NGC1850

VLT Observes a Double Stellar Cluster in the LMC

Supernovae Induce Star Formation

NGC 1850 is a double cluster in the Large Magellanic Cloud, a
satellite galaxy to the Milky Way Galaxy, deep in the southern
sky. This cluster is representative of a class of objects, young,
globular-like stellar associations, that has no counterpart in our own
Galaxy.

The peculiarity of NGC 1850 lies in its double nature: it is composed
of a main cluster which is about 40 million years old, and a second,
smaller, one (to the right of the main cluster in PR Photo 15/99) that
is only 4 million years old and is mostly composed of extremely hot
stars.

It is estimated that about 1000 stars in the main cluster have
exploded as supernovae during the past 20 million years. One theory
maintains that the birth of the younger cluster was caused by the
combined effect of these titanic explosions on the residual gas clouds
around the main cluster. They were compressed until they started to
form stars and hence a new cluster.

          ESO PR Photo 15/99 

          [Preview - JPEG: 800 x 874 pix - 1062k] 

          [High-Res - JPEG: 1040 x 1136 pix - 1.4M]

          PR Photo 15/99 is a colour a composite of three individual
exposures, taken with FORS1 at the VLT UT1 on 3 February 1999. They
were obtained through B (blue), V (green), and H-alpha (red) filters,
and each of them was bias-subtracted and flat-fielded before
combination. The field-of-view is 6.8 x 6.8 arcmin2, corresponding to
an area of just over 300 x 300 light-years2 at the distance of the
Large Magellanic Cloud. The exposure times were 60, 60 and 450 seconds
and the image quality was 1.0, 0.7 and 0.8 arcsec (FWHM) for the B, V,
and H-alpha frames, respectively. The intensity scale is linear for
the B and V images and logarithmic for H-alpha, in order to enhance
the fine structure of the faintest parts of the nebulosity. North is
33° to the right of the vertical.

PR Photo 15/99 is a composite of blue and green images plus an image
in the light of Hydrogen. It shows that there is indeed still much gas
around NGC 1850.

While part of this may well be the remnant of the "parent" gas cloud
(i.e. the one from which both clusters were born), the presence of
filaments and of various sharp "shocks", e.g. to the left and below
NGC 1850, offers support to the theory of supernova-induced star birth
in the younger of the two clusters. Some "protostars" are located near
or in some of the filaments - this is interpreted as additional
evidence for that theory.

The nebulosity directly above the main cluster, that is shaped like a
"3", is the well-known supernova remnant N57D which itself may also be
associated with NGC 1850.