Explanation:
Where did all the stars go?
What used to be considered a hole in the sky
is now known to astronomers as a dark molecular cloud.
Here, a high concentration of
dust and
molecular gas
absorb practically all the visible light
emitted from background stars.
The eerily dark surroundings help make the interiors of
molecular clouds some of the coldest
and most isolated places in the universe.
One of the most notable of these
dark absorption nebulae
is a cloud toward the constellation
Ophiuchus known as Barnard 68,
pictured above.
That no stars are visible in the center indicates that
Barnard 68 is relatively nearby,
with measurements placing it about
500 light-years away and half a light-year across.
It is not known exactly how
molecular clouds like
Barnard 68 form, but it is known that these clouds are themselves
likely places
for new stars to form.
It is possible to
look right through the cloud in infrared light.
Lecture: APOD editor to give public talk in Princeton on April 11
