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  • richardmitnick 11:18 am on May 7, 2019 Permalink | Reply
    Tags: "A universe is born", , , , , , , , , , , Reionization, , The Planck epoch   

    From Symmetry: “A universe is born” 

    Symmetry Mag
    From Symmetry

    05/07/19
    Diana Kwon

    Take a (brief) journey through the early history of our cosmos.

    Timeline of the Inflationary Universe WMAP

    The universe was a busy place during the first three minutes. The cosmos we see today expanded from a tiny speck to much closer to its current massive size; the elementary particles appeared; and protons and neutrons combined into the first nuclei, filling the universe with the precursors of elements.

    By developing clever theories and conducting experiments with particle colliders, telescopes and satellites, physicists have been able to wind the film of the universe back billions of years—and glimpse the details of the very first moments in the history of our cosmic home.

    Take an abridged tour through this history:

    The Planck epoch
    Time: < 10^-43 seconds

    The Planck Epoch https:// http://www.slideshare.net ericgolob the-big-bang-10535251

    Welcome to the Planck epoch, named after the smallest scale of measurements possible in particle physics today. This is currently the closet scientists can get to the beginning of time.

    Theoretical physicists don’t know much about the earliest moments of the universe. After the Big Bang theory gained popularity, scientists thought that in the first moments, the cosmos was at its hottest and densest and that all four fundamental forces—electromagnetic, weak, strong and gravitational—were combined into a single, unified force. But the current leading theoretical framework for our universe’s beginning doesn’t necessarily require these conditions.

    The universe expands
    Time: From 10^-43 seconds to about 10^-36 seconds

    In this stage, which began either at Planck time or shortly after it, scientists think the universe underwent superfast, exponential expansion in a process known as inflation.

    Inflation

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    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    Alan Guth’s notes:
    5

    Physicists first proposed the theory of inflation in the 1980s to address the shortcomings of the Big Bang theory, which, despite its popularity, could not explain why the universe was so flat and uniform, and why its different parts began expanding simultaneously.

    During inflation, quantum fluctuations could have stretched out to produce a pattern that later determined the locations of galaxies. It might have been only after this period of inflation the universe became a hot, dense fireball as described in the Big Bang theory.

    The elementary particles are born
    Time: ~10^-36 seconds

    When the universe was still very hot, the cosmos was like a gigantic accelerator, much more powerful than the Large Hadron Collider, running at extremely high energies. In it, the elementary particles we know today were born.

    Scientists think that first came exotic particles, followed by more familiar ones, such as electrons, neutrinos and quarks. It could be that dark matter particles came about during this time.

    3
    Quarks APS/Alan Stonebraker

    The quarks soon combined, forming the familiar protons and neutrons, which are collectively known as baryons. Neutrinos were able to escape this plasma of charged particles and began traveling freely through space, while photons continued to be trapped by the plasma.

    Standard Model of Particle Physics

    The first nuclei emerge
    Time: ~1 second to 3 minutes

    Scientists think that when the universe cooled enough for violent collisions to subside, protons and neutrons clumped together into nuclei of the light elements—hydrogen, helium and lithium—in a process known as Big Bang nucleosynthesis.

    Protons are more stable than neutrons, due to their lower mass. In fact, a free neutron decays with a 15-minute half-life, while protons may not decay at all, as far as we know.

    So as the particles combined, many protons remained unpaired. As a result, hydrogen—protons that never found a partner—make up around 74% of the mass of “normal” matter in our cosmos. The second most abundant element is helium, which makes up approximately 24%, followed by trace amounts of deuterium, lithium, and helium-3 (helium with a three-baryon core).

    Periodic table Sept 2017. Wikipedia

    Scientists have been able to accurately measure the density of baryons in our universe. Most of those measurements line up with theorists’ estimations of what the quantities ought to be, but there is one lingering issue: Lithium calculations are off by a factor of three. It could be that the measurements are off, but it could also be that something we don’t yet know about happened during this time period to change the abundance of lithium.

    The cosmic microwave background becomes visible
    Time: 380,000 years

    Hundreds of thousands of years after inflation, the particle soup had cooled enough for electrons to bind to nuclei to form electrically neutral atoms. Through this process, which is also known as recombination, photons became free to traverse the universe, creating the cosmic microwave background.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    Today, the CMB is one of the most valuable tools for cosmologists, who probe its depths in search of answers for many of the universe’s lingering secrets, including the nature of inflation and the cause of matter-antimatter asymmetry.

    Shortly after the CMB became detectable, neutral hydrogen particles formed into a gas that filled the universe. Without any objects emitting high-energy photons, the cosmos was plunged into the dark ages for millions of years.

    Dark Energy Camera Enables Astronomers a Glimpse at the Cosmic Dawn. CREDIT National Astronomical Observatory of Japan

    The earliest stars shine
    Time: ~100 million years

    The dark ages ended with the formation of the first stars and the occurrence of reionization, a process through which highly energetic photons stripped electrons off neutral hydrogen atoms.

    Reionization era and first stars, Caltech

    Scientists think that the vast majority of the ionizing photons emerged from the earliest stars. But other processes, such as collisions between dark matter particles, may have also played a role.

    At this time, matter began to form the first galaxies. Our own galaxy, the Milky Way, contains stars that were born when the universe was only several hundred million years old.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Our sun is born
    Time: 9.2 billion years

    3
    NASA

    The sun is one of a few hundred billion stars in the Milky Way. Scientists think it formed from a giant cloud of gas that consisted mostly hydrogen and helium.

