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  • richardmitnick 8:07 am on May 20, 2017 Permalink | Reply
    Tags: , , , , , EarthSky, How long to travel to Alpha Centauri?   

    From EarthSky: “How long to travel to Alpha Centauri?” 

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    EarthSky

    May 16, 2017
    Deborah Byrd

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    Artist’s concept via Breakthrough Starshot.

    Outer space is big. Really, really, really big. And that’s why NASA has no plans at present to send a spacecraft to any of the several thousand known planets beyond our solar system. Meanwhile, with respect to star travel, NASA isn’t the only game in town anymore. In April 2016, Russian high-tech billionaire Yuri Milner announced a new and ambitious initiative called Breakthrough Starshot, which intends to pour $100 million into proof-of-concept studies for an entirely new technology for star travel, aimed at unmanned space flight at 20% of light speed, with the goal of reaching the Alpha Centauri system – and, presumably, its newly discovered planet Proxima b – within 20 years. Is it possible? No one knows yet, but Alpha Centauri is an obvious target. It’s the nearest star system to our sun at 4.3 light-years away. That’s about 25 trillion miles (40 trillion km) away from Earth – nearly 300,000 times the distance from the Earth to the sun. Follow the links below to learn more about why star travel is so formidable, and about how we might accomplish it.

    Why won’t a conventional rocket work?

    Warp drive?

    Breakthrough Starshot

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    These 4 conventional spacecraft are headed out of the solar system. A 5th spacecraft, New Horizons, will also eventually leave the solar system.

    NASA/New Horizons spacecraft

    But conventional spacecraft move slowly in contrast to the vast distances between stars. It’ll be tens of thousands of years before one of these craft encounters a star. Image via Wikimedia Commons.

    Why won’t a conventional rocket work? Consider the Space Shuttles, which traveled only a few hundred kilometers above Earth’s surface, into Earth orbit. If Earth were the size of a sand grain, this distance would be about the width of a hair in contrast to a 6-mile (10-km) distance to Alpha Centauri.

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    The Space Shuttles weren’t starships, but we have built starships. Five craft from Earth are currently on their way out of the solar system, headed into interstellar space. They are the two Pioneer spacecraft, the two Voyager spacecraft, and the New Horizons spacecraft. All are moving extremely slowly relative to the speed needed to travel among the stars.

    NASA Pioneer II

    NASA/Voyager 1

    So … consider the two Voyagers – Voyager 1 and Voyager 2 – launched in 1977. Neither Voyagers is aimed toward Alpha Centauri, but if one of them were – assuming it maintained its current rate of speed – it would requires take tens of thousands of years to this next-nearest star. Eventually, the Voyagers will pass other stars. In about 40,000 years, Voyager 1 will drift within 1.6 light-years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light-years from Sirius, the brightest star in the sky. Hmm, 4.3 light-years. That’s the distance between us and Alpha Centauri.

    What about the New Horizons spacecraft, the first spacecraft ever to visit Pluto and its moons. NASA’s New Horizons spacecraft travels at 36,373 miles per hour (58,536 km/h). Launched from Earth in mid-January, 2006, it reached Pluto in mid-July, 2015 … nine-and-a-half years later. If New Horizons were aimed toward the Alpha Centauri system, which it isn’t, it would take this spacecraft about 78,000 years to get there.

    So conventional rockets won’t work because they are too slow.

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    What a spaceship with warp drive might look like. Credit: Mark Rademaker/Mike Okuda/Harold White/NASA.

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    Illustration via the Anderson Institute.

    Warp drive? What if we could travel faster than light? Countless sci-fi books and movies are built around the concept, which brings with its challenges to physicists’ understanding of how space and time actually work. Still, a few years ago, Dr. Harold “Sonny” White – who leads NASA’s Advanced Propulsion Team at Johnson Space Center – claimed to have made a discovery which made plausible the idea of faster-than-light travel, via a concept known as the Alcubierre warp drive.

    This concept is based on ideas put forward by Mexican physicist Miguel Alcubierre in 1994. He suggested that faster-than-light travel might be achieved by distorting spacetime, as shown in the illustration above.

    Harold “Sonny” White has been working to investigate these ideas further. They are highly speculative, but possibly valid, and involve a solution of the Einstein field equations, specifically how space, time and energy interact. In June of 2014, White unveiled images of what a faster-than-light ship might look like. Artist Mark Rademaker based these designs on White’s theoretical ideas. He said creating them took more than 1,600 hours, and they are very cool. See the 2014 faster-than-light spacecraft designs on this Flickr page.

    The video below presents Harold White’s talk at the SpaceVision 2013 Space Conference in November, 2013 in Phoenix. He talks about the concepts and progress in warp-drive development over recent decades.


    One hour

    s it faster-than-light travel possible, via the Alcubierre warp drive? As with conventional propulsion systems, the problem is energy. In this case, it’s the type of energy the warp drive would need. Daily Kos reported:

    In order to form the warp field/bubble, a region of space-time with negative energy density (i.e. repulsing space-time) is necessary. Scientific models predict exotic matter with a negative energy may exist, but it has never been observed. All forms of matter and light have a positive energy density, and create an attractive gravitational field.

    So faster-than-light travel via the Alcubierre warp drive is highly speculative, to say the least.

    With current technologies, it’s not possible.

    However, if it could be accomplished, it would reduce the travel time to Alpha Centauri from thousands of years to just days.

    Want technical details on the Alcubierre warp drive? Read this 2014 article at Daily Kos.

    Or try this January 2017 article on the Alcubierre warp drive, at Phys.org

    NASA has a whole area on its website about faster-than-light travel, in which it basically says … it’s not currently possible.

    Breakthrough Starshot. In April, 2016, Yuri Milner’s organization Breakthrough Initiatives announced a $100 million investment in proof-of concept studies for an all-new way to get to the stars.

    Well, not all new., exactly. The Breakthrough Starshot project relies on technologies that are being tested now, and also on some new technologies that have been around only a few years. But it does put these technologies together in a way that’s entirely new, and extremely visionary.

    The Breakthrough Starshot team has some heavy hitters, including physicist Stephen Hawking and Facebook’s Mark Zuckerberg. It proposes to use the $100 million to learn whether it’s possible to use a 100-gigawatt light beam and light sails to propel some 1,000 ultra-lightweight nanocraft to 20% of light speed. If it’s shown to be possible, such a mission could (hypothetically) reach Alpha Centauri within about 20 years of its launch.

    There are a lot of appealing things about this project. For example, the use of lightsails is currently in the process of being tested by another organization, the Planetary Society, with a publicly funded project called LightSail.

    But the most appealing thing is that the Breakthrough Starshot project is truly innovative, yet still grounded in current, cutting-edge science and technology. Just realize that all existing spacecraft are huge and clunky in contrast to the gram-scale nanostarships – dubbed StarChips – being proposed by Breakthrough Starshot. Can tiny, light ships – on sails pushed by a light beam – fly 1,000 times faster than the fastest spacecraft built up to now? That’s what Breakthrough Starshot is exploring with its ongoing proof-of-concept studies.

    Starshot envisions launching a mothership carrying the 1,000 tiny spacecraft to a high-altitude orbit. Each craft is a gram-scale wafer, carrying cameras, photon thrusters, power supply, navigation and communication equipment, and “constituting a fully functional space probe,” the Starshot team has said.

