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  • richardmitnick 9:26 am on January 10, 2020 Permalink | Reply
    Tags: , Astronomy magazine, , , , CMB - Cosmic Microwave Background would deal the final deathblow to the steady state model., , , Georges Lemaître and the “primeval atom.”, Steady State theory   

    From Astronomy Magazine: “The Steady State: When astronomers tried to overthrow the Big Bang” 

    Astronomy magazine

    From Astronomy Magazine

    January 6, 2020
    Mara Johnson-Groh

    Some astronomers didn’t like the religious implications of a universe with a beginning. Their alternative was the so-called “steady state model.”

    1
    NASA/ESA/S. Beckwith(STScI) and The HUDF Team

    It all started with a Big Bang. Or maybe it didn’t. In the mid-20th century, most physicists were split on how the universe began — or if it even had a beginning at all. Today, scientists agree that the Big Bang theory best describes the birth of our universe nearly 14 billion years ago. The idea now has a lot of observational evidence, but in the 1940s and ’50s it was still widely debated.

    The Big Bang theory roused the public and religious realms perhaps even more than the scientific community, which had previously accepted an idea called the steady state model. “It was not only a scientific controversy, it also included some broader aspects, ideological and religious aspects. And that was one reason why it was so publicly controversial,” says Helge Kragh, a science historian and professor emeritus at the Niels Bohr Institute. “The steady state theory was, especially in England, often associated with atheism, and the Big Bang theory with Christian theism.” If the universe had a creation point, then it probably had a creator, the thinking went.

    Beginnings of Cosmology

    Humans have always held ideas about how the universe originated. But it wasn’t until advances in the 20th century, including Albert Einstein’s theories of relativity, that astronomers could really form educated ideas about how the universe formed.

    Alexander Friedmann, a Russian physicist, was the first to realize that applying the rules of relativity across large scales described a universe that changed over time. With a mathematical approach, he showed the universe could have started small before expanding over enormous distances and, in some cases, eventually collapsing back in on itself.

    Observations carried outby Lowell Observatory’s V.M. Slipher and, later, Edwin Hubble, showed that the universe was in fact expanding.

    Edwin Hubble looking through a 100-inch Hooker telescope at Mount Wilson in Southern California, 1929 discovers the Universe is Expanding

    Edwin Hubble at Caltech Palomar Samuel Oschin 48 inch Telescope, (credit: Emilio Segre Visual Archives/AIP/SPL)

    And this helped confirm these initial ideas of the Big Bang. Two years later, the Belgian physicist Georges Lemaître published a paper describing how the expanding universe had started as a tiny, hot, dense speck, which he called the “primeval atom.” Ordained as a Catholic priest, Lemaître reported the finding as a happy coincidence of cosmology and theology in an early draft of the paper, though the comment was removed for the final publication of the paper.

    Two decades later, George Gamow would develop theories on the fallout of a hot-birthed universe — namely, how it would create neutrons and protons — and published a popular book on the subject. It even caught the eye of Pope Pius XII, who was taken by the parallels between the scripture of Genesis and the scientific theory.

    Unlike the church, Einstein wasn’t initially happy with the idea of a changing universe, preferring one invariable on large scales. British astronomer Fred Hoyle wasn’t happy, either. Along with two other scientists, he developed a counter-theory — the steady state model. The steady state model suggested that the universe had no beginning and had always been expanding. To explain why the universe looks identical in all directions, it proposed tiny traces of matter, too small to be experimentally measured, were continually being created.

    This model initially garnered support of around half of the scientific community — albeit one that was very small at the time — and became the Big Bang theory’s biggest rival.

    “This [debate between theories] was not in the mainstream of physics research,” says David Kaiser, science historian and physics professor at MIT. “Basically no one paid attention or very little attention, even among professional physicists and astronomers.”

    But as evidence started gathering, that would change.

    New Evidence

    Observations of distant ultra-bright galaxies in the 1950s suggested the universe was changing, and measurements of the helium content in the universe didn’t match the steady state model’s predictions. In 1964, the monumental discovery of the cosmic microwave background radiation [CMB] — direct evidence of a young, hot universe — would deal the final deathblow to the steady state model.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    Cosmic Background Radiation per Planck

    “It really seems to suggest … the universe had very different conditions in early times than today,” Kaiser says. “And that was just not what the steady state model suggests.”

    In an ironic twist, Hoyle used the term “Big Bang” in an attempt to dismiss the theory in a BBC interview. Though his own theory would be largely lost to history, the irreverent name would stick.

    To his death, Hoyle would never submit to the Big Bang theory. A small subset of cosmologists still work on resurrecting a steady state model; but, on the whole, the community overwhelmingly supports the Big Bang theory.

    “There are a couple of other puzzles, so cosmologists don’t think we’re done, but they’re now kind of patching or filling in some holes to the original Big Bang models — certainly not replacing it,” Kaiser says.

    Saul Perlmutter [The Supernova Cosmology Project] shared the 2006 Shaw Prize in Astronomy, the 2011 Nobel Prize in Physics, and the 2015 Breakthrough Prize in Fundamental Physics with Brian P. Schmidt and Adam Riess [The High-z Supernova Search Team] for providing evidence that the expansion of the universe is accelerating.

    See the full article here .


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    Astronomy is a magazine about the science and hobby of astronomy. Based near Milwaukee in Waukesha, Wisconsin, it is produced by Kalmbach Publishing. Astronomy’s readers include those interested in astronomy and those who want to know about sky events, observing techniques, astrophotography, and amateur astronomy in general.

    Astronomy was founded in 1973 by Stephen A. Walther, a graduate of the University of Wisconsin–Stevens Point and amateur astronomer. The first issue, August 1973, consisted of 48 pages with five feature articles and information about what to see in the sky that month. Issues contained astrophotos and illustrations created by astronomical artists. Walther had worked part time as a planetarium lecturer at the University of Wisconsin–Milwaukee and developed an interest in photographing constellations at an early age. Although even in childhood he was interested to obsession in Astronomy, he did so poorly in mathematics that his mother despaired that he would ever be able to earn a living. However he graduated in Journalism from the University of Wisconsin Stevens Point, and as a senior class project he created a business plan for a magazine for amateur astronomers. With the help of his brother David, he was able to bring the magazine to fruition.[citation needed]. He died in 1977.

     
  • richardmitnick 9:45 pm on December 8, 2019 Permalink | Reply
    Tags: "Did the solar system form in a bubble?", , Astronomy magazine, , ,   

    From Astronomy Magazine: “Did the solar system form in a bubble?” 

    Astronomy magazine

    From Astronomy Magazine

    January 2, 2018 [Just now in social media]
    Jake Parks

    Researchers have laid out a new, comprehensive theory for how the solar system formed — inside the bubble of a long-dead, giant star.