    Today
    Time: 13.8 billion years

    Today, our cosmos sits at a cool 2.7 Kelvin (minus 270.42 degrees Celsius). The universe is expanding at an increasing rate, in a manner similar to (but many orders of magnitude slower than) inflation.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Physicists think that dark energy—a mysterious repulsive force that currently accounts for about 70% of the energy in our universe—is most likely driving that accelerated expansion.

    Dark energy depiction. Image: Volker Springle/Max Planck Institute for Astrophysics/SP)

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:40 pm on December 17, 2017 Permalink | Reply
    Tags: , , Atacama Desert of Chile so important for Optical Astonomy, , Carnegie Institution for Science Las Campanas Observatory, , , Earliest Black Hole Gives Rare Glimpse of Ancient Universe, , , Reionization,   

    From Quanta: “Earliest Black Hole Gives Rare Glimpse of Ancient Universe” 

    Quanta Magazine
    Quanta Magazine

    December 6, 2017 [Today in social media]
    Joshua Sokol

    1
    Olena Shmahalo/Quanta Magazine

    2
    The two Carnegie Magellan telescopes: Baade (left) and Clay (right)

    Astronomers have at least two gnawing questions about the first billion years of the universe, an era steeped in literal fog and figurative mystery. They want to know what burned the fog away: stars, supermassive black holes, or both in tandem? And how did those behemoth black holes grow so big in so little time?

    Now the discovery of a supermassive black hole smack in the middle of this period is helping astronomers resolve both questions. “It’s a dream come true that all of these data are coming along,” said Avi Loeb, the chair of the astronomy department at Harvard University.

    The black hole, announced today in the journal Nature, is the most distant ever found. It dates back to 690 million years after the Big Bang. Analysis of this object reveals that reionization, the process that defogged the universe like a hair dryer on a steamy bathroom mirror, was about half complete at that time.

    First Stars and Reionization Era, Caltech

    The researchers also show that the black hole already weighed a hard-to-explain 780 million times the mass of the sun.

    A team led by Eduardo Bañados, an astronomer at the Carnegie Institution for Science in Pasadena, found the new black hole by searching through old data for objects with the right color to be ultradistant quasars — the visible signatures of supermassive black holes swallowing gas. The team went through a preliminary list of candidates, observing each in turn with a powerful telescope at Las Campanas Observatory in Chile.

    4
    Carnegie Institution for Science Las Campanas Observatory telescopes in the southern Atacama Desert of Chile approximately 100 kilometres (62 mi) northeast of the city of La Serena,near the southern end and over 2,500 m (8,200 ft) high.

    On March 9, Bañados observed a faint dot in the southern sky for just 10 minutes. A glance at the raw, unprocessed data confirmed it was a quasar — not a nearer object masquerading as one — and that it was perhaps the oldest ever found. “That night I couldn’t even sleep,” he said.

    3
    Eduardo Bañados at the Las Campanas Observatory in Chile, where the new quasar was discovered. Courtesy of Eduardo Bañados. Baade and Clay in the background.

    The new black hole’s mass, calculated after more observations, adds to an existing problem. Black holes grow when cosmic matter falls into them. But this process generates light and heat. At some point, the radiation released by material as it falls into the black hole carries out so much momentum that it blocks new gas from falling in and disrupts the flow. This tug-of-war creates an effective speed limit for black hole growth called the Eddington rate. If this black hole began as a star-size object and grew as fast as theoretically possible, it couldn’t have reached its estimated mass in time.

    Other quasars share this kind of precocious heaviness, too. The second-farthest one known, reported on in 2011, tipped the scales at an estimated 2 billion solar masses after 770 million years of cosmic time.

    These objects are too young to be so massive. “They’re rare, but they’re very much there, and we need to figure out how they form,” said Priyamvada Natarajan, an astrophysicist at Yale University who was not part of the research team. Theorists have spent years learning how to bulk up a black hole in computer models, she said. Recent work suggests that these black holes could have gone through episodic growth spurts during which they devoured gas well over the Eddington rate.

    Bañados and colleagues explored another possibility: If you start at the new black hole’s current mass and rewind the tape, sucking away matter at the Eddington rate until you approach the Big Bang, you see it must have initially formed as an object heavier than 1,000 times the mass of the sun. In this approach, collapsing clouds in the early universe gave birth to overgrown baby black holes that weighed thousands or tens of thousands of solar masses. Yet this scenario requires exceptional conditions that would have allowed gas clouds to condense all together into a single object instead of splintering into many stars, as is typically the case.

    Cosmic Dark Ages

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    Cosmic Dark Ages. ESO.

    Even earlier in the early universe, before any stars or black holes existed, the chaotic scramble of naked protons and electrons came together to make hydrogen atoms. These neutral atoms then absorbed the bright ultraviolet light coming from the first stars. After hundreds of millions of years, young stars or quasars emitted enough light to strip the electrons back off these atoms, dissipating the cosmic fog like mist at dawn.

    3
    Lucy Reading-Ikkanda/Quanta Magazine

    Astronomers have known that reionization was largely complete by around a billion years after the Big Bang.

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    At that time, only traces of neutral hydrogen remained. But the gas around the newly discovered quasar is about half neutral, half ionized, which indicates that, at least in this part of the universe, reionization was only half finished. “This is super interesting, to really map the epoch of reionization,” said Volker Bromm, an astrophysicist at the University of Texas.

    When the light sources that powered reionization first switched on, they must have carved out the opaque cosmos like Swiss cheese.

    Inflationary Universe. NASA/WMAP

    But what these sources were, when it happened, and how patchy or homogeneous the process was are all debated. The new quasar shows that reionization took place relatively late. That scenario squares with what the known population of early galaxies and their stars could have done, without requiring astronomers to hunt for even earlier sources to accomplish it quicker, said study coauthor Bram Venemans of the Max Planck Institute for Astronomy in Heidelberg.

