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                         "The real hero is always a hero by mistake;
he dreams of being an honest coward like everybody else."  -Umberto
Eco, author of "Foucault's Pendulum," who died on February 19, 2016




THE DAILY ASTRONOMER
Monday, February 22, 2016
Biggest Black Hole?!


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Hiatus over!
Illness followed by insanely busy Laser Fest week.

i.e.,  hooky

Let's proceed…

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The headline is quite simple: "Astronomers have found the largest
black hole yet discovered!"    However, this straightforward headline
prompts many questions:   Where is this black hole?  How much does it
"weigh?"   How can astronomers find a black hole if it isn't visible?
 How can they know a black hole's mass and size?  Actually, what is a
black hole?    How did it form?    How can they know that it is the
largest black hole?     Will it devour Earth?  (That last question is
generally asked whenever a black hole is found.)     Today's DA
attempts to address these questions and to introduce readers to this
behemoth of a black hole.



The first is the easiest to answer.   Astronomers have discovered a
supermassive black hole within the nucleus of galaxy NGC 4889*,
located about 300 million light years from Earth in the constellation
Coma Bernices.       As for its "weight,"** this behemoth black hole
strains the scale springs at 21 billion solar masses, meaning it is 21
billion times more massive than our Sun.       Even by super massive
black hole standards, this thing is monstrously massive



Astronomers generally "find" black holes by searching for powerful
x-ray sources that are close to active stars. They know that a black
hole's powerful tidal forces can strip gases from a stellar companion.
These gases will then form an accretion disc around the black hole's
"event horizon," which, being the region from which light cannot
escape, defines its outer boundary.   These gases experience
differential rotation, as the material closest to the event horizon
revolves much more quickly than more distant gases. The  resultant
frictional forces heats the gases to extreme temperatures which then
produce x-rays.     However, supermassive black holes are a different
matter.   Astronomers assume that most galaxies contain a supermassive
black hole in their nuclei.  Our Milky Way Galaxy, for instance,  is
host to a supermassive black hole more than 4 billion times more
massive than the Sun.      Astronomers detect and discern supermassive
black hole properties by analyzing the motions of nearby stars.
  The more massive the black holes, the faster the stars around them
move.       It is by this indirect method that astronomers can
estimate a supermassive black hole's mass. This mass also relates
directly to a supermassive black hole's size, so to know one value is
to then know the other.    The greater the mass, the larger the size.



Supermassive black hole formation is a different process than stellar
mass black hole formation.     Stars at least 15 times more massive
than the Sun will become black holes at the end of their life cycles.
  Stars remain stable because the internal energy pressure
counterbalances the star's constant gravitational contraction.   This
energy pressure results from core thermonuclear reactions that fuse
light elements into heavier nuclei.  At the very end of its life, a
highly massive star will reach the "iron stage," when superheated iron
nuclei fills the core.    No other fusion reactions are then possible
because iron fusion is an "endothermic process," meaning that more
energy is required to fuse iron than the fusion reaction would impart
back into the star.    The counterbalance between the energy pressure
and gravity is violently disrupted. The star's outer layers collapse
onto the core and then they explode outward as a supernova.  The
internal remnant is crushed down into a small volume of immense
density.  The gravitational attraction is so powerful that not even
light can escape from it, hence the term "black hole."



Supermassive black holes likely form through myriad accretions of
stellatr mass black holes, which would naturally be comparatively
abundant in the dense interior galactic regions.   These
agglomerations produce a different type of black hole.  While black
holes are intensely dense, supermassive black holes are more spread
out and have an average density comparable to that of water. Their
immense masses, not their vanishingly small volumes, make them black
holes.



As for the 'largest black hole' designation.  Astronomers cannot be
sure if this black hole is, indeed the largest.    They can only
cvompare this one to those already discovered.    Approximately 100
billion galaxies populate the Universe, some of which are too distant
to allow the close scutiny that astronomers train on more proximate
galaxies.   Therefore,  it is unlikely that astronomers will ever be
able to proclaim any supermassive black hole as the most massive.


Finally, this black hole poses no danger to us, whatsoever, as it is
300 million light years away.  Even if the Sun became a black hole -it
can't-, Earth would not be swallowed by it.   Our planet would merely
continue to orbit around it, albeit at a slightly slower rate as the
Sun would lose some matter in the process of becoming a black hole.



Be it ever so formidable, this behemoth black hole will not imperil
our humble planet Earth.











*NGC 4889.    The "NGC" stands for "New General Catalogue," a catalog
of celestial objects first compiled by John Louis Emil Dreyer
(1852-1926).   Since its initial 1888 publication, the NGC has
undergone numerous revisions.



** In astronomical/physical circles, homocide is frowned upon, but
using the terms "mass" and "weight" interchangeably is unpardonable.
 Here on the third world, we're accustomed to mixing those terms
freely, but they aren't the same.    Mass measures an object's
inertia, or resistance to changes in its motion.  The more massive the
object, the more it resists your efforts to push it or, if it's
moving, slow it down.  "Weight" refers to the gravitational force
exerted on an object by a given planet.     This weight is
proportional to mass.  The more massive an Earth bound object, the
more it will weigh.     However, if an object were transported from
Earth to, let's say, the moon, its mass would remain constant, but its
weight would be one-sixth its original value because the moon is less
massive than Earth and its gravitational pull correspondingly weaker.