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.

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: W. Blair (JHU) and D. Malin (David Malin Images)

NOTE TO EDITORS: For additional information, please contact
William P. Blair, Department of Physics and Astronomy, Johns Hopkins
University, 3400 North Charles Street, Baltimore, MD 21218-2686,
(phone) 410-516-8447, (fax) 410-516-5494, (e-mail) wpb@pha.jhu.edu or

Keith Noll, Hubble Heritage Team, Space Telescope Science
Institute, 3700 San Martin Drive, Baltimore, MD 21218, (phone)
410-338-1828, (fax) 410-338-4579, (e-mail) noll@stsci.edu

Electronic images and additional information are available at

The Space Telescope Science Institute (STScI) is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA),
for NASA, under contract with the Goddard Space Flight Center,
Greenbelt, MD. The Hubble Space Telescope is a project of
international cooperation between NASA and the European Space
Agency (ESA).