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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.

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  • richardmitnick 8:15 am on October 28, 2016 Permalink | Reply
    Tags: , Astronomy magazine, ,   

    From Astronomy: “The outer solar system keeps getting weirder’ 

    Astronomy magazine

    astronomy.com

    October 27, 2016
    Nola Taylor Redd

    q
    WikiMedia Commons

    Several newly discovered objects on the outskirts of the solar system suggest that something strange is afoot. While some scientists point to the odd behavior of the newfound residents as further proof for the existence of the hypothetical Planet Nine (a yet-unseen superEarth proposed to inhabit the outskirts) not everyone is convinced.

    The new inhabitants include a small icy world with one of the longest known orbits and several smaller objects clustered together extremely far from the sun.

    The newest of these objects is L91, an icy world that can travel as far from the sun as 1430 astronomical units (AU), or 1,430 times the Earth-sun distance, one of the longest known orbital periods. L91 never draws closer to the sun than 50 AUs, farther away than even Pluto.

    And L91’s distant path is shifting.

    “It’s orbit is changing in quite a remarkable way,” astrophysicist Michele Bannister told scientists last week at the American Astronomical Society’s Division for Planetary Sciences in Pasadena, California. Bannister, an astrophysicist at Queen’s University Belfast, identified minute changes in the object’s orbit that could come from the passing gravity of other stars or interactions with the hypothetical Planet Nine. Simulations by the team suggest that the tiny tugs are more likely to come from beyond the solar system, whether distant stars or galactic winds.

    Konstantin Batygin, an astronomer at the California Institute of Technology, said, “I think it’s a story that’s not implausible, but I also think it’s not needed.” Batygin, who announced the existence of Planet Nine last January, thinks the unusual orbits of L91 and other newfound objects are more likely explained by the hypothetical planet.

    Bannister and her team spotted L91 using the Outer Solar System Origins Survey, a 4-year survey hunting distant moving objects using the Canada-France-Hawaii Telescope. L91’s mass and size remains unknown.

    “It’s right at the limit of what we could actually detect in the sky,” Bannister said.

    ‘Something is happening’

    L91 isn’t the only new object in the sky. Another team of astronomers reported a handful of smaller icy bodies traveling beyond Neptune. Similarities in the orbits of objects like these led to the proposal of Planet Nine.

    “A lot is going on in the outer solar system,” said Scott Sheppard of the Carnegie Institution for Science in Washington, D.C. Sheppard is part of a team of astronomers conducting the largest, deepest survey of trans-Neptunian objects, whose orbits take them farther out than Neptune. The team found several new objects clustered in the outer edges of the solar system.

    One of these objects, 2014 FE72, is the first known to come from the Oort Cloud, the icy shell around the solar system where comets are born.

    Oort Cloud NASA
    Oort Cloud NASA

    With an orbit that takes it out more than 3,000 AUs, it may also suffer from the influence of passing stars or the gravity of Planet Nine

    Sheppard and his colleagues have been mapping the sky in detail since 2007. So far, they’ve only covered about 10 percent of what he calls “the most interesting part of the sky.”

    But not all scientists are convinced that the increasing number of odd orbits points to Planet Nine.

    “We did search some parts of the sky more thoroughly than others,” says astronomer Katherine Volk, a planetary scientist at the University of Arizona. Volk analyzed the growing studies offered up as evidence for the hypothetical planet, and remains skeptical that it is the only conclusion. “You find things where you’re looking,” she says.

    She pointed out that the similarities in orbits, or clustering, of the objects could be related to their similar positions in the sky.

    “If the clustering persists at the end of [Sheppard’s] survey, it will be more convincing,” she said.

    At the same conference, Batygin reported that Planet 9 could be responsible for the backwards, or retrograde, orbit of some of the solar system’s centaurs. Orbiting among the outer planets, centaurs cross the orbits of their larger neighbors. And Elizabeth Bailey, a graduate student at Caltech working with Batygin, reported that Planet 9 could have tilted the orbit of the solar system’s planets with respect to the sun, solving another long-standing astronomical mystery.

    Again, Volk isn’t convinced that the research proves the existence of Planet Nine, though she said Batygin and Bailey’s had drawn reasonable conclusions.
    “There are all these different, slightly odd things,” she said. “No one piece of evidence is really convincing me that for sure there is a planet there, [but] the fact that there are multiple things probably says something is happening.”

    See the full article here .

