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  • richardmitnick 8:33 am on February 17, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , ,   

    From Astronomy Magazine: “Celebrating Pluto’s discovery” 

    Astronomy magazine

    Astronomy Magazine

    February 15, 2018
    Alison Klesman

    1
    This is Pluto as it appeared to the New Horizons spacecraft during its approach of the dwarf planet in July 2015. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

    On February 18, 1930, Pluto was discovered by astronomer Clyde W. Tombaugh at the Lowell Observatory in Flagstaff, Arizona.

    Lowell Observatory, in Flagstaff, Arizona, USA

    Compared with the major planets in our solar system, Pluto has had a shorter but rockier history. Originally hailed as our solar system’s ninth planet, Pluto was reclassified as a dwarf planet by a 2006 vote of the International Astronomical Union — a move that remains controversial and challenged to this day.

    Pluto, regardless of the category into which it is sorted, has played a vital role in our understanding of the formation and evolution of our solar system. We now know it is part of a family of objects called the Kuiper Belt, comprised of icy, rocky remnants from the solar nebula’s earliest days. The Pluto system itself is larger than initially believed; its largest moon, Charon, wasn’t discovered until 1978, and only in the past two decades have astronomers uncovered four more tiny moons using the world’s most powerful telescopes.

    2
    An artist’s concept shows New Horizons flying through the Pluto system. Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

    Until 2015, Pluto remained a dim dot through Earthbound telescopes, and a mere few pixels on images taken by the orbiting Hubble Space Telescope. On July 14, 2015, the New Horizons spacecraft flew past the Pluto system, forever changing our view of this distant world. Astronomy celebrated the accomplishment with our Year of Pluto, a wealth of fascinating articles looking back over our past expectations, guesses, and dreams about Pluto, and highlighting the unrivaled success of and the wealth of information unlocked by New Horizons over the course of just a few short hours.

    Circling the Sun on an elliptical orbit tilted relative to the plane of the planets, Pluto takes about 248 (Earth) years to make one trip; the tiny, icy world has not yet completed even a single orbit since its discovery. But despite its distance and its still-controversial status, Pluto remains one of the most beloved and fascinating objects in our solar system. Below, you can find links to some of our favorite articles on the history of Pluto, leading up to its discovery, its naming, and the 2015 flyby. Or we invite you to explore our full library of Pluto articles here: Year of Pluto.

    And if, like many, you believe Pluto should regain its place among the rightful planets of our solar system, stay tuned — Astronomy will be featuring an exclusive on the definition of the word planet, and how we might rethink it, in an upcoming magazine issue and online bonus feature.

    See the full article here .

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  • richardmitnick 8:19 am on February 17, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , , Lensed quasar RXJ1131−1231,   

    From Astronomy: “Astronomers report a possible slew of extragalactic exoplanets” 

    Astronomy magazine

    Astronomy Magazine

    February 09, 2018
    Mara Johnson-Groh

    Could a distant galaxy be home to a large population of unbound planets?

    1
    Astronomers have identified a population of rogue planets – planets not bound to or orbiting parent stars – in a lensing galaxy sitting between Earth and a distant quasar.
    NASA/JPL-Caltech

    Discoveries of exoplanets in our galaxy exceed 3,700 to date, but if that’s not enough for you, astronomers are now probing outside of the Milky Way to find exoplanets in other galaxies. A group of researchers at the University of Oklahoma has just announced the discovery of a large population of free-floating planets in a galaxy 3.8 billion light-years away. Their results were published February 2 in The Astrophysical Journal Letters.

    The researchers used a method known as quasar microlensing, which has traditionally been used to study the disk-like regions around supermassive black holes where material gathers as it spirals in toward the event horizon.

    2
    Credit: NASA/Jason Cowan (Astronomy Technology Center).

    When a distant quasar is eclipsed by a closer galaxy, the intervening galaxy will create several magnified replica images of the quasar. These replicas are further magnified by stars in the interloping galaxy to create a final super-magnified image that can be used to study the quasar in detail.

    Wild planets

    While studying the light emitted by the lensed quasar RXJ1131−1231 with the Chandra X-ray Observatory, the researchers noticed a particular wavelength of light emitted by iron was stronger than could be explained solely by the lensing effect of stars in the intervening galaxy.

    NASA/Chandra Telescope

    By modeling their results, the researchers concluded that the shifted energy signature was most likely caused by a huge population of planets with masses ranging from our Moon to Jupiter. The model that best matched the data found a ratio of 2,000 planets for every main sequence star in the galaxy —billions of stars. These planets are specifically “unbound” — not orbiting a star but wandering freely — as bound planets don’t have the same boosting effect seen in the data. Because the models only provided a wide range of potential planet masses, the researchers hope to identify the distribution of the sizes further with additional modeling.

