THE SOUTHWORTH PLANETARIUM
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70 Falmouth Street  Portland, Maine 04103
43.6667° N,                    70.2667° W
Founded January 1970
        "Newton's 4th Law:  Never chose to kick the football when you
win the overtime coin toss!"



THE DAILY ASTRONOMER
Monday, December 28, 2015
Galactic Fusion



Looming high in our winter evening sky, and poised between the
circumpolar queen Cassiopeia and her recumbent daughter, Andromeda,
one will find the immensely large  Andromeda Galaxy.    Only when
viewed through a powerful telescope, will the Andromeda Galaxy's
magnificence be evident.    When otherwise observed, it appears as
little more than a light patch conspicuous only in the darkest skies.
    Over time, however, the Andromeda Galaxy is destined to brighten
as it moves closer to the Milky Way.    More correctly, the Andromeda
and Milky Way Galaxies are moving toward each other, propelled
inexorably by gravity toward a merger that will occur five to seven
billion years in the future.     This merger -we hesitate to employ
the verb "collision,"- will create a super galaxy populated by more
than one trillion stars!

The strange magic of mathematical astronomy enables astronomers to not
only estimate when this merger will occur, but also to understand what
will transpire between the galaxies during this encounter.    They
will likely describe elegant arcs around each other, reminiscent of
choreographed dancers who pirouette slowly apart prior to merging at a
common center.    Observations of other galactic mergers throughout
the Universe have lent astronomers insight into what happens when
these mammoth structures, well, collide.

Recently, an image captured by the Wide Field Planetary Camera 2 on
board the Hubble Space Telescope shows NGC 6502: two galaxies merging
230 million light years away.  (To see an image of this galaxy, go to:
  http://usm.maine.edu/planet/da-7-december-2015
     We are now posting the DA on our web-site.  These posts include
all associated images.]

This image provides a snap shot of a merger that will eventually
transform the individual galaxies into a larger system that might bear
little resemblance to either galaxy.  While most stars will become
incorporated into the mega-sized galaxy, many will be propelled into
the vast chasm of intergalactic space.  (Some astronomers estimate
that millions of "rogue" stars might be flying through the void
separating galaxies at this very moment.) Also, gas clouds within both
galaxies will experience gravitational compressions, which will then
initiate another wave of prodigious star formation.

Throughout our lifetime, we'll see very little change in NGC 6502.
An entire galactic merger sequence requires millions of years for
completion.      However, continued observations of this merger and
others will help us understand precisely what will happen billions of
years from now, when the Milky Way and Andromeda Galaxies combine into
one.     At the moment, they are 2.2 million light years away and
approaching each other at 300,000 miles an hour: a glacial pace by
galactic standards.