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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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