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  • richardmitnick 6:37 pm on October 26, 2016 Permalink | Reply
    Tags: 2MASX J17222717+3207571, , Astronomy magazine, Largest 'depleted galaxy' holds clues to how it formed   

    From Astronomy: “Largest ‘depleted galaxy’ holds clues to how it formed” 

    Astronomy magazine

    astronomy.com

    October 26, 2016
    Allen Zeyher

    The largest “depleted galaxy” ever observed apparently did not form according to the most popular model.

    The galaxy, designated 2MASX J17222717+3207571, is remarkable for its size (a total stellar mass of 4.44 trillion solar masses) and for the stars missing from its core (175 billion solar masses). By comparison, the Milky Way tips the cosmic scale at a meager 60 billion solar masses.

    2
    This image shows the giant elliptical galaxy 2MASX J17222717+3207571, also known as A2261-BCG (NASA / ESA / M. Postman / Space Telescope Science Institute / T. Lauer / National Optical Astronomy Observatory / the CLASH team)

    Astronomers call a galactic core “depleted” when the mass density of stars in its core does not follow the progression set by the outer part of the galaxy. The density of stars in most galaxies increases smoothly from the outer edge to the center. Astronomers can plot the actual progression in a galaxy and compare it with the expected, smooth progression. In some galaxies, the actual number of stars in the central bulge falls short of what is expected.

    Depleted cores show up in only a small percentage of galaxies, but they are fairly common in very large galaxies, according to Alister Graham, a professor of astronomy at Swinburne University of Technology’s Centre for Astrophysics and Supercomputing. “It’s only galaxies with a spheroidal distribution of stars more massive than about 200 billion solar masses. As a general rule, this excludes all spiral galaxies.”

    After a close inspection of what was thought to be the largest depleted galaxy core last year and finding that the initial analysis was mistaken, Graham and Paolo Bonfini, from Centro de Radioastronomía y Astrofísica in Mexico, decided to take a closer look at the next two largest depleted galaxies.

    Graham and Bonfini, who was the lead author, published their results in the Sept. 23, 2016, Astrophysical Journal (Vol. 829, No. 81, The Quest for the Largest Depleted Galaxy Core: Supermassive Black Hole Binaries And Stalled Infalling Satellites.

    The smaller of the two galaxies, designated 2MASX J09194427+5622012, appears to have formed by the merger of two similar-size smaller galaxies. Each of the two merging galaxies had a supermassive black hole at its center. As the two cores merged into each other, some of the stars were flung out, the way an Earth spacecraft gains speed as it slingshots around a gas giant planet such as Jupiter.

    “Some stars may be kicked right out of the galaxy,” says Graham, “while others now orbit in the middle and outer regions of the galaxy.”

    Galaxy ’012 apparently formed through the “binary black hole scouring scenario,” a widely accepted model for how galaxies merge and form depleted cores.

    The revelation came from the bigger depleted galaxy, which shows no evidence of containing a supermassive black hole. Galaxy ’571 has a core that is evenly distributed with stars — except for a handful of dense knots of stars near the core’s edge.

    “When this model was first introduced, the cores it produced were so large, and the central mass deficits so great, that it was considered excessive,” says Graham. “Nothing so big had ever been observed. But that all changed with 2MASX J17222717+3207571 (‘571), which perfectly matches the unusually large, constant-density core seen in the simulations.”

    3
    Hubble Space Telescope image of the giant galaxy 2MASX J17222717+3207571, showing several semidigested galaxies around its heavily depleted core.
    NASA, ESA, Paolo Bonfini

    The pudding scenario

    The pair of supermassive black holes dominate the action in what astronomers call the “scouring scenario,” slinging normal stars aside as they plunge toward each other. Imagine a rock falling into a swimming pool of water.

    Without the black holes, a tightly bound star core being drawn into a uniformly distributed star core is more like a chunk of chocolate sinking into a pool of warm pudding. Astronomers refer to the idea more precisely as the “stalled perturber scenario.”

    The pudding metaphor has limitations, of course. For example, around the edges of the tightly bound core, individual stars exchange kinetic energy with the surrounding stars, some of which are ejected.

    The core of galaxy ’571 may have started life with a typical undepleted density peak in the middle, but when it started swallowing its small satellite galaxies, its core density started to even out.

    “The inner stellar density gradient in the big galaxy is eroded away as the satellites sink in,” explains Graham. “The satellites sink (their orbital energy is reduced) while the centrally located stars of the big galaxy are ejected out (their orbital energy increases). Once the core has a constant density, the satellites’ in-fall is stalled; they loiter at the boundary of this core for a very long time.”