    1
    Astronomers believe that planets, asteroids, and other solar system bodies form from the disk of dust and debris around a young star. But what happens before that?

    Astronomers know that our solar system formed about 5 billion years ago from material left over from previous generations of stars. However, beyond that, it gets a little murky.

    The prevailing theory is that a nearby supernova explosion compressed a dense cloud of gas and dust until it collapsed in on itself due to its own gravity. As the cloud condensed, it grew hotter and spun faster. Eventually, the center of the cloud grew so hot it began fusing hydrogen into helium and became the star we lovingly call the Sun.

    But according to a study published December 22 in The Astrophysical Journal, the solar system instead may have formed inside the dense shell of an enormous bubble within a giant star. The study not only provides a fantastical scenario for our solar system’s formation, but also addresses a long-standing mystery concerning our solar system’s chemical makeup.

    The new theory for how the solar system formed starts with an extremely massive star known as a Wolf-Rayet star. Of all the stars in the universe, these stars burn the hottest. Because they are so hot, they also have exceptionally strong stellar winds.

    As a Wolf-Rayet star sheds its outer layers – a normal end-of-life process for a giant star – its strong stellar winds plow through its loosely held cloak of material, forming densely shelled bubbles. According to the study, the solar system could have formed inside of one of these bubbles.

    Since such a huge amount gas and dust is trapped inside, “the shell of such a bubble is a good place to produce stars,” said Nicolas Dauphas, co-author of the study and professor of geophysical sciences at the University of Chicago, in a press release.

    3
    This simulation shows how bubbles form over the course of 4.7 million years from the intense stellar winds off a massive star. UChicago scientists postulated how our own solar system could have formed in the dense shell of such a bubble. Courtesy of V. Dwarkadas & D. Rosenberg .Despite the many impressive discoveries humans have made about the universe, scientists are still unsure about the birth story of our solar system.

    The researchers estimate that this stellar-womb process is so effective that it could account for the formation of 1 to 16 percent of all Sun-like stars.

    Although the unconventional theory may seem a bit superfluous, the researchers proposed it because it also addresses a long-standing mystery of the early solar system: Why did it have so much aluminium-26 and so little iron-60 when compared to the rest of the galaxy?

    Previous studies of meteorite samples have shown that the early solar system was ripe with the isotope aluminium-26, while other studies have shown it was deficient in the isotope iron-60. However, since supernovae explosions produce both of these isotopes, “it begs the question of why one was injected into the solar system and the other was not,” said Vikram Dwarkadas, co-author of the study and professor of astronomy and astrophysics at the University of Chicago.

    This is what brought the researchers to Wolf-Rayet stars, which produce lots of aluminium-26, but zero iron-60.

    “The idea is that aluminum-26 flung from the Wolf-Rayet star is carried outwards on grains of dust formed around the star,” said Dwarkadas. “These grains have enough momentum to punch through one side of the shell, where they are mostly destroyed – trapping the aluminum inside the shell.” Over time, the bubble stops pushing outward and falls back in on itself due to gravity. This collapsing bubble is where the researcher’s think our solar system could have formed.

    Though the researcher’s new theory is far from accepted, its ability to explain the observed chemical composition of the solar system is sure to lead to future studies. In 2023, the NASA spacecraft OSIRIS-REx will return a sample of the ancient asteroid Bennu to Earth. Perhaps this will help astronomers unravel our solar system’s origin story?

    See the full article here .


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  • richardmitnick 5:29 pm on December 8, 2019 Permalink | Reply
    Tags: "Astronomers weigh a white dwarf using gravitational lensing", , Astronomy magazine, , , , Stein 2051B is a white dwarf 17 light-years away.   

    From Astronomy Magazine: “Astronomers weigh a white dwarf using gravitational lensing” 

    Astronomy magazine

    From Astronomy Magazine

    June 07, 2017 [Just now in social media]
    Alison Klesman

    1
    Stein 2051B is a white dwarf 17 light-years away. In 2014, it passed close enough to a background star (seen to the lower left of the white dwarf) to bend its light, as seen from Earth. Credit: NASA, ESA, and K. Sahu (STScI)

    Einstein’s theory of general relatively changed the way scientists look at the universe. The presence of mass bends spacetime like a bowling ball depressing a mattress, causing light to curve as it travels through these depressions on its way to Earth. In 1919, Sir Arthur Eddington confirmed this effect by measuring the deflection of background stars caused by our Sun during a total solar eclipse. Nearly a century later, astronomers have used the Hubble Space Telescope (HST) to measure this effect caused by a star outside our solar system for the first time.

    This groundbreaking result was announced today at the 230th Meeting of the American Astronomical Society by Kailash Sahu of the Space Telescope Science Institute. Sahu’s team used HST to capture the deflection of light from a background star as a white dwarf, the remnant core of a star once like our Sun, passed in front of it as seen from Earth. Although this deflection was tiny – about 1,000 times smaller than the deflection measured by Eddington in 1919 – the precision achievable with Hubble allowed astronomers to see it clearly. From the deflection, they were able to measure the mass of the white dwarf, called Stein 2051B, in a new way that independently confirms the theoretical mass-radius relationship for white dwarfs. This is good news, because the mass-radius relationship is the foundation for astronomers’ use of these objects as standard distance indicators in cosmology. The work will appear this month in the journal Science.

    To find a suitable pair of stars to accomplish this task, Sahu’s team first combed through a catalog of 10,000 stars with large proper motions, or movements on the sky as seen from Earth. Based on the motions of these stars, the team projected the stars’ positions forward in time to find a pair that would pass close enough to each other (when projected on the sky, not in physical space) to produce a bend in starlight measurable with HST.

    Their choice: Stein 2051B, a white dwarf 17 light-years from Earth. According to the team’s calculations, Stein 2051B would pass in front of a distant background star, about 5,000 light-years away, causing the background starlight to bend by 2 milliarcseconds. In more understandable terms, seeing that bend would be like trying to watch an insect crawl across the face of a quarter from a distance of about 1,500 miles (2,400km).

    The team enlisted Hubble to observe the stars over eight epochs, or points in time, with observations taken in the time leading up to, during, and after the event, which occurred in March 2014. And, indeed, they did observe a deflection of the background light as the white dwarf passed in front of the distant source.

    This work represents two firsts in astronomy. One, it’s the first time a deflection due to general relativity has been measured using a star other than our Sun. And two, as Sahu explained during the press conference, measuring the mass of Stein 2051B is the first “clean test for [the] mass-radius relationship.”

    The mass-radius relationship for white dwarfs leads to a limit called the Chandrasekhar limit. If a white dwarf accumulates mass past this limit (by stealing it off a binary companion), it will explode as a supernova, which can be seen from vast distances and can be used by astronomers to measure very large distances accurately. But if this relationship is different than we currently understand it, it would affect distance measurements based on white dwarf supernovae.

