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  • richardmitnick 12:11 pm on February 21, 2020 Permalink | Reply
    Tags: "When Betelgeuse goes supernova what will it look like from Earth?", , Astronomy magazine, , , , what will it look like from Earth?"   

    From Astronomy Magazine: “When Betelgeuse goes supernova, what will it look like from Earth?” 

    From Astronomy Magazine

    February 14, 2020
    Eric Betz

    Astronomers simulated what humans will see on Earth when the star Betelgeuse explodes as a supernova sometime in the next 100,000 years.

    1
    A plume of gas nearly the size of our solar system erupts from Betelgeuse’s surface in this artist’s illustration of real observations gathered by astronomers using the Very Large Telescope in Chile. European Southern Observatory/L. Calçada.

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

    If you stargaze on a clear winter night, it’s hard to miss the constellation Orion the Hunter, with his shield in one arm and the other arm stretched high to the heavens.

    Orion Nebula ESO/VLT

    A bright red dot called Betelgeuse marks Orion’s shoulder, and this star’s strange dimming has captivated skygazers for thousands of years. Aboriginal Australians may have even worked it into their oral histories.

    Today, astronomers know that Betelgeuse varies in brightness because it’s a dying, red supergiant star with a diameter some 700 times larger than our Sun. Someday, the star will explode as a supernova and give humanity a celestial show before disappearing from our night sky forever.

    That eventual explosion explains why astronomers got excited when Betelgeuse started dimming dramatically in 2019. The 11th-brightest star dropped in magnitude two-and-a-half-fold. Could Betelgeuse have reached the end of its life? While unlikely, the idea of a supernova appearing in Earth’s skies caught the public’s attention.

    And now new simulations are giving astronomers a more precise idea of what humans will see when Betelgeuse does eventually explode sometime in the next 100,000 years.

    2
    Astronomers used a software program called MESA+STELLA to simulate what humans might see when the star Betelgeuse explodes. They also included observations gathered during Supernova 1987A, which exploded in the Large Magellanic Cloud. Jared Goldberg/University of California, Santa Barbara/MESA+STELLA.

    SN1987a from NASA/ESA Hubble Space Telescope in Jan. 2017 using its Wide Field Camera 3 (WFC3).

    Large Magellanic Cloud. Adrian Pingstone December 2003

    Supernova seen from Earth

    With all the speculation about what a Betelgeuse supernova would look like from Earth, University of California, Santa Barbara, astronomer Andy Howell got tired of the back-of-the-envelope calculations. He put the problem to a pair of UCSB graduate students, Jared Goldberg and Evan Bauer, who created more precise simulations of the star’s dying days.

    The astronomers say there’s still uncertainty over how the supernova would play out, but they were able to augment their accuracy using observations taken during Supernova 1987A, the closest known star to explode in centuries.

    Life on Earth will be unharmed. But that doesn’t mean it will go unnoticed. Goldberg and Bauer found that when Betelgeuse explodes, it will shine as bright as the half-Moon — nine times fainter than the full Moon — for more than three months.

    “All this brightness would be concentrated into one point,” Howell says. “So it would be this incredibly intense beacon in the sky that would cast shadows at night, and that you could see during the daytime. Everyone all over the world would be curious about it, because it would be unavoidable.”

    Humans would be able to see the supernova in the daytime sky for roughly a year, he says. And it would be visible at night with the naked eye for several years, as the supernova aftermath dims.

    “By the time it fades completely, Orion will be missing its left shoulder,” adds Sarafina Nance, a University of California, Berkeley, graduate student who’s published several studies of Betelgeuse.

    3
    This comparison image shows the star Betelgeuse before and after its unprecedented dimming. The observations, taken with the SPHERE instrument on ESO’s Very Large Telescope in January 2019 and December 2019, show how much the star has faded and how its apparent shape has changed. ESO/M. Montargès et al.

    ESO SPHERE extreme adaptive optics system and coronagraphic facility on the extreme adaptive optics system and coronagraphic facility on the VLT MELIPAL UT3, Cerro Paranal, Chile, with an elevation of 2,635 metres (8,645 ft) above sea level

    The Betelgeuse show

    There’s no need to worry about the stellar explosion. A supernova has to happen extremely close to Earth for the radiation to harm life — perhaps as little as several dozen light-years, according to some estimates. Betelgeuse is far outside that range, with recent studies [The Astronomical Journal] suggesting it sits roughly 724 light-years away, well outside the danger zone.