    Numerical confirmation

    Graham and Bonfini ran computer simulations and found that the structure of the core of galaxy ’571 is consistent with a large galaxy with a roughly constant-density core and no supermassive black hole swallowing a much smaller galaxy with a tightly bound core but also without a supermassive black hole.

    “It is hard to know exactly the history of mergers and activity for any one galaxy,” but the stalled perturber scenario remains a valid idea, according to Christopher Conselice, a professor of astrophysics at the University of Nottingham in the U.K. Conselice was not involved in Bonfini and Graham’s study. “The arguments they give are fairly solid, but the other possibilities still remain. More data is needed, and especially more simulations need to be carried out to interpret what we observe.”

    Located at the center of a cluster containing hundreds of galaxies, galaxy ’571 continues to grow by swallowing the smaller galaxies around it, says Graham. The remnants of the dense cores of five of those swallowed galaxies can be seen in images of galaxy ’571. They hover near the edge of galaxy ’571’s core as monuments to their past life.

    “For a couple of decades now, SMBHs [supermassive black holes] have been the go-to bad boy when people observe the damaged cores of galaxies,” says Graham. “While they are undoubtedly guilty of many of these crimes, some of the damage may have resulted from poor satellite galaxies that have been captured. I already have plans to revisit images of some 100 nearby galaxies known to have damaged cores and look for possible (previously overlooked or ignored) remnants of semidigested galaxies.”

    See the full article here .

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  • richardmitnick 11:15 am on October 4, 2016 Permalink | Reply
    Tags: , Astronomy magazine, , , ,   

    From Astronomy: Women in STEM – “How Vera Rubin discovered dark matter” 

    Astronomy magazine

    astronomy.com

    October 04, 2016
    Sarah Scoles

    1
    A young Vera Rubin was already observing the stars when she was an undergraduate at Vassar College, where she earned her bachelor’s degree in astronomy in 1948. Archives & Special Collections, Vassar College Library

    In the late 1970s, Vera Rubin and Kent Ford of the Carnegie Institution of Washington stared, confused, at the punch-card readouts from their observations of the Andromeda Galaxy.

    Andromeda Galaxy Adam Evans
    Andromeda Galaxy, Adam Evans”

    The vast spiral seemed to be rotating all wrong. The stuff at the edges was moving just as fast as the stuff near the center, apparently violating Newton’s Laws of Motion (which also govern how the planets move around our Sun). While the explanation for that strange behavior didn’t become clear to Rubin until two years later, these printouts represented the first direct evidence of dark matter.

    Scientists now know that dark matter comprises some 84 percent of the universe’s material. Its invisible particles swarm and stream and slam through the whole cosmos. It affects how stars move within galaxies, how galaxies tug on each other, and how all that matter clumped together in the first place. It is to the cosmos like air is to humans: ubiquitous, necessary, unseen but felt. The discovery of this strange substance deserves a Nobel Prize. But, for Rubin, none has come, although she has long been a “people’s choice” and predicted winner.

    In the past few years, scientists have gotten that free trip to Sweden for demonstrating that neutrinos have mass, for inventing blue LEDs, for isolating graphene’s single carbon layer, and for discovering dark energy. All of these experiments and ideas are worthy of praise, and some, like dark energy, even tilted the axis of our understanding of the universe. But the graphene work began in 2004; dark energy observations happened in the late ’90s; scientists weighed neutrinos around the same time; and blue LEDs burst onto the scene a few years before that. Rubin’s work on dark matter, on the other hand, took place in the 1970s. It’s like the committee cannot see her, although nearly all of astrophysics feels her influence.

    Rubin is now 87. She is too infirm for interviews. And because the Nobel can only be awarded to the living, time is running out for her.

    Emily Levesque, an astronomer at the University of Washington in Seattle who has spoken out about Rubin’s notable lack of a Nobel, says, “The existence of dark matter has utterly revolutionized our concept of the universe and our entire field; the ongoing effort to understand the role of dark matter has basically spawned entire subfields within astrophysics and particle physics at this point. Alfred Nobel’s will describes the physics prize as recognizing ‘the most important discovery’ within the field of physics. If dark matter doesn’t fit that description, I don’t know what does.”