    3
    RX J1131-1231 is about 6 billion light-years away. It is a lensed quasar; gravitational lensing caused by an intervening elliptical galaxy (center, yellow) has magnified and multiplied the image of RX J1131 into four images (pink) as seen with the Chandra X-ray Observatory.
    X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI

    NASA/ESA Hubble Telescope

    These preliminary results may just be the first out of the floodgates. “There are also other galaxies we’re working on,” says Xinyu Dai, lead author of the paper and researcher at the University of Oklahoma. “We think there are some signatures showing the presence of a small mass population, but we need to run detailed models to see if this is true or not.”

    Other Sightings

    This isn’t the first time astronomers have claimed a discovery of an exoplanet outside our galaxy. A signature consistent with a three-Earth-mass planet was detected in a galaxy 4 billion light-years away, but the one-time chance nature of the alignment causing the microlensing meant the discovery could not be confirmed with further observations. Similarly, a different version of microlensing using a star instead of a galaxy was previously used to probe the Andromeda Galaxy. A team found deviations in the light that they believed could be caused by an exoplanet six times as massive as Jupiter, but again the detection was never confirmed.

    The interloper star HIP 13044 was reported to itself host an exoplanet 25 percent larger than Jupiter, but subsequent follow-up found no evidence for the planet. Though this star is currently a part of the Milky Way, it originally came from a small galaxy that collided with the Milky Way six billion years ago.

    Vagabond stars like HIP 13044 may provide our best chance for examining exoplanets from other galaxies in detail. With current telescope technology, microlensing can point to a detection in other galaxies, but it cannot fully probe the properties of these candidates. Finding relatively nearby exoplanets around stars that originated abroad, however, may help us learn more about how exoplanets form and whether there are differences between planets born in different galaxies.

    See the full article here .

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  • richardmitnick 2:15 pm on December 1, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , , , The Sculptor dwarf galaxy   

    From Astronomy: “Astronomers measure the motions of stars in a nearby galaxy” 

    Astronomy magazine

    astronomy.com

    November 28, 2017
    Alison Klesman

    This first glimpse raises questions about the dark matter models we use.

    1
    The Sculptor dwarf galaxy is a satellite of the Milky Way, appearing here as a faint “cloud” of stars. ESO.

    When you look up at the night sky, the stars appear fixed — but things are not as they appear. In fact, every star in our galaxy is moving. While it’s easy for astronomers to measure whether a star is moving toward or away from us, it’s much harder to measure a star’s motion in the plane of the sky, or side to side. This is because the stars are so very distant, it takes years for even the most minute change to become visible. It’s why the constellations have appeared essentially the same over time; but given enough time, they will eventually warp and change as the motion of the stars that make them up becomes apparent.

    This “sideways” motion, called proper motion, has only ever been measured for stars in the Milky Way — until now. Recently, a group of astronomers combined data from the Hubble Space Telescope and the European Gaia mission to measure the proper motions of several stars in the Sculptor dwarf galaxy, a small, nearby satellite of the Milky Way. Their work, published yesterday in Nature Astronomy, now presents a possible challenge to the standard models of dark matter haloes believed to surround galaxies such as our own.

    The Gaia mission measures the positions of stars very precisely.

    ESA/GAIA satellite

    While most of these stars are in our Milky Way, its targets do include some stars in nearby galaxies, such as the Sculptor dwarf. The Hubble Space Telescope has also observed some of these same stars, measuring their positions 12 years ago.

    NASA/ESA Hubble Telescope

    Davide Massari of the University of Groningen and colleagues at the Kapteyn Astronomical Institute were able to combine the Gaia and Hubble data — no easy feat, as the two measure position differently — to find that 15 stars could be accurately tracked between the two epochs.

    “We determined how the stars move in this small galaxy,” Massari explained in a press release. “But our measured value was very surprising, as the standard models didn’t allow it.” Those standard models describe the expected distribution of dark matter in a huge halo around the Milky Way, inside which the Sculptor dwarf is embedded. That dark matter should dictate how the stars move; disagreement could mean the models are wrong and need updating.

    However, there is another explanation for the stars’ seemingly strange motions. “The models assume all stars to be in a single population of stars,” Massari said. But the Sculptor galaxy has at least two known populations of stars, one more compact and one more extended. The stars in each population experience different impacts from dark matter. If the stars measured in the study all belong to the compact population, it would explain why their motions disagree with the dark matter models, preserving those models with no need for alteration.

    In addition to measuring the motions of stars inside the Sculptor dwarf, the team also improved measurements of the galaxy’s orbit around the Milky Way. “This orbit is much wider than expected,” said Massari. “Previously, it was believed that the current spheroidal shape of Sculptor was in part the result of some close passages, but our measurements show that this is not the case.”

    As more Gaia measurements come in, they will continue to help astronomers chart the motions of stars in our galaxy and many others. This information will help us form a better picture of the galaxy we live in and the behavior of those around us, including the influence of the dark matter we can’t see.

    See the full article here .

