Astronomers Spot The Great Orion Nebula's Successor (Forwarded)

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For Release: EMBARGOED until 12:30 p.m. EST, Wednesday, January 11, 2006

Release No.: 06-05

Astronomers Spot The Great Orion Nebula's Successor

Washington, DC -- Astronomers announced today that they have found the
next Orion Nebula. Known as W3, this glowing gas cloud in the
constellation Cassiopeia has just begun to shine with newborn stars.
Shrouds of dust currently hide its light, but this is only a temporary
state. In 100,000 years -- a blink of the eye in astronomical terms -- it
may blaze forth, delighting stargazers around the world and becoming the
Grand Nebula in Cassiopeia..

"The Grand Nebula in Cassiopeia will appear in our sky just as the Great
Nebula in Orion fades away," said Smithsonian astronomer Tom Megeath
(Harvard-Smithsonian Center for Astrophysics), who made the announcement
in a press conference at the 207th meeting of the American Astronomical
Society. "Even better, its home constellation is visible year-round from
much of the northern hemisphere."

The Orion Nebula is one of the most famous and easily viewed deep-sky
sights. It holds special significance for researchers as the nearest
region of massive star formation.

The star formation process begins in a dark cloud of cold gas, where small
lumps of material begin to contract. Gravity draws the gas into hot
condensations that ignite and become stars. The most massive stars produce
hot winds and intense light that blast away the surrounding cloud. But
during the process of destruction, stellar radiation lights up the cloud,
creating a bright nebula for stargazers to admire.

"Orion may seem very peaceful on a cold winter night, but in reality it
holds very massive, luminous stars that are destroying the dusty gas cloud
from which they formed," said Megeath. "Eventually, the cloud of material
will disperse and the Orion Nebula will fade from our sky."

Orion's Trapezium

Of special interest to Megeath is a system of four bright, massive stars
at the center of Orion known as the Trapezium. These stars bathe the
entire nebula with powerful ultraviolet radiation, lighting up nearby gas.
Even a modest telescope reveals the Trapezium surrounded by billowing
ripples of matter gleaming eerily across the vastness of space. Yet the
Trapezium is only the tip of the iceberg, surrounded by more than 1000
faint, low-mass stars similar to the Sun.

"The question we want to answer is: why are these massive stars sitting in
the center of the cluster?" said Megeath.

There are two competing theories to explain the Trapezium's location. One
holds that the Trapezium stars formed apart from each other but descended
to the center of the cluster, ejecting a spray of low-mass stars in the
process. The other leading theory is that the Trapezium stars formed
together in the center of the cluster and have not moved from their
birthplace.

"Obviously, we can't go back in time and look at the Trapezium when it was
still forming, so we try to find younger examples in the sky," explained
Megeath.

Such proto-Trapeziums would still be buried in their birth cocoons, hidden
to visible-light telescopes but detectable by radio and infrared
telescopes. Searches at those longer wavelengths have identified many
regions where massive stars are forming, but could not determine whether
the protostars were alone or in collections of four or more stars that
could be considered Trapeziums.

Cassiopeia's Trapezium

Megeath and his colleagues examined one such protostellar clump in W3
using the NICMOS instrument on NASA's Hubble Space Telescope and the
National Science Foundation's Very Large Array. They discovered that the
object, which was thought to be a binary star, actually contained four or
five young, massive protostars, making it a likely proto-Trapezium.

These protostars are so young that they appear to be still growing by
accreting gas from the surrounding cloud. All of the stars crowd into a
small area only about 500 billion miles across (just under one-tenth of a
light-year), making this cluster more than 100,000 times denser than stars
in the Sun's neighborhood. This suggests that the massive stars in Orion's
Trapezium formed together in the center of the cluster.

The same physical processes that have carved the Orion Nebula now are
molding the W3 nebula. The massive stars in this compact group are
starting to eat away at the surrounding gas with ultraviolet radiation and
fast stellar outflows. Eventually, they will destroy their dense cocoon
and emerge to form a new Trapezium in the center of W3. However, the final
form of the nebula and the time that it will reach maximum brilliance are
uncertain.

"Who knows, in 100,000 years the emerging Grand Nebula in Cassiopeia may
replace the fading Orion Nebula as a favorite object for amateur
astronomers," said Megeath. "In the meantime, I think it will be a
favorite target for professional astronomers trying to solve the riddle of
massive star formation."

Megeath's colleagues on this work were Thomas Wilson (European Southern
Observatory) and Michael Corbin (Arizona State University).

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.

Note to editors: High-resolution images to accompany this release are
online at
http://www.cfa.harvard.edu/press/pr0605image.html