Thursday, June 23, 2022

3607 - MILKY WAY GALAXY - new developments?

  -  3607 -   MILKY WAY  GALAXY  -  new developments?    Milky Way Galaxy has at least one major collision that happened early in the Milky Way’s development.  History of the Milky Way:


---------------------  3607  -     MILKY WAY  GALAXY  -  new developments?

-  When the Khoisan hunter-gatherers of sub-Saharan Africa gazed upon the meandering trail of stars and dust that split the night sky, they saw the embers of a campfire. Polynesian sailors perceived a cloud-eating shark. The ancient Greeks saw a stream of milk, gala, which would eventually give rise to the modern term “galaxy.”

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-  In the 20th century, astronomers discovered that our silver river is just one piece of a vast island of stars, and they penned their own galactic origin story.  Our Milky Way galaxy came together nearly 14 billion years ago when enormous clouds of gas and dust coalesced under the force of gravity. 

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-  Over time, two structures emerged, a vast spherical “halo,” and later, a dense, bright disk.   Billions of years after that, our own solar system spun into being inside this disk.  When we look out at night, we see spilt milk which is an edge-on view of the disk splashed across the sky.

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-  On April 25, 2018, a European spacecraft by the name of “Gaia” released a staggering quantity of information about the sky.  Gaia’s years-long data set described the detailed motions of roughly 1 billion stars. Previous surveys had mapped the movement of just thousands. 

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-  Astronomers found that parts of the disk appeared impossibly ancient. They also found evidence of epic collisions that shaped the Milky Way’s violent youth, as well as new signs that the galaxy continues to churn in an unexpected way.

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-  The Gaia satellite has revolutionized our understanding of the Milky Way since its launch in December 2013.  These results have spun a new story about our galaxy’s turbulent past and its ever-evolving future. The theme is that the Milky Way is not a static object. Things are changing rapidly everywhere.

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-  To peer back to the galaxy’s earliest days, astronomers seek stars that were around back then. These stars were fashioned only from hydrogen and helium, the cosmos’s rawest materials. These smaller stars from this early stock are also slow to burn, so many are still shining.

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-  Researchers had assembled a catalog of 42 such ancients, known as ultra metal-poor stars.  To astronomers, any atom bulkier than helium qualifies as “metallic“. According to the standard story of the Milky Way, these stars should be swarming throughout the halo, the first part of the galaxy to form. By contrast, stars in the disk, which was thought to have taken perhaps an additional billion years to spin itself flat should be contaminated with heaver elements such as carbon and oxygen.

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-  Gaia’s data release extracted the 42 ancient stars from the full data set, then tracked their motions. He found that most were streaming through the halo, as predicted. But some, roughly 1 in 4, weren’t. Rather, they appeared stuck in the disk, the Milky Way’s youngest region. 

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-  Follow-up research confirmed that the stars really are long-term residents of the disk, and not just passing through. From two recent surveys astronomers amassed a library of roughly 5,000 “metal-poor stars“. A few hundred of them appear to be permanent denizens of the disk.

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-  About 1 in 10 of these stars lie flat in circular, sunlike orbits. And a third research group found stars of various metallic ties, and therefore various ages,  moving in flat disk orbits. 

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-  How did these anachronisms get there?  Perhaps pockets of pristine gas managed to dodge all the metals expelled from supernovas for eons, then collapsed to form stars that looked deceptively old. Or the disk may have started taking shape when the halo did, nearly 1 billion years ahead of schedule.

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-  In digital simulations, a Milky Way like galaxy forms and evolves over 13.8 billion years from the early universe to the present day. The distribution calculates the invisible dark matter; the temperature of gas and the density of stars.  In these digital simulations, a Milky Way like galaxy forms and evolves over 13.8 billion years from the early universe to the present day.

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-  At the Supercomputing Center, a single simulation required three months of computing time.  It was repeated the exercise six times.  Five produced Milky Way doppelgängers. Two of those featured substantial numbers of metal-poor disk stars.  How did those ancient stars get into the disk?  They were stellar immigrants. 

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-  Some of them were born in clouds that predated the Milky Way. Then the clouds just happened to deposit some of their stars into orbits that would eventually form part of the galactic disk. Other stars came from small “dwarf” galaxies that slammed into the Milky Way and aligned with an emerging disk.

