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  1. #1151
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    Cool, nebulous ring around Milky Way's supermassive black hole
    National Radio Astronomy Observatory | 5 June 2019

    New observations reveal a never-before-seen disk of cool, interstellar gas wrapped around the supermassive black hole at the center of the Milky Way.


    New ALMA observations reveal a never-before-seen disk of cool, interstellar gas wrapped around the supermassive black hole at the center of the Milky Way. This nebulous disk gives astronomers new insights into the workings of accretion: the siphoning of material onto the surface of a black hole. The results are published in the journal Nature.

    Through decades of study, astronomers have developed a clearer picture of the chaotic and crowded neighborhood surrounding the supermassive black hole at the center of the Milky Way. Our galactic center is approximately 26,000 light-years from Earth and the supermassive black hole there, known as Sagittarius A* (A "star"), is 4 million times the mass of our Sun.

    We now know that this region is brimming with roving stars, interstellar dust clouds, and a large reservoir of both phenomenally hot and comparatively colder gases. These gases are expected to orbit the black hole in a vast accretion disk that extends a few tenths of a light-year from the black hole's event horizon.

    Until now, however, astronomers have been able to image only the tenuous, hot portion of this flow of accreting gas, which forms a roughly spherical flow and showed no obvious rotation. Its temperature is estimated to be a blistering 10 million degrees Celsius (18 million degrees Fahrenheit), or about two-thirds the temperature found at the core of our Sun. At this temperature, the gas glows fiercely in X-ray light, allowing it to be studied by space-based X-ray telescopes, down to scale of about a tenth of a light-year from the black hole.

    In addition to this hot, glowing gas, previous observations with millimeter-wavelength telescopes have detected a vast store of comparatively cooler hydrogen gas (about 10 thousand degrees Celsius, or 18,000 degrees Fahrenheit) within a few light-years of the black hole. The contribution of this cooler gas to the accretion flow onto the black hole was previously unknown.

    Although our galactic center black hole is relatively quiet, the radiation around it is strong enough to cause hydrogen atoms to continually lose and recombine with their electrons. This recombination produces a distinctive millimeter-wavelength signal, which is capable of reaching Earth with very little losses along the way.

    With its remarkable sensitivity and powerful ability to see fine details, the Atacama Large Millimeter/submillimeter Array (ALMA) was able to detect this faint radio signal and produce the first-ever image of the cooler gas disk at only about a hundredth of a light-year away (or about 1000 times the distance from the Earth to the Sun) from the supermassive black hole. These observations enabled the astronomers both to map the location and trace the motion of this gas. The researchers estimate that the amount of hydrogen in this cool disk is about one tenth the mass of Jupiter, or one ten-thousandth of the mass of the Sun.

    By mapping the shifts in wavelengths of this radio light due to the Doppler effect (light from objects moving toward the Earth is slightly shifted to the "bluer" portion of the spectrum while light from objects moving away is slightly shifted to the "redder" portion), the astronomers could clearly see that the gas is rotating around the black hole. This information will provide new insights into the ways that black holes devour matter and the complex interplay between a black hole and its galactic neighborhood.

    "We were the first to image this elusive disk and study its rotation," said Elena Murchikova, a member in astrophysics at the Institute for Advanced Study in Princeton, New Jersey, and lead author on the paper. "We are also probing accretion onto the black hole. This is important because this is our closest supermassive black hole. Even so, we still have no good understanding of how its accretion works. We hope these new ALMA observations will help the black hole give up some of its secrets."
    ___________________________________

    This is really cool news because it is about our, the Milky Way's, black hole. The image above is an "indirect" image of Sgr A*, the black hole at the galactic center of our Milky Way.
    Last edited by ilan; 06-10-2019 at 12:21 PM.
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  2. #1152
    Moderator at Work ilan's Avatar
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    Satellites from Elon Musk’s SpaceX and Amazon could ruin view of the night sky, say astronomers
    Tom Huddleston Jr., CNBC | Mon, Jun 10 2019 11:21 AM EDT Updated Mon, Jun 10 2019 1:16 PM EDT


    SpaceX Falcon 9 rocket successfully launches carrying the Es’hail-2 communications satellite for the country of Qatar on November 15, 2018 at the Kennedy Space Center in Florida.
    NurPhoto | Getty Images
    Tech giants like Elon Musk’s SpaceX and Jeff Bezos’ Amazon have plans to launch constellations of thousands of satellites aimed at providing global internet access. But astronomers are worried that adding the masses of satellites to Earth’s orbit could screw up our view of the night sky, as well as disrupt scientific research.

