Aviv University statement: “NASA’s new James Webb space telescope discovered recently distant galaxies whose light we receive from the cosmic dawn, around 300 million years after the Big Bang. Our new research studies an even earlier and more mysterious era: the cosmic dark ages, only 50 million years after the Big Bang. Conditions in the early Universe were quite different from today. “The new study combines current knowledge of cosmic history with various options for radio observations, in order to reveal what can be discovered. Specifically, we computed the intensity of radio waves as determined by the density and temperature of the hydrogen gas at various times, and then showed how the signals can be analyzed in order to extract from them the desired results.” Expansion of the Universe (Credit: NASA/WMAP Science Team) For astronomers hoping to push the boundaries of cosmology, the Cosmic Dark Ages offer an opportunity to study the first stars and galaxies in the Universe. For their study, Barkana and Mondal argue that a lunar radio observatory could measure radio signals to determine the composition of the early Universe, the expansion rate of the cosmos (thereby testing the theory of Dark Energy), and perhaps gain insight into the mystery of Dark Matter. These are all integral to the Standard Model of Cosmology, known as the Lambda-Cold Dark Matter (LCDM) model. They also found that with an array consisting of multiple radio antennas, scientists could accurately measure the amount of hydrogen and helium shortly after the Big Bang. A precise determination of both would reveal valuable information on how ordinary matter formed from hydrogen, which fueled the creation of the first stars, gradually giving rise to heavier elements, planets, and eventually life. Last, they found that with an even larger array of lunar antennas, it will also be possible to measure the weight of cosmic neutrinos – a critical parameter in developing physics beyond the Standard Model of Particle Physics. As Prof. Barkana concluded: “When scientists open a new observational window, surprising discoveries usually result. With lunar observations, it may be possible to discover various properties of dark matter, the mysterious substance that we know constitutes most of the matter in the Universe, yet we do not know much about its nature and properties. Clearly, the cosmic dark ages are destined to shed new light on the Universe.” Further Reading: EurekAlert, Nature The post A Radio Telescope on the Moon Could Help Us Understand the First 50 Million Years of the Universe appeared first on Universe Today.

[s-c-i-guy]

Within 180 million years of the Big Bang, stars were born

After 12 years of experimental effort, a team of scientists, led by Arizona State University astronomer Judd Bowman, has detected the fingerprints of the earliest stars in the universe. Using radio signals, the detection provides the first evidence for the oldest ancestors in our cosmic family tree, born by a mere 180 million years after the universe began

Long ago, about 400,000 years after the beginning of the universe, the universe was dark. There were no stars or galaxies, and the universe was filled primarily with neutral hydrogen gas.

Then, for the next 50-100 million years, gravity slowly pulled the densest regions of gas together until ultimately the gas collapsed in some places to form the first stars.

What were those first stars like and when did they form? How did they affect the rest of the universe? These are questions astronomers and astrophysicists have long pondered.

Now, after 12 years of experimental effort, a team of scientists, led by ASU School of Earth and Space Exploration astronomer Judd Bowman, has detected the fingerprints of the earliest stars in the universe. Using radio signals, the detection provides the first evidence for the oldest ancestors in our cosmic family tree, born by a mere 180 million years after the universe began.

"There was a great technical challenge to making this detection, as sources of noise can be a thousand times brighter than the signal -- it's like being in the middle of a hurricane and trying to hear the flap of a hummingbird's wing." says Peter Kurczynski, the National Science Foundation program officer who supported this study. "These researchers with a small radio antenna in the desert have seen farther than the most powerful space telescopes, opening a new window on the early universe."

Radio Astronomy

To find these fingerprints, Bowman's team used a ground-based instrument called a radio spectrometer, located at the Australia's national science agency (CSIRO) Murchison Radio-astronomy Observatory (MRO) in Western Australia. Through their Experiment to Detect the Global EoR Signature (EDGES), the team measured the average radio spectrum of all the astronomical signals received across most of the southern-hemisphere sky and looked for small changes in power as a function of wavelength (or frequency).

As radio waves enter the ground-based antenna, they are amplified by a receiver, and then digitized and recorded by computer, similar to how FM radio receivers and TV receivers work. The difference is that the instrument is very precisely calibrated and designed to perform as uniformly as possible across many radio wavelengths.