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-   With Gaia, astronomers have found direct evidence of these cataclysmic collisions. Astronomers assumed that the Milky Way had a hectic youth.  In every direction, they saw a huge number of halo stars ping-ponging back and forth in the center of the Milky Way in the same peculiar way,  This was a clue that they had come from a single dwarf galaxy.

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-  The galactic wreckage was everywhere. Perhaps half of all the stars in the inner 60,000 light-years of the halo, extending hundreds of thousands of light-years in every direction, came from this lone collision, which may have boosted the young Milky Way’s mass by as much as 10%. 

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-  The incoming galaxy was named “Gaia-Enceladus“, after the Greek goddess Gaia, one of the primordial deities, and her Titan son Enceladus.   When the Milky Way and Gaia-Enceladus collided, perhaps 10 billion years ago, the Milky Way’s delicate disk may have suffered widespread damage. 

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-  Astronomers debate why our galactic disk seems to have two parts: a thin disk, and a thicker one where stars bungee up and down while orbiting the galactic center.  The first ancient disk formed pretty fast, and then we think Gaia-Enceladus destroyed it.

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-  Hints of additional mergers have been spotted in bundles of stars known as “globular clusters“.  Galaxy simulations to train a neural network to scrutinize globular clusters by their ages, makeup, and orbits. From that data, the neural network could reconstruct the collisions that assembled the galaxies.

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-   All these mergers have led some astronomers to suggest that the halo may be made almost exclusively of immigrant stars. Models from the 1960s and ’70s predicted that most Milky Way halo stars should have formed in place. But as more and more stars have been identified as galactic interlopers, astronomers may not need to assume that many, if any, stars are natives.

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-  The Milky Way has enjoyed a relatively quiet history in recent eons, but newcomers continue to stream in. Stargazers in the Southern Hemisphere can spot with the naked eye a pair of dwarf galaxies called the Large and Small Magellanic Clouds. Astronomers long believed the pair to be our steadfast orbiting companions, like moons of the Milky Way.

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-  Then a series of Hubble Space Telescope observations between 2006 and 2013 found that they were more like incoming meteorites.  The clouds were coming in hot at about 330 kilometers per second, nearly twice as fast as had been predicted. ( 738, 189 miles per hour)

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-  The speedy clouds were extremely hefty, 10 times bulkier than previously thought.  The problem with looking for galaxy-wide motion is that the Milky Way is a raging blizzard of stars, with astronomers looking outward from one of the snowflakes.

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-   Calculations were used to neutralize the motions of the Earth and the sun, and to average out the motion of halo stars so that the halo’s outer fringe could serve as a stationary backdrop.  When this calibrated the data formed in this way, they found that the Earth, the sun, and the rest of the disk in which they sit are lurching in one direction, not toward the Large Magellanic Cloud’s current position, but toward its position around a billion years ago.

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-  The Milky Way is an object in balance. It may spin and slip through space, but most astronomers assumed that after billions of years, the mature disk and the halo had settled into a stable configuration.

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-   Even after 14 billion years, mergers continue to sculpt the overall shape of the galaxy. This realization is just the latest change in how we understand the great stream of milk across the sky.

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-  Astronomers produced the most comprehensive image of radio emission from the nearest actively feeding supermassive black hole to Earth.  The emission is powered by a central black hole in the galaxy Centaurus A, about 12 million light years away.

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-  As the black hole feeds on in-falling gas, it ejects material at near light-speed, causing 'radio bubbles' to grow over hundreds of millions of years.  When viewed from Earth, the eruption from “Centaurus A” now extends eight degrees across the sky, the length of 16 full Moons laid side by side.

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-  It forms a disc around the black hole, and as the matter gets ripped apart going close to the black hole, powerful jets form on either side of the disc, ejecting most of the material back out into space, to distances of more than a million light years.

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-  Previous radio observations could not handle the extreme brightness of the jets and details of the larger area surrounding the galaxy were distorted, but our new image overcomes these limitations.

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-  Astronomers were been able to combine the radio observations with optical and X-ray data, to help us better understand the physics of these supermassive black holes.

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-   Clouds of cold gas condense in the galactic halo and rain down onto the central regions, feeding the supermassive black hole.  Triggered by this rain, the black hole vigorously reacts by launching energy back via radio jets that inflate the spectacular lobes.

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June 23, 2022          MILKY WAY  GALAXY  -  new developments?          3607                                                                                                                                         

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