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  • richardmitnick 1:13 pm on September 1, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , , Halo photometry, Scientists find that the stars in the Pleiades are variable   

    From Astronomy: “Scientists find that the stars in the Pleiades are variable” 

    Astronomy magazine

    Astronomy Magazine

    August 28, 2017
    Alison Klesman

    1
    The Pleiades is a young star cluster known for its seven brightest stars, called the Seven Sisters. NASA, ESA and AURA/Caltech

    The Pleiades is one of the most recognizable groups of stars in the northern sky. While to the naked eye this feature appears as seven bright stars, the Pleiades is actually a young open cluster about 100 million years old, containing 100 or more member stars. Though this cluster is less than 500 light-years from Earth, there is still much astronomers don’t know about it, in large part because its stars are too bright to observe with world-class telescopes. But now, a team of international astronomers has found a way around the problem, using the Kepler Space Telescope to discover and study variability in the Pleiades’ brightest stars.

    NASA/Kepler Telescope

    The work was led by Tim White of the Stellar Astrophysics Centre at Aarhus University in Denmark, and published August 11 in Monthly Notices of the Royal Astronomical Society. In their paper, they outline a new technique, called “halo photometry,” which is able to spot relative brightness changes in stars, even if they’re too bright to study directly. The algorithm looks at pixels on the camera detector next to, rather than those that fall directly on, the brightest part of stars. The algorithm measures changes in the values of those pixels to identify variability. As a result, the team discovered that the seven bright stars of the Pleiades are variable stars.

    Most of the stars are slowly pulsating B-type stars. These massive, bright stars change brightness every one to five days. Such stars are poorly understood, so adding the stars in the Pleiades to the current list of known variables and studying the Kepler data will help astronomers better understand the processes that affect these stars.

    But one star, Maia, was different. Maia exhibits regular changes every 10 days; curious, the team followed up by observing the star with the Hertzsprung SONG Telescope. By looking at spectra, which identify the chemical components of the star, they determined that the brightness changes Kepler saw co-occur with changes in the element manganese in the star’s atmosphere. Rather than pulsating like the other stars do, Maia’s changes appear to be “caused by a large chemical spot on the surface of the star, which comes in and out of view as the star rotates with a ten day period,” said co-author Victoria Antoci, an Assistant Professor at the Stellar Astrophysics Centre, in a press release.

    Funny enough, astronomers 60 years ago thought they had detected variability in Maia, but on the order of hours, not days. From those detections a new class of variables, Maia variables, was born — but now, says White, “Our new observations show that Maia is not itself a Maia variable!”

    2
    Kepler captured brightness variations in the Seven Sisters; astronomers noticed that one star, Maia, showed variability different from the others. Aarhus University/T. White

    Kepler’s forte is studying brightness changes in stars associated with the transit of orbiting planets. The satellite’s ability to accurately measure fluctuations in starlight also makes it an ideal tool to identify and study any cause of brightness changes from a star, such as pulsations or starspots. Kepler is now in its K2 mission, which has allowed the spacecraft to continue observing, even after the systems responsible for pointing the telescope failed.

    Kepler did not identify any transiting exoplanets during this study; however, the team says their new algorithm will allow Kepler and other planet-hunting telescopes to better search for planets around bright stars, which would have been otherwise skipped because they saturate the detector. They have also released the halo photometry algorithm as free open-source software for the community to use.

    See the full article here .

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  • richardmitnick 10:29 am on August 6, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , , MU69,   

    From Astronomy: “New Horizons may visit twice the object for the same price” 

    Astronomy magazine

    Astronomy Magazine

    August 04, 2017
    John Wenz

    MU69 could be hiding a strange secret: it’s one object, not two.

    1
    2014 MU69 is New Horizons’ next target. Now, data indicate it could be a contact binary – two objects orbiting each other so closely that they touch. NASA/JHUAPL/SwRI/Alex Parker.

    NASA/New Horizons spacecraft

    New Horizons is getting the ultimate two-for-one deal.

    The intrepid craft, which flew through the Pluto system in 2015, is en route to 2014 MU69, an icy remnant from our solar system’s formation that lives in the Kuiper Belt. While initially thought to be a chunk of ice less than a few dozen miles in size, a recent occultation event has revealed that MU69 might be even weirder.

    The object appears to have an odd shape, based on the occultation data (taken when an object passes in front of a background star). In a press release, NASA officials said that it’s either football shaped or, more intriguingly, a type of object called a contact binary.

    2
    If MU69 is not a contact binary, it might instead be football shaped. NASA/JHUAPL/SwRI/Alex Parker.

    A contact binary is composed of two objects close enough that they actually touch in an orbital dance around each other that leaves them relatively intact. The comet 67P explored by ESA’s Rosetta probe is believed to be a contact binary.

    We’ll find out for sure in 2019, when New Horizons flies by the object – or objects.

    See the full article here .

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  • richardmitnick 4:35 pm on April 20, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , The largest SETI initiative ever is reviewing 11 promising signals that probably aren’t aliens   

    From Astronomy: “The largest SETI initiative ever is reviewing 11 promising signals that probably aren’t aliens” 

    Astronomy magazine

    Astronomy Magazine

    April 20, 2017
    John Wenz

    1
    The Robert C. Byrd Radio Telescope at the Green Bank Observatory in West Virginia is one of the primary receivers looking for promising SETI signals.

