July 10, 2001
Photo No: H2001-25
Hubble Snaps Picture of Remarkable Double Cluster
The double cluster NGC 1850, found in one of our neighboring
galaxies, the Large Magellanic Cloud, is an eye-catching object. It is
a young, "globular-like" star cluster -- a type of object unknown in
our own Milky Way Galaxy. Moreover, NGC 1850 is surrounded
by a filigree pattern of diffuse gas, which scientists believe was
created by the explosion of massive stars.
NGC 1850, imaged here with the NASA Hubble Space Telescope,
is an unusual double cluster that lies in the bar of the Large
Magellanic Cloud, a satellite galaxy of our own Milky Way. After
the 30 Doradus complex, NGC 1850 is the brightest star cluster in
the Large Magellanic Cloud. It is representative of a special class
of objects -- young, globular-like star clusters -- that have no
counterpart in our galaxy. The two components of the cluster are
both relatively young and consist of a main, globular-like cluster in
the center and an even younger, smaller cluster, seen below and
to the right, composed of extremely hot, blue stars and, fainter red
T-Tauri stars. The main cluster is about 50 million years old; the
smaller cluster is only 4 million years old.
One of Hubble's main contributions to the study of NGC 1850 is in
the investigation of star formation at both ends of the stellar mass
scale -- the low-mass T-Tauri stars and the high-mass OB stars.
T-Tauri stars are young, solar-class stars that are still forming, so
young that they may have not started converting hydrogen to helium,
which is how our Sun produces its energy. Instead they radiate energy
released by their own gravitational contraction. By investigating
these stars astronomers learn about the births and lives of low-mass
stars. T-Tauri stars tend to occur in crowded environments, but are
themselves faint, making them difficult to distinguish with
ground-based telescopes. However, Hubble's fine angular resolution
can pick out these stars, even in galaxies other than our own.
Hubble also has advantages when studying very massive stars. These
stars emit large amounts of energetic ultraviolet radiation, which is
absorbed by the Earth's atmosphere. From its position above the
atmosphere, Hubble can detect ultraviolet light from these massive
stars. The Hubble data can then be analyzed and used to characterize
the stars' properties.
This Hubble image is a good example of the interaction between gas,
dust, and stars. Millions of years ago massive stars in the main
cluster exploded as supernovas, forming the spectacular filigree
pattern of diffuse gas visible in the image. It is believed that the
birth of new stars can be triggered by the enormous forces in the
shock fronts where the supernova blast waves hit and compress the
gas. The nebulous gas is part of the N103 super bubble and looks
similar to the well-known supernova remnant Cygnus Loop in our
own Milky Way.
NGC 1850 lies in the southern constellation of Dorado, the Goldfish,
sometimes known as the Swordfish. This image was created from
five archival exposures obtained with Hubble's Wide Field Planetary
Camera 2 between April 3, 1994 and February 6, 1996.
Image credits: NASA, ESA, and Martino Romaniello (European Southern