    There’s no way to prove why Rubin remains prize-less. But a webpage showing images of past winners looks like a 50th-reunion publication from a boys’ prep school. No woman has received the Nobel Prize in physics since 1963, when Maria Goeppert Mayer shared it with Eugene Wigner and J. Hans Jensen for their work on atomic structure and theory. And the only woman other than Mayer ever to win was Marie Curie. With statistics like that, it’s hard to believe gender has nothing to do with the decision.

    Some, like Chanda Prescod-Weinstein of the Massachusetts Institute of Technology, have called for no men to accept the prize until Rubin receives it. But given the human ego and nearly million-dollar prize amount, that’s likely to remain an Internet-only call to action.

    No room for women

    Rubin isn’t unfamiliar with discrimination more outright than the Nobel committee’s. Former colleague Neta Bahcall of Princeton University tells a story about a trip Rubin took to Palomar Observatory outside of San Diego early in her career. For many years, the observatory was a researcher’s man cave. Rubin was one of the first women to gain access to its gilt-edged, carved-pillar grandeur. But while she was allowed to be present, the building had no women’s restroom, just urinal-studded water closets.

    “She went to her room, she cut up paper into a skirt image, and she stuck it on the little person image on the door of the bathroom,” says Bahcall. “She said, ‘There you go; now you have a ladies’ room.’ That’s the type of person Vera is.”

    Rubin has continued to champion women’s rights to — and rights within — astronomy. “She frequently would see the list of speakers [at a conference],” says Bahcall, “and if there were very few or no women speakers, she would contact [the organizers] and tell them they have a problem and need to fix it.”

    But, as Rubin told science writer Ann Finkbeiner for Astronomy in 2000, she is “getting fed up. . . . What’s wrong with this story is that nothing’s changing, or it’s changing so slowly.”

    An early start

    Rubin, born in 1928, first found her interest in astronomy when her family moved to Washington, D.C. Windows lined the wall next to her bed. She watched the stars move, distant and unreachable. “What fascinated me was that if I opened my eyes during the night, they had all rotated around the pole,” she told David DeVorkin in 1995 as part of the American Institute of Physics oral history interview series. “And I found that inconceivable. I just was captured.”

    She started watching meteor showers and drew maps of the streaks, which striped the sky for a second and then were gone. She built a telescope and chose astronomical topics for English papers, using every subject as an opportunity to peer deeper into the universe. “How could you possibly live on this Earth and not want to study these things?” she wondered, retelling the story to DeVorkin.

    While her parents supported her, it was a different story at school. When she told her physics teacher, for instance, that she had received a scholarship to Vassar College, he said, “As long as you stay away from science, you should do OK.”

    She didn’t.

    2
    Rubin and Kent for (white hat) check on their equipment at Lowell Observatory in 1965 during one of their first observing runs together. Carnegie Institution, Department of Terrestrial Magnetism

    Rotation of the universe

    After receiving her bachelor’s degree from Vassar, Rubin enrolled in graduate school in astronomy at Cornell University in Ithaca, New York. Ensconced in Ithaca’s gorges and working with astronomer Martha Stahr Carpenter, Rubin began to hunt around for a master’s thesis idea. Carpenter was obsessed with galaxies and how their innards moved. “Her course in galaxy dynamics really set me off on a direction that I followed almost my entire career,” said Rubin.

    One day, her new husband, Robert Rubin, brought her a journal article by astronomer George Gamow. In it, Gamow wondered, “What if we took the way solar systems rotate and applied it to how galaxies move in the universe?”

    Rubin wondered, “What if, indeed?” and took that wonder a step further. She began to measure how galaxies moved. Did some cluster together in their travel through space — perhaps rotating around a pole, like the planets rotate around the common Sun? Was it random?

    While gathering data, she found a plane that was denser with galaxies than other regions. She didn’t know it at the time, and no one else would discover it for years, but she had identified the “supergalactic plane,” the equator of our home supercluster of galaxies.

    When she presented her thesis, William Shaw, one of her advisers, told her just two things: One, the word data is plural. Two, her work was sloppy. But, he continued, she should consider presenting it at the American Astronomical Society (AAS) meeting. Or, rather, she should consider having it presented for her. Because she was pregnant with her first child — due just a month before the meeting — and not a member of the society, he graciously volunteered to give a talk on her results. “In his name,” she clarified to DeVorkin. “Not in my name. I said to him, ‘Oh, I can go.’ ”

    She called her talk “Rotation of the Universe,” ascribing the ambitious title to “the enthusiasm of youth,” as she recalled. At the AAS meeting, she didn’t know anyone, and she thought of herself as a different category of human. “I put these people in a very special class. They were professional astronomers, and I was not,” she said, showcasing a classic case of impostor syndrome, a psychological phenomenon in which people don’t feel they deserve their accomplishments and status and will inevitably be exposed as frauds. “One of the biggest problems in my life [during] those years was really attempting to answer the question to myself, ‘Will I ever really be an astronomer?’ ”

    The “real astronomers” pounced on her result (except, notably, Martin Schwarzschild, who defined how big black holes are). “My paper was followed by a rather acrimonious discussion,” she told DeVorkin. “I didn’t know anyone, so I didn’t know who these people were that were getting up and saying the things they said. As I recall, all the comments were negative.”