    Mission controllers would deploy the nanocraft – send them on their way – one by one. A ground-based laser array called a light beamer would be used to focus light on the sails of the ships, to accelerate individual craft to the target speed “within minutes.”

    The plan is to stick four cameras (two-megapixels each) on the nanocraft, allowing for some elementary imaging. The data would be transmitted back to Earth using a retractable meter-long antenna, or perhaps even using the lightsail to facilitate laser-based communications that could focus a signal back towards Earth.

    The original idea was to send the spacecraft flying through the Alpha Centauri system without slowing down. After all, how can they slow down? It turns out someone has already figured out a possible way. In early 2017 two scientists announced the results of their study of a possible braking method, using the radiation and gravity of the Alpha Centauri stars themselves. We don’t know yet if such a thing can work, but it’s heartening to see scientists getting involved in this idea!

    Clearly, the Breakthrough Starshot project is one that’s worth watching.

    On April 20 and 21, 2017, Breakthrough Initiatives held the second of what it says will be an annual conference – called Breakthrough Discuss – aimed at bringing together leading astronomers, engineers, astrobiologists and astrophysicists. This year, they held the conference at Stanford University and focused it on discoveries of potentially habitable planets in nearby star systems, including Alpha Centauri. Videos related to discussions at the conference are archived on Breakthrough’s Facebook page, if you’re interested.

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    Illustration via FutureHumanEvolution.com

    Bottom line: At 4.3 light-years away, the Alpha Centauri system is the nearest star system to our Earth and sun, but getting there would be extremely difficult.

    See the full article here .

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  • richardmitnick 12:37 pm on May 14, 2017 Permalink | Reply
    Tags: , , EarthSky, , What’s a safe distance between us and a supernova?   

    From EarthSky: “What’s a safe distance between us and a supernova?” 

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    EarthSky

    May 7, 2017
    EarthSky

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    Artist’s illusration of a supernova, or exploding star, via http://SmithsonianScience.org

    A supernova is a star explosion – destructive on a scale almost beyond human imagining. If our sun exploded as a supernova, the resulting shock wave probably wouldn’t destroy the whole Earth, but the side of Earth facing the sun would boil away. Scientists estimate that the planet as a whole would increase in temperature to roughly 15 times hotter than our normal sun’s surface. What’s more, Earth wouldn’t stay put in orbit. The sudden decrease in the sun’s mass might free the planet to wander off into space. Clearly, the sun’s distance – 8 light-minutes away – isn’t safe. Fortunately, our sun isn’t the sort of star destined to explode as a supernova. But other stars, beyond our solar system, will. What is the closest safe distance? Scientific literature cites 50 to 100 years as the closest safe distance between Earth and a supernova. Follow the links below to learn more.

    What would happen if a supernova exploded near Earth?

    How many potential supernovae are located closer to us than 50 to 100 light-years?

    What about Betelgeuse?

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    Betelgeuse and Bellatrix: Orion’s Shoulders

    How often do supernovae erupt in our galaxy?

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    This image shows the remnant of Supernova 1987A seen in light of very different wavelengths. ALMA data (in red) shows newly formed dust in the centre of the remnant. Hubble (in green) and Chandra (in blue) data show the expanding shock wave.
    Date 6 January 2014
    Source http://www.eso.org/public/images/eso1401a/
    Author ALMA (ESO/NAOJ/NRAO)/A. Angelich. Visible light image: the NASA/ESA Hubble Space Telescope. X-Ray image: The NASA Chandra X-Ray Observatory

    NASA/ESA Hubble Telescope

    NASA/Chandra Telescope

    What would happen if a supernova exploded near Earth? Let’s consider the explosion of a star besides our sun, but still at an unsafe distance. Say, the supernova is 30 light-years away. Dr. Mark Reid, a senior astronomer at the Harvard-Smithsonian Center for Astrophysics, has said:

    “… were a supernova to go off within about 30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions. X-rays and more energetic gamma-rays from the supernova could destroy the ozone layer that protects us from solar ultraviolet rays. It also could ionize nitrogen and oxygen in the atmosphere, leading to the formation of large amounts of smog-like nitrous oxide in the atmosphere.”

    What’s more, if a supernova exploded within 30 light-years, phytoplankton and reef communities would be particularly affected. Such an event severely deplete the base of the ocean food chain.

    Suppose the explosion were slightly more distant. An explosion of a nearby star might leave Earth and its surface and ocean life relatively intact. But any relatively nearby explosion would still shower us with gamma rays and other high-energy radiation. This radiation could cause mutations in earthly life. Also, the radiation from a nearby supernova could change our climate.

    No supernova has been known to erupt at this close distance in the known history of humankind. The most recent supernova visible to the eye was Supernova 1987A, in the year 1987. It was approximately 168,000 light-years away.

    Before that, the last supernova visible to the eye was was documented by Johannes Kepler in 1604. At about 20,000 light years, it shone more brightly than any star in the night sky. It was even visible in daylight! But it didn’t cause earthly effects, as far as we know.

    How many potential supernovae are located closer to us than 50 to 100 light-years? The answer depends on the kind of supernova.

    A Type II supernova is an aging massive star that collapses. There are no stars massive enough to do this located within 50 light-years of Earth.

    But there are also Type I supernovae – caused by the collapse of a small faint white dwarf star. These stars are dim and hard to find, so we can’t be sure just how many are around. There are probably a few hundred of these stars within 50 light-years.

    The star IK Pegasi B is the nearest known supernova progenitor candidate. It’s part of a binary star system, located about 150 light years from our sun and solar system.

    The main star in the system – IK Pegasi A – is an ordinary main sequence star, not unlike our sun. The potential Type I supernova is the other star – IK Pegasi B – a massive white dwarf that’s extremely small and dense. When the A star begins to evolve into a red giant, it’s expected to grow to a radius where the white dwarf can accrete, or take on, matter from A’s expanded gaseous envelope. When the B star gets massive enough, it might collapse on itself, in the process exploding as a supernova.

    What about Betelgeuse? Another star often mentioned in the supernova story is Betelgeuse, one of the brightest stars in our sky, part of the famous constellation Orion. Betelgeuse is a supergiant star. It is intrinsically very brilliant.

    Such brilliance comes at a price, however. Betelgeuse is one of the most famous stars in the sky because it’s due to explode someday. Betelgeuse’s enormous energy requires that the fuel be expended quickly (relatively speaking), and in fact Betelgeuse is now near the end of its lifetime. Someday soon (astronomically speaking), it will run out of fuel, collapse under its own weight, and then rebound in a spectacular Type II supernova explosion. When this happens, Betelgeuse will brighten enormously for a few weeks or months, perhaps as bright as the full moon and visible in broad daylight.

    When will it happen? Probably not in our lifetimes, but no one really knowns. It could be tomorrow or a million years in the future. When it does happen, any beings on Earth will witness a spectacular event in the night sky, but earthly life won’t be harmed. That’s because Betelgeuse is 430 light-years away. Read more about Betelgeuse as a supernova.