    The Search for Extraterrestrial Intelligence (SETI) has been going for nearly 60 years now, and there have been plenty of false alarms in that time and nothing substantial. Now, a giant SETI initiative is looking into its initial round of data to follow up on 11 signals that they think could be aliens … but admit probably aren’t. Good to check, though, just in case.

    Two years ago, billionaire Yuri Milner put $100 million into a decade-long search for aliens known as the Breakthrough Listen initiative. It was the widest-scale SETI project announced since Project Phoenix in 1995, which itself was the successor of a cancelled 10 year, $100 million SETI effort by NASA.

    Breakthrough Listen is spearheaded by SETI Berkeley and taps into the wider SETI community to listen in worldwide for radio signals that might be artificial. They’ve also opened up the data to the public at large to look for narrowband signals — those in a specific wavelength that are more likely to be from a non-natural source. There are 692 targets in the initial rounds of data.

    The news is coming out of a two-day conference in California from the Breakthrough Initiatives organization, which is also sponsoring Breakthrough Starshot, a project based on using laser propulsion to power tiny spacecraft to the Alpha Centauri system (specifically Proxima Centauri) in a matter of decades.

    A live broadcast will take place today on Facebook at 6:10 p.m. EST (3:10 p.m. PST) with Andrew Siemion of SETI Berkeley discussing the initial results. You can watch it here.

    See the full article here .

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  • richardmitnick 10:47 am on April 19, 2017 Permalink | Reply
    Tags: , Astronomy magazine, Baryonic matter, Finding the Milky Way’s hydrogen halo   

    From Astronomy: “Finding the Milky Way’s hydrogen halo” 

    Astronomy magazine

    Astronomy Magazine

    April 19, 2017
    Alison Klesman

    2
    In 2012, Chandra spotted a hot hydrogen halo around the Milky Way. Now, astronomers are peering into the cooler hydrogen component of our galactic halo. NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A.Gupta et al.

    Our galaxy is missing matter — baryonic matter, to be specific. Baryonic matter consists of baryons: particles such as protons and neutrons. It’s the everyday matter around you and makes up every element on the periodic table. Astronomers have been puzzled by the fact that the Milky Way and other galaxies are missing baryonic matter when the mass of their easily measured components, the disk and the bulge, are summed. Recent observations have indicated that galaxies may host a diffuse halo of gas out to great distances (hundreds of thousands of light-years), which is particularly hard to detect but could account for the missing matter. And now, as all-sky surveys amass ever more data, astronomers are finally starting to uncover more information about these halos.

    In a paper published in Nature Astronomy April 18, authors Huanian Zhang and Dennis Zaritsky describe their research exploring the Milky Way’s galactic halo of cool, diffuse hydrogen gas by observing the light of other galaxies as it passes through the halo on its way to Earth. When this light is broken up by a prism, it forms a spectrum that contains key details about the material the light has traveled through, which includes not only the matter in the distant galaxy from which it came, but also any intervening matter the light may have encountered on its journey — such as our galactic halo.

    This type of line-of-sight observation has been used before to study the galaxy’s halo, but has typically been limited to a few bright objects such as distant quasars (the extremely bright disks of gas and dust around supermassive black holes) or distant stars in our own galaxy’s halo. But with the ongoing releases of data from surveys such as the Sloan Digital Sky Survey (SDSS), millions of distant galaxy spectra are available for use. The vast amount of data allows astronomers to more easily separate out effects from the “nearby” gas in our galaxy’s halo as the light passes through it.

    Zhang and Zaritsky compiled a sample of 732,225 galaxy spectra from the 12th data release of the SDSS. By “stacking” or combining these spectra together, they were able to essentially boost the otherwise weak signal of the galaxy’s hydrogen halo, making it much easier to observe and characterize. The result was a clear detection of hydrogen-alpha, a specific “thumbprint” left on the light as it passed through the neutral hydrogen of the galactic halo.

    Based on the stacked signal, the pair determined that the gas could be moving at speeds up to 435 miles per second (700 kilometers per second). It has no net infall or loss, meaning it stays in the halo for the most part, rather than streaming away as outflows or falling inward to provide fuel for new stars. They also estimate the gas’ temperature could be about 21,000 degrees Fahrenheit (11,700 degrees Celsius).

    However, because Zhang and Zaritsky’s work combines hundreds of thousands of observations from all over the sky, it can’t provide fine details about the gas’ smaller-scale motions or temperature distribution. The work also focuses on only one component of many believed to belong to this galactic halo. In addition to cool hydrogen gas, the halo is thought to contain isolated hydrogen clouds and diffuse hot hydrogen gas that is visible in X-rays and was spotted by NASA’s Chandra X-ray Observatory.

    This work does help to lay the foundation for future exploration of this difficult-to-see but extremely massive component of our galaxy, which contains as much matter as all the stars in the bulge and disk of the galaxy put together. The authors conclude that more line-of-sight observations and analysis of additional spectral signatures left by this gas will help to flesh out the developing picture of our galaxy’s massive hydrogen halo.

    See the full article here .