The signals detected by the radio spectrometer in this study came from primordial hydrogen gas that filled the young universe and existed between all the stars and galaxies. These signals hold a wealth of information that opens a new window on how early stars -- and later, black holes, and galaxies -- formed and evolved.

"It is unlikely that we'll be able to see any earlier into the history of stars in our lifetimes," says Bowman. "This project shows that a promising new technique can work and has paved the way for decades of new astrophysical discoveries."

This detection highlights the exceptional radio quietness of the MRO, particularly as the feature found by EDGES overlaps the frequency range used by FM radio stations. Australian national legislation limits the use of radio transmitters within 161.5 miles (260 km) of the site, substantially reducing interference which could otherwise drown out sensitive astronomy observations.

The results of this study have been recently published in Natureby Bowman, with co-authors Alan Rogers of the Massachusetts Institute of Technology's Haystack Observatory, Raul Monsalve of the University of Colorado, and Thomas Mozdzen and Nivedita Mahesh also of ASU's School of Earth and Space Exploration.

Unexpected results

The results of this experiment confirm the general theoretical expectations of when the first stars formed and the most basic properties of early stars.

"What's happening in this period," says co-author Rogers of MIT's Haystack Observatory, "is that some of the radiation from the very first stars is starting to allow hydrogen to be seen. It's causing hydrogen to start absorbing the background radiation, so you start seeing it in silhouette, at particular radio frequencies. This is the first real signal that stars are starting to form, and starting to affect the medium around them."

The team originally tuned their instrument to look later in cosmic time, but in 2015 decided to extend their search. "As soon as we switched our system to this lower range, we started seeing things that we felt might be a real signature," Rogers says. "We see this dip most strongly at about 78 megahertz, and that frequency corresponds to roughly 180 million years after the Big Bang," Rogers says. "In terms of a direct detection of a signal from the hydrogen gas itself, this has got to be the earliest."

The study also revealed that gas in the universe was probably much colder than expected (less than half the expected temperature). This suggests that either astrophysicists' theoretical efforts have overlooked something significant or that this may be the first evidence of non-standard physics: Specifically, that baryons (normal matter) may have interacted with dark matter and slowly lost energy to dark matter in the early universe, a concept that was originally proposed by Rennan Barkana of Tel Aviv University.

"If Barkana's idea is confirmed," says Bowman, "then we've learned something new and fundamental about the mysterious dark matter that makes up 85 percent of the matter in the universe, providing the first glimpse of physics beyond the standard model."

The next steps in this line of research are for another instrument to confirm this team's detection and to keep improving the performance of the instruments, so that more can be learned about the properties of early stars. "We worked very hard over the last two years to validate the detection," says Bowman, "but having another group confirm it independently is a critical part of the scientific process."

Bowman would also like to see an acceleration of efforts to bring on new radio telescopes like the Hydrogen Epoch of Reionization Array (HERA) and the Owens Valley Long Wavelength Array (OVRO-LWA).

"Now that we know this signal exists," says Bowman, "we need to rapidly bring online new radio telescopes that will be able to mine the signal much more deeply."

The antennas and portions of the receiver used in this experiment were designed and constructed by Rogers and the MIT Haystack Observatory team. The ASU team and Monsalve added the automated antenna reflection measurement system to the receiver, outfitted the control hut with the electronics, constructed the ground plane and conducted the field work for the project. The current version of EDGES is the result of years of design iteration and ongoing detailed technical refinement of the calibration instrumentation to reach the levels of precision necessary for successfully achieving this difficult measurement.

NSF Video

[fumpkins]

Dark Matter May Have an Electric Charge

. Dark matter, the things that’s assumed to make up about a quarter of deep space yet does not appear to communicate with light at all, might have a small electric charge, inning accordance with a brand-new research study.

. So far, dark matter has actually made its existence understood just through gravity, by yanking on stars and galaxies. But now, astrophysicists Julian Mu ñoz and Abraham Loeb of Harvard University recommend that a little portion of dark matter particles might have a small electric charge– implying it might communicate with regular matter through the electro-magnetic force.

. If real, this concept would not just represent a huge action in comprehending dark matter, however it would likewise discuss a current secret that’s been puzzling cosmologists.