    2
    Gravitational lensing occurs when mass causes light to bend, due to the depression it leaves in spacetime. The effect measured by Sahu’s team was 1,000 times smaller than the effect caused by our Sun. Credit: NASA, ESA, and A. Feild (STScI)

    Three other white dwarf masses have been measured by astronomers. If this doesn’t seem like many, that’s because it’s not. Furthermore, the masses of those white dwarfs, including Sirius B, the tiny companion to the brightest star in the Northern Hemisphere, were all measured using the fact that they’re in binary systems. When two stars circle each other, astronomers can use information about the motions of the stars and the inferred mass of the non-white dwarf companion to calculate the mass of the white dwarf. This method, though, could be affected by a process called mass transfer between the stars, which would contaminate the mass-radius relationship measured.

    While Stein 2051B does have a binary companion, it’s so far away from the white dwarf – at least 55 astronomical units, or 5 billion miles (8 billion km) away – that the two cannot be exchanging mass.

    The final result? Displaying a graphic showing the mass-radius relation as a black line, Sahu explained, “Once we put [it] on this mass-radius relation … it should fall on this black curve here, and it falls right on that. So when I saw that it was right exactly on here, I almost fell off my chair.”

    Stein 2051B is about 68 percent the mass of our Sun and about 2.7 billion years old. It is comprised of helium and carbon, which is exactly what astronomers expect for the remnant core of a Sun-like star. Stein 2051B’s perfect fit to the predictions made by the mass-radius relationship confirms our current evolutionary theory of white dwarfs and agrees with our understanding of the physics of the matter that makes up these objects. “This is really a confirmation of the theory that we have been using so far,” Sahu said.

    And the success of Stein 2051B is only the beginning. Next up for Sahu’s group is trying to make this measurement using Proxima Centauri, but Sahu stressed that this method could be used to measure masses of neutron stars, black holes, and isolated massive stars as well.

    “For a star, the single most important thing for the star is its mass. If we know the mass, we know what its radius will be, how bright it would be, how long it will live, what will happen after it dies. Everything depends on the mass of the star,” he said. “But we do not have a very good handle on measuring the mass in a model-independent way … So this at least gives another method to determine the stellar mass in a completely model-independent way.”

    Now that this method can be applied to other objects to more easily weigh them, astronomers have a new, powerful tool at their fingertips able to provide details that before now have been calculated using models that rely on proxy measurements such as the type of light coming from the star or its motion in a binary system. This new, “clean” way of obtaining stellar masses will boost the measurements astronomers are capable of making in many fields, especially as the era of the James Webb Space Telescope dawns next year.

    See the full article here .


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  • richardmitnick 5:13 pm on October 25, 2019 Permalink | Reply
    Tags: "How the Milky Way devours its neighbors", , Astronomy magazine,   

    From Astronomy Magazine: “How the Milky Way devours its neighbors” 

    Astronomy magazine

    From Astronomy Magazine

    October 25, 2019
    Ray Jayawardhana

    1
    OMEGA CENTAURI (NGC 5139) — the Milky Way’s biggest and brightest globular cluster — may be the nucleus of a dwarf galaxy captured long ago by the Milky Way. Daniel Phillips

    On a clear moonless night, the arc of the Milky Way overhead seems the very picture of serenity. Yet its gentle glow masks a life of turmoil. Episodes of violence, plunder, and cannibalism pervade astronomers’ emerging picture of our galaxy’s history.

    Unraveling this story, with the help of painstaking observations and sophisticated computer simulations, could shed light on how the Milky Way acquired its present form. It could also help astronomers understand galaxy evolution in general.

    4
    THE MILKY WAY climbs majestically above the 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile. Despite its peaceful appearance, our galaxy has devoured untold numbers of dwarf galaxies. K. Don/NOAO/AURA/NSF

    The classical view of the galaxy’s origin, proposed more than four decades ago, starts with a single large gas cloud that collapsed when the universe was in its infancy. In 1978, however, Leonard Searle and Robert Zinn, then at the Carnegie Observatories in Pasadena, California, introduced a new twist.

    The astronomers suggested that some globular clusters — dense knots of hundreds of thousands of stars in the galactic halo — joined the Milky Way after its central regions and disk already had taken shape. Ever since, various astronomers have argued that ­certain globular clusters are stolen goods, wrested away from other smaller galaxies as they merged with the Milky Way.

    Clusters orbiting the galactic center “backward” — opposite to the orbits of the Sun and most other stars — are among the most likely interlopers. Many researchers think Omega Centauri (NGC 5139), the most massive globular known, could be the nucleus of a disrupted dwarf galaxy.

    This more chaotic picture agrees better with current theory about how galaxies evolved from an initially near-homogeneous universe. The favored model goes by the name “cold dark matter” (CDM).

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

    This theory assumes dark matter — the mysterious substance whose gravity dominates over normal matter — consists of slow-moving (hence “cold”) particles.

    From the bottom up

    The CDM scenario, explored in numerous theoretical calculations and simulations, suggests structure formed from the bottom up. Large galaxies grew from the mergers of smaller clumps. Galaxies grouped into clusters and still-larger superclusters. One challenge for the CDM model is that it predicts many more dwarf galaxies in our cosmic neighborhood than astronomers observe.

    It could be that the Milky Way and other large galaxies, like the nearby Andromeda Galaxy (M31), already have gobbled up most of their smaller brethren or distorted them so much they are difficult to spot even in our own backyard.

    A massive galaxy exerts powerful tidal forces because the gravitational pull acting on the near side of a neighbor significantly exceeds that acting on the far side. These forces overwhelm the gravity binding a dwarf galaxy together and rip it apart. The tides draw gas and stars into long trails or streams that eventually disperse. Once the “loot” mixes in with the big galaxy’s contents, tracing its origin proves far from easy.

    The vast majority of mergers that built our galaxy probably happened early in its history. But the Milky Way continues to des­troy and swallow its remaining neighbors.

    6
    THE LARGE MAGELLANIC CLOUD provides a major portion of the Magellanic Stream, a 600,000-light-year-long concentration of gas perhaps stripped by the Milky Way from this irregular satellite galaxy and its neighbor, the Small Magellanic Cloud.
    Andreas B’ker & Axel Martin

    Big news from small galaxies

    The Magellanic Stream has often been held up as the poster child of an ongoing merger.

    10

    The stream consists of gas stripped from two irregular satellite galaxies well known to Southern Hemisphere observers: the Large and Small Magellanic Clouds. First identified more than 40 years ago, the stream trails the motions of the galaxies for some 600,000 light-years. The so-called Leading Arm stretches between the clouds and our galaxy.