    How often do supernovae erupt in our galaxy? No one knows. Scientists have speculated that the high-energy radiation from supernovae has already caused mutations in earthly species, maybe even human beings.

    One estimate suggests there might be one dangerous supernova event in Earth’s vicinity every 15 million years. Another says that, on average, a supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years. So you see we really don’t know. But you can contrast those numbers to a few million years for the time humans are thought to have existed on the planet – and four-and-a-half billion years for the age of Earth itself.

    And, if you do that, you’ll see that a supernova is certain to occur near Earth – but probably not in the foreseeable future of humanity.

    Bottom line: Scientific literature cites 50 to 100 years as the closest safe distance between Earth and a supernova.

    See the full article here .

    See the full article <a href="http://1 EarthSky See the full article here . Please help promote STEM in your local schools. STEM Icon Stem Education Coalition

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  • richardmitnick 9:25 am on May 1, 2017 Permalink | Reply
    Tags: , , , Chariklo rings, , EarthSky,   

    From EarthSky: “Simulating the smallest ring world’ 

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    EarthSky

    April 30, 2017
    Deborah Byrd

    Chariklo is the smallest space body known to have rings. A new supercomputer simulation by Japanese researchers suggests a life expectancy for the rings of only 1 to 100 years.

    The Center for Computational Astrophysics in New York said on Friday (April 28, 2017) that Japanese researchers have modeled the two known rings around 10199 Chariklo, a possible dwarf planet orbiting the sun between the major planets Saturn and Uranus. They say it’s the first time an entire ring system has been simulated using realistic sizes for the ring particles while also taking into account collisions and gravitational interactions between the particles. They also created the visuals on this page, including the video above, which lets you dive into Chariklo’s ring system. Note that Chariklo itself is really potato-shaped and no doubt pocked with craters; the round, smooth shape in the video is for purposes of the simulation.

    These researchers’ work is published in the peer-reviewed March 2017 edition of The Astrophysical Journal Letters.

    Chariklo is a tiny world.

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    An artist’s rendering of the minor planet 10199 Chariklo, with rings.
    Observations at many sites in South America, including ESO’s La Silla Observatory, have made the surprise discovery that the remote asteroid Chariklo is surrounded by two dense and narrow rings. This is the smallest object by far found to have rings and only the fifth body in the Solar System — after the much larger planets Jupiter, Saturn, Uranus and Neptune — to have this feature. The origin of these rings remains a mystery, but they may be the result of a collision that created a disc of debris. This artist’s impression shows a close-up of what the rings might look like.
    ESO/L. Calçada/M. Kornmesser/Nick Risinger (skysurvey.org)

    Its estimated size about 200 miles (334 km) by about 140 miles (226 km) by about 100 miles (172 km). Our solar system’s major outer planets (Jupiter, Saturn, Uranus, Neptune) all are known to have rings. These planets’ rings are composed of particles estimated to range from inches to several feet (centimeters to meters) in size. Chariklo’s gravitational attraction is small relative to the major planets, so its rings – which were discovered in 2014 – are likely only temporary.

    Although Chariklo is small, and although its gravity is relatively weak, its rings are as opaque as those around Saturn and Uranus. Thus, the researchers said, Chariklo offered an ideal chance to model a complete ring system.

    The team said their simulation revealed information about the size and density of the particles in the rings. They found that Chariklo’s inner ring should be unstable without help. So – the researchers said – the ring particles must be much smaller than previously thought. Or it means that an undiscovered shepherd satellite around Chariklo is stabilizing the ring.

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    Visualization constructed from simulation of Chariklo’s double ring. Note that Chariklo itself is really potato-shaped and no doubt pocked with craters; the round, smooth shape here is for purposes of the simulation. Image via Shugo Michikoshi, Eiichiro Kokubo, Hirotaka Nakayama, 4D2U Project, NAOJ/ CFCA.

    The researchers – Shugo Michikoshi (Kyoto Women’s University/University of Tsukuba) and Eiichiro Kokubo (National Astronomical Observatory of Japan, or NAOJ) modeled Chariklo’s rings using the supercomputer ATERUI*1 at NAOJ. They calculated the motions of 345 million ring particles with the realistic size of a few meters taking into account the collisions and mutual gravitational attractions between the particles.

    Chariklo is the largest member of a class known as the Centaurs, orbiting between Saturn and Uranus in the outer solar system. These bodies are categorized like asteroids, but, whereas most asteroids lie in the asteroid belt between Mars and Jupiter – closer to the sun – Centaurs may have come from the Kuiper Belt, which is visualized as extending from the orbit of the outermost major planet Neptune to approximately 50 Earth-sun units (AU) from our sun. Centaurs have unstable orbits that cross the giant planets’ orbit. Chariklo’s orbit gazes that of Uranus. Because their orbits are frequently perturbed, Centaurs like Chariklo are expected to only remain in their orbits only for millions of years, in contrast to our Earth and the other major planets which have been orbiting for billions of years around our sun.

    The new computer visualization suggests that the density of Chariklo’s ring particles must be less than half the density of Chariklo itself. And they show a striped pattern forming in the inner ring due to interactions between the particles. They use the term “self-gravity wakes” for this pattern (see the image below). These self-gravity wakes accelerate the break-up of the ring, the researchers said.

    But perhaps the most surprising result of the new study is a recalculated life expectancy for Chariklo’s rings. The study suggests the rings may be able to reamin around Chariklo for only one to 100 years! That’s much shorter than previous estimates, and it’s less than an eye-blink in astronomical terms.

    So what we are seeing with Chariklo and its ring system is likely a very temporary and dynamic situation. Things in space tend to happen on a vastly-longer timescales than we humans are used to, but sometimes things do happen on human timescales. Chariklo’s rings may be an example!

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    Simulation of Chariklo’s ring system. The researchers said they used a ring particle density equal to half of Chariklo’s density, in order to maintain the rings’ overall structure. In the close-up view (right) complicated, elongated structures are visible. These structures are called self-gravity wakes. The numbers along the axes indicate distances in km. Image via Shugo Michikoshi / CFCA.

    See the full article here .

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  • richardmitnick 12:58 pm on April 18, 2017 Permalink | Reply
    Tags: , , , , , , EarthSky   

    From EarthSky: “Who needs dark energy?” 

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    EarthSky

    April 17, 2017
    Brian Koberlein

    Dark energy is thought to be the driver for the expansion of the universe. But do we need dark energy to account for an expanding universe?

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    Image via Brian Koberlein/ One Universe at a Time.

    Our universe is expanding. We’ve known this for nearly a century, and modern observations continue to support this. Not only is our universe expanding, it is doing so at an ever-increasing rate. But the question remains as to what drives this cosmic expansion. The most popular answer is what we call dark energy. But do we need dark energy to account for an expanding universe? Perhaps not.

    The idea of dark energy comes from a property of general relativity known as the cosmological constant. The basic idea of general relativity is that the presence of matter https://briankoberlein.com/2013/09/09/the-attraction-of-curves/. As a result, light and matter are deflected from simple straight paths in a way that resembles a gravitational force. The simplest mathematical model in relativity just describes this connection between matter and curvature, but it turns out that the equations also allow for an extra parameter, the cosmological constant, that can give space an overall rate of expansion. The cosmological constant perfectly describes the observed properties of dark energy, and it arises naturally in general relativity, so it’s a reasonable model to adopt.