. Curious cooling

. InFebruary, astronomers revealed the very first detection of an evasive signal from hydrogen gas from the cosmic dawn, the duration about 180 million years after the Big Bang when the very first stars started to shine. At this time, the hydrogen gas drifting in between the stars was cold– cooler than the cosmic microwave background, the remaining radiation from the Big Bang that showers deep space. [Big Bang to Civilization: 10 Amazing Origin Events]

. Because hydrogen is cooler than this afterglow, the gas takes in the radiation– in specific, radiation with a wavelength of 21 centimeters. By determining the absorption of radiation by hydrogen, astronomers can much better comprehend the cosmic dawn, a fairly unidentified period of cosmic history. Using a radio antenna in Western Australia called the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), a group of astronomers had the ability to discover this absorption for the very first time.

. “This is in and of itself an amazing scientific discovery,”Mu ñoz informed LiveScience But more than that, he included, the astronomers discovered that two times as numerous photons were soaked up by the hydrogen than anticipated. For the gas to take in a lot radiation, it would need to be even cooler than researchers believed.

. Mu ñoz and Loeb proposed that dark matter may be the offender for the curious cooling. In a paper released May 30 in the journal Nature, they discovered that if less than 1 percent of the dark matter had about one-millionth of the electric charge of an electron, then this evasive matter might pull heat from the hydrogen– much like how ice cool your lemonade. “Ice, here, is the dark matter,” Mu ñoz stated.

. Their concept isn’t really entirely brand-new. Decades back, physicists proposed that dark matter particles might have electric charge.

. And it’s not the only description for this cooling. In a March 1 paper in the journal Nature, Rennan Barkana, a cosmologist at Tel Aviv University in Israel, proposed that a more basic type of dark matter, which does not always have charge, might cool regular matter and discuss the EDGES information.

. Both dark matter propositions make comparable forecasts, stated Barkana, who was not associated with the existing research study.

. “This is a time for cautious optimism and keeping an open mind, about both the radio observation and the interpretation,”Barkana informed Live Science.

. Dozens of concepts

. Dark matter is simply among lots of concepts proposed to discuss the abnormality. For circumstances, rather of the gas being cooler, the background radiation may be hotter than anticipated, with some unique procedure producing more radiation that has yet to be represented. Or, there might just be mistakes in the analysis or measurement.

. Indeed, the EDGES observation is the very first of its kind, and though the group invested 2 years examining and verifying the analysis, scientists will require more information to validate the perplexing outcomes.

. “If EDGES is correct, I don’t think there’s any conventional explanation that’s compelling,” stated Steven Furlanetto, an astrophysicist at the University of California, Los Angeles, who was not associated with the research study. “You really need to go to one of these nonstandard physics scenarios, and in that case, I think it’s wide open.”

. Mu ñoz, nevertheless, prefers the dark matter description. “If EDGES is indeed right, it seems very hard for this not to be the result of dark matter,” he stated.

. Several instruments all over the world are currently getting ready to make more comprehensive observations. Unlike EDGES, some experiments, such as a radio telescope in South Africa called the Hydrogen Epoch of Reionization Array (HERA), will have the ability to determine how the absorption differs throughout the sky. If a little portion of dark matter is electrically charged as Mu ñoz and Loeb state, then it will develop an unique pattern in this variation– supplying a crucial test for electrically charged dark matter.

. Originally released on Live Science.

New post published on: https://livescience.tech/2018/06/03/dark-matter-may-have-an-electric-charge/

[jaguarmen99]

米アリゾナ州立大学（Arizona State University）などの天文学者チームは28日、宇宙がビッグバン（Big Bang）で誕生した直後に生まれた宇宙最古の星々「ファーストスター」に由来する電波を、史上初めて検出したと発表した。この観測結果に科学界は騒然となっている。 　ファーストスターの痕跡検出に向けた取り組みは10年前から続けられてきたが、実際に観測できるのはまだ何年も先になると予想されていた。観測結果は今後、別の実験によって裏づけられる必要があるが、一部からは既に、ノーベル賞を受賞した2015年の重力波検出以降で最大級の天文学的発見だとの声も上がっている。 　今回の発見は、宇宙の大部分を構成すると考えられている謎の透明物質「暗黒物質（ダークマター）」の謎を解明する手がかりとなることも期待されている。 　検出されたのは、今から136億年前、ビッグバンによる宇宙誕生からわずか1億8000万年後にすでに活動を始めていたファーストスターの痕跡で、オーストラリアの砂漠に設置されたダイニングテーブルほどの大きさの電波分光計により観測された。 　この電波には、誰もが驚き、歓喜するような興味深い情報が含まれていた。英科学誌ネイチャー（Nature）に掲載された論文によると、初期宇宙の温度がマイナス270度と、これまで推定されていたより2倍も低温だったとみられることが、観測データから判明したのだ。 　ネイチャー誌に同時掲載された別の関連論文では、ダークマターがこれに関与している可能性が示唆されている。同論文を執筆したイスラエル・テルアビブ大学（Tel Aviv University）のレナン・バルカナ（Rennan Barkana）氏によると、この極度の低温状態は、通常物質がダークマターと相互作用してエネルギーを受け渡したことで説明できる可能性があるという。(c)AFP/Mariëtte Le Roux