    Some models suggest the Milky Way created these filaments. But a decade ago, Nitya Kallivayalil, then at MIT, and her colleagues found that the Magellanic Clouds are moving unexpectedly fast. Unless our galaxy has far more mass than we think, the clouds may be on their first pass — and tides alone likely could not produce the stream.

    The Milky Way also seems to be disrupting other Local Group dwarfs. University of Virginia astronomer Steven Majewski leads one of several groups that have discovered tidal debris from several of these dwarfs, including those in the constellations Carina, Leo, Ursa Minor, and Sculptor.

    Perhaps the most dramatic case of a cannibalized Milky Way satellite is the Sagittarius Dwarf Spheroidal Galaxy.

    11
    Sagittarius Dwarf Spheroidal Galaxy

    Rodrigo Ibata, then a graduate student at Cambridge ­University, found it almost by accident.

    In 1994, Ibata was studying the motions and chemical compositions of stars in our galaxy’s bulge. While collecting spectra of his sample stars at the Anglo-Australian Telescope in Australia, Ibata noticed a few of the reddest stars had velocities different from all the others.


    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    Even stranger, the stars appeared to be moving together. On the next couple of nights, he took spectra of more red stars. They all shared the same unusual motion.

    When Ibata returned to Cambridge, he and his colleagues scanned archival photographic plates of that region of sky, then plotted the positions of red stars similar in brightness to those he had found with peculiar velocities. This exercise revealed the contours of a hitherto unknown galaxy. It lies roughly perpendicular to the Milky Way’s disk and about 100,000 light-years away, on the far side of the galactic center.

    It had been hiding behind the Milky Way’s thick veil of stars and dust. What’s more, the newly found dwarf spheroidal galaxy, named Sagittarius after the constellation that contains its center, has a rather contorted appearance. This represents clear evidence of bullying by the dwarf’s massive neighbor.

    During the past 20 years, astronomers have attempted to chart the dwarf galaxy’s full extent. Recent maps show its debris scattered in a giant arc that wraps around the Milky Way. Ibata’s team and others argue that several globular clusters previously thought to belong to our galaxy actually came from the Sagittarius dwarf. Other stolen clusters and individual stars may exist, but they’re already so well mixed in with the Milky Way’s own that astronomers can’t trace their origins.

    The surprise discovery of the Sagittarius dwarf raised the possibility others like it may lurk undetected. Astronomers imagined spaghetti-like strands crisscrossing the Milky Way, each filament retaining a faint memory of the path taken by its long-since-destroyed parent galaxy or globular cluster. Scientists tried to identify streams of stars with peculiar motions and odd chemical abundance patterns, which might betray their alien origins.

    The tides turn to Sloan

    For researchers in pursuit of these elusive fossils, the Sloan Digital Sky Survey has turned out to be a treasure trove.

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    Initiated in 2000 and now in its fourth phase, the multi-wavelength survey covers one-third of the sky.

    Michael Odenkirchen and Eva Grebel, then at the Max Planck Institute for Astronomy in Germany, and their colleagues quickly discovered two tidal trails. The trails emerge from a sparse and remote glob­ular cluster cataloged as Palomar 5.

    12
    Palomar 5, Serpens Dwarf

    One of these trails has now been traced across more than 20° of sky, spanning some 25,000 light-years.

    Scientists think Palomar 5 lost much of the observed debris in the past 2 billion years. Simulations suggest this ­cluster will break apart completely the next time it crosses the Milky Way’s disk, just 100 million years from now. Other researchers have since identified an even larger debris arc associated with the glob­ular cluster NGC 5466.

    7
    THE ANDROMEDA GALAXY (M31) looks serene when viewed from Earth, but it disguises a history of rampant cannibalism.
    T.A. Rector/B.A. Wolpa/NOAO/AURA/NSF

    In 2003, Heidi Jo Newberg of Rensselaer Polytechnic Institute in Troy, New York, Brian Yanny of Fermilab outside Chicago, and their colleagues reported the discovery of a “ring” of stars beyond the visible edge of the Milky Way’s disk. They named it the Monoceros Stream because its center lies toward that constellation.

    13
    Monoceros Ring

    The Monoceros Stream’s stars stood out in the Sloan data because they have unusual colors. The colors arise from the stars’ lack of heavy ­elements — meaning all those natural elements heavier than helium. Some ­scientists think the stream originates from a dwarf galaxy in the constellation Canis Major that’s being torn apart by the Milky Way’s gravitational tides.

    In 2006, Mario Juric of Prince­ton University and his colleagues reported discovery of a remarkable increase in stellar density toward the constellation Virgo. The structure turned up in a 3-D map of about 48 million stars the team made from Sloan data.

    At an estimated distance of 30,000 light-years, the density structure lies well within the Milky Way’s confines. The most likely explanation is that these “extra” stars belong to a slowly dissolving dwarf galaxy.

    A team led by Kathy Vivas of the Center for Astronomical Investigations in Vene­zuela had noticed hints of such a beast a few years earlier. The researchers were searching for a type of pulsating variable star known as RR Lyrae stars. “We saw a high density of RR Lyrae stars in the region — more than 20 of them — and speculated that they belonged to a small galaxy being cannibalized by the Milky Way,” she says. In light of the Sloan findings, “It appears that the stellar stream we detected is itself part of a larger structure.”

    Field of streams

    Later in 2006, Cambridge University’s Vasily Belokurov and Daniel Zucker and their collaborators identified a number of other trails and lumps in Sloan images taken toward the north galactic pole, not far from the direction of the previously known Sagittarius and Monoceros streams. So many tidal trails populate this region that the researchers dubbed it the “field of streams.”

    One of these trails covers 30° of sky. It contains two globular clusters deficient in heavy elements and could be the “orphan” of yet another disrupted dwarf galaxy. At least three more faint Milky Way satellites, all showing signs of distortion, turn up in the Sloan survey. Taken together, these findings are “a striking demonstration of multiple merger events going on in the Milky Way right now,” Yanny says.

    6

    Astronomers now have little doubt our galaxy has enriched itself at the expense of others. “In fact, the majority of globular clusters might be relics of accretion events,” claims Julio Navarro, an astrophysicist at the University of Victoria.

    As supporting ­evidence, Navarro points to the agreement between the distribution of globular clusters around the Milky Way and the density profile of accreted stars in his group’s simulations of
    galaxy formation. He finds a similar match between models and observations of our galaxy’s near twin, the Andromeda Galaxy. This suggests galactic cannibalism might be rampant.

    Our exotic neighbors

    But, the “stolen goods” may not be found just in the galaxy’s outer reaches. Some interlopers may lurk in the solar neighborhood, too. Timothy Beers of the University of Notre Dame and his collab­orators identified a group of stars in the Milky Way’s disk that shares the chemical abundance pattern of stars in Omega Centauri, and may have come from the same disrupted parent galaxy.