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  • richardmitnick 3:01 pm on April 18, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , Can you imagine the sky in five million years?, ,   

    From Astronomy: “Can you imagine the sky in five million years?” 

    Astronomy magazine

    Astronomy Magazine

    April 13, 2017
    Alison Klesman

    Now you don’t have to — Gaia has the answer.

    1
    In five million years, the sky will look a little different. The constellations will be unrecognizable, and many of the stars we can see today will have moved significantly. ESA/Gaia/DPAC

    Have you ever wondered what it would be like to stare up at the sky millions of years from today? Would things look exactly the same, or would the sky be totally unrecognizable? Wonder no longer — the European Space Agency (ESA) has just released a video answering that exact question.

    Since July 2014, ESA’s Gaia mission has been charting the positions of stars in the Milky Way with higher accuracy than ever before. Its goal is to create a three-dimensional map of our galaxy, which is uniquely challenging because we’re trying to make a map from inside the galaxy, rather than being able to take a step back and view it from outside.

    ESA/GAIA satellite

    With such precise stellar positions, however, comes something else: stellar motions. The stars seem perpetually fixed in the sky — sure, they rise and set, and change throughout the year as we go around the Sun, but they always form the same patterns. A significant percentage of the constellations most of us know are those derived, after all, by the Greeks just a little under 2,000 years ago. So, of course, it’s natural to assume that the stars just don’t move, because they’ve looked pretty much the same for thousands of years.

    But thousands of years is but an eyeblink in the lifetime of a galaxy, and the notion that the stars don’t change positions is false. The stars do move, largely in bulk as they rotate around the center of the Milky Way, but sometimes they zip off in random directions dictated by the conditions of their formation or past interactions. This latter effect is exacerbated by perspective — the closer a star is to us, the more it will appear to move. This perspective effect is also essentially how Gaia measures stellar positions so accurately, using a technique called parallax that causes nearby stars to shift against the background as Earth orbits the Sun.

    But largely, from our perspective, the stars are just so far away that even though they’re moving at hundreds of kilometers per second, they seem pretty fixed to the casual observer. Now, though, ESA has released a video containing 2,057,050 stars that have been measured well enough to predict where they are and where they’re going in the future. The overall motion of a star from our point of view against the background of extremely far away stars is called proper motion, and that’s the basis for the stellar motions in this video. Using the projected proper motions of the stars in the Gaia catalog, the result is a fast-forwarded trip through time that ends with the sky as it would appear from Earth in 5 million years. Each frame in the video represents the passage of 750 years.


    Copyright: ESA/Gaia/DPAC

    There are a few key takeaway points from this video. At first, very little appears to happen, but that’s an illusion. Consider the constellations. They’re two-dimensional projections on a three-dimensional sky, which means that although the stars form a picture, virtually none of the stars in a given constellation are at the same distance from us. In the video, you can spot Orion on the far right, just below the bright plane of the galaxy. The Big Dipper (technically an asterism, not a constellation) appears in the upper left, high above the galaxy’s plane.

    When you hit play, the constellations are quickly distorted beyond all recognition within about 100,000 years — literally just a few frames into the video. That’s because the stars nearer to us appear to move significantly, while those farther away don’t appear to move as much. None of the stars move in tandem, so the patterns are torn apart. So while our current constellations may last for thousands more years, between ten and a hundred thousand years from now, astronomers will need to come up with some new patterns.

    Next, keep in mind that this video has some limitations. The first frame seems to show intricate structure and even stripes in the plane of the Milky Way, but those are actually just artificial data artifacts in areas where Gaia hasn’t measured the positions of stars (or hasn’t measured them accurately enough to predict a believable proper motion). Those artifacts are washed out pretty quickly, though, as closer stars move into the areas where less data exists.

    Some dark areas, though, are clouds of interstellar dust, which block the light from stars sitting behind them. Those stars aren’t visible today, so the video doesn’t include the “new” stars we might see popping out from behind the clouds as the millennia scroll by. The clouds themselves can also move, which similarly isn’t taken into account here. The motion of these clouds over time would basically change the detailed structure of the Milky Way we see when we look up in the sky, like subtly shifting the stripes on a tiger’s back.

    Finally, the stars themselves aren’t eternal. Because it takes time for light to travel across space, you may wonder if the stars you’re seeing in the sky are even really there. For the most part, the answer is yes, simply because stars live so long compared to humans (or human civilization), that the chances of one disappearing in a human lifetime are pretty small. But, if you wait a few hundred thousand years, that won’t be true — that’s when the bright red star in Orion’s shoulder, Betelgeuse, is expected to go supernova. We’ll notice about 600 years later (give or take a few hundred years, because the distance to Betelgeuse is fairly hard to pin down), when the star grows very bright, then dims away past naked-eye visibility. Orion’s really going to start falling apart then, because the bright star that marks one of his knees, Rigel, will go out similarly relatively soon after.

    So keep in mind that although this video carries the stars through the next five million years, not all of the stars you see will make it that long. Some will disappear, and new ones might become visible. Regardless of the changes that occur, the sky is changing — but with the data we currently possess, we can now take a peek at what the far future holds in store.

