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  1. #1271
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    A second black hole at our galaxy’s center?
    EarthSky Voices in SPACE | December 15, 2019

    There’s a supermassive black hole – 4 million times our sun’s mass – in the center of our Milky Way galaxy. Astronomers who’ve measured star movements near this central black hole are now saying there might be a 2nd companion black hole near it.


    At the center of our galaxy is a supermassive black hole in the region known as Sagittarius A. It has a mass of about 4 million times that of our sun. Image via ESA/ C. Carreau.
    Do supermassive black holes have friends? The nature of galaxy formation suggests that the answer is yes, and in fact, pairs of supermassive black holes should be common in the universe.

    I am an astrophysicist and am interested in a wide range of theoretical problems in astrophysics, from the formation of the very first galaxies to the gravitational interactions of black holes, stars and even planets. Black holes are intriguing systems, and supermassive black holes and the dense stellar environments that surround them represent one of the most extreme places in our universe.

    The supermassive black hole that lurks at the center of our galaxy, called Sgr A*, has a mass of about 4 million times that of our sun. A black hole is a place in space where gravity is so strong that neither particles or light can escape from it. Surrounding Sgr A* is a dense cluster of stars. Precise measurements of the orbits of these stars allowed astronomers to confirm the existence of this supermassive black hole and to measure its mass. For more than 20 years, scientists have been monitoring the orbits of these stars around the supermassive black hole. Based on what we’ve seen, my colleagues and I show that if there is a friend there, it might be a second black hole nearby that is at least 100,000 times the mass of the sun.

    Supermassive black holes and their friends

    Almost every galaxy, including our Milky Way, has a supermassive black hole at its heart, with masses of millions to billions of times the mass of the sun. Astronomers are still studying why the heart of galaxies often hosts a supermassive black hole. One popular idea connects to the possibility that supermassive holes have friends.

    To understand this idea, we need to go back to when the universe was about 100 million years old, to the era of the very first galaxies. They were much smaller than today’s galaxies, about 10,000 or more times less massive than the Milky Way. Within these early galaxies the very first stars that died created black holes, of about tens to thousand the mass of the sun. These black holes sank to the center of gravity, the heart of their host galaxy. Since galaxies evolve by merging and colliding with one another, collisions between galaxies will result in supermassive black hole pairs – the key part of this story. The black holes then collide and grow in size as well. A black hole that is more than a million times the mass of our sun is considered supermassive.

    If indeed the supermassive black hole has a friend revolving around it in close orbit, the center of the galaxy is locked in a complex dance. The partners’ gravitational tugs will also exert its own pull on the nearby stars disturbing their orbits. The two supermassive black holes are orbiting each other, and at the same time, each is exerting its own pull on the stars around it.

    The gravitational forces from the black holes pull on these stars and make them change their orbit; in other words, after one revolution around the supermassive black hole pair, a star will not go exactly back to the point at which it began.

    Using our understanding of the gravitational interaction between the possible supermassive black hole pair and the surrounding stars, astronomers can predict what will happen to stars. Astrophysicists like my colleagues and me can compare our predictions to observations, and then can determine the possible orbits of stars and figure out whether the supermassive black hole has a companion that is exerting gravitational influence.

    Using a well-studied star, called S0-2, which orbits the supermassive black hole that lies at the center of the galaxy every 16 years, we can already rule out the idea that there is a second supermassive black hole with mass above 100,000 times the mass of the sun and farther than about 200 times the distance between the sun and the Earth. If there was such a companion, then I and my colleagues would have detected its effects on the orbit of SO-2.

    But that doesn’t mean that a smaller companion black hole cannot still hide there. Such an object may not alter the orbit of SO-2 in a way we can easily measure.

    The physics of supermassive black holes

    Supermassive black holes have gotten a lot of attention lately. In particular, the recent image of such a giant at the center of the galaxy M87 opened a new window to understanding the physics behind black holes.

    The proximity of the Milky Way’s galactic center – a mere 24,000 light-years away – provides a unique laboratory for addressing issues in the fundamental physics of supermassive black holes. For example, astrophysicists like myself would like to understand their impact on the central regions of galaxies and their role in galaxy formation and evolution. The detection of a pair of supermassive black holes in the galactic center would indicate that the Milky Way merged with another, possibly small, galaxy at some time in the past.