    In classical relativity, the presence of a cosmological constant simply means that cosmic expansion is just a property of spacetime. But our universe is also governed by the quantum theory, and the quantum world doesn’t play well with the cosmological constant. One solution to this issue is that quantum vacuum energy might be driving cosmic expansion, but in quantum theory vacuum fluctuations would probably make the cosmological constant far larger than what we observe, so it isn’t a very satisfactory answer.

    Despite the unexplainable weirdness of dark energy, it matches observations so well that it has become part of the concordance model for cosmology, also known as the Lambda-CDM model. Here the Greek letter Lambda is the symbol for dark energy, and CDM stands for Cold Dark Matter.

    In this model there is a simple way to describe the overall shape of the cosmos, known as the Friedmann–Lemaître–Robertson–Walker (FLRW) metric. The only catch is that this assumes matter is distributed evenly throughout the universe. In the real universe matter is clumped together into clusters of galaxies, so the FLRW metric is only an approximation to the real shape of the universe. Since dark energy makes up about 70% of the mass/energy of the universe, the FLRW metric is generally thought to be a good approximation. But what if it isn’t?

    A new paper argues just that. Since matter clumps together, space would be more highly curved in those regions. In the large voids between the clusters of galaxies, there would be less space curvature. Relative to the clustered regions, the voids would appear to be expanding similarly to the appearance of dark energy. Using this idea the team ran computer simulations of a universe using this cluster effect rather than dark energy. They found that the overall structure evolved similarly to dark energy models.

    That would seem to support the idea that dark energy might be an effect of clustered galaxies.

    It’s an interesting idea, but there are reasons to be skeptical. While such clustering can have some effect on cosmic expansion, it wouldn’t be nearly as strong as we observe. While this particular model seems to explain the scale at which the clustering of galaxies occur, it doesn’t explain other effects, such as observations of distant supernovae which strongly support dark energy. Personally, I don’t find this new model very convincing, but I think ideas like this are certainly worth exploring. If the model can be further refined, it could be worth another look.

    Paper: Gabor Rácz, et al. Concordance cosmology without dark energy. Monthly Notices of the Royal Astronomical Society Letters: DOI: 10.1093/mnrasl/slx026 (2017)


    Dark Energy Camera [DECam], built at FNAL

    DECam at Cerro Tololo, Chile, housing DECam

    See the full article here .

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  • richardmitnick 12:38 pm on April 15, 2017 Permalink | Reply
    Tags: , , , , EarthSky, , Is there life on Saturn’s moon?,   

    From EarthSky: “Is there life on Saturn’s moon?” 

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    EarthSky
    April 15, 2017
    Daniela Breitman

    Enceladus, one of 62 moons in a confirmed orbit around Saturn, has been in the spotlight since the Cassini spacecraft began orbiting Saturn, weaving among its moons and rings, in 2004. It was only when Cassini turned its instruments toward Enceladus that we learned of the moon’s powerful geysers and subsurface saltwater ocean. This week, scientists made another fascinating announcement about this Saturn moon. They say they now have strong evidence for a habitable area on the floor of Enceladus’ ocean. Their paper on this subject was published in the peer-reviewed journal Science on April 13, 2017.

    The ocean of Enceladus is covered by a layer of surface ice. The moon’s geysers emerge from the subsurface ocean through cracks in the ice. When the Cassini spacecraft flew through plumes of gas and icy particles that make up Enceladus’ geysers on October 28, 2015, it detected a significant amount of molecular hydrogen. Scientists confirmed this week that the best explanation for this observation is that hydrothermal reactions occurring on Enceladus’ ocean floor. They may be similar to hydrogen-generating interactions taking place at Earth’s hydrothermal vents.

    This discovery means the small, icy moon Enceladus might have a source of chemical energy that could be useful for living microbes, if any exist there.

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    Scientists have suggested that water interacts with the rocky core of Enceladus, thereby producing hydrogen. The detection of molecular hydrogen in the plumes of Enceladus supports this idea. Image via NASA.

    Hydrothermal vents are common on Earth. They are fissures in the ocean crust through which geothermally heated water escapes. In other words, they are regions where water interacts with Earth’s magma. Earthly hydrothermal vents are home to many fascinating bacteria. Yellowstone’s Grand Prismatic Spring is an example of a hydrothermal area with a rich bacterial life.

    Life has not been discovered beneath the icy crust of Enceladus. But the detection of hydrogen is strong evidence that all the necessary conditions for life are present. Hunter Waite of the Southwest Research Institute in San Antonio and lead author of the new Enceladus study, said in a statement:

    Although we can’t detect life, we’ve found that there’s a food source there for it. It would be like a candy store for microbes.

    Microbes on Enceladus could produce their energy through a chemical reaction known as methanogenesis, which consists of burning hydrogen and carbon dioxide dissolved in the ocean water to form methane and water.

    This reaction is at the core of the development of life on Earth.

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    The so-called tiger stripes and geysers of Enceladus, photographed by the Cassini-Huygens probe in October, 2015. Image via NASA.

    NASA/ESA/ASI Cassini Spacecraft

    ESA Huygens Probe from Cassini landed on Titan

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    This Cassini image from 2005 shows Enceladus’ geysers – backlit – spewing into space. By flying the craft through the plume from geysers like this one, scientists obtained evidence for molecular hydrogen, possibly produced via hydrothermal processes on the floor on Enceladus’ ocean. Image via NASA.

    Scientists considered other explanations for Cassini spacecraft’s 2015 detection of molecular hydrogen within Enceladus’ geysers, for example, hydrogen leaking from the moon’s rocky core in ways other than hydrothermal reactions. The scientists who’ve studied these observations most closely, however, now feel that hydrothermal reactions are the best explanation.

    Liquid water, an energy source, and the right chemicals (carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur) are the three main requirements for life as we know it. Now scientists discovered all of these life-ingrediants – except phosphorus and sulphur – on Enceladus.

    The paper published in Science presents a detailed analysis of the possibility of methanogenesis on Enceladus. The calculations are inconclusive as to whether methanogenesis is happening or not around the hydrothermal vents of Enceladus. Nevertheless, this discovery is a big step in characterising the habitability of the ocean of Enceladus.

    Bottom line: In April, 2017, scientists announced that molecular hydrogen in the plumes of Enceladus, one of Saturn’s moons, may be due to methanogenesis, a process that implies microbial life.

    See the full article here .

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  • richardmitnick 2:33 pm on April 11, 2017 Permalink | Reply
    Tags: , , EarthSky, , Molecular clocks track human evolution   

    From EarthSky: “Molecular clocks track human evolution” 

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    EarthSky

    April 9, 2017
    Bridget Alex, Harvard University
    Priya Moorjani, Columbia University

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    Our cells have a built-in genetic clock, tracking time… but how accurately?. Image via http://www.shutterstock.com

    DNA holds the story of our ancestry – how we’re related to the familiar faces at family reunions as well as more ancient affairs: how we’re related to our closest nonhuman relatives, chimpanzees; how Homo sapiens mated with Neanderthals; and how people migrated out of Africa, adapting to new environments and lifestyles along the way. And our DNA also holds clues about the timing of these key events in human evolution. The Conversation

    When scientists say that modern humans emerged in Africa about 200,000 years ago and began their global spread about 60,000 years ago, how do they come up with those dates? Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as radiocarbon dating and Potassium-argon dating. However, these methods require ancient remains to have certain elements or preservation conditions, and that is not always the case. Moreover, relevant fossils or artifacts have not been discovered for all milestones in human evolution.