    More data points may be on the way. For radio astronomers, who are gearing up to search for emissions from the neutral hydrogen itself, this discovery shows that they are looking in the right time period. “The good news is that there will be neutral hydrogen for them to see,” said Loeb. “We were not sure about that.”

    The team also hopes to identify more quasars that date back to the same time period but in different parts of the early universe. Bañados believes that there are between 20 and 100 such very distant, very bright objects across the entire sky. The current discovery comes from his team’s searches in the southern sky; next year, they plan to begin searching in the northern sky as well.

    “Let’s hope that pans out,” said Bromm. For years, he said, the baton has been handed off between different classes of objects that seem to give the best glimpses at early cosmic time, with recent attention often going to faraway galaxies or fleeting gamma-ray bursts. “People had almost given up on quasars,” he said.

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 5:22 pm on June 4, 2017 Permalink | Reply
    Tags: , , , , , Reionization, ,   

    From WIRED: “Cosmic Discoveries Fuel a Fight Over the Universe’s Beginnings” 

    Wired logo

    06.04.17
    Ashley Yeager

    1
    Light from the first galaxies clears the universe. ESO/L. Calçada

    Not long after the Big Bang, all went dark. The hydrogen gas that pervaded the early universe would have snuffed out the light of the universe’s first stars and galaxies. For hundreds of millions of years, even a galaxy’s worth of stars—or unthinkably bright beacons such as those created by supermassive black holes—would have been rendered all but invisible.

    Eventually this fog burned off as high-energy ultraviolet light broke the atoms apart in a process called reionization.

    Reionization era and first stars, Caltech

    But the questions of exactly how this happened—which celestial objects powered the process and how many of them were needed—have consumed astronomers for decades.

    Now, in a series of studies, researchers have looked further into the early universe than ever before. They’ve used galaxies and dark matter as a giant cosmic lens to see some of the earliest galaxies known, illuminating how these galaxies could have dissipated the cosmic fog. In addition, an international team of astronomers has found dozens of supermassive black holes—each with the mass of millions of suns—lighting up the early universe. Another team has found evidence that supermassive black holes existed hundreds of millions of years before anyone thought possible. The new discoveries should make clear just how much black holes contributed to the reionization of the universe, even as they’ve opened up questions as to how such supermassive black holes were able to form so early in the universe’s history.

    First Light

    In the first years after the Big Bang, the universe was too hot to allow atoms to form. Protons and electrons flew about, scattering any light. Then after about 380,000 years, these protons and electrons cooled enough to form hydrogen atoms, which coalesced into stars and galaxies over the next few hundreds of millions of years.

    Starlight from these galaxies would have been bright and energetic, with lots of it falling in the ultraviolet part of the spectrum. As this light flew out into the universe, it ran into more hydrogen gas. These photons of light would break apart the hydrogen gas, contributing to reionization, but as they did so, the gas snuffed out the light.

    2
    Lucy Reading-Ikkanda/Quanta Magazine

    To find these stars, astronomers have to look for the non-ultraviolet part of their light and extrapolate from there. But this non-ultraviolet light is relatively dim and hard to see without help.

    A team led by Rachael Livermore, an astrophysicist at the University of Texas at Austin, found just the help needed in the form of a giant cosmic lens.

    Gravitational Lensing NASA/ESA

    These so-called gravitational lenses form when a galaxy cluster, filled with massive dark matter, bends space-time to focus and magnify any object on the other side of it. Livermore used this technique with images from the Hubble Space Telescope to spot extremely faint galaxies from as far back as 600 million years after the Big Bang—right in the thick of reionization.

    NASA/ESA Hubble Telescope

    In a recent paper that appeared in The Astrophysical Journal, Livermore and colleagues also calculated that if you add galaxies like these to the previously known galaxies, then stars should be able to generate enough intense ultraviolet light to reionize the universe.

    Yet there’s a catch. Astronomers doing this work have to estimate how much of a star’s ultraviolet light escaped its home galaxy (which is full of light-blocking hydrogen gas) to go out into the wider universe and contribute to reionization writ large. That estimate—called the escape fraction—creates a huge uncertainty that Livermore is quick to acknowledge.

    In addition, not everyone believes Livermore’s results. Rychard Bouwens, an astrophysicist at Leiden University in the Netherlands, argues in a paper submitted to The Astrophysical Journal that Livermore didn’t properly subtract the light from the galaxy clusters that make up the gravitational lens.

    6

    As a result, he said, the distant galaxies aren’t as faint as Livermore and colleagues claim, and astronomers have not found enough galaxies to conclude that stars ionized the universe.

    If stars couldn’t get the job done, perhaps supermassive black holes could. Beastly in size, up to a billion times the mass of the sun, supermassive black holes devour matter. They tug it toward them and heat it up, a process that emits lots of light and creates luminous objects that we call quasars. Because quasars emit way more ionizing radiation than stars do, they could in theory reionize the universe.

    The trick is finding enough quasars to do it. In a paper posted to the scientific preprint site arxiv.org last month, astronomers working with the Subaru Telescope announced the discovery of 33 quasars that are about a 10th as bright as ones identified before.


    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA

    With such faint quasars, the astronomers should be able to calculate just how much ultraviolet light these supermassive black holes emit, said Michael Strauss, an astrophysicist at Princeton University and a member of the team.

    The researchers haven’t done the analysis yet, but they expect to publish the results in the coming months.

    The oldest of these quasars dates back to around a billion years after the Big Bang, which seems about how long it would take ordinary black holes to devour enough matter to bulk up to supermassive status.