    That’s not all that monitoring the surrounding stars can tell us. Measurements of the star S0-2 allowed scientists to carry out a unique test of Einstein’s general theory of relativity. In May 2018, S0-2 zoomed past the supermassive black hole at a distance of only about 130 times the Earth’s distance from the sun. According to Einstein’s theory, the wavelength of light emitted by the star should stretch as it climbs from the deep gravitational well of the supermassive black hole.

    The stretching wavelength that Einstein predicted – which makes the star appear redder – was detected and proves that the theory of general relativity accurately describes the physics in this extreme gravitational zone. I am eagerly awaiting the second closest approach of S0-2, which will occur in about 16 years, because astrophysicists like myself will be able to test more of Einstein’s predictions about general relativity, including the change of the orientation of the stars’ elongated orbit. But if the supermassive black hole has a partner, this could alter the expected result.

    Finally, if there are two massive black holes orbiting each other at the galactic center, as my team suggests is possible, they will emit gravitational waves. Since 2015, the LIGO-Virgo observatories have been detecting gravitational wave radiation from merging stellar-mass black holes and neutron stars. These groundbreaking detections have opened a new way for scientists to sense the universe.

    Any waves emitted by our hypothetical black hole pair will be at low frequencies, too low for the LIGO-Virgo detectors to sense. But a planned space-based detector known as LISA may be able to detect these waves, which will help astrophysicists figure out whether our galactic center black hole is alone or has a partner.


    Smadar Naoz, Associate Professor of Physics & Astronomy, University of California, Los Angeles
    _______________________________________

    It's nice to have a friend, especially during the holiday season. - ilan
    Last edited by ilan; 12-24-2019 at 08:46 PM.
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  2. #1272
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    Quote Originally Posted by ilan View Post

    It's nice to have a friend, especially during the holiday season. - ilan
    lmao

    Here I was worried about there being one in our Galaxy....now there may be more
    pepisee

  3. #1273
    Moderator at Work ilan's Avatar
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    A giant star is acting strange, and astronomers are buzzing
    Nadia Drake, Science | 26 December 2019

    The red giant Betelgeuse is the dimmest seen in years, prompting some speculation that the star is about to explode. Here's what we know.


    The Constellation Orion, The Hunter from Greek Mythology, is shown on the right. The three stars at the center of the constellation represent the hunter's belt. Betelgeuse is isolated on left.
    THE CONSTELLATION ORION is one of the most recognizable patterns in the night sky, visible around the world. But if you’ve looked at Orion recently and thought something seemed off, you’re not wrong: The giant red star Betelgeuse, which marks the hunter’s right shoulder, is the dimmest it’s been in almost a century.

    Normally, Betelgeuse is among the 10 brightest stars in the sky. However, the red giant began dimming in October, and by mid-December, the star had faded so much it wasn’t even in the top 20, Villanova University’s Edward Guinan reported in an Astronomer’s Telegram.

    “Now the outline of Orion is noticeably different with Betelgeuse so faint,” he says.

    To be clear, dimming alone isn’t all that odd for a star like Betelgeuse. It’s what’s known as a variable star, and its shifts in brightness have been closely studied for decades. However, it is unusual for one of the sky’s most prominent points of light to fade so noticeably, prompting scientists to consider the possibility that something more exciting could be about to happen: Betelgeuse might explode and die, briefly blazing brighter than the full moon before vanishing from our night sky forever.

    Huge, red stars like Betelgeuse live fast and die violently, exploding in stellar events called supernovae that are visible across vast distances. So, while Betelgeuse is a relatively young star—only about 8.5 million years old—astronomers know that it is nearing the end of its life.

