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Reflection
Nebula
Just
weeks
after NASA
astronauts
repaired
the Hubble
Space
Telescope
in
December
1999, the
Hubble
Heritage
Project
snapped
this
picture of
NGC 1999,
a
reflection
nebula in
the
constellation
Orion.
Like fog
around a
street
lamp, a
reflection
nebula
shines
only
because
the light
from an
embedded
source
illuminates
its dust;
the nebula
does not
emit any
visible
light of
its own.
The nebula
is famous
in
astronomical
history
because
the first
Herbig-Haro
object was
discovered
immediately
adjacent
to it (it
lies just
outside
the new
Hubble
image).
Herbig-Haro
objects
are now
known to
be jets of
gas
ejected
from very
young
stars.
The nebula
is
illuminated
by a
bright,
recently
formed
star,
visible
just to
the left
of center.
This star
is
cataloged
as V380
Orionis,
and its
white
color is
due to its
high
surface
temperature
of about
10,000
degrees
Celsius,
nearly
twice that
of our own
sun. Its
mass is
estimated
to be 3.5
times that
of the
sun. The
star is so
young that
it is
still
surrounded
by a cloud
of
material
left over
from its
formation,
here seen
as the NGC
1999
reflection
nebula.
NGC 1999
shows a
remarkable
jet-black
cloud near
its
center,
located
just to
the right
and lower
right of
the bright
star. This
dark cloud
is an
example of
a "Bok
globule,"
named
after the
late
University
of Arizona
astronomer
Bart Bok.
The
globule is
a cold
cloud of
gas,
molecules
and cosmic
dust,
which is
so dense
it blocks
all of the
light
behind it.
The
globule is
seen
silhouetted
against
the
reflection
nebula
illuminated
by V380
Orionis.
Astronomers
believe
that new
stars may
be forming
inside Bok
globules,
through
the
contraction
of the
dust and
molecular
gas under
their own
gravity. |