    This is why another recent discovery [ApJ] is so puzzling. A team of researchers led by Richard Ellis, an astronomer at the European Southern Observatory, was observing a bright, star-forming galaxy seen as it was just 600 million years after the Big Bang.

    The galaxy’s spectrum—a catalog of light by wavelength—appeared to contain a signature of ionized nitrogen. It’s hard to ionize ordinary hydrogen, and even harder to ionize nitrogen. It requires more higher-energy ultraviolet light than stars emit. So another strong source of ionizing radiation, possibly a supermassive black hole, had to exist at this time, Ellis said.

    One supermassive black hole at the center of an early star-forming galaxy might be an outlier. It doesn’t mean there were enough of them around to reionize the universe. So Ellis has started to look at other early galaxies. His team now has tentative evidence that supermassive black holes sat at the centers of other massive, star-forming galaxies in the early universe. Studying these objects could help clarify what reionized the universe and illuminate how supermassive black holes formed at all. “That is a very exciting possibility,” Ellis said.

    All this work is beginning to converge on a relatively straightforward explanation for what reionized the universe. The first population of young, hot stars probably started the process, then drove it forward for hundreds of millions of years. Over time, these stars died; the stars that replaced them weren’t quite so bright and hot. But by this point in cosmic history, supermassive black holes had enough time to grow and could start to take over. Researchers such as Steve Finkelstein, an astrophysicist at the University of Texas at Austin, are using the latest observational data and simulations of early galactic activity to test out the details of this scenario, such as how much stars and black holes contribute to the process at different times.

    His work—and all work involving the universe’s first billion years—will get a boost in the coming years after the 2018 launch of the James Webb Space Telescope, Hubble’s successor, which has been explicitly designed to find the first objects in the universe.

    NASA/ESA/CSA Webb Telescope annotated

    Its findings will probably provoke many more questions, too.

    See the full article here .

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  • richardmitnick 12:39 pm on August 8, 2016 Permalink | Reply
    Tags: , , , , , Reionization   

    From Astronomy: “When did the lights turn on in the universe?” 

    Astronomy magazine

    Astronomy.com

    August 08, 2016
    Nola Taylor Redd

    1
    A map showing the history of the universe, including the shift from neutral to ionized hydrogen resulting in the universe we see today.
    NAOJ

    The early universe hides behind the cloak of its Dark Ages, a period of time light can’t seem to pierce. Even the length of those unseen years remains uncertain. As part of its efforts to probe the secrets of those hidden years, the European Space Agency’s Planck Satellite recently announced the most precise constraints on the universe’s evasive era, for the first time revealing that the first stars and their galaxies are enough to light up the darkness.

    ESA/Planck
    ESA/Planck

    Trying to pierce the veil of darkness has been a decades-long struggle to look back in time nearly 14 billion years. After the Big Bang, the hot universe quickly cooled down, and the simplest atomic particles formed. The protons and electrons of the early universe constantly collided, creating a hot soup that kept light from passing. The Dark Ages had begun.

    As the gas cooled down, and the expanding galaxy stretched space-time, the particles recombined to form neutral hydrogen. Like the rising dawn, the universe grew gradually more transparent, its gradual glow imprinted on the radio noise scientists recognize as the Cosmic Microwave Background (CMB). The universe remained dark, however, because nothing produced visible light.

    Cosmic Microwave Background per ESA/Planck
    Cosmic Microwave Background per ESA/Planck

    Gravity worked hard to change that. It didn’t take long for the force to begin pulling material together, forming the first stars and galaxies. Bright galaxies know as quasars, whose central supermassive black holes produce powerful jets of light and matter, also populated the early universe. Heat from the young objects broke the neutral hydrogen apart over time in the process known as reionization, with slow-sweeping bubbles of light spreading outward from the bright objects. As the bubbles grew and overlapped, the universe once again became visible, and the Dark Age ended. (The change of state in hydrogen that allowed a visible universe is called the Epoch of Reionization.)

    Perhaps one of the most challenging attributes of the Dark Age is the difficulty inherent in nailing down just when it ended and how long it lasted. Because light didn’t shine from the start of the Dark Age, scientists must rely on the glow from the CMB to provide them with clues to when recombination brought particles together to make the universe gradually more transparent. Observations of early galaxies and quasars, the brightest objects in the universe, help narrow down how long the lights were off.

    Planck’s most recent results suggest that the time of reionization, when light from the first objects began to break apart molecules once again, occurred about 55 million years later than previous studies placed it.

    “It is certainly clear that we are now measuring a later onset of reionization,” says Planck Project Scientist Jan Tauber said by email.

    Planck Scientist Graca Rocha, of the Jet Propulsion Laboratory, stresses that Planck’s measurements have become more precise over time. Rocha, who presented a portion of the research at the American Astronomical Society meeting in San Diego, California in June, pointed to the error bar in the calculations, a number that has grown smaller over time. The most recent results have an error of less than nine-thousandanths.

    “We are narrowing the range of reionization, when the first stars start to form,” Rocha told Astronomy. “People are thrilled about the shift down.”

    Strange objects begone

    The first early estimates suggested that reionization wrapped up extremely fast, requiring unusual astronomical bodies to clear the darkness. Tension mounted as the scientists sought to reconcile multiple forms of observation. Planck’s new numbers helped to relieve some of the pressure as the more precise calculations suggested that novel things were unnecessary after all.

    “Those early measurements required ‘strange objects’ to reionize the universe, but those concerns have now been dissipated by Planck,” Tauber says.