    But the supernova could still impact Earth in some surprising ways. For example, Howell points out that many animals use the Moon for navigation and are confused by artificial lights. Adding a second object as bright as the Moon could be disruptive. It’s not only wildlife that would be disturbed, either; ironically, astronomers themselves would have a hard time.

    “Astronomical observations are already difficult when the Moon is bright,” Howell says. “There would be no ‘dark time’ for a while.”

    Even studying Betelgeuse would be a unique challenge. The bright light would overwhelm their instruments.

    “We couldn’t observe it with most ground-based telescopes, or most in space, either, like Swift or the Hubble Space Telescope,” he adds. Instead, they’d have to modify their telescopes to collect far less light.

    NASA Neil Gehrels Swift Observatory

    NASA/ESA Hubble Telescope

    And if Betelgeuse does defy the odds and blow up in our lifetimes, astronomers say there will be ample warning. Instruments on Earth would start detecting neutrinos or gravitational waves generated by the explosion as much as a day in advance.

    “Imagine a good fraction of the world staying up and staring at Betelgeuse, waiting for the light show to start, and a cheer going up around the planet when it does,” Howell says.

    4
    This collage zooms in on the constellation Orion (left) to one of the sharpest images ever taken of Betelgeuse (far right).
    ESO, P. Kervella, Digitized Sky Survey 2 and A. Fuji.

    To catch a dying star

    But for scientists, Betelgeuse doesn’t have to explode to be interesting. It’s big and bright, making it relatively easy to study.

    “It’s fascinating from an astronomer’s perspective because we can study a star that is nearing the end of its life quite closely,” Nance says. “There’s some fascinating physics going on in the internal structure of Betelgeuse.”

    Their best guess as to what’s going on right now stems from what astronomers already know about the star and others like it. As Nance explains, that research shows Betelgeuse’s brightness could be changing for a number of reasons. Some astronomers even suspect that several different dimming mechanisms are playing out at once.

    As their nuclear fuel runs out near the ends of their lives, red supergiant stars start to bloat and form growing envelopes of gas and dust. And as this envelope gets bigger, the star’s brightness grows. But that’s not the only way a star like Betelgeuse can dim and brighten. Red supergiant stars also have enormous convective cells on their surfaces — like much larger versions of those on our Sun — where turbulence makes hot material rise from inside the star. Once it reaches the surface, part of that material erupts violently into space like a giant, radioactive belch, which can temporarily change its brightness.

    And Betelgeuse’s dimming could even be evidence that it is about to explode. As material erupts from a dying star’s surface, it typically collides, which makes it shine brighter. However, Nance says it’s possible that this material is shrouding the star instead, making it dimmer.

    Whatever the root cause, the strange behavior should ultimately offer new insights into the dying days of red supergiant stars. And humanity will have a front-row seat.

    “Betelgeuse provides a great setting for astronomers to study these last stages of nuclear burning before it explodes,” Nance says.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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. He died in 1977.

     
  • richardmitnick 11:45 am on February 14, 2020 Permalink | Reply
    Tags: "The Sun's death could mean new life in the outer solar system", "These are the “delayed gratification habitable worlds” says planetary scientist Alan Stern of the Southwest Research Institute., Any humans left around might find refuge on Pluto and other distant dwarf planets out in the Kuiper Belt., , Astronomy magazine, , , , The slow death will kill off life on Earth but it may also create habitable worlds in what’s currently the coldest reaches of the solar system.   

    From Astronomy Magazine: “The Sun’s death could mean new life in the outer solar system” 

    From Astronomy Magazine

    February 6, 2020 [Just now in social media]
    Eric Betz

    What will happen to the solar system when the Sun dies? It might be the end of planet Earth, but life could still find a way.

    1
    The future red giant sun bakes planet Earth. Fsgregs/Wikimedia Commons.

    In roughly 5 billion years, the Sun will run out of energy and drastically alter the solar system. Oceans will be baked dry. Entire planets will be consumed. And long-icy worlds will finally enjoy their day in the Sun.

    Our star is powered by nuclear fusion, and it turns hydrogen into helium in a process that converts mass into energy. Once the fuel supply is gone, the Sun will start growing dramatically. Its outer layers will expand until they engulf much of the solar system, as it becomes what astronomers call a red giant.

    And what will happen to the planets once the Sun enters the red giant phase? The solar system’s denouement is still a subject of debate among scientists. Exactly how far the dying Sun will expand, and how conditions will change, aren’t yet clear. But a few things seem likely.

    The slow death will kill off life on Earth, but it may also create habitable worlds in what’s currently the coldest reaches of the solar system.

