Press Release

Hubble’s Panoramic Portrait of a Vast Star-Forming Region

By SpaceRef Editor
July 26, 2001
Filed under , ,

A panoramic view of a vast, sculpted area of gas and dust
where thousands of stars are being born has been captured by
NASA’s Hubble Space Telescope.

The image, taken by Hubble’s Wide Field and Planetary
Camera 2, is online at
http://oposite.stsci.edu/pubinfo/pr/2001/21 and
http://www.jpl.nasa.gov/images/wfpc . The camera was designed
and built by NASA’s Jet Propulsion Laboratory, Pasadena,
Calif.

The photo offers an unprecedented, detailed view of the
entire inner region of the fertile, star-forming 30 Doradus
Nebula. The mosaic picture shows that ultraviolet radiation
and high-speed material unleashed by the stars in the cluster,
called R136 (the large blue blob left of center), are weaving
a tapestry of creation and destruction, triggering the
collapse of looming gas and dust clouds and forming pillar-
like structures that incubate newborn stars.

The 30 Doradus Nebula is in the Large Magellanic Cloud, a
satellite galaxy of the Milky Way located 170,000 light-years
from Earth. Nebulas like 30 Doradus are signposts of recent
star birth. High-energy ultraviolet radiation from young,
hot, massive stars in R136 causes surrounding gaseous material
to glow. Previous Hubble telescope observations showed that
R136 contains several dozen of the most massive stars known,
each about 100 times the mass of the Sun and about 10 times as
hot. These stellar behemoths formed about 2 million years ago.

The stars in R136 produce intense “stellar winds,”
streams of material traveling at several million miles an
hour. These winds push the gas away from the cluster and
compress the inner regions of the surrounding gas and dust
clouds (seen in the image as the pinkish material). The
intense pressure triggers the collapse of parts of the clouds,
producing a new star formation around the central cluster.
Most stars in the nursery are not visible because they are
still encased in cocoons of gas and dust.

This mosaic image of 30 Doradus consists of five
overlapping pictures taken between January 1994 and September
2000 by the Wide Field and Planetary Camera 2. Several color
filters enhance important details in the stars and the nebula.
Blue corresponds to the hot stars. The greenish color denotes
hot gas energized by the central cluster of stars. Pink
depicts the glowing edges of the gas and dust clouds facing
the cluster, which are being bombarded by winds and radiation.
Reddish-brown represents the cooler surfaces of the clouds,
which are not receiving direct radiation from the central
cluster.

Additional information about the Hubble Space Telescope
is at http://www.stsci.edu . More information about the Wide
Field and Planetary Camera 2 is at http://wfpc2.jpl.nasa.gov .

The Space Telescope Science Institute, Baltimore, Md.,
manages space operations for Hubble for NASA’s Office of Space
Science, Washington, D.C. The institute is operated by the
Association of Universities for Research in Astronomy, Inc.,
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. JPL is a division of the California Institute of
Technology in Pasadena.

Background Text: Hubble Space Telescope’s Wide Field Camera Reveals
Splendor of ‘Supergiant’ Nebula

The 30 Doradus Nebula is the largest object of its
kind in the Local Group of galaxies, which includes Andromeda (M31),
Triangulum (M33), our Milky Way, and numerous smaller systems. The
nebula is relatively nearby, located in a small satellite galaxy
of the Milky Way called the Large Magellanic Cloud, 170,000 light-years
from Earth. (A light-year is the distance light travels in one year
at a speed of 186,000 miles per second, or about 6 trillion miles.)

Such nebulae, which astronomers call "ionized hydrogen regions,"
are the "signposts" of recent star birth. High-energy
ultraviolet radiation from young, short-lived, massive, hot stars
causes the surrounding gaseous material to glow by fluorescent processes.
In keeping with its premier status, the most spectacular cluster
of massive stars in the Local Group powers 30 Doradus. This compact
cluster is called R136, so named because of its designation in an
early catalogue of the brightest stars in the Magellanic Clouds,
compiled at the Radcliffe Observatory in South Africa. Hubble telescope
observations have shown that R136 contains several dozen of the
most massive stars known, each about 100 times the mass of Sun and
about 10 times as hot. The cluster also harbors many thousands of
smaller stars. For many years it defied analysis from ground-based
observations, and was once even suggested to be a single "superstar,"
about 3,000 times the mass of the Sun!

