1.03 Star Birth

The constellation of Orion is one region of the night sky where interstellar nurseries are found. The first picture shows how a time exposure photograph brings out the rich colour of the different types of stars. Most of the nebula is not visible in this picture as the dust in the clouds absorbs light rather than radiating it. Some nebulosity is visible most noticeably the great nebula in the lower middle section of the image. The dust in the nebula obscures the light produced by the protostars and the newly formed stars that lie within the main cloud. As previously stated the dust content of the nebula is extremely small compared to the overall mass of the cloud (1 to 2 %). However it still enough to prevent the direct observation of star birth. The radiation from the forming stars however does heat the surrounding cloud. Therefore if we observe the infra red radiation from the same region of the sky the cloud is clearly visible as are the brighter regions where star formation is taking place. This can be seen in the second picture.

visible light image of orion
infra red image of orion

The images cover the same region of the sky. To help compare them the bright star to the left at the top edge of the image (Betelgeuse) is visible in both pictures. So too is the great nebula. In the infra red image the horse head nebula situated above the great nebula appears just as prominent.

Stellar wind

When a new star is born the nuclear reactions within the core create a stellar wind (a stream of high speed particles flowing outward from the star) this gradually blows away the remaining gas and dust surrounding the star. The photograph below shows a relatively young star cluster (The Pleiades cluster in the constellation of Taurus which is about 50 million years old) . Most of the nebula surrounding the original protostars has now been dispersed and the stars are clearly visible. The faint bluish haze around the stars still show the remains of the original dense nebula.

The Pleiades cluster

At this stage of its evolution the loss of mass due to the stellar wind is extremely small (our sun looses only about 10-14 of its total mass each year).