    Her paper was never published.

    Back into the field

    For six months after her first child was born, Rubin stayed home. But while she loved having a child, staying at home emptied her. She cried every time The Astrophysical Journal arrived at the house. “I realized that as much as we both adored this child, there was nothing in my background that had led me to expect that [my husband] would go off to work each day doing what he loved to do, and I would stay home with this lovely child,” she said to DeVorkin. “I really found it very, very hard. And it was he who insisted that I go back to school.”

    She was accepted into a Ph.D. program at Georgetown University in Washington, D.C., and she discovered that galaxies did clump together, like iron filings, and weren’t randomly strewn. The work, though now part of mainstream astronomy, was largely ignored for decades; that lack of reinforcement perhaps contributed to her lingering, false feeling that she wasn’t a real astronomer. As she described it, “My husband heard my question often, ‘Will I ever really be an astronomer?’ First I thought when I’d have a Ph.D., I would. Then even after I had my Ph.D., I wondered if I would.”

    3
    Rubin operates the 2.1-meter telescope at Kitt Peak National Observatory. Kent Ford’s spectograph is attached so they can measure the speed of matter at different distances from galaxies’ centers. NOAO/AURA/NSF

    Mysteriously flat

    In 1965, after a stint as a professor at Georgetown, Rubin began her work at the Carnegie Institution’s Department of Terrestrial Magnetism in Washington, D.C., where she met astronomer Kent Ford and his spectacular spectrometer, which was more sensitive than any other at the time.

    A spectrometer takes light and splits it up into its constituent wavelengths. Instead of just showing that a fluorescent bulb glows white, for instance, it would show how much of that light is blue and how much yellow, and which specific wavelengths of blue and yellow. Ford’s spectrometer stood out from others at the time because it employed state-of-the-art photomultipliers that let researchers study small regions of galaxies, and not simply the entire objects.

    With this device, Ford and Rubin decided to look at quasars — distant galaxies with dynamic, supermassive black holes at their centers. But this was competitive work: Quasars had just been discovered in 1963, and their identity was in those days a mystery that everyone wanted to solve. Rubin and Ford didn’t have their own telescope and had to request time on the world-class instruments that astronomers who worked directly for the observatories could access all the time. Rubin didn’t like the competition.

    “After about a year or two, it was very, very clear to me that that was not the way I wanted to work,” she told Alan Lightman in another American Institute of Physics oral history interview. “I decided to pick a problem that I could go observing and make headway on, hopefully a problem that people would be interested in, but not so interested [in] that anyone would bother me before I was done.”

    Rubin and Ford chose to focus on the nearby Andromeda Galaxy (M31). It represented a return to Rubin’s interest in galaxy dynamics. “People had inferred what galaxy rotations must be like,” said Rubin, “but no one had really made a detailed study to show that that was so.” Now, because of Ford’s out-of-this-world spectrograph, they could turn the inferences into observations.

    When they pointed the telescope at M31, they expected to see it rotate like the solar system does: Objects closer to the center move faster than ones toward the edge. Mass causes gravity, which determines the speed of rotation. Since most of the stars, dust, and gas — and therefore gravity — is clustered in the middle of galaxies, the stuff on the periphery shouldn’t feel much pull. They concentrated their observations on Hydrogen-II (HII) regions — areas of ionized hydrogen gas where stars have recently formed — at different distances from the galaxy’s center. But no matter how far out they looked, the HII regions seemed to be moving at the same speed. They weren’t slowing down.

    “We kept going farther and farther out and had some disappointment that we never saw anything,” says Ford. “I do remember my puzzling at the end of the first couple of nights that the spectra were all so straight,” said Rubin, referring to the unchanging speed of the various HII regions.

    They didn’t know what, if anything, it meant yet.

