FIRESTORM OF STAR
BIRTH SEEN IN A LOCAL GALAXY
This festively colorful nebula, called NGC 604,
is one of the largest known seething cauldrons of
star birth in a nearby galaxy. NGC 604 is similar
to familiar star-birth regions in our Milky Way
galaxy, such as the Orion Nebula, but it is vastly
larger in extent and contains many more recently
This monstrous star-birth region contains more
than 200 brilliant blue stars within a cloud of
glowing gases some 1,300 light-years across, nearly
100 times the size of the Orion Nebula. By contrast,
the Orion Nebula contains just four bright central
stars. The bright stars in NGC 604 are extremely
young by astronomical standards, having formed a
mere 3 million years ago.
Most of the brightest and hottest stars form a
loose cluster located within a cavity near the center
of the nebula. Stellar winds from these hot blue
stars, along with supernova explosions, are responsible
for carving out the hole at the center. The most
massive stars in NGC 604 exceed 120 times the mass
of our Sun, and their surface temperatures are as
hot as 72,000 degrees Fahrenheit (40,000 Kelvin).
Ultraviolet radiation floods out from these hot
stars, making the surrounding nebular gas fluoresce.
NGC 604 lies in a spiral arm of the nearby galaxy
M33, located about 2.7 million light-years away
in the direction of the constellation Triangulum.
M33, a member of the Local Group of galaxies that
also includes the Milky Way and the Andromeda Galaxy,
can be seen easily with binoculars. NGC 604 itself
can be seen with a small telescope, and was first
noted by the English astronomer William Herschel
in 1784. Within our Local Group, only the Tarantula
Nebula in the Large Magellanic Cloud exceeds NGC
604 in the number of young stars, even though the
Tarantula Nebula is slightly smaller in size.
NGC 604 provides Hubble astronomers with a nearby
example of a giant star-birth region. Such regions
are small-scale versions of more distant "starburst"
galaxies, which undergo an extremely high rate of
star formation. Such starbursts are believed to
have been common in the early universe, when the
star-formation rate was much higher. Supernovae
exploding in these galaxies created the first chemical
elements heavier than hydrogen and helium.
The image of NGC 604 was assembled from observations
taken with Hubble's Wide Field Planetary Camera
2 in 1994, 1995, and 2001. Color filters were used
to isolate light emitted by hydrogen, oxygen, nitrogen,
and sulfur atoms in the nebula and ultraviolet,
visible and infrared light from the stars within
NGC 604 and the nearby spiral arms of M33. Image
processors from the Hubble Heritage team at the
Space Telescope Science Institute combined these
various filter images to create this color picture.
Credit: NASA and The Hubble Heritage Team
Acknowledgment: D. Garnett (U. Arizona),
J. Hester (ASU), and J. Westphal (Caltech)
Special Thanks: Lindsay
Sargeant (RIT/Heritage Summer Intern 2003)