    Analyzing DNA from present-day and ancient genomes provides a complementary approach for dating evolutionary events. Because certain genetic changes occur at a steady rate per generation, they provide an estimate of the time elapsed. These changes accrue like the ticks on a stopwatch, providing a “molecular clock.” By comparing DNA sequences, geneticists can not only reconstruct relationships between different populations or species but also infer evolutionary history over deep timescales.

    Molecular clocks are becoming more sophisticated, thanks to improved DNA sequencing, analytical tools and a better understanding of the biological processes behind genetic changes. By applying these methods to the ever-growing database of DNA from diverse populations (both present-day and ancient), geneticists are helping to build a more refined timeline of human evolution.

    How DNA accumulates changes

    Molecular clocks are based on two key biological processes that are the source of all heritable variation: mutation and recombination.

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    Mutations are changes to the DNA code, such as when one nucleotide base (A, T, G or C) is incorrectly subbed for another.. Image via http://www.shutterstock.com

    Mutations are changes to the letters of DNA’s genetic code – for instance, a nucleotide Guanine (G) becomes a Thymine (T). These changes will be inherited by future generations if they occur in eggs, sperm or their cellular precursors (the germline). Most result from mistakes when DNA copies itself during cell division, although other types of mutations occur spontaneously or from exposure to hazards like radiation and chemicals.

    In a single human genome, there are about 70 nucleotide changes per generation – minuscule in a genome made up of six billion letters. But in aggregate, over many generations, these changes lead to substantial evolutionary variation.

    Scientists can use mutations to estimate the timing of branches in our evolutionary tree. First they compare the DNA sequences of two individuals or species, counting the neutral differences that don’t alter one’s chances of survival and reproduction. Then, knowing the rate of these changes, they can calculate the time needed to accumulate that many differences. This tells them how long it’s been since the individuals shared ancestors.

    Comparison of DNA between you and your sibling would show relatively few mutational differences because you share ancestors – mom and dad – just one generation ago. However, there are millions of differences between humans and chimpanzees; our last common ancestor lived over six million years ago.

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    Bits of the chromosomes from your mom and your dad recombine as your DNA prepares to be passed on. Chromosomes image via http://www.shutterstock.com.

    Recombination, also known as crossing-over, is the other main way DNA accumulates changes over time. It leads to shuffling of the two copies of the genome (one from each parent), which are bundled into chromosomes. During recombination, the corresponding (homologous) chromosomes line up and exchange segments, so the genome you pass on to your children is a mosaic of your parents’ DNA.

    In humans, about 36 recombination events occur per generation, one or two per chromosome. As this happens every generation, segments inherited from a particular individual get broken into smaller and smaller chunks. Based on the size of these chunks and frequency of crossovers, geneticists can estimate how long ago that individual was your ancestor.

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    Gene flow between divergent populations leads to chromosomes with mosaic ancestry. As recombination occurs in each generation, the bits of Neanderthal ancestry in modern human genomes becomes smaller and smaller over time. Image via Bridget Alex.

    Building timelines based on changes

    Genetic changes from mutation and recombination provide two distinct clocks, each suited for dating different evolutionary events and timescales.

    Because mutations accumulate so slowly, this clock works better for very ancient events, like evolutionary splits between species. The recombination clock, on the other hand, ticks at a rate appropriate for dates within the last 100,000 years. These “recent” events (in evolutionary time) include gene flow between distinct human populations, the rise of beneficial adaptations or the emergence of genetic diseases.

    The case of Neanderthals illustrates how the mutation and recombination clocks can be used together to help us untangle complicated ancestral relationships. Geneticists estimate that there are 1.5-2 million mutational differences between Neanderthals and modern humans. Applying the mutation clock to this count suggests the groups initially split between 750,000 and 550,000 years ago.

    At that time, a population – the common ancestors of both human groups – separated geographically and genetically. Some individuals of the group migrated to Eurasia and over time evolved into Neanderthals. Those who stayed in Africa became anatomically modern humans.

    6
    An evolutionary tree displays the divergence and interbreeding dates that researchers estimated with molecular clock methods for these groups. Image via Bridget Alex.

    However, their interactions were not over: Modern humans eventually spread to Eurasia and mated with Neanderthals. Applying the recombination clock to Neanderthal DNA retained in present-day humans, researchers estimate that the groups interbred between 54,000 and 40,000 years ago. When scientists analyzed a Homo sapiens fossil, known as Oase 1, who lived around 40,000 years ago, they found large regions of Neanderthal ancestry embedded in the Oase genome, suggesting that Oase had a Neanderthal ancestor just four to six generations ago. In other words, Oase’s great-great-grandparent was a Neanderthal.

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    Comparing chromosome 6 from the 40,000-year-old Oase fossil to a present-day human. The blue bands represent segments of Neanderthal DNA from past interbreeding. Oase’s segments are longer because he had a Neanderthal ancestor just 4–6 generations before he lived, based on estimates using the recombination clock. Image via Bridget Alex.

    The challenges of unsteady clocks

    Molecular clocks are a mainstay of evolutionary calculations, not just for humans but for all forms of living organisms. But there are some complicating factors.

    The main challenge arises from the fact that mutation and recombination rates have not remained constant over human evolution. The rates themselves are evolving, so they vary over time and may differ between species and even across human populations, albeit fairly slowly. It’s like trying to measure time with a clock that ticks at different speeds under different conditions.

    One issue relates to a gene called Prdm9, which determines the location of those DNA crossover events. Variation in this gene in humans, chimpanzees and mice has been shown to alter recombination hotspots – short regions of high recombination rates. Due to the evolution of Prdm9 and hotspots, the fine-scale recombination rates differ between humans and chimps, and possibly also between Africans and Europeans. This implies that over different timescales and across populations, the recombination clock ticks at slightly different rates as hotspots evolve.

    Another issue is that mutation rates vary by sex and age. As fathers get older, they transmit a couple extra mutations to their offspring per year. The sperm of older fathers has undergone more rounds of cell division, so more opportunities for mutations. Mothers, on the other hand, transmit fewer mutations (about 0.25 per year) as a female’s eggs are mostly formed all at the same time, before her own birth. Mutation rates also depend on factors like onset of puberty, age at reproduction and rate of sperm production. These life history traits vary across living primates and probably also differed between extinct species of human ancestors.

    Consequently, over the course of human evolution, the average mutation rate seems to have slowed significantly. The average rate over millions of years since the split of humans and chimpanzees has been estimated as about 1×10?? mutations per site per year – or roughly six altered DNA letters per year. This rate is determined by dividing the number of nucleotide differences between humans and other apes by the date of their evolutionary splits, as inferred from fossils. It’s like calculating your driving speed by dividing distance traveled by time passed. But when geneticists directly measure nucleotide differences between living parents and children (using human pedigrees), the mutation rate is half the other estimate: about 0.5×10?? per site per year, or only about three mutations per year.