    The project took years and involved treks westward to telescopes. Ford recalls flying to Flagstaff, Arizona, dragging the spectrograph from the closet, working for a few nights at Lowell, and then throwing the instrument into a Suburban so they could drive it to Kitt Peak. “We both thought we were better at guiding the telescope,” he says. They raced each other to be first to the eyepiece.

    The data came out on punch cards, which Rubin spent hours analyzing in a cubbyhole beneath a set of stairs. They all showed the same thing.

    Rubin and Ford moved on from M31 to test other galaxies and their rotation curves. Like an obsessive artist, each painted the same picture. Although the result contradicted theory, and although they didn’t understand what it meant, no one doubted their data. “All you had to do was show them a picture of the spectrum,” Rubin told Lightman. “It just piled up too fast. Soon there were 20, then 40, then 60 rotation curves, and they were all flat.”

    A dark answer

    Dark matter existed as a concept, first proposed by astronomers like Jan Oort in 1932 and Fritz Zwicky in 1933, who also noticed discrepancies in how much mass astronomers could see and how much physics implied should be present. But few paid their work any attention, writing their research off as little more than cosmological oddities. And no one had bagged such solid evidence of it before. And because no one had predicted what dark matter’s existence might mean for galaxy dynamics, Rubin and Ford initially didn’t recognize the meaning of their flat rotation curves.

    “Months were taken up in trying to understand what I was looking at,” Rubin told journalist Maria Popova. “One day I just decided that I had to understand what this complexity was that I was looking at, and I made sketches on a piece of paper, and suddenly I understood it all.”

    If a halo of dark matter graced each galaxy, she realized, the mass would be spread throughout the galaxy, rather than concentrating in the center. The gravitational force — and the orbital speed — would be similar throughout.

    Rubin and Ford had discovered the unseeable stuff that influences not only how galaxies move, but how the universe came to be and what it will become. “My entire education highlighted how fundamental dark matter is to our current understanding of astrophysics,” says Levesque, “and it’s hard for me to imagine the field or the universe without it.”

    Within a few years of the M31 observations, physicists like Jeremiah Ostriker and James Peebles provided the theoretical framework to support what Rubin and Ford had already shown, and dark matter settled firmly into its celebrated place in the universe.

    In more recent years, the Planck satellite measured the dark matter content of the universe by looking at the cosmic microwave background, the radiation left over from the Big Bang. The clumps of matter in this baby picture of the universe evolved into the galaxy superclusters we see today, and it was dark matter that clumped first and drew the regular matter together.

    Data from galaxy clusters now also confirms dark matter and helps scientists measure how much of it exists within a given group — a modern echo of Zwicky’s almost forgotten work. When light from more distant sources passes near a cluster, the gravity — from the cluster’s huge mass — bends the light like a lens.

    The amount of bending can reveal the amount of dark matter.

    No matter which way or where scientists measure Rubin’s discovery, it’s huge.

    And while no one knows what all the dark matter is, scientists have discovered that some small fraction of it is made of neutrinos — tiny, fast-moving particles that don’t really interact with normal matter. Measurements from the cosmic microwave background, like those being taken by experiments called POLARBEAR in Chile and BICEP2 and BICEP3 in Antarctica, will help pin down how many neutrinos are streaming through the universe and how much of the dark matter they make up.

    Some setups, like the Gran Sasso National Laboratory in Italy and the Deep Underground Science and Engineering Laboratory in South Dakota, are trying to detect dark matter particles directly, when they crash into atoms in cryogenically cooled tanks filled with liquefied noble gases. So far, they haven’t managed to capture a dark matter particle in action. But researchers are taking dark matter — whatever it is — into account when they think about how the universe evolves.

    The Nobel committee may overlook Rubin, passing by her as if they can’t see what all of astrophysics feels. But that won’t hurt her legacy, says Levesque: It will hurt the legacy of the Nobel itself. “It would then permanently lack any recognition of such groundbreaking work,” Levesque says.

    Rubin herself has never spoken about how she deserves a Nobel Prize. She simply continued her scientific work until recently, all the while influencing the origins, evolutions, and fates of other scientists. “If they didn’t get a job or they didn’t get a paper published, she would cheer people up,” says Bahcall. “She kept telling her story about how there are ups and downs and you stick with it and keep doing what you love doing.”

    Rubin, herself, loves trying to understand the universe, and in doing so, she has changed everyone’s understanding of it. That carries more weight than some medal from Sweden. But let Sweden recognize that for what it is: worthy of a prize.

    See the full article here .

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