    “We now know that the first galaxies that we can already observe are enough to reionize the universe at the time shown by the [Cosmic Microwave Background].”

    Since its launch in 2009, Planck has probed the early universe, seeking to learn more about when the Dark Ages started and ended. Over three quarters of a decade, the spacecraft has helped to improve the understanding of the unseen era by penetrating the veil of darkness around it.

    The more sophisticated analysis reveals that the first objects didn’t begin to separate the fog of particles until “quite late,” Tauber says. Planck reveals that the universe was no more than 10 percent ionized by the time the universe was 475 million years old. It also demonstrated that the process wrapped up quickly, within about 250 million years.

    “This model is very consistent with observations of the earliest galaxies,” Tauber says.

    These galaxies allow scientists to estimate the total amount of light available to the early universe to split the particles once again.

    “So the Planck- and CMB-based estimates are now in full agreement with direct observations.”

    See the full article here .

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  • richardmitnick 11:36 am on May 16, 2016 Permalink | Reply
    Tags: , , , , , Reionization   

    From NOVA: “Revealing the Universe’s Mysterious Dark Age” 

    PBS NOVA

    NOVA

    06 Apr 2016 [They just put this in social media]
    Marcus Woo

    The universe wasn’t always like this. Today it’s filled with glittering galaxies, scattered across space like city lights seen from above. But there was a time when all was dark. Really dark.

    Dark Ages Universe ESO
    Dark Ages Universe ESO

    1
    A time-lapse visualization of what the cosmic web’s emergence might have looked like. No image credit

    First, a very brief history of time: from the Big Bang, the universe burst onto the scene as a tiny but glowing inferno of energy. Immediately, it expanded and cooled, dimming into darkness as particles condensed out of the hot soup like droplets of morning dew. Electrons and protons coalesced into atoms, which formed stars, galaxies, planets, and eventually us.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    But a crucial piece still eludes scientists. It’s a gap of several hundred million years that was filled with darkness—a darkness both literal and metaphorical. Astronomers call this period the dark ages, a time that’s not just bereft of illumination, but also devoid of data.

    The Big Bang left a glowing imprint on the entire sky called the cosmic microwave background,,,

    Cosmic Microwave Background per ESA/Planck
    Cosmic Microwave Background per ESA/Planck

    ESA/Planck
    ESA/Planck
    ,,,representing the universe when it was 380,000 years old. Increasingly precise measurements of this radiation have revealed unprecedented details about the earliest cosmic moments. But from then until the emergence of galaxies big and bright enough for today’s telescopes, scientists don’t have any information. Ever mysterious, these dark ages are the final frontier of cosmology.

    And it’s a fundamental frontier. It represents the universe’s most formative years, when it matured from a primordial soup to the cosmos we recognize today.

    Even without much direct data about this era, researchers have made great strides with theory and computer models, simulating the universe through the birth of the first stars. Soon, they may be able to put those theories to the test. In a few years, a suite of new telescopes with new capabilities will start peering into the darkness, and for the first time, astronomers will reach into the unknown.

    The Final Frontier

    Considering that it’s the entire universe they’re trying to understand, cosmologists have done a pretty good job. Increasingly powerful telescopes have allowed them to peer to greater distances, and because the light takes so long to reach the telescopes, astronomers can see farther back in time, capturing snapshots of a universe only a few hundred million years old, just as it emerged from the dark ages. Given that the universe is now 13.7 billion years old, that’s like taking a picture of the cosmos as a toddler.

    That makes the cosmic microwave background, or CMB, clike a detailed ultrasound. This radiation contains the first photons that escaped the yoke of the universe’s primordial plasma. When the universe was a sea of radiation and particles, photons couldn’t travel freely because they kept running into electrons. But about 380,000 years after the Big Bang, the universe had cooled enough that protons were able to lasso electrons into an orbit to form hydrogen atoms. Without electrons in their way, the newly liberated photons could now fly through the cosmos and, more than 13 billion years later, enter the detectors of instruments like the Planck satellite, giving cosmologists the earliest picture of the universe.

    But from this point on, until the universe was a few hundred million years old—the limit of today’s telescopes—astronomers have nothing. It’s as if they have a photo album documenting a person’s entire life, with pictures of young adulthood, adolescence, childhood, and even before birth, but nothing from when the person learned to talk or walk—years of drastic changes.

    That doesn’t mean astronomers have no clue about this period. “People have thought about the first stars since the 1950s,” says Volker Bromm, a professor of astronomy at the University of Texas, Austin. “But they were very speculative because we did not know enough cosmology.” Not until the 1980s did researchers develop more accurate theories that incorporated dark matter, the still-unknown type of particle or particles that comprises about 85% of the matter in the universe. But the first key breakthrough came in 1993, when NASA’s COBE satellite measured the CMB for the first time, collecting basic but crucial data about what the universe was like at the very beginning—the so-called initial conditions of the cosmos. Theorists such as Martin Rees, now the Astronomer Royal of the United Kingdom, and Avi Loeb, a professor of astrophysics at Harvard, realized you could plug these numbers into the equations that govern how the first gas clouds and stars could form. “You could feed them into a computer simulation,” Loeb says. “It’s a well-defined problem.”

    Both Rees and Loeb would influence Bromm, then a graduate student at Yale. Rees and his early work in the 1980s, in particular, inspired Tom Abel, who was a visiting scientist during the 1990s at the University of Illinois, Urbana-Champaign. Independently, Abel and Bromm would make some of the first computer models of their kind to simulate the first stars. “That really opened the field,” Loeb says. “When I started, there were maybe one or a few people even willing to discuss this subject.”

