THE SOUTHWORTH PLANETARIUM
207-780-4249       www.usm.maine.edu/planet
70 Falmouth Street  Portland, Maine 04103
43.6667° N,                    70.2667° W
Founded January 1970
              "Wonder about what?"



THE DAILY ASTRONOMER
Tuesday, March 8, 2016
The Most Distant Known Galaxy


We wonder if the Hubble Space Telescope, though technically an
inanimate object, might be afflicted with a severe inferiority
complex.   A psychoanalyst who specializes in orbit-bound space craft
might conclude that such a complex stems from the Hubble Space
Telescope's early post-deployment days (1990). During its
construction, its main mirror was ground half a shade (a micron) too
fine.   This error resulted in astigmatism which prevented it from
capturing clear images.  NASA scientists only became aware of this
mistake when the HST started conveying Rorschach blobs that should
have appeared as galaxies.    Though it was heralded as a masterwork
prior to deployment, the Hubble Space Telescope quickly became an
abject laughingstock: orbiting helplessly above an Earth that must
have seemed like a rowdy school bus resounding with derisive guffaws.

Only in 1993, when Space Shuttle astronauts repaired its damaged
optics, did the HST start performing up to its potentialities.
Breathless awe replaced cruel laughter.  Respect replaced ridicule and
the Hubble Space Telescope has been a highly esteemed, nay, revered
spacecraft ever since.    Yet, though its accomplishments have been
innumerable and the clarity of its images unrivaled, the Hubble Space
Telescope behaves as though it still has something to prove.    After
all, the victims of ridicule feel it sting long after their
antagonists have forgotten all about it.     Moreover, in 2018, the
James Webb Telescope, Hubble's "successor," is due to be launched and
the accolades that have been heaped onto Hubble like so much
descending confetti will be directed toward this presumptuous upstart.

Perhaps it is for this reason that the Hubble Space Telescope captured
an image GN-z11, the most distant galaxy yet observed.   This
billion-solar mass behemoth is so far away that astronomers believed
that only the Webb Telescope would have been able to image it. Well,
there, then!

An international team of astronomers used the Hubble Space Telescope's
Wide Field Camera 3 (WFC3) to discover this infant galaxy deeply
embedded in the darkness with the constellation Ursa Major.    Through
analysis of its spectrum,*  they estimate that this galaxy formed
merely 400 million years after the Big Bang!      Though this time
period seems long to us mortals, it is not much time for entire
galaxies to take form after the Universe was born.   Astronomers
actually once believed that a galaxy couldn't develop in such a brief
time span.      This discovery has compelled them to re-evaluate their
previous assumptions.

This galaxy is twenty five times smaller than the Milky Way and
contains only one percent of our galaxy's mass: about a billion times
more massive than the Sun.     However, it is seen to be accumulating
matter at a prodigious rate, indicating that the process by which
galaxies form is more rapid than once believed.

This finding have excited astronomers who are now confident that
they'll find other comparably young galaxies after the Webb Space
Telescope is deployed.   They most assuredly will, but, please don't
say that to the Hubble Space Telescope.





*The light emitted from a distant source is 'split' into its component
colors, or its spectrum.    By studying the positions of absorption
lines within the spectrum can they determine the galaxy's recession
speed.    These lines occupy fixed positions when the light source is
stationary.  When the light source moves, the lines shift: toward the
blue end when approaching and toward the red end when receding.
This shift occurs because the light waves are either compressed or
elongated by the object's motion in the same manner that a police
siren's waves are stretched or pushed together due to the cruiser
motion.     By measuring this shift, astronomers can determine the
celestial object's speed.    Through Hubble's Law, this speed relates
directly to the object's distance.  The greater the recession speed,
the more distant the object.