HUBBLE PEEKS INTO A STELLAR NURSERY IN A NEARBY GALAXY
NASA's Hubble Space Telescope has
peered deep into a neighboring galaxy to reveal
details of the formation of new stars. Hubble's
target was a newborn star cluster within the Small
Magellanic Cloud, a small galaxy that is a satellite
of our own Milky Way. The new images show young,
brilliant stars cradled within a nebula, or glowing
cloud of gas, cataloged as N 81.
These massive, recently formed stars
inside N 81 are losing material at a high rate,
sending out strong stellar winds and shock waves
and hollowing out a cocoon within the surrounding
nebula. The two most luminous stars, seen in the
Hubble image as a very close pair near the center
of N 81, emit copious ultraviolet radiation, causing
the nebula to glow through fluorescence.
Outside the hot, glowing gas is cooler
material consisting of hydrogen molecules and dust.
Normally this material is invisible, but some of
it can be seen in silhouette against the nebular
background,as long dust lanes and a small, dark,
elliptical-shaped knot. It is believed that the
young stars have formed from this cold matter through
Few features can be seen in N 81
from ground-based telescopes, earning it the informal
nick-name "The Blob." Astronomers were not sure
if just one or a few hot stars were embedded in
the cloud, or if it was a stellar nursery containing
a large number of less massive stars. Hubble's high-resolution
imaging shows the latter to be the case, revealing
that numerous young, white-hot stars---easily visible
in the color picture---are contained within N 81.
This crucial information bears strongly
on theories of star formation, and N 81 offers a
singular opportunity for a close-up look at the
turbulent conditions accompanying the birth of massive
stars. The brightest stars in the cluster have a
luminosity equal to 300,000 stars like our own Sun.
Astronomers are especially keen to study star formation
in the Small Magellanic Cloud, because its chemical
composition is different from that of the Milky
Way. All of the chemical elements, other than hydrogen
and helium, have only about one-tenth the abundances
seen in our own galaxy.
The study of N 81 thus provides an
excellent template for studying the star formation
that occurred long ago in very distant galaxies,
before nuclear reactions inside stars had synthesized
the elements heavier than helium.
The Small Magellanic Cloud, named
after the explorer Ferdinand Magellan, lies 200,000
light-years away, and is visible only from the Earth's
southern hemisphere. N 81 is the 81st nebula cataloged
in a survey of the SMC carried out in the 1950's
by astronomer Karl Henize, who later became an astronomer-astronaut
who flew into space aboard NASA's space shuttle.
The Hubble Heritage image of N 81
is a color representation of data taken in September,
1997, with Hubble's Wide Field Planetary Camera
2. Color filters were used to sample light emitted
by oxygen ([O III]) and hydrogen (H-alpha, H-beta).
N 81 is the target of investigations
by European astronomers Mohammad Heydari-Malayeri
from the Paris Observatory in France; Michael Rosa
from the Space Telescope-European Coordinating Facility
in Munich, Germany; Hans Zinnecker of the Astrophysical
Institute in Potsdam, Germany; Lise Deharveng of
Marseille Observatory, France; and Vassilis Charmadaris
of Cornell University, USA (formerly at Paris Observatory).
Members of this team are interested in understanding
the formation of hot, massive stars, especially
under conditions different from those in the Milky
Credit: NASA and The Hubble
Heritage Team (STScI/AURA)
Acknowledgment: Mohammad Heydari-Malayeri (Paris