    Theorists like Bromm and Abel, now a professor at Stanford, have since pieced together a blow-by-blow account of the dark ages. Here’s how they think it all went down.

    Then There Was Light

    In the earliest days, during the time that we see in the CMB, the entire universe was bright and as hot as the surface of the sun. But the universe kept expanding and cooling, and after nearly 15 million years, it was as cool as room temperature. “In principle, if there were planets back then, you could’ve had life on them if they had liquid water on their surface,” Loeb says. The temperature continued to fall, and the infrared radiation that suffused the universe lengthened, shifting to radio waves. “Once you cool even further, the universe became a very dark place,” Loeb says. The dark ages had officially begun.

    Meanwhile, the simulations show, things began to stir. The universe was bumpy, with regions of slightly higher and lower densities, which grew from the random quantum fluctuations that emerged in the Big Bang. These denser regions coaxed dark matter to start clumping together, forming a network of sheets and filaments that crisscrossed the universe. At the intersections, denser globs of dark matter formed. Once these roundish halos grew to about 10,000 times the mass of the Sun, Abel says—a few tens of millions of years after the Big Bang—they had enough gravity to corral hydrogen atoms into the first gas clouds.

    Those clouds could then accumulate more gas, heating up to hundreds of degrees. The heat generated enough pressure to prevent further contraction. Soon, the clouds settled into enormous, but rather dull, balls of gas about 100 light years in diameter, Abel says.

    But if the dark matter halos reached masses 100,000 times that of the sun, they could accrue enough gas that the clouds could heat up to about 1000 degrees—and that’s when things got interesting. The surplus energy allowed hydrogen atoms to merge two at a time and form hydrogen molecules—picture two balls attached with a spring. When two hydrogen molecules collide, they vibrate and emit photons that carry away energy.

    When that happens, the molecules are converting the vibrating energy that is heat into radiation that’s lost into space. These interactions cooled the gas, slowing down the molecules and allowing the clouds to collapse. As the clouds grew denser, their temperatures and pressures soared, igniting nuclear fusion. That’s how the first stars were born.

    These first stars, which formed by the time the universe was a couple hundred million years old, were much bigger than those in today’s universe. By the early 2000s, Abel’s simulations, which he says are the most realistic and advanced yet, showed that the first stars weighed about 30 to 300 times the mass of the sun. Using different techniques and algorithms, Bromm says he arrived at a similar answer. For the first time, researchers had a good idea as to what the first objects in the universe were like.

    Massive stars consume fuel like gas-guzzling SUVs. They live fast and die young, collapsing into supernovae after only a few million years.

    Supernova remnant Crab nebula. NASA/ESA Hubble
    Supernova remnant Crab nebula. NASA/ESA Hubble

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    In cosmic timescales, that’s the blink of an eye. “You really want to think of fireworks at these early times,” Abel says. “Just flashing everywhere.”

    In general, the first stars were sparse, separated by thousands of light years. Over the next couple hundred million years, though, guided by the clustering of dark matter, the stars started grouping together to form baby galaxies. During this cosmic dawn, as astronomers call it, galaxies merged with one another and became bigger galaxies. Only after billions and billions of years would they grow into those like our own Milky Way, with hundreds of billions of stars.

    Lifting the Fog

    But there’s more to the story. The first stars shone in many wavelengths, and especially strongly in ultraviolet. The universe’s expansion would’ve stretched this light to visible and infrared wavelengths, which many of our best telescopes are designed to detect. Problem is, during the time of the first stars, a thick fog of neutral hydrogen gas blanketed the whole universe. This gas absorbed shorter-wavelength ultraviolet light, obscuring the view from telescopes. Fortunately, though, this fog would soon lift.

    “This state of affairs can’t last for very long,” says Richard Ellis, an astronomer at the European Southern Observatory in Germany.

    ESO 50 Large
    ESO

    “These ultraviolet photons have sufficient energy to break apart the hydrogen atom back into an electron and a proton.” The hydrogen was ionized, turning into a lone proton that could no longer absorb ultraviolet. The gas was now transparent.

    During this so-called period of reionization, galaxies continued to grow, producing more ultraviolet light that ionized the hydrogen surrounding them, clearing out holes in the fog. “You can imagine the hydrogen like Swiss cheese,” Loeb says. Those bubbles grew, and by the time the universe was around 800 million years old, the ultraviolet radiation ionized the hydrogen between the galaxies, leaving the entire cosmos clear and open to the gaze of telescopes. The dark ages were over, revealing a universe that looked more or less like it does today.

    Seeing into the Dark

    Of course, many details have to be worked out. Astronomers like Ellis are focusing on the latter stages of the dark ages, using the most powerful telescopes to extract clues about this reionization epoch.

    One big question has been whether the ultraviolet light from early galaxies was enough to ionize the whole universe. If it wasn’t, astronomers would have to find another exotic source—like black holes that blast powerful, ionizing jets of radiation—that would have finished the job.

    To find the answer, Ellis and a team of astronomers stretched the Hubble Space Telescope to its limits, extracting as much light as possible from one small patch of sky. These observations reached some of the most distant corners of the universe, discovering some of the earliest galaxies ever seen, during the heart of this reionization era. Their observations suggested that galaxies—large populations of small galaxies, in particular—did seem to have enough ultraviolet light to ionize the universe. Maybe nothing exotic is needed.

    NASA/ESA  Hubble Deep Field
    NASA/ESA Hubble Deep Field

    But to know exactly how it happened, astronomers need new telescopes, like the James Webb Space Telescope set for launch in 2018.

    NASA/ESA/CSA Webb Telescope annotated
    “NASA/ESA/CSA Webb Telescope annotated

    “With the current facilities, it’s just an imponderable,” Ellis says. “We don’t have the power to study these galaxies in any detail.”