宇宙最初の星を初観測 米チーム発表に科学界沸く　写真2枚　国際ニュース：AFPBB News

[livioacerbo]

Whisper From the First Stars Sets Off Loud Dark Matter Debate

Whisper From the First Stars Sets Off Loud Dark Matter Debate

The news about the first stars in the universe always seemed a little off. Last July, Rennan Barkana, a cosmologist at Tel Aviv University, received an email from one of his longtime collaborators, Judd Bowman. Bowman leads a small group of five astronomers who built and deployed a radio telescope in remote western Australia. Its … Continue reading “Whisper From the First Stars Sets Off Loud Dark…

[proviralmedia-blog]

When Stars Were Born: Earliest Starlight’s Effects Are Detected One possibility, suggested by Rennan Barkana of Tel Aviv University in Israel, is that the primordial hydrogen could have gotten chilled by interacting with the dark matter that also permeates the cosmos.

[petloverus-blog]

When Stars Were Born: Earliest Starlight’s Effects Are Detected One possibility, suggested by Rennan Barkana of Tel Aviv University in Israel, is that the primordial hydrogen could have gotten chilled by interacting with the dark matter that also permeates the cosmos.

[spicefacts-blog]

When Stars Were Born: Earliest Starlight’s Effects Are Detected

When Stars Were Born: Earliest Starlight’s Effects Are Detected

[ad_1]

One possibility, suggested by Rennan Barkana of Tel Aviv University in Israel, is that the primordial hydrogen could have gotten chilled by interacting with the dark matter that also permeates the cosmos.

“If true, this would be the first clue about the properties of dark matter, beyond its gravitational pull which is how its presence has been inferred,” said Dr. Barkana, who published…

[endtimeheadlines]

Israeli and US Astronomers May Have Found Mysterious ‘Dark Matter’

A team of American and Israeli astronomers may have uncovered the first-ever proof of the existence of the mysterious “dark matter,” one of the building blocks of the universe, while attempting to detect the earliest stars in the universe through radio wave signals.  The discovery by the team, led by Prof. Judd Bowman of Arizona State University, which was published this week in the journal Nature by Prof. Rennan Barkana,

Head of the Department of Astrophysics at Tel Aviv University’s School of Physics and Astronomy, suggests that the signal is proof of interactions between normal matter and dark matter in the early universe. “Dark matter is the key to unlocking the mystery of what the universe is made of,” said Barkana. “We know quite a bit about the chemical elements that make up the earth, the sun and other stars, but most of the matter in the universe is invisible and known as ‘dark matter.’” READ MORE

[usviraltrends-blog]

New Post has been published on https://usviraltrends.com/signal-from-age-of-the-first-stars-could-shake-up-search-for-dark-matter-science-2/

Signal from age of the first stars could shake up search for dark matter | Science

In the Australian outback, small radio antennas were used to detect a 13.6-billion-year-old signal.

COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION

By Adrian ChoFeb. 28, 2018 , 1:00 PM

Using radio antennas the size of coffee tables, a small team of astronomers has glimpsed the cosmic dawn, the moment billions of years ago when the universe’s first stars began to shine. The observation also serves up surprising evidence that particles of dark matter—the unseen stuff that makes up most of the universe’s matter—may be much lighter than physicists thought.

If it holds up, the result could sharpen cosmologists’ picture of the early universe and shake up the search for dark matter. “It’s going to generate a huge amount of interest,” says Kevork Abazajian, a theoretical cosmologist at the University of California (UC), Irvine. But others worry that the subtle radio signal reported by the team could be an artifact. “I don’t think that right now, at least in my mind, it’s a clear discovery,” says Aaron Parsons, an experimental cosmologist at UC Berkeley.