    Another such grouping includes the relatively nearby red giant star Arcturus. The members of this group move through space in a similar manner to one another, but much slower than most other stars in their vicinity. They also share a distinct chemical imprint.

    “You can make a plausible though not conclusive case that these stars came from a disrupted satellite galaxy,” says Navarro. His simulations show tidal debris not only can accumulate in the galaxy’s halo, but also contribute to the disk. “It may be that most metal-poor stars in the Milky Way’s disk originated in various accreted satellites,” he argues.

    Sloan researchers have also discovered two distinct populations of stars in the galaxy’s halo. The groups orbit the galaxy’s center in opposite directions, providing more evidence for multiple mergers in the past. Unfortunately, it’s probably impossible to pin down just how many neighbors the Milky Way has devoured during its long history. There could have been hundreds of small early mergers, or just a few major collisions that dominated.

    A study of 20,000 stars in four dwarf spheroidal galaxies found a puzzling paucity of extremely metal-poor stars. This suggests the Milky Way’s current small neighbors may differ fundamentally from those it devoured in the distant past.

    Detailed observations of large numbers of stars in the galactic halo could provide more clues to the Milky Way’s history. A survey project known as RAVE, for RAdial Velocity Experiment, has measured the velocities and compositions of 483,330 stars. Meanwhile, Sloan’s APOGEE-2 survey will collect spectra of another 300,000 stars in both the northern and southern skies by the time it wraps up in the autumn of 2020.

    Our galaxy clearly has had a colorful, if not dramatic, history. But the story is far from complete. The challenge for astronomers will be to weave it together from a million pieces scattered in space and time.

    The cannibal next door

    With evidence of the Milky Way’s cannibalism all around us, it seems logical our galaxy’s near twin, the massive Andromeda Galaxy (M31), should show signs, too. The nearest large galaxy to our own, the spiral behemoth M31, lies approximately 2.5 million light-years away. That vast distance makes it difficult for astronomers to discern relic stars left behind by past mergers.

    Despite the challenges, astronomers have made progress. In 1993, a team led by Tod Lauer of the National Optical Astronomy Observatories in Tucson discovered what appear to be two dense knots — called a double nucleus — at M31’s center. The researchers needed the Hubble Space Telescope’s sharp eyes to separate the two structures. Some astronomers spec­ulated that one of the clumps originated in a satellite galaxy that had collided with M31.

    One problem with this story: The two clumps should have merged in less than 100 million years — a short time compared with the several-billion-year age of the stars in those knots. Most researchers now prefer an alternate explanation, proposed by Scott Tremaine of Princeton University. He thinks both knots belong to a single elongated disk of stars having a supermassive black hole at one focus.

    More convincing evidence of M31’s cannibalism came to light in 2001. At that time, astronomers were conducting a deep panoramic imaging survey of the Andromeda Galaxy’s halo with the 2.5-meter Isaac Newton Telescopeon La Palma in the Canary Islands.

    ING Isaac Newton 2.5m telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, Spain, Altitude 2,344 m (7,690 ft)

    Rodrigo Ibata of Strasbourg Observatory in France and his collaborators discovered an extended stream of stars protruding from Andromeda. Astronomers have dubbed this feature the Giant Southern Stream.

    Some researchers have proposed that the Giant Southern Stream consists of stars torn from one of Andromeda’s two close companions, the dwarf satellite galaxies M32 and NGC 205. According to Puragra Guhathakurta of the University of California at Santa Cruz, there’s no hard evidence for this explanation.

    The more likely scenario, Guhathakurta says, is that Andromeda has completely devoured a dwarf galaxy. If this is true, the Giant Southern Stream may be just one segment of an extended debris trail looping around the giant galaxy. The trail marks the dwarf galaxy’s extended death spiral into Andromeda.

    A team led by Guhathakurta has reported evidence linking the Giant Southern Stream to several other locations in Andromeda where large numbers of stars appear to move as a group. The researchers believe these features are parts of a continuous star stream. “We think we are seeing the debris trail of a small, chemically rich galaxy that fell into Andromeda,” Guhathakurta says.

    More recently, the Sloan survey revealed a giant, ­diffuse clump of stars just outside M31’s disk that could be the remnants of another satellite galaxy being torn apart by Andromeda’s tides. The exact nature of this structure remains a mystery, however. Many astronomers continue to search Andromeda for clues to its voracious and chaotic history.

    See the full article here .


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  • richardmitnick 11:25 am on August 30, 2019 Permalink | Reply
    Tags: "Life on alien worlds could be more diverse than on Earth", , Astronomy magazine, , , ,   

    From Astronomy Magazine: “Life on alien worlds could be more diverse than on Earth” 

    Astronomy magazine

    From Astronomy Magazine

    August 23, 2019
    Mara Johnson-Groh

    Earth is the only place in the universe where we know life exists. But with billions of other star systems out there, it might not be the best place for life.

    1
    When you stack up the most promising recent exoplanet finds, as illustrated here, it becomes clear none is Earth’s true twin. But even more habitable worlds may be out there waiting to be found. NASA/Ames/JPL-Caltech

    Earth is the only place in the universe where we know life exists. But with billions of other star systems out there, it might not be the best place for life. In a new study [Goldschmidt2019 Barcelona], astronomers modeled the potential for life on other watery planets and found some conditions that can create oceans maximized for habitability.

    The model suggests that watery planets with dense atmospheres, continents, and long days — slowly rotating planets that is — were most conducive to life. These conditions stimulate ocean circulation, which brings nutrients from the depths to the surface where it’s available for biologic activity.

    “The research shows us that conditions on some exoplanets with favorable ocean circulation patterns could be better suited to support life that is more abundant or more active than life on Earth,” Stephanie Olson, a University of Chicago researcher who lead the new study, said in a press release.

    To date, over 4,000 exoplanets have been confirmed, and a handful of those worlds orbit at a safe enough distance from their host star to have liquid water on the surface. These habitable zone planets are at the forefront of the search for alien life and the new research, presented Friday at the Goldschmidt Conference in Barcelona, Spain, will help astronomers narrow down that search.

    Previous studies looking at exoplanet habitability had largely neglected the role that oceans play in regulating global climate and heat transportation. The researchers focused in on this niche, using a computer model to compare different combinations of climates and ocean habitats that could exist on exoplanets across the galaxy. The study aimed to look for things like upwelling, a type of ocean circulation driven by wind.

    Upwelling and ocean circulation have long played a major role in sustaining life in Earth’s oceans. And since the oceans and atmospheres are interlinked, the evolution of life in the oceans has been reflected in certain chemical changes in the atmosphere. It’s unlikely astronomers will directly see life on other planets, but seeing these so-called biosignatures in exoplanet atmospheres could be possible with the next generation of telescopes. Ultimately, this research will help scientists select the best candidates out of the growing census of exoplanets for follow up study.