    For the divergence between Neanderthals and modern humans, the slower rate provides an estimate between 765,000-550,000 years ago. The faster rate, however, would suggest half that age, or 380,000-275,000 years ago: a big difference.

    To resolve the question of which rates to use when and on whom, researchers have been developing new molecular clock methods, which address the challenges of evolving mutation and recombination rates.

    New approaches for better dating

    One approach is to focus on mutations that arise at a steady rate regardless of sex, age and species. This may be the case for a special type of mutation that geneticists call CpG transitions by which the C nucelotides spontaneously become T’s. Because CpG transitions mostly do not result from DNA copying errors during cell division, their rates should be mainly independent of life history variables – and presumably more uniform over time.

    Focusing on CpG transitions, geneticists recently estimated the split between humans and chimps to have occurred between 9.3 and 6.5 million years ago, which agrees with the age expected from fossils. While in comparisons across species, these mutations seem to happen more like clockwork than other types, they are still not completely steady.

    Another approach is to develop models that adjust molecular clock rates based on sex and other life history traits. Using this method, researchers calculated a chimp-human divergence consistent with the CpG estimate and fossil dates. The drawback here is that, when it comes to ancestral species, we can’t be sure of life history traits, like age at puberty or generation length, leading to some uncertainty in the estimates.

    The most direct solution comes from analyses of ancient DNA recovered from fossils. Because the fossil specimens are independently dated by geologic methods, geneticists can use them to calibrate the molecular clocks for a given time period or population.

    This strategy recently resolved the debate over the timing of our divergence with Neanderthals. In 2016, geneticists extracted ancient DNA from 430,000-year-old fossils that were Neanderthal ancestors, after their lineage split from Homo sapiens. Knowing where these fossils belong in the evolutionary tree, geneticists could confirm that for this period of human evolution, the slower molecular clock rate of 0.5×10?? provides accurate dates. That puts the Neanderthal-modern human split between 765,000 to 550,000 years ago.

    As geneticists sort out the intricacies of molecular clocks and sequence more genomes, we’re poised to learn more than ever about human evolution, directly from our DNA.

    Bridget Alex, Postdoctoral College Fellow, Department of Human Evolutionary Biology, Harvard University and Priya Moorjani, Postdoctoral Research Fellow in Biological Sciences, Columbia University

    See the full article here .

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  • richardmitnick 8:54 am on April 8, 2017 Permalink | Reply
    Tags: , , , , , , EarthSky   

    From EarthSky: “Large asteroid coming close on April 19” 

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    EarthSky

    April 8, 2017
    Eddie Irizarry

    Asteroid 2014 JO25 will pass safely at 4.6 times the moon’s distance. It’s 60 times the diameter of the asteroid that penetrated the atmosphere over Chelyabinsk, Russia in 2013. People with small telescopes might be able to spot it.

    A big asteroid will have a safely sweep past Earth on April 19, 2017. It’ll come so close – and it’s known so far in advance – that scientists will be able to study the space rock using both radar and optical observations. The flyby should also be visible in amateur telescopes. Asteroid 2014 JO25 was discovered by astronomers at the Catalina Sky Survey near Tucson, Arizona in May 2014. It appears to be roughly 2,000 feet (650 meters) in size, with a surface about twice as reflective as that of Earth’s moon. The asteroid will safely pass at some 1,098,733 miles (1,768,239 km ) from our planet or about 4.6 times the distance from Earth to the moon.

    After analyzing the orbit of Asteroid 2014 JO25, astronomers have realized the April 19 encounter is the closest this asteroid has come to Earth for at least 400 years and will be its closest approach for at least the next 500 years. There is no danger as the space rock’s orbit is well known.

    2014 JO25 is classified as a Potentially Hazardous Asteroid by the Minor Planet Center. The asteroid will sweep close enough to allow good radar observations. NASA has said they will study this asteroid using the Goldstone Radar in California from April 16 to 21.

    NASA DSCC Goldstone Antenna in the Mojave Desert, California USA

    The Arecibo Observatory plans to do high resolution imaging using radar from April 15 to 20.

    NAIC/Arecibo Observatory, Puerto Rico, USA

    Radar observations will provide a better understanding of the space rock’s size and shape.

    Preliminary estimates indicate the asteroid’s size is about 60 times the diameter of the asteroid that penetrated the atmosphere over Chelyabinsk, Russia in February, 2013. NASA said:

    “There are no known future encounters by 2014 JO25 as close as the one in 2017 through 2500. It will be among the strongest asteroid radar targets of the year. The 2017 flyby is the closest by an asteroid at least this large since the encounter by 4179 Toutatis at four lunar distances in September 2004. The next known flyby by an object with a comparable or larger diameter will occur when 800-m-diameter asteroid 1999 AN10 approaches within one lunar distance in August 2027.”

    For backyard observers, the exciting news is that asteroid 2014 JO25 might be be visible moving across the stars though 8″-diameter and bigger telescopes. Can it be seen with smaller telescopes? Maybe, but in order to be able to detect its motion across the stars, at least an 8″ scope will be required. The asteroid will not be visible to the unaided eye, as it may show a brightness or magnitude between 10 and 11.

    The asteroid is currently located in the direction of the sun, but – during the first hours of April 19 – the space rock will come into view for telescopes as it crosses the constellation of Draco. Then, during the night of April 19, asteroid 2014 JO25 will seem to move across the skies covering the distance equivalent to the moon’s diameter in about 18 minutes.

    That’s fast enough for its motion to be detected though an amateur telescope. The best strategy to catch the space rock in your telescope is to observe a star known to be in the asteroid’s path, and wait for it.

    If you are looking at the correct time and direction, the asteroid will appear as a very slowly moving “star.” Although its distance from us will make the space rock appear to move slowly, it is in fact traveling though space at a speed of 75,072 mph (120,816 km/h)!

    Because it will appear to move very slowly, observers should take a good look at a reference star for a few minutes (not seconds) to detect the moving object.

    Although asteroid 2014 JO25 will be closest to Earth on the morning of Wednesday, April 19, 2017, (around 7:24 a.m. Central Time / 12:24 UTC) the space rock may look a bit brighter (but still only visible in telescopes) during the night of April 19, because the asteroid will be at a higher elevation in our skies.

    Will it be visible from both hemispheres? Yes. Observers in the Northern Hemisphere will be able to locate the asteroid both on the predawn hours and during the night of April 19. From South America, the space rock will only be visible during the night of April 19, at over 25 degrees above the northern horizon. Observers in Africa and Australia will also be able to spot the asteroid on April 19-20.

    The asteroid’s nearness to Earth at the time of closest approach might cause a slight parallax effect. That means the space rock’s apparent nearness on our sky’s dome to a fixed star might differ slightly, as seen from different locations across Earth. Thus, if you don’t see the asteroid at the expected time, scan one more field of view up and down from your reference star, that is, the star you are waiting to see the asteroid to pass by.

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    At 3:40 a.m. Central Time on April 19, asteroid 2014 JO25 will be located in front of the constellation Draco the Dragon, as seen here. Illustration by Eddie Irizarry using Stellarium.