    The Astronomical Union International — the world’s largest organization of professional astronomers with over 13,000 members — issued a statement last week to complain about SpaceX’s launch of its first batch of satellites at the end of May. While that launch only sent about 60 satellites into orbit, SpaceX eventually plans a network of satellites, called Starlink, that would consist of nearly 12,000 satellites flying in low Earth orbit (within 1,200 miles of the planet’s surface). Roughly half of those satellites are reportedly expected to launch within the next six years.

    And SpaceX isn’t the only company launching satellite networks, as Amazon has a similar plan in the works, called Project Kuiper, that would put over 3,200 satellites in low Earth orbit over several years in order to provide broadband internet access around the world.

    In its statement, the IAU argues that an uncrowded night sky is “not only essential to advancing our understanding of the Universe of which we are a part, but also as a resource for all humanity and for the protection of nocturnal wildlife,” the statement reads. “We do not yet understand the impact of thousands of these visible satellites scattered across the night sky and despite their good intentions, these satellite constellations may threaten both.”

    The IAU’s statement came after some astronomers — both amateur and professional — took to social media following last month’s SpaceX Starlink launch to voice their own concerns. Dutch scientist Marco Langbroek tweeted a video showing the Startlink satellites streaking across the night sky, though reports noted that the satellites would eventually drift apart (and into higher orbit) rather than being clustered together.

    Soon after, an astronomer at the Harvard-Smithsonian Center for Astrophysics, Jonathan McDowell, tweeted that the Starlink satellites were “brighter than we had expected,” while Southwest Research Institute planetary astronomer Alex Parker wrote in a tweet Langbroek’s video “gives me pause” because the satellites’ brightness.

    “If SpaceX launches all 12,000, they will outnumber stars visible to the naked eye,” Parker wrote on Twitter.

    Amazon did not immediately respond to CNBC Make It’s request for comment.

    In a statement provided to CNBC Make It, a SpaceX spokesperson said the company continues to monitor its orbiting satellites while noting that “the observability of the Starlink satellites is dramatically reduced as they raise orbit to greater distance and orient themselves with the phased array antennas toward Earth and their solar arrays behind the body of the satellite.”

    However, in a series of late-May tweets, Musk claimed that the current thousands of satellites in orbit pose little to no problems for astronomers, and that SpaceX is working to ensure its satellites will not hurt the view of the night sky. “We’ll make sure Starlink has no material effect on discoveries in astronomy,” Musk wrote. “We care a great deal about science.”

    In fact, Musk also said that he had asked SpaceX to reduce the brightness of future Starlink satellites, and SpaceX has worked with the U.S. National Science Foundation, which oversees the National Radio Astronomy Observatory, to help ensure that the Starlink satellites do not run afoul of “international radio astronomy protection standards,” the NSF said in a statement this week.

    “NSF is aware of concerns from the research community and looks forward to careful analysis of potential impacts on optical and infrared astronomy,” a spokesperson for NSF said in a statement provided to CNBC Make It. “NSF’s mission is to fund basic research, as well as the instruments and facilities that enable such research. We value input from stakeholders about possible impacts on any area of the research ecosystem and will work with our federal, private and academic partners to ensure research capabilities are safeguarded.”

    SpaceX and Amazon will eventually commercialize their satellite internet networks, with SpaceX CEO Musk predicting his company’s network could reap upwards of $30 billion per year in revenue.

    More than 2,000 satellites are currently estimated to be orbiting Earth, though roughly 1,300 of those are in low Earth orbit, according to data from the Union of Concerned Scientists.
    _____________________________________

    Hopefully, the all mighty dollar will not ruin the night sky and astronomical research. Unlike what we did with the oceans, we should not export pollution into outer space. - ilan
    Last edited by ilan; 06-11-2019 at 12:29 PM.
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  3. #1153
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    Powerful superflares could pose a threat to Earth
    Jake Parks, Astronomy | Tuesday, June 11, 2019

    Young and active stars often experience wildly strong eruptions. Now we know our older, calmer Sun may occasionally throw similar tantrums.