    See the full article here .

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  • richardmitnick 2:43 pm on January 7, 2017 Permalink | Reply
    Tags: , Astronomy magazine, Contact binaries, Two stars will merge in 2022 and explode into red fury   

    From Astronomy: “Two stars will merge in 2022 and explode into red fury” 

    Astronomy magazine

    astronomy.com

    January 06, 2017
    John Wenz

    Get ready for a big nova event.

    1
    STScI

    In 2022, there will be a spectacular sky show. Two stars will merge into one, pushing out excess gas into an explosion known as a red nova. At magnitude 2, it will be as bright as Polaris in the sky, and just behind Sirius and Vega in brightness. The collision in the constellation of Cygnus will be visible for up to six months.

    That’s pretty impressive. What’s more impressive: we’ve never been able to predict a nova before. But Lawrence Molnar, a professor of astronomy and physics at Calvin College, was able to find a pair of oddly behaving stars giving an indication of what might happen.

    The objects, termed KIC 9832227, are currently contact binaries. Contact binary refers to two objects that are so close they are currently touching. The object was discovered by Kepler [Unclear, Kepler space telescope or Johannes Kepler. Probably the telecope]. The expected outcome is a merger between the two stars that will put on quite a show. Because both are low mass stars, the expected temperature is low, with Molnar terming it a “red nova.”

    So how does Molnar know what will happen? After all, as he puts it, it’s “a very specific prediction that can be tested, and a big explosion.” He and his team have an example to look at: V1309 Scorpii. (https://astrobites.org/2012/08/01/two-stars-merged-and-we-got-to-watch/) First observed in 2008, astronomers were able to watch the light curve as the event unfolded. First, there were a few “booms” in the sky. Then, a spectacular light show unfolded. Using precovery data, astronomers were able to trace back the evolution from 2001 on, giving a big picture of the decade of progression of the event.

    How did they know it was a merging star?

    “V1309 was (brightening) before the explosion,” Molnar said in a press conference at the 229th meeting of the American Astronomical Society. “It isn’t doing it today. That’s the smoking gun of a merging star.”

    Using Kepler data, Molnar found that KIC 9832227 fit the lightcurve of V1309 almost perfectly. All radial velocity measurements seem to indicate a contact binary, and by aligning the light curve to the period in time, he and his team came to the conclusion that the merger would complete in 2022.

    “We don’t know if it’s right or wrong, but it’s the first time we can make a prediction,” Molnar says. At 2nd magnitude, it’ll be easy if it see if the prediction was correct.

    “You won’t need a telescope in 2022 to tell me if I was wrong or I was right,” he says.

    See the full article here .

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  • richardmitnick 8:33 am on December 8, 2016 Permalink | Reply
    Tags: , Astronomy magazine, , Captured moons of the giant planets   

    From Astronomy: “Captured moons of the giant planets” 

    Astronomy magazine

    Astronomy Magazine

    December 06, 2016
    Liz Kruesi

    1
    Phoebe was the first irregular satellite discovered around Saturn. That was in 1898. By 1997, the number had crept up to 10. In the next 10 years, the count exploded, reaching 107. Now astronomers are trying to figure out where these satellites came from and how they got to their current locations. Ron Miller for Astronomy

    This article originally appeared in the February 2011 issue of Astronomy magazine.

    For more than a century, astronomers have known that natural satellites in the solar system don’t only orbit in close, nearly circular tracks in the same plane as their host worlds. Sometimes objects have distant and highly elliptical orbits, and they are called irregular satellites. Often their trajectories are tilted to the planet’s plane. Their orbits also tend to precess, meaning they trace out more of a loop-de-loop pattern instead of a simple ellipse. And most irregular satellites orbit in the direction opposite their planets’ rotations, called retrograde motion.

    Astronomers believe ordinary satellites formed with their planets. However, the characteristics of irregular satellites imply they did not form in this way, but instead were captured. But when, and how?

    In the late 20th and early 21st centuries, astronomers discovered a surprising number of irregular satellites. They had known about Saturn’s oddball Phoebe and Jupiter’s Himalia since the early 1900s. But then the tally jumped from 10 to 107 in less than 10 years thanks to technological advancements. The count has slowed recently while scientists put more of their efforts into characterizing the bodies they know of and learning where they came from.

    Where are they?

    The irregular-satellite haul geared up as astronomers attached wide-field CCD cameras to large telescopes. In 1997, Brett Gladman, now at the University of British Columbia, and colleagues used the Hale Telescope at Palomar Observatory to discover two satellites orbiting Uranus.

    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA
    Caltech Palomar 200 inch Hale Telescope interior
    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA

    While this team focused on Uranus, Neptune, and Saturn, David Jewitt, now at the University of California, Los Angeles, and Scott Sheppard, now at the Carnegie Institution of Washington, discovered the majority of the objects around Jupiter. They used both the Canada-France-Hawaii and Subaru telescopes atop Mauna Kea for their searches.