    Other astronomers are focusing not on the galaxies, but the hydrogen fog itself. It turns out that the spins of a hydrogen atom’s proton and electron can flip-flop in direction. When the spins go from being aligned to unaligned, the atom releases radiation at a wavelength of 21 centimeters, or 8.27 inches, a telltale signal of neutral hydrogen that astronomers call the 21-cm line. The expanding universe would have stretched this signal to the point where it became a collection of radio waves. The more distant the source of light, the more the radiation gets stretched. By using arrays of radio telescopes to measure the extent of this stretching, astronomers can map the distribution of hydrogen at different points in time. They could then track how those holes in the gas grew and grew until the gas was all ionized.

    “It’s surveying the volume of the universe on a scale that you can’t imagine doing in any way other than through this method—it’s really quite incredible,” says Aaron Parsons, an astronomer at the University of California, Berkeley, who’s leading a project called HERA, which will consist of 352 radio antennae in South Africa.

    HERA NSF
    NSF HERA, South Africa

    Once online, the telescope could give an unprecedented view of reionization. “You can almost imagine making a movie of how the first stars galaxies formed, how they interacted, heated up, ionized, and turned into the galaxies we recognize today.”

    Other telescopes like LOFAR in the Netherlands and the Murchison Widefield Array in Australia will make similar measurements.

    ASTRON LOFAR Map
    ASTRON LOFAR Map

    ASTRON LOFAR Radio Antenna Bank
    ASTRON LOFAR Radio Antenna Bank

    SKA Murchison Widefield Array
    SKA Murchison Widefield Array

    But HERA will be more sensitive, Parsons says. And already with 19 working antennae in place, it might be closest to success, adds Loeb, who isn’t part of the HERA team. “Within a couple years, we should have the first detection of the 21-cm line from this epoch of reionization, which would be fantastic because it would allow us to see the environmental effect of ultraviolet radiation from the first stars and first galaxies on the rest of the universe.”

    This kind of data is crucial for informing computer models like the kind that Abel and Bromm have developed. But despite their successes, theorists are at the point where they need data to test whether their models are accurate.

    Unfortunately, that data won’t be pictures of the first stars. Even the most powerful telescopes won’t be able to see the brightest of them. The first galaxies contain only a few hundred stars and are just too small and faint. “We’ll come ever closer,” Abel says. “It’s very difficult to imagine we’ll actually see those in the near future, but we’ll see their brighter cousins.”

    In fact, the darkest of times, during the couple hundred million years between the CMB and the appearance of the first stars, may always remain beyond astronomers’ grasp. “We currently don’t have any idea of how you could get any direct information about that period,” he says.

    Still, new telescopes over the next few decades promise to reveal much of the dark ages and whether the story theorists are telling is true or even more fantastic than they had thought. “Even though I’m a theorist, I’m modest enough to acknowledge the fact that nature is sometimes more imaginative than we are,” Loeb says. “I’m open to surprises.”

    See the full article here .

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

     
  • richardmitnick 12:48 pm on February 22, 2016 Permalink | Reply
    Tags: , , , Lyα-emitting galaxies, Reionization   

    From AAS NOVA: ” Galactic Teamwork Makes Distant Bubbles” 

    AASNOVA

    Amercan Astronomical Society

    22 February 2016
    Susanna Kohler

    Big Bang to today
    Original version: NASA; modified by Ryan Kaldari

    During the period of reionization that followed the dark ages of our universe, hydrogen was transformed from a neutral state, which is opaque to radiation, to an ionized one, which is transparent to radiation. But what generated the initial ionizing radiation? The recent discovery of multiple distant galaxies offers evidence for how this process occurred.

    Two Distant Galaxies

    We believe reionization occurred somewhere between a redshift of z = 6 and 7, because Lyα-emitting galaxies drop out at roughly this redshift. Beyond this distance, we’re generally unable to see the light from these galaxies, because the universe is no longer transparent to their emission. This is not always the case, however: if a bubble of ionized gas exists around a distant galaxy, the radiation can escape, allowing us to see the galaxy.

    This is true of two recently-discovered Lyα-emitting galaxies, confirmed to be at a redshift of z~7 and located near one another in a region known as the Bremer Deep Field. The fact that we’re able to see the radiation from these galaxies means that they are in an ionized HII region — presumably one of the earlier regions to have become reionized in the universe.

    But on their own, neither of these galaxies is capable of generating an ionized bubble large enough for their light to escape. So what ionized the region around them, and what does this mean for our understanding of how reionization occurred in the universe?

    A Little Help From Friends

    A team of scientists led by Marco Castellano (Rome Observatory, INAF) investigated the possibility that there are other, faint galaxies near these two that have helped to ionize the region. Performing a survey using deep field Hubble observations, Castellano and collaborators found an additional 6 galaxies in the same region as the first two, also at a redshift of z~7!

    The authors believe these galaxies provide a simple explanation of the ionized bubble: each of these faint, normal galaxies produced a small ionized bubble. The overlap of these many small bubbles provided the larger ionized region from which the light of the two originally discovered galaxies was able to escape.

    How normal is this clustering of galaxies found by Castellano and collaborators? The team demonstrates via cosmological modeling that the number density of galaxies in this region is a factor of 3–4 greater than would be expected at this distance in a random pointing of the same size.

    These results greatly support the theoretical prediction that the first ionization fronts in the universe were formed in regions with significant galaxy overdensities. The discovery of this deep-field collection of galaxies strongly suggests that reionization was driven by faint, normal star-forming galaxies in a clumpy process.
    Citation

    M. Castellano et al 2016 ApJ 818 L3. doi:10.3847/2041-8205/818/1/L3

    See the full article here .