    NASA captured a solar flare April 17, 2016, in 4K quality.

    Astronomers have learned over the past decade that even large solar flares — powerful bursts of radiation — from our Sun are actually small potatoes compared to some of the flares we see around other stars. It’s now common to spot “superflares” hundreds to thousands of times more powerful than the Sun’s flares from stars hundreds of light-years away. Earlier this year, researchers even identified a star that emitted a turbocharged flare some 10 billion times more energetic than those typically seen bursting from the Sun.

    These superflares are mainly observed in young, active stars. But new research presented Monday at the 234th Meeting of the American Astronomical Society in St. Louis shows that even our middle-aged, relatively docile Sun is capable of producing some astoundingly powerful flares — albeit only once every one to two millennia. The work was also published May 3 in The Astrophysical Journal.

    “Young stars have superflares once every week or so,” said the study’s lead author, Yuta Notsu of the University of Colorado Boulder, in a press release. “For the Sun, it’s once every few thousand years on average.”

    Roughly speaking, about 30 to 50 percent of superflares produced by the Sun can strike the Earth, Notsu said. This means that we can expect a superflare about 100 times bigger than normal to strike Earth about once every 10,000 years or so.

    And we could be overdue. “Our study shows that superflares are rare events,” Notsu said. “But there is some possibility that we could experience such an event in the next 100 years or so.”

    Sizing up superflares

    To carry out the study, Notsu and his team first teased through data from the Kepler Space Telescope, which spent the past decade looking for planets by monitoring how stars change in brightness over time. Working from a sample of about 90,000 Sun-like stars, the researchers identified more than 1,000 superflares from about 300 stars.

    At first, they thought these stars would be rapidly rotating. That’s because quickly spinning stars tend to have strong magnetic fields that easily get tangled up, which is thought to kick off flares. But a fast spin is apparently not a requirement for strong eruptions. By bolstering their brightness data with size estimates from the Gaia satellite, the researchers were able to determine how fast their flaring stars were spinning. They found that, as expected, stars that rotate once every few days had superflares about 20 times as powerful as more slowly spinning stars like the Sun, which rotates about once every 25 days. However, Sun-like stars were still seen producing hazardous superflares.

    Brace yourself

    The confirmation that slowly rotating, Sun-like stars can still throw out powerful superflares is surely intriguing, but it’s also a bit nerve-wracking.

    “When our Sun was young, it was very active because it rotated very fast and probably generated more powerful flares,” said Notsu. “But we didn’t know if such large flares occur on the modern Sun with very low frequency.”

    There is one historical point of reference, though. In September 1859, a solar flare sent a wave of charged particles washing over our planet. It triggered one of the most powerful geomagnetic storms ever recorded: the Carrington Event. As the particles slammed into Earth’s protective magnetic field, they triggered beautiful aurorae that stretched as far south as Hawaii and Cuba. But the Carrington Event didn’t just produce pretty lights in the sky. It also wreaked havoc on telegraph networks spread across North America and Europe. In fact, there are reports of the cosmically overcharged telegraph lines starting fires and shocking telegraph operators during the event.

    If a moderate flare like the Carrington Event notably disrupted electronic systems in the mid-1800s, what would a superflare some 100 times stronger do today?

    “If a superflare occurred 1,000 years ago, it was probably no big problem. People may have seen a large aurora,” Notsu said. “Now, it’s a much bigger problem because of our electronics.”

    How big that problem will be is yet to be determined. “More accurate evaluations of the effects of superflares is a next urgent task,” Notsu told Astronomy, “but we can now expect things such as large-scale blackouts, satellite communication failure, and strong radiation in space,” which can do serious damage to instruments and astronauts alike.

    To prepare ourselves for what may be an inevitable strike by a superflare, Notsu says we need to work on protecting our electronics by investing in radiation shielding and backup systems.

