Sunday, April 2, 2023

3938 - GALACTIC BLACKHOLE - at center of our galaxy?

 

-   3938 -  GALACTIC  BLACKHOLE  -  at center of our galaxy?   The doomed cloud is 3,000 times longer than the distance from the Earth to the Sun.  It provides clues to the strange and extreme environment around a black hole 4 million times more massive than the Sun.


--------  3938  -  GALACTIC  BLACKHOLE  -  at center of our galaxy?

-   26,000 light years away, a strange and enormous cloud is being stretched and strained under the tremendous tidal forces of “Sagittarius A*”, the name of the supermassive black hole at the center of our galaxy. In just 13 years, astronomers expect this cloud, known as X7, to be torn to shreds by this extreme environment.

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-    When X7 was first noticed in 2007, astronomers described it as a comet-shaped object close to the galactic center. X7 was classed as a “G object”, a group of oddball blobs of gas that orbit the supermassive black hole Sagittarius A* (Sgr A*) at the center of the Milky Way that act like gas clouds when far from the black hole only to hold together like stars as they draw closer in their orbits.

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-    X7 was vastly more massive than any comet, about 50 times the mass of Earth. Over the last decade-and-a-half, though, astronomers have been able to watch X7 stretch and shift in real-time.

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-    In that time, X7 grew twice as long as it once was, indicating that it is being stretched out by Sgr A* like a noodle. It’s still relatively small and relatively light,  and that’s why it gets stretched, because it’s vulnerable to the forces of the black hole.

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-    A filament like X7 is an extreme object in an extreme environment. Even though it’s traveling at 490 miles per second, its orbit around the supermassive black hole at the center of the Milky Way would take 170 years if it were to complete it successfully.

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-    It was only created a few decades ago, and in a few decades, it’s going to be destroyed. And a few decades, even a hundred years, is a very short timescale on astronomical scales.

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-    When it was first detected, astronomers thought it might be the result of a jet or wind blown out from a nearby star, “S0-73”. But looking over data from the last 20 years, the team found the two aren’t moving in the same direction, nor are they in quite the same three-dimensional volume.

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-  They suspect  X7 is the result of a close scrape between two binary stars. In the extreme tidal environment around a supermassive black hole, binary stars are common, and so are the collisions and mergers between them. If two stars grazed against each other, a long stream of gas and dust would be ejected from their violent collision, which would match the shape and behavior of X7.

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-    Even though it’s zooming around the center of our galaxy at tremendous speeds, X7 will be ripped apart by Sagittarius A*’s tidal forces long before it completes its next 170-year orbit. In 2036, the team estimates, X7 will reach its “periapse passage”, its closest approach to the black hole.

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-    Even though X7 is zipping around Sagittarius A* 26,000 light years away (and its fate was sealed about 25,987 years ago), that’s still 794,000 light years closer than the next-closest supermassive black hole, in the dwarf galaxy Leo. This means astronomers will have a close-up view of what happens to a gas cloud very close to a supermassive black hole.

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-   Along with the Keck telescopes used to observe it since 2002, the JWST is scheduled to take a look at the Sagittarius A* and X7.  JWST observes in different spectra than the Keck observatory.   This will give us insights into its structure.

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-    Using observations taken with the Atacama Large Millimeter Array (ALMA), a radio observatory sited in Chile, astronomers have determined that the galaxy “COS-87259”, containing this new supermassive black hole is very extreme, forming stars at a rate 1000 times that of our own Milky Way and containing over a billion solar masses worth of interstellar dust. The galaxy shines bright from both this intense burst of star formation and the growing supermassive black hole at its center.

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-    The black hole is considered to be a new type of primordial black hole, one heavily enshrouded by cosmic “dust”, causing nearly all of its light to be emitted in the mid-infrared range of the electromagnetic spectrum. This growing supermassive black hole is generating a strong jet of material moving at near light speed through the host galaxy.

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-   Today, black holes with masses millions to billions of times greater than that of our own Sun sit at the center of nearly every galaxy. How these supermassive black holes first formed remains a mystery for scientists, particularly because several of these objects have been found when the Universe was very young.

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-    Because the light from these sources takes so long to reach us, we see them as they existed in the past; in this case, just 750 million years after the Big Bang, which is approximately 5% of the current age of the Universe.

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-    What is particularly astonishing about this new object is that it was identified over a relatively small patch of the sky typically used to detect similar objects, less than 10 times the size of the full moon, suggesting there could be thousands of similar sources in the very early Universe. This was completely unexpected from previous data.

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-    The only other class of supermassive black holes we knew about in the very early Universe are “quasars”, which are active black holes that are relatively unobscured by cosmic dust.