    “The biggest question now is when it will explode in a supernova,” UC Berkeley’s Sarafina Nance, who studies Betelgeuse and stellar explosions, said on Twitter. “Disclaimer: I don't think it's going to explode any time soon,” she added during an interview with National Geographic. “But I am excited [for] when it does.”
    ______________________________________________

    I used an image from another article and captioned it to fit this article and to provide a little background information. - ilan
    Last edited by ilan; 12-27-2019 at 12:10 AM.
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  4. #1274
    Moderator at Work ilan's Avatar
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    We're All Made of Stardust. Here's How.
    The Smithsonian Channel


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    Aliens definitely exist and they could be living among us on Earth, says Britain's first astronaut
    Rob Picheta, CNN | Updated 11:37 AM ET, Mon January 6, 2020


    Sharman became the first Briton in space in 1992

    Aliens definitely exist, Britain's first astronaut has said -- and it's possible they're living among us on Earth but have gone undetected so far.

    Helen Sharman, who visited the Soviet Mir space station in 1991, told the Observer newspaper on Sunday that "aliens exist, there's no two ways about it."

    "There are so many billions of stars out there in the universe that there must be all sorts of different forms of life," she went on. "Will they be like you and me, made up of carbon and nitrogen? Maybe not."

    Then, in a tantalizing theory that should probably make you very suspicious of your colleagues, Sharman added: "It's possible they're here right now and we simply can't see them."

    Sharman was the first of seven Britons to enter space.

    The chemist spent eight days as a researcher on the space mission when she was 27, making her one of the youngest people to enter orbit.

    NASA rovers are trawling Mars for evidence of past or present life forms, but humankind's endless fascination with extraterrestrial life forms has so far proved fruitless.

    Sharman is not the only person to speculate that we've had brushes with aliens, though.

    A former Pentagon official who led a secret government program to research potential UFOs, revealed in 2017, told CNN at the time that he believes there is evidence of alien life reaching Earth.

    Elsewhere in her interview, Sharman said there is "no greater beauty than looking at the Earth from up high."

    "I'll never forget the first time I saw it," she added.

    Sharman also discussed her frustration with observers defining her by her sex. "People often describe me as the first British woman in space, but I was actually the first British person. It's telling that we would otherwise assume it was a man," she said.

    "When Tim Peake went into space, some people simply forgot about me. A man going first would be the norm, so I'm thrilled that I got to upset that order."
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  6. #1276
    Moderator at Work ilan's Avatar
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    A huge meteorite smashed into Earth nearly 800,000 years ago. We may have finally found the crater
    Michelle Lim, CNN | January 9, 2020


    The crater may lie beneath the Bolaven plateau volcanic field in Laos.

    (CNN) One of the largest known meteorites to hit Earth struck nearly 800,000 years ago, but the exact spot where it smashed into our planet has been a mystery -- until now.

    The crater may lie beneath lava in a 910 cubic kilometer (218 cu mi) area of the Bolaven plateau volcanic field in the southeast Asian nation of Laos, according a paper published in the Proceedings of the National Academy of Sciences journal.

    A meteorite is a an object from space that survives a trip through the atmosphere and falls on the Earth's surface. The meteorite that crashed into Earth over 790,000 years ago was 2 kilometers (1.2 miles) wide, and the impact was so great that debris was flung across Asia, Australia, and Antarctica.

    The first clues leading to the impact site came from small, pebble-like glassy objects called tektites. Scientists believe tektites formed from Earth material that melted upon meteorite impact and were thrown into our atmosphere, before falling back to the ground.

    "Their existence means that the impacting meteorite was so large and its velocity so fast that it was able to melt the rocks that it hit," Professor Kerry Sieh, principal investigator with the Earth Observatory of Singapore and one of the paper's authors, told CNN.

    Tektites between 750,000 to 35.5 million years old have been found across the planet in areas called strewn fields. These strewn fields are found on every continent except Antarctica, according to the Jackson School Museum of Earth History at the University of Texas at Austin.

    Scientists have largely been able to determine the source crater for tektites, with the exception of one -- the Australasian field. It extends all the way from southern China to south Australia, and is the largest known tektite field, covering about 10% of the earth's surface.

    "There have been many, many attempts to find the impact site and many suggestions, ranging from northern Cambodia, to central Laos, and even southern China, and from eastern Thailand to offshore Vietnam," Sieh said.