    Any humans left around might find refuge on Pluto and other distant dwarf planets out in the Kuiper Belt, a region past Neptune packed with icy space rocks. As our Sun expands, these worlds will suddenly find themselves with the conditions necessary for the evolution of life.

    “These are the “delayed gratification habitable worlds,” says planetary scientist Alan Stern of the Southwest Research Institute.

    “Late in the life of the Sun — in the red giant phase — the Kuiper Belt will be a metaphorical Miami Beach,” Stern says.

    Kuiper Belt. Minor Planet Center

    Let’s take a quick jaunt through our solar system in the last days of the Sun.

    2
    The life cycle of the sun takes it from the life-giving star we know today into a swelling red giant and, eventually, a planetary nebula surrounding a tiny white dwarf. ESO/S. Steinhöfel.

    Mercury

    Throughout solar system history, the innermost planet has been baked by the Sun. But even today, Mercury still clings to some icy patches. As our star ages, it will vaporize those remaining volatiles before eventually vaporizing the entire planet in a slow-motion version of Star Wars’ Death Star.

    Venus

    Venus is sometimes called “Earth’s twin” because the neighboring worlds are so similar in size and composition. But Venus’ hellish surface shares little in common with Earth’s Goldilocks-perfect conditions. As the Sun expands, it will burn up Venus’ atmosphere. Then, it too will be consumed by the Sun.

    Earth

    While the Sun may have 5 billion years left before it runs out of fuel, life on Earth will likely be wiped out long before that happens. That’s because the Sun is actually already growing brighter. By some estimates, it could be as little as a billion years before the Sun’s radiation becomes too much for life on Earth to handle.

    That might sound like a long time. But, in comparison, life has already existed on this planet for well over 3 billion years.

    And, when the Sun does turn into a red giant, the Earth will also be vaporized — perhaps just a few million years after Mercury and Venus have been consumed. All the rocks and fossils and remains of the creatures that have lived here will be gobbled up by the Sun’s growing orb, wiping out any lingering trace of humanity’s existence on Earth.

    But not all scientists agree with this interpretation. Some suspect the Sun will stop growing just before fully engulfing our planet. Other scientists have suggested schemes for moving Earth deeper into the solar system by slowly increasing its orbit. Thankfully, this debate is still purely academic for all of us alive today.

    Mars

    Even our young Sun’s radiation was too much for Mars to hold onto an atmosphere capable of protecting complex life. However, recent evidence has shown that Mars may still have water lurking just beneath its surface. Mars may escape the Sun’s actual reach — it’s at the borderline — but that water will likely all be gone by the time the red giant star takes over the inner solar system.

    The gas giant planets

    As our red giant Sun engulfs the inner planets, some of their material will likely get thrown deeper into the solar system, to be assimilated into the bodies of the gas giants.

    3
    Here, the ringed planet shows a side never visible from Earth. Cassini took 96 backlit photos for this mosaic on April 13, 2017. Because the sun shines through the rings, the thinnest parts glow brightest, and the thicker rings are dark.
    NASA/JPL-Caltech/Jan Regan

    However, the approaching boundary of our star will also vaporize Saturn’s beloved rings, which are made of ice. The same fate likely awaits today’s icy ocean worlds, like Jupiter’s moon Europa and Saturn’s Enceladus, whose thick blankets of ice would be lost to the void.

    The new habitable zone?

    Once our Sun has become a red giant, Pluto and its cousins in the Kuiper Belt — plus Neptune’s moon Triton — may be the most valuable real estate in the solar system.

    Today, these worlds hold abundant water ice and complex organic materials. Some of them could even hold oceans beneath their icy surfaces — or at least did in the distant past. But surface temperatures on dwarf planets like Pluto commonly sit at an inhospitable hundreds of degrees below freezing.

    But by the time Earth is a cinder, the temperatures on Pluto will be similar to our own planet’s average temperatures today.

    5
    Pluto as imaged by the New Horizons mission. The distant, icy world could one day be a balmy refuge.
    NASA/JHU-APL/SwRI.

    “When the Sun becomes a red giant, the temperatures on Pluto’s surface will be about the same as the average temperatures on Earth’s surface now,” Stern says. In research published in the journal Astrobiology in 2003, he looked at the prospects of life in the outer solar system after the Sun enters its red giant phase.