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-    These quasars are extremely rare at these distances similar to COS-87259, with only a few tens located over the full sky. The surprising discovery of COS-87259 and its black hole raises several questions about the abundance of very early supermassive black holes, as well as the types of galaxies in which they typically form.

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-   These results suggest that very early supermassive black holes were often heavily obscured by dust, perhaps as a consequence of the intense star formation activity in their host galaxies.

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-  Astronomers have also just discovered what may be the largest black hole known to date.   The giant black hole has a mass of 30 billion suns and sits at the center of a galaxy located hundreds of millions of light-years from Earth.

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-     Astronomers discovered the black hole during observations of a galaxy located farther away from Earth than the one centered around the monster black hole, while using the gravity of the foreground galaxy to magnify the background object.

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-    This effect, known as gravitational lensing, is a result of gravity bending the light around extremely massive objects. Serving as nature's own telescope, gravitational lensing frequently helps astronomers to increase the magnification of objects too distant to be properly visible to human-made telescopes.

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-    This particular black hole, which is roughly 30 billion times the mass of our sun, is one of the biggest ever detected and on the upper limit of how large we believe black holes can theoretically become.

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-    The team arrived at the size of the black hole by analyzing the magnification of the foreground object in a series of images taken by the Hubble Space Telescope. Using sophisticated computer modeling, the scientists were able to simulate how much light bends around the foreground galaxy where the black hole resides. They tested thousands of black hole sizes before arriving at a solution that matched the observations.

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-    Most of the biggest black holes that we know about are in an active state, where matter pulled in close to the black hole heats up and releases energy in the form of light, X-rays, and other radiation.

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-   Gravitational lensing makes it possible to study inactive black holes, something not currently possible in distant galaxies. This approach could let us detect many more black holes beyond our local universe and reveal how these exotic objects evolved further back in cosmic time.

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-   An event horizon marks the boundary at the outer edge of a black hole.  The event horizon is the spherical outer boundary of a black hole loosely considered to be its "surface."

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-   It is the point that the gravitational influence of the black hole becomes so great that not even light is fast enough to escape it. As a result of the fact that Albert Einstein's theory of special relativity tells us that no signal can exceed the speed of light in a vacuum humanity can never hope to obtain a signal from the one-way boundary that is an event horizon.

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-    As such event horizons effectively act as cosmic gatekeepers preventing us from ever directly observing the secrets that lie at the heart of black holes. Yet they can reveal a great deal about the environment around them.

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-    When an item gets near an event horizon, a witness would see the item's image redden and dim as gravity distorted light coming from that item. At the event horizon, this image would effectively fade to invisibility.

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-   Within the event horizon, one would find the black hole's singularity, where previous research suggests all of the object's mass has collapsed to an infinitely dense extent.

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-    This means the fabric of space and time around the singularity has also curved to an infinite degree, so the laws of physics as we currently know them break down.

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-    In a distant galaxy, a supermassive black hole spewing radiation at near light speed has shifted its angle by a whopping 90 degrees to point directly toward Earth, a sharp turn that's puzzling physicists.

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-   Active galactic nuclei (AGN) are the hungry black holes at the cores of many other galaxies, and they accrete matter and spew powerful jets of high-energy particles known as relativistic jets.

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-    “PBC J2333.9-2343”, a large galaxy about 4 million light-years across, was previously classified as a radio galaxy, meaning its AGN's gargantuan jets of radiation were pointed perpendicular to our line of sight.

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-    But new research reclassifies the galaxy as a blazar, meaning the black hole's jets are now pointed directly at Earth. This means the galaxy's jets shifted by a "dramatic" degree.

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-    The relativistic jet of its supermassive black hole had changed its direction.   It was observed across nearly the entire electromagnetic spectrum, from radio waves to gamma-rays. Their observations showed that this galaxy had characteristics typical of blazars: It brightened and dimmed like a blazar, and it had similar jets. The object was most likely a blazar.

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-  They also observed two lobes, areas where an AGN's jets interact with surrounding gas, where some jets had previously made their mark. This blazar's lobes are "very old.  These dormant lobes are evidence that the jets have, in fact, changed direction.

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-     It's not totally unprecedented for a galaxy's jets to appear in different places. But in prior examples, there were two sets of lobes, meaning two separate jets turning on and off.

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-    What caused this great shift? Astronomers are still working that out. Current theories include a galaxy merger, where another large galaxy collided with PBC J2333.9-2343, jostling the orientation of everything within it. More observations are needed to figure out this mystery.

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                   March 21, 2023    GALACTIC  BLACKHOLE  -  at center of our galaxy?              3926                                                                                                                          

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