The data come from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), a $2 million array of three radio antennas in the outback of Western Australia. The five EDGES researchers searched for signs that the hydrogen atoms that pervaded the newborn universe had absorbed microwaves lingering from the big bang.

The absorption marks the moment just after the first stars began to shine. Before that moment, the atoms’ internal states were in equilibrium with the microwaves, emitting as much radiation as they absorbed. But light from the first stars jostled the atoms’ innards, disrupting the equilibrium and enabling the atoms to absorb more of the microwaves than they emit.

The expansion of the universe stretches the absorption signal from its original 21-centimeter wavelength to longer radio wavelengths. However, radio noise from our galaxy is 30,000 times more intense. To subtract it, EDGES researchers relied on the noise’s smooth, precisely predictable spectrum. This week in Nature, they report detecting the tiny absorption signal—the cumulative shadows, they conclude, of hydrogen clouds that existed between 180 million and 250 million years after the big bang.

It’s the first thing scientists have seen in the time between the cosmic microwave background, 380,000 years after the big bang, and the oldest known galaxy, which shone 400 million years later, says EDGES leader Judd Bowman. “This is really the only possible probe that we have of the time before the stars,” says Bowman, who is an experimental astrophysicist at Arizona State University in Tempe. Ultimately, scientists hope to use the absorption signal or the fainter emission of 21-centimeter radiation from gas clouds at slightly later times to map the 3D distribution of hydrogen during these so-called cosmic dark ages, tracing its evolution into embryonic galaxies.

The absorption is more than twice as strong as predicted, which suggests that the hydrogen was significantly colder than previously thought. The gas must have lost heat to something even colder, and the only colder thing around was dark matter, which was coalescing into the clumps that would seed the formation of galaxies, reasons Rennan Barkana, an astrophysicist at Tel Aviv University in Israel. In a second paper in Nature, Barkana argues that to cool the hydrogen, the dark matter particles must have been less than five times as massive as a hydrogen atom. Otherwise the atoms would have bounced off them without losing energy and getting colder, just as a Ping-Pong ball will bounce off a bowling ball without slowing down.

Many dark matter searches have targeted hypothetical weakly interacting massive particles, which are generally expected to weigh hundreds of times as much as a hydrogen atom. As those searches have come up empty, some physicists have begun searching for lighter dark matter particles. The new result may encourage them, Abazajian says.

However, it’s too early to rule out a more mundane explanation for the unexpectedly strong absorption, cautions Katherine Freese, an astrophysicist at the University of Michigan in Ann Arbor. “Is [this scenario] the only way to explain this? Of course not.”

A more pressing question is whether the signal is an experimental artifact, Parsons says. The measurements rely on calibrations that could produce false signals if they are off by just a few hundredths of a percent, he says. Bowman says he and his colleagues “have gone as far as we can go to ensure that there isn’t an error, but, of course, we’re eager for others to confirm the result.”

Confirmation could come from other experiments that are probing the dark ages. Parsons leads one, called the Hydrogen Epoch of Reionization Array in South Africa, which is trying not just to detect the faint signals, but to map them across the sky. They may soon show whether cosmic dawn has really broken.

[ca-se-passe-la-haut]

Les toutes premières étoiles de l'Univers localisées 180 millions d'années après le Big Bang

Une belle découverte est annoncée cette semaine dans la revue Nature : la localisation dans le temps des premières étoiles de l'Univers : 180 millions d'années après le Big Bang, grâce à la détection de l'excitation du gaz interstellaire qu'elles ont produit par leur rayonnement UV. Et cette découverte apporte également une information non prévue concernant la matière noire...

La quête de l'époque de réionisation de l'Univers, l'époque où sont apparues les premières galaxies, donc les premières étoiles, est une quête de longue haleine. Elle nécessite de sonder l'Univers toujours plus loin et toujours plus tôt dans l'histoire cosmique. Judd Bowman (Arizona State University) et ses collaborateurs, eux, ont choisi une méthode très particulière pour sonder les premières centaines de millions d'années de l'Univers à la recherche des toutes premières étoiles. Ces premières étoiles, peu de temps après leur allumage, devaient rayonner intensément en ultra-violet et ce rayonnement est suffisamment énergétique pour ioniser et exciter le gaz neutre qui peuplait le milieu interstellaire et intergalactique. Ce rayonnement UV doit notamment altérer l'état excité de l'atome d'hydrogène caractérisé par sa raie à 21 cm (la raie dite hyperfine).