    Earth will be toast, but Pluto will be balmy and brimming with the same sorts of complex organic compounds that existed when life first evolved on our own planet. Stern says Pluto will likely have a thick atmosphere and a liquid-water surface. Collectively, the worlds — from cometlike space rocks to dwarf planets like Eris and Sedna — in this new habitable zone will have three times as much surface area as all four of the inner solar system planets combined.

    This might seem like an academic discussion only relevant to our distant descendants — if they’re lucky enough to survive billions of years from now. However, as Stern points out, there are around 1 billion red giant stars in the Milky Way galaxy today. That’s a lot of places for living beings to evolve — and then perish as their stars consume them.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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. He died in 1977.

     
  • richardmitnick 1:49 pm on February 7, 2020 Permalink | Reply
    Tags: "These dwarf planets are just as strange as Pluto", 2007 OR10, , Astronomy magazine, , , , Makemake, Orcus, Quaoar, ,   

    From Astronomy Magazine: “These dwarf planets are just as strange as Pluto” 

    From Astronomy Magazine

    February 3, 2020
    Eric Betz

    A new generation of ground-based telescopes and proposed space missions could soon reveal their secrets.

    1
    The dwarf planet Pluto, imaged by NASA’s New Horizons mission. NASA/Johns Hopkins University Applied Physics
    Laboratory/Southwest Research Institute

    NASA/New Horizons spacecraft

    Deep in the outer solar system, billions of miles from Earth, lurks a realm of small, icy worlds called dwarf planets. Astronomers know relatively little about these dim and distant objects, but in recent years, new evidence has revealed that the tiny planets can hold a surprising range of features, from oceans and mountains to canyons, dunes and volcanoes.

    Much of what astronomers know about dwarf planets comes from the NASA New Horizons spacecraft’s 2015 Pluto flyby. Pluto thrilled scientists with its towering mountain ranges made of ice. Its surprising geological complexity leaves astronomers eager to see the diversity of similar worlds in the Kuiper Belt — a donut-shaped region beyond Neptune packed with icy space rocks both large and small.

    Kuiper Belt. Minor Planet Center

    So far, the International Astronomical Union, the astronomy world’s official record keeper, recognizes just five dwarf planets: Ceres, Eris, Haumea, Makemake, and Pluto. But astronomers keep finding new dwarf planet candidates every year.

    What is a dwarf planet? According to the IAU, a dwarf planet is a world orbiting the Sun that’s big enough for its gravity to make round, but may “orbit in a zone that has many other objects in it.”

    Here’s a rundown of some of the most potentially exciting and unexplored dwarf planets.

    2007 OR10

    Like other icy planetesimals in the Kuiper Belt, 2007 OR10 takes a wild ride around our solar system. A year on this dwarf planet candidate lasts 550 Earth years and takes it almost as close to the Sun as Neptune before plunging more than twice as far out as Pluto.

    Scientists still aren’t sure about its diameter, but estimates put it at about two-thirds of Pluto’s. That leaves 2007 OR10 as the largest unnamed world in the solar system. (An online vote last year hosted by Brown and his team of co-discoverers suggested the name Gonggong, after a Chinese water god known for sowing chaos.)
    Standing on its surface, the icy ground would look dark and red, like Pluto. Indeed, 2007 OR10 is one of the reddest worlds astronomers know of. That reddish hue hints at the presence of complex organic compounds astronomers call tholins. Carl Sagan first discovered tholins, which form when ultraviolet light hits carbon-rich molecules like methane, in the lab during an experiment aimed at replicating the conditions of early Earth. The tarry substance is found on Pluto and likely exists on worlds throughout the Kuiper Belt.

    Research published in 2011 also showed that 2007 OR10 has a fresh surface covered in water ice. Astronomers think it’s evidence of cryovolcanoes, where slushy ice erupts from below the surface like lava.

    6
    An artist’s impression of 2007 OR10. Its reddish hue may come from compounds known as tholins. NASA

    Makemake

    This frigid world, named for a Rapa Nui god, is among the largest objects known in the Kuiper Belt. Surface temperatures on Makemake (pronounced MAH-keh MAH-keh) match up well with Pluto’s, reaching as low as negative 230 degrees Celsius. A year on Makemake lasts about 300 Earth years.

    What little is known about Makemake’s surface suggests the world is covered in bright ices that are extremely cold, while its moon, MK2, is as black as charcoal. Some research has suggested the potential dwarf planet is also littered with pellets of methane as much as half an inch across.