    “One of the things we don’t really understand particularly well in the exoplanet community is how oceans on some of these planets might be working,” said Chris Reinhard, professor at the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, who was not involved in the new study. “Part of that is because we haven’t had the computer models or people working on them to really explore these things, so there’s a lot to learn. This is a really huge step in the right direction to figure some of those things out.”

    See the full article here .


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  • richardmitnick 10:03 am on July 31, 2019 Permalink | Reply
    Tags: "Astronomers Once Watched a Star Turn Directly Into a Black Hole", , Astronomy magazine, , , , Curiosity News   

    From Astronomy Magazine via Curiosity: “Astronomers Once Watched a Star Turn Directly Into a Black Hole” 

    Astronomy magazine

    From Astronomy Magazine

    via

    2
    Curiosity

    2
    Curiosity

    Most dying stars go out with a bang — a supernova, more specifically. But scientists recently observed a star that went out with a whisper, skipping the supernova phase and going straight into a black hole. The discovery not only teaches us more about stars, but it could also uncover the mysteries behind some of the universe’s most massive black holes.

    Go Directly to Black Hole, Do Not Pass Go

    Scientists at Ohio State University have, for some time, been watching a galaxy 22 million light-years away. That galaxy, called NGC 6946 and nicknamed the “Fireworks Galaxy,” sees a large number of supernovae that scientists observe via the help of the Large Binocular Telescope (LBT).

    In 2009, scientists noticed that one star, N6946-BH1, was beginning to weaken. In 2015, it disappeared — no big flash, no epic supernova. The scientists concluded that it had instead become a black hole, something that scientists usually believe can only happen after a supernova. Scientists aptly called this unusual trajectory a “massive fail,” and published their results in the Monthly Notices of the Royal Astronomical Society.

    3
    Star N6946-BH1 before and after it vanished out of sight by imploding to form a black hole. Image: NASA, ESA, and C. Kochanek (OSU).

    “The typical view is that a star can form a black hole only after it goes supernova,” said Ohio State astronomy professor and study researcher Christopher Kochanek in the press release. “If a star can fall short of a supernova and still make a black hole, that would help explain why we don’t see supernovae from the most massive stars.”

    5
    The doomed star, named N6946-BH1, was 25 times as massive as our sun. It began to brighten weakly in 2009. But, by 2015, it appeared to have winked out of existence. By a careful process of elimination, based on observations researchers eventually concluded that the star must have become a black hole. This may be the fate for extremely massive stars in the universe. Image: NASA, ESA, and P. Jeffries (STScI)

    What This Could Tell Us About Black Holes

    Scientists still don’t know how often stars go through massive fails, but researcher Scott Adams predicts that it occurs in about 10 to 30 percent of massive stars.

    The findings could help explain the origins of very massive black holes, since they may be easier to form if no supernova is necessary. That’s because the explosion of the supernova ends up blasting out the star’s outer layers, leaving behind less mass to create a black hole. If no supernova was involved, more of the star’s mass would be available to transform into a more massive black hole.

    See the full article here .


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  • richardmitnick 7:53 am on July 26, 2019 Permalink | Reply
    Tags: , Astronomy magazine, , , , , Dark Stars,   

    From Astronomy Magazine- “Dark stars: The seeds of supermassive black holes?” 

    Astronomy magazine

    From Astronomy Magazine

    July 19, 2019
    Jake Parks

    The early universe was a very different place than it is now. But it may have been the perfect environment for a strange class of giant, puffy stars that used dark matter as fuel.

    1
    Dark matter annihilations may have fueled some of the universe’s first stars, allowing them to grow into giant, puffy clouds that are millions of times the mass and billions of times the brightness of the Sun. Astronomy: Roen Kelly after NSF.

    Powered by dark matter, dark stars are hypothetical objects that may have inhabited the early universe. If they existed, these mysterious beasts would not only have been the first stars to form in the cosmos, they also might explain how supermassive black holes got their start.

    Fueled by dark matter

    2
    Astronomy: Roen Kelly

    Normal stars all power themselves in the same way: nuclear fusion. Stars are so massive that they’re constantly on the verge of collapsing in on themselves. But as gravity squeezes a star, it generates so much heat in the star’s core that it smooshes the atoms together, releasing energy. This energy provides just enough outward pressure to precisely counterbalance a star’s gravitational collapse.

    But for dark stars, the story’s a little different.

    Theories suggest that dark stars would be mostly made from the same material as normal stars — namely, hydrogen and helium. But because these hypothetical dark stars would have formed in the early universe, when the cosmos was a lot denser, they also likely contain a small but significant amount of dark matter in the form of Weakly Interacting Massive Particles (WIMPs) — a leading dark matter candidate.

    These WIMPs are thought to serve as their own antimatter particles, they can annihilate with one another, producing pure energy. Within a dark star, these extremely powerful WIMP annihilations could offer enough outward pressure to prevent the star’s collapse without the need for core fusion.

    According to dark star researcher Katherine Freese, the Kodosky Endowed Chair of Physics at UT-Austin, WIMPs only make up about 0.1 percent of a dark star’s total mass. But just this tiny bit of WIMP fuel could keep a dark star chugging along for millions or even billions of years.

    3
    Astronomy: Roen Kelly

    What did dark stars look like?

    Dark stars don’t just behave differently than normal stars. They also look different.

    Because dark stars don’t rely on core fusion to stave off gravitational collapse, they’re not extremely compressed like normal stars. Instead, dark stars are likely giant, puffy clouds that shine extremely bright. Due to their bloated nature, Freese says, dark stars could even reach diameters of up to about 10 astronomical units (AU), where 1 AU is the average Earth-Sun distance of 93 million miles (150 million kilometers).

    4
    Astronomy: Roen Kelly

    “They can keep growing as long as there is dark matter fuel,” Freese told Astronomy. “We’ve assumed they can get up to 10 million times the mass of the Sun and 10 billion times as bright as the Sun, but we don’t really know. There is no cutoff in principle.”

    Searching for dark stars

    One of the hurdles to proving dark stars truly exist, though, is that these ironically bright objects depend on dark-matter annihilations to survive. However, such annihilations primarily occurred in the very early universe, when dark-matter particles were sharing close quarters. So, in order to spot ancient dark stars, we need telescopes capable of peering back to the extremely distant past.

    Fortunately, according to Freese, the upcoming James Webb Space Telescope should be able to spot dark stars — as long as we know what to look for.

    NASA/ESA/CSA Webb Telescope annotated

    “They would look completely different from hot stars,” Freese told Astronomy. “Dark stars are cool [17,500 °F (9,700 °C)]. So, they would look more like the Sun in terms of frequency of light, even though they’re much brighter. That combination of cool and bright is hard to explain with other objects.”

