Saturday, January 21, 2023

3833 - BLACKHOLES - previously hidden?

 

+     -  3833  -   BLACKHOLES  -  previously hidden.    Astronomers have uncovered more than 400 previously hidden black holes feeding on stars and dust in the center of galaxies.  Many of the new black holes, discovered using NASA's “Chandra X-ray Observatory,” remained unknown until now because they are buried beneath cocoons of dust.

           


            ---------  3833  -  BLACKHOLES  -  previously hidden?

            -    Supermassive black holes, which can be millions of times heavier than the sun, live in the center of almost every galaxy in the universe. These colossal objects produce bright beams of energy as they feed on gas, dust, and stars in their immediate vicinity, creating what are known as “Active Galactic Nuclei” (AGN).

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            -    AGN are particularly bright in the X-ray portion of the electromagnetic spectrum.   They also leave telltale visible patterns in optical light, which identify them as AGN.

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            -    But certain objects have been spotted giving off tons of X-rays without the specific optical signatures associated with AGN, named "X-ray bright optically normal galaxies" or "XBONGs."

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            -     The researchers identified 820 XBONGs located between 550 million and 7.8 billion light-years from Earth, the largest such sample ever built.  ( The radius of the galaxy is 50 billion lightyears ).   X-rays penetrate dust, while optical light gets obscured by it.  Are these 820 XBONGs might be black holes surrounded by large amounts of dust?

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            -    If that were the case, the lowest energy X-ray light would get slightly absorbed by the dust, while the most powerful X-ray light would continue to shine brightly through it. The astronomers saw exactly this pattern in around 50% of the XBONGs, suggesting that they are AGNs buried in dusty cocoons.

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            -    "What are the other half?". One possibility is that Chandra is seeing extremely distant clusters of galaxies, which would shine bright in X-rays but lack the characteristic optical signature identifying them as AGN. This could explain around 20% of the remaining XBONGs.

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            -    The final 30% are likely galaxies whose optical light is particularly powerful, bright enough to wash out the optical AGN signature, which could happen when such galaxies are particularly far away.

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            January 20, 2022            BLACKHOLES  -  previously hidden       3833                                                                                                                           

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            --------------------- ---  Saturday, January 21, 2023  ---------------------------

             

             

             

             

                     

             

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