    5
    This illustration shows Makemake’s bright red surface and the inferred darker surface of the moon, known as MK2.
    NASA/SwRI/Alex Parker

    Triton

    Today, Triton isn’t a dwarf planet and it isn’t in the Kuiper Belt. Instead, it’s a large, icy moon of the planet Neptune with some seriously peculiar properties. Its orbit carries in the opposition direction of other large moons in the solar system, called retrograde motion, and it has a geologically active surface with strong signs of ice volcanoes.

    Triton’s similarities to Pluto, as well as its orbit, lead astronomers to suspect that the moon initially formed as a dwarf planet in the Kuiper Belt and was later captured by Neptune. But whereas Pluto is thought to have an ancient ocean that froze over time, astronomers think Triton may still have a liquid water ocean beneath its surface thanks to Neptune’s intense gravity.

    If true, that would make Triton one of the most habitable known worlds. And whereas NASA likely won’t have a mission to Pluto’s other far-flung cousins in the outer solar system in the near future, scientists are already seriously considering a mission dedicated to visiting Neptune. “We would learn a lot about dwarf planets with a mission to Neptune,” Stern says.

    6
    A mosaic photo of Neptune’s moon Triton taken by the Voyager 2 spacecraft.
    NASA/JPL/USGS

    NASA/Voyager 2

    NASA JPL


    Sedna

    Sedna is one of the reddest objects in the solar system — likely a sign of tholins — and it has one of the strangest orbits known. The potential dwarf planet takes roughly 11,400 years to circle the Sun, meaning just about one year has passed there since the dawn of agriculture on Earth.

    Sedna’s orbit leads some to rank it as the most important find in the region beyond Neptune. That’s because it’s unlikely that the world formed where it is now. One possibility is that a passing star may have knocked Sedna out of the Oort Cloud — a circumstellar cloud of icy space rocks orbiting far from the Sun — and onto its current orbit. It’s hard to guess at what its surface looks like because astronomers have never seen a large object from that region up close.

    “I call Sedna a fossil record of the earliest solar system,” Mike Brown, the Caltech astronomer who co-discovered Sedna, said in a Discover Magazine interview back in 2006. “Eventually, when other fossil records are found, Sedna will help tell us how the Sun formed and the number of stars that were close to the Sun when it formed.”

    7
    An artist’s conception of Sedna, one of the reddest objects known in our solar system. NASA/JPL-Caltech/R. Hurt

    Quaoar

    It’s now been roughly two decades since Quaoar was discovered. And while this dwarf planet spans just half the diameter of Pluto, that doesn’t necessarily make it a less interesting world. Right now, Quaoar is orbiting at about 42 astronomical units, where 1 AU equals the Earth-Sun distance.

    Quaoar is roughly the same size as Pluto’s large moon Charon, where the New Horizons mission recently revealed a stunning diversity of landscapes, from mountains to canyons, valleys, craters and plains. Charon is also covered in water ice and features a giant tectonic belt of canyons that stretch four times longer than the Grand Canyon and twice as deep. Astronomers suspect this gash, called Argo Chasma, formed when an ocean froze inside Charon and cracked the dwarf planet open like a soda can left in the freezer too long.

    In the years since Quaoar’s discovery, astronomers have detected water ice there. And some scientists suggest it may have cryovolcanoes. Its relatively bright surface also hints that the world may have been geologically active in the not-too-distant past.

    8
    An artist’s illustration of Quaoar (pronounced “kwa-whar”). NASA and G. Bacon (STScI)

    Orcus

    Some have called Orcus the “anti-Pluto” because of their many similarities but opposing orbits. Right now, Orcus is at its farthest point from the Sun, while Pluto is near the closest point of its orbit. Both worlds eventually pass even closer to the Sun than Neptune. And on Pluto, these close passes create a thin but temporary atmosphere.

    Like Pluto and Eris, Orcus also boasts a large moon, named Vanth, which may be the third largest moon orbiting beyond Neptune. Vanth’s orbit clings to Orcus at an uncomfortably close 5,600 miles (9,000 km) — the dwarf planet itself is just some 600 miles (965 km) in diameter.

    If Earth’s own Moon orbited at a similar distance relative to size, it would sit several times closer than it does now.

    And these two objects seem to have very different surfaces. Whereas Vanth has a reddish hue common to Kuiper Belt objects, Orcus has a much lighter surface with signs of water ice. Is this system a slightly smaller version of the Pluto-Charon system? Or are these worlds something else entirely? Only a higher-resolution view will reveal the truth.

    9
    Orcus can be seen in the green circle at top right. California Institute of Technology

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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. He died in 1977.

     
  • 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 .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • 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 .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • 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 .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
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