    “It is an exciting prospect that an entirely new type of star may be discovered in these upcoming data,” Freese and her colleagues wrote in a review paper.

    Seeding supermassive black holes

    If researchers are able to uncover evidence for the existence of dark stars, it would change how we think about the early stages of the universe. Darks stars would swiftly become the top candidates for the first generation of stars, which formed some 200 million years after the Big Bang.

    But dark stars might also explain one of the most nagging questions in cosmology: How did supermassive black holes first form?

    “If a dark star of a million solar masses were found [by James Webb] from very early on, it’s pretty clear that such an object would end up as a big black hole,” Freese says. “Then these could merge together to make supermassive black holes. A very reasonable scenario!”

    See the full article here .


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  • richardmitnick 8:22 am on June 21, 2019 Permalink | Reply
    Tags: , Astronomy magazine, , , , Dark matter may have punched a hole in the Milky Way   

    From Astronomy Magazine: “Dark matter may have punched a hole in the Milky Way” 

    Astronomy magazine

    From Astronomy Magazine

    June 12, 2019
    Jake Parks

    A wrecking ball of dark matter 5 million times the mass of the Sun may be the best explanation for a disrupted stream of stars.

    1
    An artist’s rendition shows the dark matter halo (blue) that astronomers believe surrounds the Milky Way. ESO/L. Calçada

    A massive clump of dark matter may have plowed through a conga line of stars streaming around the Milky Way, according to new research presented Tuesday at the 234th Meeting of the American Astronomical Society.

    The research, led by Ana Bonaca of the Harvard-Smithsonian Center for Astrophysics, reveals a curious abnormality in an otherwise uniform stream of stars orbiting in the Milky Way’s outer halo. Specifically, the researchers found an odd kink within the stream that they think was caused by a “close encounter with a massive and dense perturber,” according to the presentation’s abstract.

    Because there are no obvious culprits made of normal matter that fit the bill, the researchers believe the intervening object could be a 5 million-solar-mass blob of dark matter that ripped through the stream at over 500,000 miles (800,000 kilometers) per hour roughly half a billion years ago.

    Although this theory is far from confirmed, the unique observation does open the door to the possibility of using stellar streams like this one to constrain the properties of dark matter in the Milky Way. For example, if it was truly dark matter that tore through this stellar stream, Bonaca says it would suggest dark matter is “cold,” meaning it’s heavy, relatively slow moving (non-relativistic), and effectively clumps together.

    A cosmic bullet

    To carry out the study, Bonaca and her team used data from the ESA’s Gaia space observatory, which has observed over a billion objects with unparalleled precision. Using this data, they mapped the positions and motions of stars in the stellar stream GD-1, which astronomers believe is the remains of a 70,000-solar-mass collection of old stars (called a globular cluster) that was shredded by past gravitational interactions with the Milky Way.

    After noticing that GD-1 has an impact scar — a line of ejected stars — that indicates a past interaction, the researchers ran simulations to try to reproduce what they saw. After testing a variety of models, they found that the gravity of an object millions of times more massive than the Sun would do the trick.

    The team naturally went searching for the object responsible. “Any massive and dense object orbiting in the halo could be the perturber,” Bonaca told Astronomy, “so a wandering supermassive black hole is definitely a possibility.” But so far, the team has failed to find any objects, black holes or otherwise, with the right trajectory and mass.

    According to a preprint of their paper, “Orbit integrations back in time show that the stream encounter could not have been caused by any known globular cluster or dwarf galaxy.” This led the team to conclude the “most plausible explanation” is that GD-1 had a past encounter with a clump of dark matter, like those expected to reside in the halos of galaxies.

    Still hunting

    Bonaca admits the current research is not conclusive. “However, if we can locate where the perturber is now, that would open new research directions, including searching for additional observational evidence [indicating it is dark matter].” Such evidence could take the form of other stars or gas clouds being jostled around by the dark matter’s gravity, or even gamma-rays associated with dark matter annihilations, which occur when two dark matter particles slam into and destroy each other, releasing a flash of energy.

    Bonaca says her team recently obtained measurements of the motion of stars in the disrupted part of the stream. By mapping out where the stars are now and how they are moving, the team should be able to better calculate where the perturber could be now to locate it. That would tell them were on the sky to look for that additional evidence that the cosmic cannonball is indeed dark matter.

    But since there’s currently only one disrupted star stream to study, Bonaca and her team are also searching through more Gaia data to search for other examples like GD-1. In fact, they recently found another stream called Jhelum, which likewise has a strange structure. However, Bonaca says they currently do not have a good explanation for what might have happened to this stream.

    This research has been accepted June 6 for publication in The Astrophysical Journal. An updated version of the research is expected to be published to the preprint site arXiv.org soon.

    See the full article here .


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  • richardmitnick 10:48 am on December 28, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , , Did a nearby supernova cause one of Earth’s mass extinctions?,   

    From Astronomy Magazine: “Did a nearby supernova cause one of Earth’s mass extinctions?” 

    Astronomy magazine

    From Astronomy Magazine

    December 13, 2018
    Alison Klesman

    Astronomers say radiation arriving from a powerful stellar explosion may be the event that wiped coastal ocean animals off the planet 2.6 million years ago.

    1
    This composite image shows supernova remnant 1E 0102.2-7219, which lies 190,000 light-years away. The supernova that may have caused a mass extinction on Earth was much closer, only about 150 light-years distant. X-ray (NASA/CXC/MIT/D.Dewey et al. & NASA/CXC/SAO/J.DePasquale); Optical (NASA/STScI)

    NASA/Chandra X-ray Telescope

    NASA/ESA Hubble Telescope

    Supernovae are the explosive end stages of massive stars. About 2.6 million years ago, one such supernova lit up Earth’s sky from about 150 light-years away. A few hundred years later, after the new star had long since faded from the sky, cosmic rays from the event finally reached Earth, slamming into our planet. Now, a group of researchers led by Adrian Melott at the University of Kansas believes this cosmic onslaught is linked to a mass extinction of ocean animals roaming Earth’s waters at the time — including the Megalodon. Their work was published November 27 in Astrobiology.

    “Supernovae should have affected Earth at some time or another,” Melott said in a press release. However, in the past, it’s been hard to determine exactly how or when such events would have had an effect. But, according to the group’s paper, “a newly documented marine megafaunal extinction” lines up with the arrival of a potentially lethal influx of radiation, indicating they might be able to pin a particular supernova on a particular event.

    That event, which occurred at the Pliocene-Pleistocene boundary, caused about 36 percent of the genera in coastal waters — where the penetration of radiation would have been greater in the shallower water — to go extinct. “We have evidence of nearby [supernova] events at a specific time. We know about how far away they were, so we can actually compute how that would have affected Earth and compare it to what we know about what happened at that time,” Melott said.

    Incoming!