30 Doradus is a "Rosetta Stone" for understanding regions
of intense star formation, because it is near enough to Earth for
its stellar contents and nebular structures to be studied in detail
by the Hubble telescope. Even larger clusters and nebulae, called
starbursts, exist in the more distant universe, but they cannot
be resolved in comparable detail. Such objects are vital contributors
to the evolution of galaxies and even life, because massive stars
synthesize many of the heavier chemical elements in their nuclear
furnaces and final supernova explosions. The explosions disperse
the heavy elements to the surrounding interstellar medium, where
new stars and planetary systems form from the enriched material.

This image of 30 Doradus is a mosaic of five overlapping pointings
taken by the Hubble Telescope’s Wide Field Camera. Astronomers combined
several color filters to display different stellar and nebular features.
The picture covers a field of 200 by 150 light-years and for the
first time shows the full structure of the inner 30 Doradus Nebula
at Hubble’s resolution.

The Hubble telescope has provided at least two major advances in
our understanding of giant nebulae. First, it has shown that they
are not uniformly filled with glowing gas as previously thought.
Rather, the brightest emission occurs at narrow interfaces between
a central cavity, where massive stars are propelling gas outward,
and the surrounding dense dust and gas clouds. The radiation produced
by massive stars is so intense that it blows off the stars’ outer
layers in "stellar winds." These winds, in turn, push
surrounding gas outward from the stellar cluster, generating compression
zones at the inner faces of the clouds. This pressure can trigger
the collapse of parts of the clouds, producing a new generation
of star formation around the original cluster’s periphery.

The second Hubble telescope revelation about such regions is that
this process of "triggered" star formation often, or perhaps
always, involves massive dust and gas pillars oriented toward the
central cluster. Such pillars form when a particularly dense dust
and gas concentration shields material behind it from evaporation
and dissipation by the energy coming from the stars. Observations
at radio and infrared wavelengths, which can penetrate the dust,
show that the same process creates new stars in the heads of the
pillars. The new image of 30 Doradus reveals the full extent of
the interfaces surrounding the central cluster and shows numerous
dust and gas pillars oriented toward the cluster on or near the
interfaces. Newborn stars within several of the pillars already
have been discovered in images taken by the Hubble telescope’s infrared
camera, the Near Infrared Camera and Multi-Object Spectrometer.

Hubble telescope observations of other nebulae, together with those
of 30 Doradus, provide a time sequence of the gestation and birth
of new stars within pillars surrounding the initial cluster. The
story begins with the famous Eagle Nebula (M16) pillars. They contain
few bright infrared sources, but radio astronomers subsequently
discovered luminous sources in the heads of the pillars. These bright
objects are almost certainly protostars, which are still too cool
to emit at infrared wavelengths. But they will continue to collapse
and heat up until they do. Hubble telescope images of NGC 3603,
the largest optically visible nebula in the Milky Way, show two
massive pillars pointing toward its central cluster. Although smaller,
this cluster bears a striking resemblance to R136.

Observations by the Hubble telescope’s infrared camera have found
luminous infrared sources within several of the 30 Doradus pillars.
Moreover, images taken by the Hubble telescope’s Wide Field and
Planetary Camera 2 also reveal one young triple-stellar system that
was just born by blowing off the top of its natal pillar with its
own energetic radiation and winds. These new stars are probably
just a few hundred thousand years old, whereas R136 is about 2 million
years old. (For comparison, the Sun is 4.5 billion years old, and
its total lifespan will be 10 billion years.)

Hubble telescope pictures of other objects also allow astronomers
to trace the overall evolution of the giant nebulae, and on even
larger scales, that of entire starburst galaxies, which are often
composed of multiple giant nebulae and clusters. Central regions
that are completely devoid of gas characterize a class of nebulae
called giant shells. Only an older cluster — about 4 million
years old — remains there. The most massive stars in this central
cluster already have disappeared, since the lifetimes of stars are
inversely related to their masses. The glowing gas is located around
the periphery and is powered by a younger generation of more massive
stars. An example is NGC 604 in M33.

It is easy to foresee that 30 Doradus will become a giant shell
nebula in another 2 million years, when the most massive stars will
be gone from the central cluster. However, the new generation of
massive stars around the periphery will be in full bloom. Still
later, all of the most massive stars and nebulosity will have disappeared
from the region. Only older stellar clusters without nebulae will
remain.

Moreover, Hubble telescope images of the global structure of starburst
galaxies like NGC 4214 and the Antennae show that different regions
within them are composed of giant nebulae and clusters of different
ages, so that the temporal progression of star formation episodes
can be traced throughout. But detailed studies of nearby objects,
such as 30 Doradus, are essential to support such inferences about
the more distant ones, in which individual stars and nebular structures
cannot be resolved.

SpaceRef staff editor.