SUPERNOVA SHOCK WAVE PAINTS COSMIC PORTRAIT
Remnants from a star that exploded thousands of
years ago
created a celestial abstract portrait, as captured
in this
NASA Hubble Space Telescope image of the Pencil
Nebula.
Officially known as NGC 2736, the Pencil Nebula
is part of
the huge Vela supernova remnant, located in the
southern
constellation Vela. Discovered by Sir John Herschel
in
the 1840s, the nebula's linear appearance triggered
its
popular name. The nebula's shape suggests that it
is part
of the supernova shock wave that recently encountered
a
region of dense gas. It is this interaction that
causes
the nebula to glow, appearing like a rippled sheet.
In this snapshot, astronomers are looking along
the edge
of the undulating sheet of gas. This view shows
large,
wispy filamentary structures, smaller bright knots
of gas,
and patches of diffuse gas. The Hubble Heritage
Team used
the Advanced Camera for Surveys in October 2002
to observe
the nebula. The region of the Pencil Nebula captured
in this
image is about three-fourths of a light-year across.
The Vela
supernova remnant is 114 light-years (35 parsecs)
across. The
remnant is about 815 light-years (250 parsecs) away
from our
solar system.
The nebula's luminous appearance comes from dense
gas regions
that have been struck by the supernova shock wave.
As the
shock wave travels through space [from right to
left in the
image], it rams into interstellar material. Initially
the gas
is heated to millions of degrees, but then subsequently
cools
down, emitting the optical light visible in the
image.
The colors of the various regions in the nebula
yield clues
about this cooling process. Some regions are still
so hot
that the emission is dominated by ionized oxygen
atoms, which
glow blue in the picture. Other regions have cooled
more and
are seen emitting red in the image (cooler hydrogen
atoms).
In this situation, color shows the temperature of
the gas.
The nebula is visible in this image because it is
glowing.
The supernova explosion left a spinning pulsar
at the core
of the Vela region. Based on the rate at which the
pulsar
is slowing down, astronomers estimate that the explosion
may have occurred about 11,000 years ago. Although
no
historical records of the blast exist, the Vela
supernova
would have been 250 times brighter than Venus and
would
have been easily visible to southern observers in
broad
daylight. The age of the blast, if correct, would
imply
that the initial explosion pushed material from
the star
at nearly 22 million miles per hour. As the Vela
supernova
remnant expands, the speed of its moving filaments,
such as
the Pencil Nebula, decreases. The Pencil Nebula,
for example,
is moving at roughly 400,000 miles per hour.
Credit: NASA and The Hubble Heritage Team
(STScI/AURA)
Acknowledgment: W. Blair (JHU) and
D. Malin (David Malin Images)
|
