eso9918 — Photo Release
VLT Observes a Double Stellar Cluster in the LMC
Supernovae Induce Star Formation
27 February 1999
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 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.
The image 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.
The image 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 arcmin 2, corresponding to an area of just over 300 x 300 light-years 2 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
ESO Press Photo eso9918is 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.