    “This topic should [start to be considered] seriously from now on,” Notsu stressed.
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  4. #1154
    Moderator at Work ilan's Avatar
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    Moon to sweep by Jupiter and star Antares
    Bruce McClure in TONIGHT | June 14, 2019


    From around the world on the evenings of June 14, 15 and 16, 2019, look for the moon and then for the red supergiant star Antares and the giant gas planet, Jupiter. The moon – now in a waxing gibbous phase, moving toward full moon on the night of June 16-17 – will pass to the north of Antares and Jupiter.

    Despite the moon’s glare, you should be able to see Antares and Jupiter relatively easily. Antares counts as a 1st-magnitude star, and Jupiter is far brighter than any star (except our sun), outshining Antares by nearly 30 times. Remember, though, that Antares, being a star, shines by its light. Jupiter shines only by reflecting sunlight.

    As the Earth spins beneath the heavens, moving from west-to-east on its rotational axis, the moon, Antares and Jupiter will appear to parade westward across the sky throughout the night. However, this supposed motion of the moon, Antares and Jupiter is really a reflection of the Earth spinning on its rotational axis.

    What’s more, even as the moon goes westward throughout the night, it’s simultaneously moving eastward in front of the stars and bright planets of our solar system. Throughout the night, the moon moves about 1/2 degree (its own angular diameter) eastward in front of the constellations of the zodiac. In one day (24 hours), the moon journeys some 13 degrees eastward upon the zodiac.
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  5. #1155
    Moderator at Work ilan's Avatar
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    Something Appears to have Ripped a Huge Hole in the Milky Way and Scientists Don't Know Why
    Hannah Osborn, Newsweek | 5/16/19 AT 5:30 AM EDT


    Shutterstock

    Something appears to have torn a hole in part of the Milky Way's halo. The “dark substructure” was found via Gaia observations—a project set out to produce the most detailed 3D map of our galaxy—with Harvard scientist Ana Bonaca noticing a perturbation in a tidal stream.

    She presented her findings at the American Physical Society's April meeting.

    As first reported by LiveScience, Bonaca was focusing on tidal streams produced by stars escaping from globular clusters—normally found at the edges of a galaxy. The stellar halo of the Milky Way is full of these tidal streams.

    If there is nothing to disturb them, the streams are almost uniform in terms of their density. However, Bonaca noticed there was a hole in one. “The on-sky morphology suggests a recent, close encounter with a massive and dense perturber,” an abstract to her work reported.

    What this “perturber” is, however, is unknown. "It's a dense bullet of something," Bonaca told LiveScience. Telescopes failed to find the source—so what could it be?

    The hole is enormous, so whatever made it must also have been. "It's much more massive than a star,” she told the website. “Something like a million times the mass of the sun. So there are just no stars of that mass. We can rule that out. And if it were a black hole, it would be a supermassive black hole of the kind we find at the center of our own galaxy."

    The problem with this idea is that there are no signs of a supermassive black hole in the vicinity.


    At the moment, observations do not show any large luminous object (something made from ordinary matter, which reflects light) moving away from the hole. This led Bonaca to suggest the perturbation could have been made by dark matter. This is the mystery substance that makes up about 27 percent of the universe. Scientists know it is there because of the gravitational force it exerts on normal matter—but because it is “dark,” in that it does not reflect light, we cannot see what it is.

    “Observations permit a low-mass dark-matter subhalo as a plausible candidate,” Bonaca's abstract says.

    If it was a dense blob of dark matter that smashed through the tidal stream, it would be an exciting find for scientists, as it would provide them the opportunity of studying the elusive substance. The discovery of a dark matter “bullet” would also fit with current predictions about what dark matter is like—research suggests it is “clumpy,” in that it is not smooth and evenly distributed around the universe.

    Identifying a clump of dark matter “opens up the possibility that detailed observations of streams could measure the mass spectrum of dark-matter substructures and even identify individual substructures,” her abstract concludes.

    However, she says this still does not rule out a luminous object. "It could be that it's a luminous object that went away somewhere, and it's hiding somewhere in the galaxy," she said.

    Bocana's research is still in the early stages. She is yet to publish her findings in a peer-reviewed journal—however, LiveScience reports her presentation was welcomed by attendees.
    ________________________________________

    An interesting mystery with the perpetrator having "a million times the mass of the sun." The search is on for this stealthy monster! - ilan
    Last edited by ilan; Today at 12:59 PM.
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