    "But our study is the first to put together so many lines of evidence, ranging from the chemical nature of the tektites to their physical characteristics, and from gravity measurements to measurements of the age of lavas that could bury the crater."

    Based on the scientists' calculations, the hidden impact crater that produced the vast Australasian field of strewn tektites is about 13 kilometers (8 miles) wide and 17 kilometers (11 miles) long.

    But more still has to be done to confirm the theory.

    Scientists will next need to "drill down a few hundred meters to see if the rocks below the lavas are indeed the rocks you'd expect at an impact site -- that is, lots of evidence for melting and shattering," Sieh said.
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  7. #1277
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    What are black holes?
    Andy Briggs in SPACE | January 11, 2020


    Artist’s concept of a very typical model for a stellar-mass black hole in a binary star system. Material is being gravitationally sucked off a a blue supergiant variable star – in this case the star HDE 226868 – onto the famous black hole known as Cygnus X-1. It’s the interaction between a star and black hole in a binary system that makes stellar-mass black holes visible. Image via ESA/ Wikimedia Commons.
    A black hole is an area of space with a gravitational field so strong that nothing, not even light, can escape it. That’s why black holes appear black. In some cases, black holes are former massive stars that have been crushed to an extreme density during supernova explosions. In other cases, black holes contain the mass of millions or billions of stars.

    People often ask, if black holes are black – if light cannot escape them – how can we see them? The answer is that we see the effects black holes have on the space around themselves.

    In his general theory of relativity, published in 1915, Albert Einstein was the first to suggest that our universe contains such strange, dense, massive objects. Black holes emerge from Einstein’s equations of general relativity, as a natural consequence of the death and collapse of massive stars. The first person to formulate black holes mathematically was German mathematician Karl Schwarzschild in 1916. Theoretical physicist John Wheeler first coined the name black hole many years later, in 1967.

    Up until the 1970s, black holes were generally considered to be mathematical curiosities only. But, as observational techniques improved, they began to be taken seriously as real objects. The first physical black hole ever discovered – Cygnux X-1 – was confirmed in 1971.

    Black holes are of two main types. The first is the so-called stellar-mass black hole. These are the remnants of huge stars. When, at the end of its life, a star with more than about five times the mass of our sun explodes as a supernova, its core is suddenly and violently compressed under gravity. Depending on the star’s mass, the collapse may halt and form a neutron star, but if its mass is sufficient the core’s collapse will – in theory – continue, forming a black hole. Stellar-mass black holes have mass ranging from a minimum of about five times the mass of our sun up to about 60 times the sun’s mass. Their diameter is typically between 10 and 30 miles.

    The second type of black hole is the supermassive black hole. These can have masses many billions of times that of our sun. One example is at the center of the quasar known as TON 618; the central black hole is an estimated 66 billion solar masses. As they have simply too much mass to have formed from the death of individual stars, it is thought that supermassive black holes formed in the early history of the universe from huge collapsing clouds of interstellar hydrogen, although their exact origin is unclear and is an area of much active research. It is also possible that they have accumulated extra mass over the eons from mergers with other black holes.

    Supermassive black holes can have diameters bigger than that of our solar system. Most galaxies have a supermassive black hole at their centers: the one at the center of our own Milky Way galaxy, Sagittarius A*, has some 4 million times our sun’s mass and is some 37 million miles in diameter.
    What’s inside a black hole? By definition, we can’t observe what’s inside there, because no light – no information of any kind – can escape a black hole. But astrophysical theories suggest that, at the core of a black hole, all the black hole’s mass is concentrated into a tiny point of infinite density. This point is known as a singularity.

    It is this point – this singularity – that generates the black hole’s incredibly strong gravitational field. Consider, however, that the singularity might not exist. That’s because all known physics breaks down under the extreme conditions at the center of a black hole, where quantum effects doubtless play a large part. As we do not yet possess a quantum theory of gravity, it is impossible to describe what actually exists at core of a black hole.

