THE USM SOUTHWORTH PLANETARIUM
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70 Falmouth Street     Portland, Maine  04103
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Founded January 1970
Julian date:  2458588.35
                  "Heavens above!!!"

THE DAILY ASTRONOMER
Monday, April 15, 2019
Black Holes I

[image: supermassive_black_hole_2.jpg]

Well, we are delighted to report that our invitation to send black hole
questions elicited such a response that we will have to devote two DA's to
answering them!     Thank you to the subscribers who submitted these
queries.  I hope the responses prove helpful.
As always, please keep those cards and letters coming!   I am only using
the subscribers' initials for attribution.


*"I have a silly question about the black hole:  Is it something of concern
for our planet either in the near future or thousands of years from now?"
 -M.H.*

First, there are no silly questions!   Einstein once asked the 'silly'
question, "What would  light beam look like if I could run next to one?"
We see where that question lead him.

Now, as to your question.  The closest known black hole, V616 Monocerotis,
is 3,460  light years away.        If that, indeed, is the closest black
hole to the solar system, we can breathe easy, at least about black holes.
 Our solar system and V616 Mon will come nowhere near each other.     That
having been said, it is possible that other black holes are closer.   We
know about the black hole within the V616 system because it has a visible
companion that exhibits motions that indicate the presence of a nearby
black hole.  We wouldn't be able to observe any isolated black holes that
might be closer.    However, we really shouldn't worry about them because
there are about 100 million scattered over the entire galaxy, which is
unfathomably large.     Also, notice that Earth is about 4.5 billion years
old -if you believe the heretics-.  If a black hole had ventured close to
our planet at all during those 4.5 billion years, Earth would have been
ripped apart.      No black hole yet and I do believe we're safe.

*"Why haven't they photographed the black hole in the center of our
galaxy?  Is that farther away than the black hole they did photograph?"  -
C.S.  *

Strangely enough, the black hole in the center of our galaxy, Sagittarius
A*, isn't massive enough to have been imaged in the same way that
astronomers imaged the supermassive black hole in the center of M87.  The
M87 black hole is 6.5 billion times more massive than the Sun, whereas
Sagittarius A* is about 4 million times more massive than our parent star.
  Consequently, the M87 black hole isn't nearly as turbulent as the one in
the center of the Milky Way.   In order to image such a black hole using
the array of telescopes, it must remain "still."   A highly massive black
hole will be stationary, whereas a "lighter" one will not, making it
exceedingly difficult to image.

*"Why are black holes located in the center of galaxies?"*
*-W.L. *

Astronomers are now convinced that each galaxy contains a supermassive
black hole in its center.    It turns out that one cannot have a galaxy
without a supermassive black hole to provide the gravitational pull
necessary to maintain the galaxy's cohesion.    The supermassive black hole
forms from the inner material contained with the galaxy.  One cannot have
one without the other.       The unresolved issue pertains to the formation
order: do they form together or does the supermassive black hole form
first?  We don't know.