Or, cette modification des propriétés de l'hydrogène induite par le rayonnement UV des premières étoiles fait que l'hydrogène peut alors absorber le rayonnement radio de fond à la longueur d'onde de 21 cm, ce qui doit alors produire une distorsion spectrale dans ce fond radio. Toutes ces raies d'absorption subissent ensuite un étirement qui est dû à l'expansion de l'Univers (décalage vers les grandes longueurs d'ondes, ou redshift). C'est cette distorsion spectrale dans le fond diffus cosmologique observé aujourd'hui aux grandes longueurs d'ondes (plusieurs mètres) que Judd Bowman et son équipe ont recherché, et ont trouvé! 

Les chercheurs américains détectent, à l'aide d'un tout petit radiotélescope nommé Experiment to Detect the Global Epoch of Reionization Signature (EDGES), installé dans le désert australien (au Murchison Radio-astronomy Observatory) loin de tout parasite électromagnétique, une belle bande d'absorption sur l'ensemble du ciel, centrée à 78 MHz, avec une largeur de 19 MHz et une amplitude de 0,5 K. Or, la valeur de la limite basse de fréquence trouvée (69 MHz, qui correspond à une longueur d'onde de 4,35 m) permet de trouver l'âge cosmique minimal auquel cette raie de 21 cm a été absorbée. Le rapport des fréquences (ou inversement des longueurs d'ondes) donne directement la valeur du redshift, que l'on peut transcrire en durée depuis le Big Bang. Le redshift obtenu avec la fréquence basse de la bande d'absorption vaut z= 20,7, ce qui correspond à une époque de 180 millions d'années après le Big Bang! Les premières étoiles ont donc commencé à ioniser l'hydrogène neutre 180 millions d'années après le Big Bang. C'est la première fois que l'on obtient avec une assez bonne précision la date des toutes premières étoiles de l'Univers.

Le profil radio mesuré par Bowman et ses collègues de l'Université d'Arizona a une forme tout à fait cohérente avec ce que pouvaient donner les modèles théoriques, mais il y a un problème : l'amplitude de la raie d'absorption. Elle est plus de deux fois trop grande que les prédictions les plus optimistes!

Cet écart conséquent pourrait avoir plusieurs causes selon les chercheurs : premièrement, le gaz pourrait avoir été beaucoup plus froid que ce qu'on pensait; deuxièmement, la température du rayonnement de fond pourrait être plus élevée que prévu. Ce qui paraît sûr, c'est qu'aucun phénomène astrophysique classique ne permet d'expliquer l'écart d'amplitude observé. 

La meilleure explication pour refroidir le gaz dans les bonnes proportions serait, d'après certains spécialistes, notamment Rennan Barkana qui signe un article dans le même numéro de Nature pour accompagner cette découverte, serait d'avoir des particules de matière noire qui interagissent avec les baryons (les protons) un peu différemment de ce qu'on pensait et qui aurait une masse bien plus faible que ce que l'on cherche habituellement avec les WIMPs, de l'ordre de quelques GeV seulement.

Cette très belle observation doit maintenant être vérifiée par d'autres mesures semblables. Certaines expériences ont d'ailleurs déjà été mises en route. Ce n'est qu'un début, et nul doute que les théoriciens vont également s'emparer de cette nouvelle anomalie.

Sources

An absorption profile centred at 78 megahertz in the sky-averaged spectrum. 

J.D. Bowman et al. 

Nature. Vol. 555, March 1, 2018, p. 67

http://doi.org/10.1038/nature25792

Possible interaction between baryons and dark-matter particles revealed by the first stars

R. Barkana

Nature. Vol. 555, March 1, 2018, p. 71

http://doi.org/10.1038/nature25791

Illustrations

1) Vue d'artiste d'une étoile primordiale dont le rayonnement UV interagit avec le gaz environnant (N.R. Fuller/National Science Foundation)

2) Le système de détection radio utilisé par les auteurs en Australie  (Brett Hiscock and Lou Puls/CSIRO Australia)

via http://ift.tt/2t4kVK1