    CFHT Telescope, Mauna Kea, Hawaii, USA
    CFHT Interior
    CFHT Telescope, Mauna Kea, Hawaii, USA

    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA
    NAOJ Subaru Telescope interior
    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA

    The teams looking for irregular satellites surveyed regions called “Hill spheres” around each of the solar system’s giant planets — Jupiter, Saturn, Uranus, and Neptune. Within such an region, the planet’s gravitational pull is greater than the Sun’s. The astronomers searched each planet’s Hill sphere because if an object passes through this region at a slow pace relative to the planet’s orbital speed, the gravitational pull could capture the incoming object as a satellite.

    2
    ust a fast-moving blip, Saturn’s irregular satellite S/2004 S11 shows up on these discovery images from the Hawaii Irregular Satellites Survey. This object is about 3.8 miles (6 kilometers) wide.
    David Jewitt

    But this doesn’t mean that any region within the Hill sphere provides stable orbits. The sphere’s outer half is mostly unstable, as solar tides can tear away any satellites not firmly gravitationally attached to the planet. Thus, astronomers have found most irregular satellites within the inner half of the giant planets’ Hill spheres.

    Astronomers also haven’t found irregular satellites orbiting the poles of the planets. This region is gravitationally unstable. The “Kozai resonance” is to blame for the lack of orbiting objects here. Gravity perturbs the orbit, which becomes more elliptical to compensate. Eventually, the orbit will be so stretched out that the planet can lose control of the satellite as it reaches its path’s greatest distance, or the object can veer into the planet at its orbit’s closest approach.

    The irregular satellites have outlasted many gravitational encounters during their lifetimes, but how did they get to their locations in the first place? And what do astronomers know about these objects? First astronomers have to learn as much as possible about the satellites before determining where they came from.

    Observing these oddities

    In the past few years, scientists have stopped looking for irregular satellites and instead are analyzing those currently known. “Even if we push it to 200, it probably won’t change the picture that much,” says Jewitt.

    An object’s spectrum can tell a researcher about its composition and motion. Unfortunately, most irregular satellites are too faint for astronomers to gather such spectra. (They have detailed information for only three — Phoebe, Himalia, and Neptune’s Triton.) So instead, observational efforts measure colors and “show how color is a proxy for composition,” says Jewitt. His focus has shifted to this research using sensitive optical telescopes.

    3
    Neptune’s Triton has a surface covered in nitrogen frost. NASA/JPL/USGS

    Astronomers have collected colors for about two dozen irregular satellites that orbit Jupiter and Saturn — they’re closer and thus brighter than those around Uranus and Neptune. When astronomers analyze the colors of the irregular satellites, they find that most of the objects look similar, which implies a common source.

    But even color observations are reaching a technological limit. “A 30-meter telescope will help, or one needs to send more spacecraft to the outer solar system,” says David Nesvorny of the Southwest Research Institute in Boulder, Colorado.

    “Close-up, good physical observations are not likely to happen anytime soon,” says Sheppard. “Probably not within our lifetimes.” This means astronomers are doing what they can, now, to answer the questions about irregular satellites.

    Jewitt adds: “What’s happened in the last few years is that there’s been this burst of dynamical excitement motivated by the burst of new observations and characterizations, and so maybe that will take us somewhere to understanding these bodies.”

    Capturing bodies

    So where did irregular satellites come from? In the 1970s, three theories emerged: two related to the protoplanetary gas and dust disk in the early solar system, and the other requiring chance flybys.

    In our system’s youth, many small icy bodies (called planetesimals) orbited the Sun. The “gas drag” model says that occasionally one of these objects dove into the disk and slowed due to friction. At that point, the planet’s gravity could capture this object.

    The “pull down” method proposes that as the gas giant rapidly accreted a large amount of surrounding gas, its Hill sphere increased quickly. This trapped any nearby small bodies. However, both of these capture methods pertain to the gas giants’ formation and not to how the ice giants (Uranus and Neptune) formed. So neither provides a satisfying answer to the question of how irregular satellites ended up at the farthest planets.

    The third theory — “three-body interactions” — could partly explain the capture of these bodies. This posits that a planet and a binary planetesimal, or two planets and one small icy body, could result in an object becoming gravitationally trapped.

    4
    The Nice model is a hypothesis about the solar system’s early days. The planet’s orbits “wiggled,” passed through resonance, and migrated out. Neptune and Uranus moved into the outer disk of planetesimals and scattered them. Hal Levison

    The model implies that for each of the giant planets, the chances of capturing bodies relates to its mass — and thus the size of its Hill sphere — after the planets reach their “established” size. But more importantly, the three-body interactions don’t relate to only the planets’ formation; the model applies to later periods, too.

    Model citizens

    Even if the giant planets trapped a plethora of irregular satellites as they formed, the solar system may have undergone an upheaveal period. Any loosely bound objects would have been torn away from their parent worlds.

    In 2005, astronomers published a hypothesis regarding the giant planets’ evolution. The Nice model (pronounced “niece” and named after the city in France) suggests that the outer planets likely formed nearer to each other and closer to the Sun than they are now. The simulations imply that after the protoplanetary disk evaporated, the giant planets originally existed between 5 and 17 astronomical units (AU, the Earth-Sun distance) from the Sun. Just outside the farthest ice giant sat a disk of planetesimals that extended to about 35 AU.

