Sunday, February 26, 2023

3892 - MASSIVE BLACK HOLES - went missing?

 

-  3892  -    MASSIVE  BLACK  HOLES  -    went missing?    This is a really surprising result. If expansionary dark energy does lurk inside the cores of black holes, it will solve two long-standing puzzles faced by Einstein’s general theory of relativity, which describes how gravity affects the universe at large scales.


          -----------  3892  -   MASSIVE  BLACK  HOLES  -    went missing?

-     Astronomers are searching for signs of a supermassive black hole in the galaxy cluster Abell 2261.  Nearly all large galaxies contain central black holes, and the galaxy in the middle of Abell 2261 is expected to contain a particularly massive one.

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-    Scientists think this galaxy underwent a merger with another galaxy in the past, which could have caused a newly formed larger black hole to be ejected.    Despite careful searches with Chandra and other telescopes, astronomers do not yet know what happened to this giant black hole.

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-    Despite searching with NASA's Chandra X-ray Observatory and Hubble Space Telescope, astronomers have no evidence that a distant black hole estimated to weigh between 3 billion and 100 billion times the mass of the Sun is anywhere to be found.

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-    This missing black hole should be in the enormous galaxy in the center of the galaxy cluster Abell 2261, which is located about 2.7 billion light years from Earth.

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-    Nearly every large galaxy in the Universe contains a supermassive black hole in their center, with a mass that is millions or billions of times that of the Sun. Since the mass of a central black hole usually tracks with the mass of the galaxy itself, astronomers expect the galaxy in the center of Abell 2261 to contain a supermassive black hole that rivals the heft of some of the largest known black holes in the Universe.

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-    Astronomers looked for material that has been superheated as it fell towards the black hole and produced X-rays, but did not detect such a source.  Astronomers considered an alternative explanation, in which the black hole was ejected from the host galaxy's center. This violent event may have resulted from two galaxies merging to form the observed galaxy, accompanied by the central black hole in each galaxy merging to form one enormous black hole.

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-   When black holes merge, they produce ripples in spacetime, gravitational waves. If the huge amount of gravitational waves generated by such an event were stronger in one direction than another, the theory predicts that the new, even more massive black hole would have been sent careening away from the center of the galaxy in the opposite direction. This is called a recoiling black hole.

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-  Astronomers have not found definitive evidence for recoiling black holes and it is not known whether supermassive black holes even get close enough to each other to produce gravitational waves and merge; so far, astronomers have only verified the mergers of much smaller black holes.

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-    The galaxy at the center of Abell 2261 is an excellent cluster to search for a recoiling black hole because there are two indirect signs that a merger between two massive black holes might have taken place.

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-    First, data from the Hubble and Subaru optical observations reveal a galactic core, the central region where the number of stars in the galaxy in a given patch of the galaxy is at or close to the maximum value, that is much larger than expected for a galaxy of its size.

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-   The second sign is that the densest concentration of stars in the galaxy is over 2,000 light years away from the center of the galaxy.

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-    During a merger, the supermassive black hole in each galaxy sinks toward the center of the newly coalesced galaxy. If they become bound to each other by gravity and their orbit begins to shrink, the black holes are expected to interact with surrounding stars and eject them from the center of the galaxy.

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-    This would explain Abell 2261's large core. The off-center concentration of stars may also have been caused by a violent event such as the merger of two supermassive black holes and subsequent recoil of single, larger black hole that results.

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-  Astronomers turned to Chandra to look for material that had been superheated and produced X-rays as it fell towards the black hole. While the Chandra data did reveal that the densest hot gas was not in the center of the galaxy, they did not reveal any possible X-ray signatures of a growing supermassive black hole. no X-ray source was found in the center of the cluster, or in any of the clumps of stars, or at the site of the radio emission.

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-  They concluded that either there is no black hole at any of these locations, or that it is pulling material in too slowly to produce a detectable X-ray signal.

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-   The mystery of this gigantic black hole's location therefore continues. If Webb is unable to find the black hole, then the best explanation is that the black hole has recoiled well out of the center of the galaxy.

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-    Supermassive black holes could be the engines driving the expansion of the universe, according to research that proposes a solution to "one of the biggest problems in cosmology."

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-    By comparing supermassive black holes across nine billion years of cosmic history, astronomers have discovered a clue that the ravenous behemoths lurking at the hearts of most large galaxies may be the source of dark energy, the mysterious force that makes up 68% of the known universe and causes its accelerating expansion.

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-   Over the last century, astronomers discovered that the universe was expanding at an ever faster pace. This was surprising given that, acting on its own, gravity should be expected to slowly crumple the cosmos together in an event known as the Big Crunch.

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-    To explain the discrepancy, scientists proposed that something powerful enough to counteract gravity must exist, and was pushing everything in the universe further apart. They named that something “dark energy”.

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-    But for dark energy to reverse a cosmic collapse, it would have to be present in such enormous quantities that it makes up the vast majority of the universe.

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-   Now, the new studies have seemingly found a clue as to how the hidden phenomenon works. Comparing the masses of black holes at the centers of two sets of galaxies.  The astronomers found that throughout the universe giant black holes had ballooned to be seven to 20 times larger than they once were, a monstrous growth that couldn't be explained simply by black holes devouring stars or colliding and combining with each other.

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-  The researchers propose that black holes are growing in lockstep with the universe, overcoming the star-crushing, light-capturing forces at their cores with a hypothetical type of dark energy called vacuum energy that makes them expand ever outwards. And, somehow, they drag the entire fabric of the cosmos out with them.

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-   This is a really surprising result. If expansionary dark energy does lurk inside the cores of black holes, it will solve two long-standing puzzles faced by Einstein’s general theory of relativity, which describes how gravity affects the universe at large scales.

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-  Firstly, it would explain how the universe doesn’t collapse due to the large and ubiquitous force of gravitational attraction and, secondly, it would do away with the need for singularities (infinitesimal points where the laws of physics break down) to explain the workings of black holes' dark hearts.

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-    To confirm their theory, astrophysicists will need to ensure that nothing else is contributing to the black holes' mysterious growth by making even more detailed observations of their masses throughout time, while also closely tracking the increase to these masses with the expansion of the universe.

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February 26, 2023     MASSIVE  BLACK  HOLES  -  and universe expansion?     3892                                                                                                                          

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--------------------- ---  Sunday, February 26, 2023  ---------------------------

 

 

 

 

         

 

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