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  • richardmitnick 1:37 pm on August 5, 2015 Permalink | Reply
    Tags: , , , Reionization   

    From Keck: “New Record: Keck Observatory Measures Most Distant Galaxy” 

    Keck Observatory

    Keck Observatory

    Keck Observatory

    August 5, 2015
    SCIENCE CONTACTS
    Adi Zitrin
    California Institute of Technology
    adizitrin@gmail.com
    626-278-5854

    Richard Ellis
    California Institute of Technology
    rse@astro.caltech.edu
    626-676-5530

    MEDIA CONTACT
    Steve Jefferson
    W. M. Keck Observatory
    sjefferson@keck.hawaii.edu
    808-881-3827

    1
    Credit: Adi Zitrin, California Institute of Technology, 2015

    EGSY8p7 is the most distant confirmed galaxy whose spectrum obtained with the W. M. Keck Observatory places it at a redshift of 8.68 at a time when the Universe was less than 600 million years old. The illustration shows the remarkable progress made in recent years in probing early cosmic history. Such studies are important in understanding how the Universe evolved from an early dark period to one when galaxies began to shine. Hydrogen emission from EGSY8p7 may indicate it is the first known example of an early generation of young galaxies emitting unusually strong radiation.

    A team of astrophysicists using the W. M. Keck Observatory in Hawaii has successfully measured the farthest galaxy ever recorded and more interestingly, captured its hydrogen emission as seen when the Universe was less than 600 million years old. Additionally, the method in which the galaxy called EGSY8p7 was detected gives important insight into how the very first stars in the Universe lit-up after the Big Bang. The paper will be published shortly in the Astrophysical Journal Letters.

    Using Keck Observatory’s powerful infrared spectrograph called MOSFIRE, the team dated the galaxy by detecting its Lyman-alpha emission line – a signature of hot hydrogen gas heated by strong ultraviolet emission from newly born stars.

    Keck MOSFIRE
    MOSFIRE

    Although this is a frequently detected signature in galaxies close to Earth, the detection of Lyman-alpha emission at such a great distance is unexpected as it is easily absorbed by the numerous hydrogen atoms thought to pervade the space between galaxies at the dawn of the Universe. The result gives new insight into `cosmic reionization’, the process by which dark clouds of hydrogen were split into their constituent protons and electrons by the first generation of galaxies.

    “We frequently see the Lyman-alpha emission line of hydrogen in nearby objects as it is one of most reliable tracers of star-formation,” said California Institute of Technology (Caltech) astronomer, Adi Zitrin, lead author of the discovery paper. “However, as we penetrate deeper into the Universe, and hence back to earlier times, the space between galaxies contains an increasing number of dark clouds of hydrogen which absorb this signal.”

    Recent work has found the fraction of galaxies showing this prominent line declines markedly after when the Universe was about a billion years old, which is equivalent to a redshift of about 6. Redshift is a measure of how much the Universe has expanded since the light left a distant source and can only be determined for faint objects with a spectrograph on a powerful large telescope such as the Keck Observatory’s twin 10-meter telescopes, the largest on Earth.

    “The surprising aspect about the present discovery is that we have detected this Lyman-alpha line in an apparently faint galaxy at a redshift of 8.68, corresponding to a time when the Universe should be full of absorbing hydrogen clouds,” said co-author and Caltech astronomer Richard Ellis. “Quite apart from breaking the earlier record redshift of 7.73, also obtained at the Keck Observatory, this detection is telling us something new about how the Universe evolved in its first few hundred million years.”

    Computer simulations of cosmic reionization suggest the Universe was fully opaque to Lyman-alpha radiation in the first 400 million years of cosmic history and then gradually, as the first galaxies were born, the intense ultraviolet radiation from their young stars, burned off this obscuring hydrogen in bubbles of increasing radius which, eventually, overlapped so the entire space between galaxies became `ionized’, that is composed of free electrons and protons. At this point the Lyman-alpha radiation was free to travel through space unimpeded.

    It may be that the galaxy we have observed, EGSY8p7, which is unusually (intrinsically) luminous, has special properties that enabled it to create a large bubble of ionized hydrogen much earlier than is possible for more typical galaxies at these times,” said Sirio Belli, a Caltech graduate student who helped undertake the key observations. “EGSY8p7 was found to be both luminous and at high redshift, and its colors measured by the Hubble and Spitzer Space Telescopes indicate it may be powered by a population of unusually hot stars.”

    Because the discovery of such an early source with powerful Lyman-alpha is somewhat unexpected, it provides new insight into the manner by which galaxies contributed to the process of reionization. Conceivably the process is patchy with some regions of space evolving faster than others, for example due to variations in the density of matter from place to place. Alternatively, EGSY8p7 may be the first example of an early generation which unusually strong ionizing radiation.

    “In some respects, the period of cosmic reionization is the final missing piece in our overall understanding of the evolution of the Universe,” says Zitrin. “In addition to pushing back the frontier to a time when the Universe was only 600 million years old, what is exciting about the present discovery is that the study of sources such as EGSY8p7 will offer new insight into how this process occurred.”

    The Caltech team reporting on this discovery consists of Zitrin, Ellis, and Belli who lead an international collaboration involving astronomers at Yale and the University of Arizona, and fellow European researchers from Leiden University in the Netherlands and the University of Durham and the Univeristy College London in England.

    The research was funded in part by NASA.

    See the full article here.

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    Mission
    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.
    Keck UCal

    Keck NASA

    Keck Caltech

     
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