    According to the model, the orbits slowly “wiggled” over time. Then, about 600 million years into the model, Jupiter and Saturn passed through orbits that coincided with a 2:1 resonance (meaning, Jupiter made two revolutions for every one that Saturn made). The combined gravitational effect forced Jupiter, Saturn, Uranus, and Neptune to scatter from each other. As the planets interacted, they tweaked the orbits of any small objects in their paths.

    Uranus and Neptune both moved into the planetesimal disk. Thus, small icy bodies scattered everywhere: Some escaped the solar system, some moved toward the inner solar system and collided with planets, others remained in this disk, and the giant planets grabbed some as “new” irregular satellites.

    So what’s the proof of this early solar system upheaval? “This model makes predictions about the solar system that match observations,” explains Nesvorny. Its simulated orbits coincide with those of Jupiter, Saturn, Uranus, and Neptune. The icy bodies that remained in the disk match up with some of the objects in the Kuiper Belt — the disk of icy bodies beyond Neptune. Those that moved to the inner solar system could explain the “late heavy bombardment,” which corresponds to craters seen on our Moon’s surface.

    According to Nesvorny: “Irregular satellites were sort of a puzzle when it was realized that their loosely bound orbits do not withstand the epoch of planetary encounters.” So he and colleagues performed simulations building off the Nice model to see where the gas giants’ current irregular satellites came from. “I got an idea in 2007 that while the existing populations of irregular satellites go away, new populations can be captured from the transplanetary disk. This is because planetary encounters typically happen in a region that is rather densely populated by planetesimals.”

    During the upheaval period, our solar system was a chaotic place with frequent collisions and near misses. If a binary asteroid or binary Kuiper Belt object (KBO) came close to a massive planet, one of those objects might have been gravitationally trapped while its companion was flung away.

    5
    Phoebe’s heavily cratered surface resulted from the turmoil of the younger solar system. NASA/JPL/Space Science Institute

    Nesvorny’s team’s first paper showed how Neptune, Uranus, and Saturn got their irregular satellites. However, it couldn’t explain those at Jupiter. So it went back to their simulation and made a few changes. “They have succeeded in tweaking their model such that it does give irregular satellites at Jupiter as well,” explains Jewitt.

    Extend the model to the belt

    According to Nesvorny, the Nice model also accounts for the structures scientists see in the Kuiper Belt and its different groups of objects.

    Kuiper Belt. Minor Planet Center
    Kuiper Belt. Minor Planet Center

    The “classical” objects are named as such because their orbits are what astronomers originally expected KBOs would follow. Scientists divide them into dynamically “cold” classical and “hot” classical because the objects have slightly different characteristics. The orbits of the cold ones aren’t tilted as much as those of the hot classical KBOs. The cold bodies also appear redder and are brighter than the hot objects.

    The Kuiper Belt also contains two other groups of objects: those in resonances with Neptune (Pluto is one example); and the “scattered disk,” which occasionally pass close enough to Neptune to gravitationally interact.

    When looking at the Kuiper Belt, scientists find that while some KBOs look redder than the irregular satellites, other object groupings have colors similar to the irregular satellites. Is this a coincidence? Or were the objects from the same place?

    Perhaps the planetesimals scattered during the reshuffling event moved into the Kuiper Belt as the hot classical, resonant, and scattered disk KBOs. These were the objects that, according to the Nice model, started out between about 17 and 35 AU. Nesvorny’s team argues that the cold classical KBOs formed right where they currently are, at 45 AU. The fact that the cold and hot ones came from different populations explains why they have different characteristics.

    Collisions abound

    Not all scientists agrees that the Nice model describes where the irregular satellites come from, or that these objects are the same as KBOs. “I think the Kuiper Belt model is plausible,” says Jewitt. “I think it’s very flexible, and it can fit various measurements, which is a good thing. But I don’t see any killer evidence that that’s what happened as opposed to some other thing.”

    But that’s the whole point of testing new models — to try to disprove or prove competing ideas in order to figure out the best-fitting one. The study of irregular satellites has exploded in the past decade. “The fact that people are thinking about this is what’s exciting,” says Jewitt.

    One concept scientists do agree on is that the planets must have captured their irregular satellites, and it had to happen in the solar system’s younger days. That’s when there was a lot more “stuff” flying around. And if more objects were getting in each other’s way, collisions must have been more common. Astronomers see evidence of such collisions on the most studied irregular satellite. Observations of Jupiter’s Hill sphere show a dust density about 10 times higher than expected, which suggests a large number of collisions also probably occurred within that region.

    The quest to understand irregular satellites around the solar system’s giant planets begins with the most important questions. “Where from, and when, and how are still not really known,” says Jewitt.

    Because technology has limited the observers, this work is currently performed with computer simulations. Different groups tackle these questions from different angles. But until astronomers have their 80-foot-wide optical telescopes, such modeling is the best way they’ll get their answers.

    See the full article here .

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