    The killer radiation came in the form of cosmic rays made up of fast-moving muons, which are a few hundred times the mass of an electron, according to Melott. “They’re very penetrating. Even normally, there are lots of them passing through us. Nearly all of them pass through harmlessly, yet about one-fifth of our radiation dose comes by muons,” he said.

    But what about under abnormal conditions, such as the wave of material from a supernova? “When this wave of cosmic rays hits, multiply those muons by a few hundred. Only a small fraction of them will interact in any way, but when the number is so large and their energy so high, you get increased mutations and cancer,” Melott said. Based on the rates of muons hitting Earth from the stellar explosion, the team estimated that in human-sized animals, the cancer rate would increase by about 50 percent. But in larger animals, that effect would have also been larger. “For an elephant or a whale, the radiation dose goes way up,” he said. And because high-energy muons can penetrate hundreds of yards into water, they could have peppered the coastal waters where the extinctions occurred, essentially targeting the animals that lived there for death.

    2
    Our Local Bubble is of a bubble of hot, diffuse gas that was likely generated by one or more supernovae. NASA; modified from original version by Wikipedia User Geni.

    Tracing the Source

    The other piece of the puzzle was pinpointing the event that could have caused that wave of radiation. Iron-60 is a radioactive isotope of iron with a half-life of about 2.6 million years — which means that any iron-60 that formed with Earth is now long gone. Thus, the only way scientists could still find iron-60 today is if it arrived via cosmic means, such as “raining down” in the wave from a supernova. And there’s a huge spike of iron-60 that was deposited about 2.6 million years ago, indicating the material from a supernova event reached us then.

    As for where that supernova came from, our Sun sits inside what astronomers call the Local Bubble. It’s a relatively empty area of the interstellar medium (ISM) that fills the space between stars. The Local Bubble is a 300-light-year-wide region filled with hot, diffuse gas, bounded by the cold, dense gas of the “regular” ISM. In our region of the galaxy, several bubbles exist, and astronomers think these bubbles — including our own — were caused by supernovae, whose energy can sweep away material and heat anything that remains, forming just such a bubble.

    The Local Bubble may have been caused by not one, but a chain of supernovae, one of which went off extremely close to Earth 2.6 million years ago, depositing that layer of radioactive material. And the Local Bubble itself could have exacerbated the amount of cosmic rays Earth received, increasing the deadliness of such events. According to Melott, the boundaries of the bubble could have reflected cosmic rays back when they hit it, creating a “cosmic-ray bath” lasting 10,000–100,000 years for each supernova. A chain of supernovae going off relatively close to each other in time could send cosmic rays bouncing throughout the Local Bubble for millions of years, he said.

    All of this boils down to a tantalizing connection between the supernovae that clearly changed our local region of the galaxy and an unexplained major extinction event. “There really hasn’t been any good explanation for the marine megafaunal extinction,” Melott concluded. “This could be one.”

    See the full article here .


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  • richardmitnick 3:54 pm on May 4, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , , , Wandering supermassive black holes   

    From Astronomy Magazine: “The Milky Way’s supermassive black hole may have a dozen nomadic siblings” 

    Astronomy magazine

    Astronomy Magazine

    April 27, 2018
    Jake Parks

    New research suggests that ‘wandering’ supermassive black holes are common within many types of galaxies — including the Milky Way.

    1
    Like most galaxies, the Andromeda galaxy (pictured above) is thought to house a supermassive black hole at its core. According to new research, galaxies roughly the mass of the Milky Way also likely contain about a dozen more ‘wandering’ supermassive black holes. NASA/JPL-Caltech

    At the center of the Milky Way sits a dark and dangerous beast: Sagittarius A*.

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    Located about 26,000 light-years from Earth, our galaxy’s only known supermassive black hole is roughly 4 million times as massive as the Sun, and its immense gravitational pull can nonchalantly annihilate any object that strays too close. Fortunately for us, Sagittarius A* is like a troll under a bridge — it does not leave its post.

    This tends to be the case for most supermassive black holes (SMBHs) found throughout the universe. However, sometimes a SMBH can be forced from the center of its host galaxy, particularly if it’s involved in a galactic merger with a bigger counterpart. For example, if a small galaxy merges with a larger one, the smaller galaxy’s SMBH will likely be thrown into a wide orbit around the newly formed galaxy, therefore becoming a ‘wandering’ supermassive black hole. Though astronomers have previously found evidence of these nomadic SMBHs on the outskirts of other galaxies, their overall prevalence is still largely unknown.

    But according to a new study published April 24 in The Astrophysical Journal Letters, wandering supermassive black holes may be quite common (and even observable) within many different types of galaxies — including the Milky Way.

    To carry out the study, the researchers took advantage of a new, state-of-the-art cosmological simulation called ROMULUS25. This N-body simulation uses an advanced supercomputer called Blue Waters to model how billions of individual particles interact and evolve over time.

    U Illinois Urbana-Champaign Blue Waters Cray Linux XE/XK hybrid machine supercomputer

    Though the ROMULUS25 simulation encompasses an astounding volume of over 15,000 cubic Megaparsecs (1 Megaparsec = 3 million light-years), it is still able to resolve the internal structure of galaxies and dwarf galaxies, as well as capture the orbital evolution of SMBHs following galactic mergers.

    3
    A sample of the ROMULUS25 simulation at redshift z = 0.4. The three slices of the simulation are focused on the same central group of galaxies (about 10 times as massive as the Milky Way), and shows the distribution of dark matter (left), the distribution of stars color-coded by composition (center; red are metal poor, blue are metal rich), and the distribution of stars color-coded by age (right; red are old, blue are young). White dots mark black holes. N-Body Shop (University of Washington).

    By extracting a sample of Milky-Way-mass galaxies from the simulation, the researchers were able to determine that any galaxy roughly the mass of the Milky Way, regardless of its recent merger history or morphology, likely contains about a dozen supermassive black holes, with roughly five being located within 30,000 light-years of the galaxy’s center. Although this slew of meandering SMBHs may seem intimidating (especially considering they roam for at least a few billion years), according to the study, they pose little threat to our tiny corner of the cosmos.

    “It is extremely unlikely that any wandering supermassive black hole will come close enough to our Sun to have any impact on our solar system,” said lead author Michael Tremmel, a postdoctoral fellow at the Yale Center for Astronomy and Astrophysics, in a press release. “We estimate that a close approach of one of these wanderers that is able to affect our solar system should occur every 100 billion years or so, or nearly 10 times the age of the universe.”

    So, even though the supermassive black hole at the center of the Milky Way may have a dozen disenfranchised siblings, by the time they could pose a threat to Earth, the Sun will have likely already burnt out. In the meantime, astronomers will continue working hard to definitely prove these wandering Goliaths actually exist. And once they do, the real fun can begin.

    See the full article here .

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