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    A closer view of the space rock passing by the constellation Draco early on the morning April 19.

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    Observers using a computerized “Go To” telescope can point the instrument at star HIP 87728 a few minutes before 3:40 a.m. Central Time on April 19, and watch the asteroid passing by the magnitude 5 star in Draco. Illustration by Eddie Irizarry using Stellarium.

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    During the night of April 19, asteroid 2014 JO25 will pass though the constellations Canes Venatici and Coma Berenices. Illustration by Eddie Irizarry using Stellarium.

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    The asteroid will be close to star 41 Comae, which is very close to Beta Comae. This star is magnitude 4 and thus visible to the unaided eye. Illustration by Eddie Irizarry using Stellarium.

    9
    At around 9:30 p.m. Central Time on April 19, the space rock will be passing very close to 41 Comae Berenices (HIP 64022) a 4.8 magnitude star which is visible to the naked eye from suburban and dark skies. Illustration by Eddie Irizarry using Stellarium.

    Bottom line: Asteroid 2014 JO25 will pass safely at 4.6 times the moon’s distance. People with small telescopes might be able to spot it. Charts here and other info on how to see it.

    See the full article here .

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  • richardmitnick 4:01 pm on April 7, 2017 Permalink | Reply
    Tags: , , , , , EarthSky   

    From EarthSky: “The Coma Cluster of galaxies” 

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    EarthSky

    April 7, 2017
    Larry Sessions

    The Coma Cluster is one of the richest galaxy clusters known. How many suns and how many worlds might be located in this direction of space?

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    Almost every object you see in this photo is a galaxy. The Coma Cluster of galaxies contains as many as 10,000 galaxies, each housing billions of stars. Image via Justin Ng.

    The Coma Cluster is a group of galaxies in the faint constellation Coma Berenices, visible in medium to large amateur telescopes. Coma Berenices lies between Leo and Bootes, and as such is most conveniently viewed in the evening sky of spring and summer. The Coma Cluster is one of the richest galaxy clusters known. How many suns and how many worlds might be located in this direction of space? Follow the links below to learn more about the Coma Cluster of galaxies in the faint constellation Coma Berenices.

    The constellation Coma Berenices appears to the eye as a cluster of stars. But a telescope also reveals a vast region of distant galaxies in this part of the sky, which can be seen on this chart via SEDS

    This map shows both the Coma star cluster [Melotte 111] and the Coma galaxy cluster [(Abell 1656], in the tail end of Leo the Lion. Three stars outline a simple triangle that forms the constellation Coma Berenices.

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    Coma Supercluster http://www.atlasoftheuniverse.com/superc/com.html

    How to see the Coma Cluster of galaxies. The constellation Coma Berenices lies between the constellations Leo the Lion and Bootes the Herdsman. This part of the sky is the site of a famous open star cluster, and also of the more distant galaxy cluster, visible through telescopes. Both the star cluster and the galaxy cluster need a dark sky to be seen.

    The galaxy cluster is is near the northern border of Coma Berenices, roughly midway a long a line drawn from Rho Bootes to Delta Leonis (Zosma), near the North Galactic Pole.

    The central part of Coma Cluster of galaxies covers a roughly circular area about a degree and a half across (9 times the area of a full moon), The full cluster may extend farther, and numerous other galaxy clusters are in the same area of sky. An old but beautiful name for this region of sky is the Realm of the Galaxies.

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    Close-up on a majestic face-on spiral galaxy located deep within the Coma Cluster of galaxies. Image via NASA

    Science of the Coma Cluster

    The center of the Coma Cluster is about 320 million light years away, and it may stretch 20 million light years from side to side.

    This cluster as a whole is flying away from us at the rate of about 6,900 km/second (more than 15 million miles per hour!)

    One of the most populated galaxy clusters known, it contains as many as 10,000 or more members by some estimates. In any case there are more individual galaxies in this cluster than there are stars visible to the unaided human eye on a clear, dark night.

    Most galaxies in the cluster are elliptical, although there are a few spiral galaxies. The two brightest members are NGC 4889 and NGC 4874, both of which are giant ellipticals at least 2 to 3 times larger than our own Milky Way galaxy.

    Meanwhile, most galaxies in the Coma Cluster are dwarf galaxies, perhaps similar to the Milky Way’s companions, the Large and Small Magellanic Clouds.

    Coma Cluster in history

    Too faint to be seen by the human eye (or binoculars or even small telescopes), the ancients could not have seen the galaxy cluster and hence no mythology is associated with it. However, the Coma Cluster, also known as Abell 1656, is extremely interesting historically.

    Not only is it one of the largest and most densely populated clusters of galaxies known, it is also the source of our first ideas about the dark matter in our universe. Unseen and mysterious, this matter greatly increases the total mass and gravitational strength of the universe, further affecting its evolution and fate.

    Dark matter was unknown and unsuspected until Swiss-American astronomer Fritz Zwicky discovered it in the Coma Cluster in the 1930s. Zwicky tallied up the visible galaxies in the cluster and estimated its mass. Then he observed the motions of galaxies near the edge of the cluster, which are determined by the total gravity (and hence mass) of the cluster. Zwicky found that the mass derived from the latter method greatly exceeded that from visual inspection.

    Zwicky knew that if the law of gravity is correct — and there is no reason to doubt it — the only answer could be an additional source of mass, which he called Dunkle Materie in German.

    Today, the imprint of dark matter has been found throughout the universe, and is at least five times more prevalent than the more familiar visible matter, such as the stars and galaxies we can see.

    Bottom line: How to locate the Coma Cluster of galaxies, plus history and science surrounding this fascinating region of the night sky.

    The center of the Coma Cluster is approximately RA: 12h 59m, dec: +27° 59?

    See the full article here .

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  • richardmitnick 8:24 am on March 23, 2017 Permalink | Reply
    Tags: , , Colorado, , EarthSky, National Snow and Ice Data Center (NSIDC) in Boulder, Polar sea ice   

    From EarthSky: “Record low sea ice at both poles” 

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    EarthSky

    March 23, 2017
    Deborah Byrd

    Scientists at NASA and the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado said on March 22, 2017 that Arctic sea ice probably reached its 2017 maximum extent on March 7, and that this year’s maximum represents another record low. Meanwhile, on the opposite side of the planet, on March 3 sea ice around Antarctica hit its lowest extent ever recorded by satellites at the end of summer in the Southern Hemisphere. NASA called it:

    ” … a surprising turn of events after decades of moderate sea ice expansion.”

    Walt Meier, a sea ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland said:

    “It is tempting to say that the record low we are seeing this year is global warming finally catching up with Antarctica. However, this might just be an extreme case of pushing the envelope of year-to-year variability. We’ll need to have several more years of data to be able to say there has been a significant change in the trend.”

    Satellites have been continuously measuring sea ice in 1979, NASA said, and on February 13, the combined Arctic and Antarctic sea ice numbers were at their lowest point since.

    On February 13, total polar sea ice covered 6.26 million square miles (16.21 million square km). That’s 790,000 square miles (2 million square km) less than the average global minimum extent for 1981-2010 – the equivalent of having lost a chunk of sea ice larger than Mexico.

