Light Echoes from V838
Mon
From NASA’s Astronomy Picture of the Day
What caused this
outburst of V838 Mon? For reasons unknown,
star V838 Mon's
outer surface suddenly greatly expanded with the result that it became the
brightest star in the entire Milky Way Galaxy in
January 2002.
Then, just as suddenly,
it faded. A stellar flash like
this had never been seen before -- supernovas and novas expel
matter out into space.
Although the V838 Mon flash
appears to expel material into space, what is seen in the above
image from the Hubble
Space Telescope is actually an outwardly moving light echo of the
bright flash.
In a light echo, light
from the flash is reflected by successively more distant rings in
the complex array of ambient interstellar dust that
already surrounded the star.
V838
Mon lies about 20,000 light years away
toward the constellation of
the unicorn (Monoceros),
while the light echo above
spans about six light
years in diameter.