    Meanwhile, here is something that we are certain exists: the boundary of a black hole, known as its event horizon. It is not a physical edge. It’s just a point in space beyond which it is impossible to escape the black hole’s gravity. Once anything falling into the black hole passes the event horizon, it can never leave the black hole again, and is drawn inexorably and inevitably towards the black hole’s center. Within the event horizon, any solid object is torn apart by the fierce gravity and reduced to its constituent subatomic particles. At the event horizon, the escape velocity of the black hole reaches the speed of light.

    As black holes don’t emit any light or other detectable radiation, they can be observed only by their gravitational effects on objects in the space close to them. If there are stars or gas near the black hole, it may be actively “feeding” on them; that is, material from these nearby objects may be drawn into the hole. In this case, a black hole will possess an accretion disk, where material spirals inwards before it is consumed, like water down a drain. The accretion disk may rotate at significant percentages of the speed of light: friction between colliding particles in the disk raises its temperature to million of degrees, radiating huge quantities of x-rays which can be detected with special telescopes.

    In April 2019, the Event Horizon Telescope project revealed the first-ever direct image of a black hole, the supermassive black hole at the center of the giant elliptical galaxy M87. The image had been acquired using a global array of radio telescopes. As well as demonstrating beyond reasonable doubt that black holes exist, this amazing achievement represents the birth of a new branch of observational astronomy and has allowed General Relativity’s models of black hole behavior to be tested directly. The M87 black hole complies perfectly with these models.
    ________________________________

    A nice, quick and dirty discussion of black holes. - ilan
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    Crab Nebula: Visualize an exploded star
    Eleanor Imster and Deborah Byrd in SPACE | January 14, 2020

    A new NASA video combines visible, infrared, and X-ray view of the famous Crab Nebula, a star that exploded into view in our sky 1,000 years ago.


    NASA released the video above on January 5, 2020, saying it was created by astronomers and visualization specialists from its Universe of Learning program. These experts combined visible, infrared and X-ray vision of the famous Crab Nebula, the remains of a star that exploded into view in Earth’s sky in the year 1054. The video shows images from the Chandra X-ray Observatory and the Hubble and Spitzer space telescopes. It shows the pulsar at the heart of the Crab Nebula – the rapidly spinning, super-dense crushed core of the exploded star – which sends high-energy jets in either direction into the nebula, and which serve as what NASA calls the powerhouse “engine” of the entire system. In a statement, NASA said:

    The tiny dynamo [the pulsar] is blasting out blistering pulses of radiation 30 times a second with unbelievable clockwork precision.

    The visualization was produced by a team at the Space Telescope Science Institute (STScI) in Baltimore, Maryland; the Caltech/IPAC in Pasadena, California; and the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Massachusetts. It debuted earlier this month at the American Astronomical Society meeting in Honolulu, Hawaii.

    NASA described the video this way:

    The movie begins by showing the Crab Nebula in context, pinpointing its location in the constellation Taurus. This view zooms in to present the Hubble, Spitzer, and Chandra images of the Crab Nebula, each highlighting one of the nested structures in the system. The video then begins a slow buildup of the three-dimensional X-ray structure, showing the pulsar and a ringed disk of energized material, and adding jets of particles firing off from opposite sides of the energetic dynamo.

    Appearing next is a rotating infrared view of a cloud enveloping the pulsar system, and glowing from synchrotron radiation. This distinctive form of radiation occurs when streams of charged particles spiral around magnetic field lines. There is also infrared emission from dust and gas.
    The visible-light outer shell of the Crab Nebula appears next. Looking like a cage around the entire system, this shell of glowing gas consists of tentacle-shaped filaments of ionized oxygen (oxygen missing one or more electrons). The tsunami of particles unleashed by the pulsar is pushing on this expanding debris cloud like an animal rattling its cage.

    The X-ray, infrared, and visible-light models are combined at the end of the movie to reveal both a rotating three-dimensional multiwavelength view and the corresponding two-dimensional multiwavelength image of the Crab Nebula.
    The three-dimensional views of each nested structure give you an idea of its true dimensions. To enable viewers to develop a complete mental model, we wanted to show each structure separately, from the ringed disk and jets in stark relief, to the synchrotron radiation as a cloud around that, and then the visible light as a cage structure surrounding the entire system.
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