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    These line graphs plot monthly deviations and overall trends in polar sea ice from 1979 to 2017 as measured by satellites. The top line shows the Arctic; the middle shows Antarctica; and the third shows the global, combined total. The graphs depict how much the sea ice concentration moved above or below the long-term average. Arctic and global sea ice totals have moved consistently downward over 38 years. Antarctic trends are more muddled, but they do not offset the great losses in the Arctic. Image via Joshua Stevens/ NASA Earth Observatory.

    NASA explained the seasonal cycle of sea ice’s growth and shrinkage at Earth’s poles, and described specific weather events this year that led to the lower-than-average sea ice:

    The ice floating on top of the Arctic Ocean and surrounding seas shrinks in a seasonal cycle from mid-March until mid-September. As the Arctic temperatures drop in the autumn and winter, the ice cover grows again until it reaches its yearly maximum extent, typically in March. The ring of sea ice around the Antarctic continent behaves in a similar manner, with the calendar flipped: it usually reaches its maximum in September and its minimum in February.

    This winter, a combination of warmer-than-average temperatures, winds unfavorable to ice expansion, and a series of storms halted sea ice growth in the Arctic. This year’s maximum extent, reached on March 7 at 5.57 million square miles (14.42 million square km), is 37,000 square miles (97,00 square km) below the previous record low, which occurred in 2015, and 471,000 square miles (1.22 million square km) smaller than the average maximum extent for 1981-2010.

    Walt Meier added:

    “We started from a low September minimum extent. There was a lot of open ocean water and we saw periods of very slow ice growth in late October and into November, because the water had a lot of accumulated heat that had to be dissipated before ice could grow. The ice formation got a late start and everything lagged behind – it was hard for the sea ice cover to catch up.”

    NASA also said the Arctic’s sea ice maximum extent has dropped by an average of 2.8 percent per decade since 1979. The summertime minimum extent losses are nearly five times larger: 13.5 percent per decade. Besides shrinking in extent, the sea ice cap is also thinning and becoming more vulnerable to the action of ocean waters, winds and warmer temperatures.

    This year’s record low sea ice maximum extent might not necessarily lead to a new record low summertime minimum extent, since weather has a great impact on the melt season’s outcome, Meier said. But, he added:

    ” … it’s guaranteed to be below normal.”

    Meanwhile, in Antarctica, this year’s record low annual sea ice minimum of 815,000 square miles (2.11 million square km) was 71,000 square miles (184,000 square km) below the previous lowest minimum extent in the satellite record, which occurred in 1997. NASA explained:

    “Antarctic sea ice saw an early maximum extent in 2016, followed by a very rapid loss of ice starting in early September. Since November, daily Antarctic sea ice extent has continuously been at its lowest levels in the satellite record. The ice loss slowed down in February.”

    This year’s record low happened just two years after several monthly record high sea ice extents in Antarctica and decades of moderate sea ice growth. The Arctic and Antarctica are very different places; the Arctic is an ocean surrounded by northern continents, while Antarctica is a continent surrounded by ocean. In recent years, climage scientists have pointed to this difference to help explain why the poles were reacting to the trend of warming global temperatures differently.

    But many had said they expected sea ice to begin decreasing in Antarctica, as Earth’s temperatures continue to warm. Claire Parkinson, a senior sea ice researcher at Goddard, said on March 22:

    “There’s a lot of year-to-year variability in both Arctic and Antarctic sea ice, but overall, until last year, the trends in the Antarctic for every single month were toward more sea ice.

    Last year was stunningly different, with prominent sea ice decreases in the Antarctic.

    To think that now the Antarctic sea ice extent is actually reaching a record minimum, that’s definitely of interest.”

    3
    There’s no real reason Earth’s poles should react in the same way, or at the same rate, to global warming. A fundamental difference between Arctic (left) and Antarctic (right) regions is that the Arctic is a frozen ocean surrounded by continents, while the Antarctic is a frozen continent surrounded by oceanic waters. Map via NOAA/ climate.gov/ researchgate.net.

    Bottom line: Considering both poles in February 2017, Earth essentially lost the equivalent of a chunk of sea ice larger than Mexico, in contrast to the average global minimum for 1981-2010.

    See the full article here .

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  • richardmitnick 8:42 am on March 22, 2017 Permalink | Reply
    Tags: , , , , EarthSky, , Star’s death spiral into black hole   

    From EarthSky: “Star’s death spiral into black hole” 

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    EarthSky

    March 22, 2017
    Eleanor Imster

    NASA said on March 20, 2017 that scientists used data from its Swift satellite to get a comprehensive look at a star’s death spiral into a black hole.


    NASA/SWIFT Telescope

    The star was much like our sun. The black hole contains some 3 million times the mass of our sun and lies at the center of a galaxy 290 million light-years away. As the black hole tore the star apart, it produced what scientists call a tidal disruption event. They’ve labeled this particular event – an eruption of optical, ultraviolet, and X-ray light, which began reaching Earth in 2014 – as ASASSN-14li.

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    Astronomers report the detection of flows of hot, ionized gas in high-resolution X-ray spectra of a nearby tidal disruption event, ASASSN-14li in the galaxy PGC 43234. This artist’s impression shows a supermassive black hole at the center of PGC 43234 accreting mass from a star that dared to venture too close to the galaxy’s center. Image credit: ESA / C. Carreau.

    The scientists have now used Swift’s data to map out how and where these different wavelengths were produced, as the shattered star’s debris circled the black hole. The video animation above is an artist’s depiction of what these scientists believe happened. They said it took awhile for debris from the star to be swallowed up by the black hole.

    Dheeraj Pasham, an astrophysicist at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, and the lead researcher of the study, said:

    “We discovered brightness changes in X-rays that occurred about a month after similar changes were observed in visible and UV light. We think this means the optical and UV emission arose far from the black hole, where elliptical streams of orbiting matter crashed into each other.”

    Their study was published March 15, 2017 in the Astrophysical Journal Letters.

    A tidal disruption event happens when a star passes too close to a very massive black hole. ASASSN-14li is the closest tidal disruption discovered in 10 years, so of course astronomers are studying it as extensively as they can. During events like this, tidal forces from a black hole may convert the star into a stream of debris. Stellar debris falling toward the black hole doesn’t fall straight in, however, but instead collects into a spinning accretion disk, encircling the hole.

    The accretion disk is the source of all the action, as observed by earthly astronomers.

    Within the disk, star material becomes compressed and heated before eventually spilling over the black hole’s event horizon, the point beyond which nothing can escape and astronomers cannot observe.

    The animation above, from NASA’s Goddard Space Flight Center illustrates:

    … how debris from a tidally disrupted star collides with itself, creating shock waves that emit ultraviolet and optical light far from the black hole. According to Swift observations of ASASSN-14li, these clumps took about a month to fall back to the black hole, where they produced changes in the X-ray emission that correlated with the earlier UV and optical changes.

    According to the scientists, the ASASSN-14li black hole’s event horizon is typically about 13 times bigger in volume than our sun. Meanwhile, the accretion disk formed by the disrupted star might extend to more than twice Earth’s distance from the sun.

    Bottom line: A team of scientists used observations from NASA’s Swift satellite have mapped the death spiral of a star as it was destroyed by the black hole at the center of its galaxy.

    See the full article here .

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