Protostars

(Section Not Complete)

The image adjacent right shows starbirth regions in the Eagle Nebula (M16), which is about 7000 light years away in the constellation Serpens (Ref). The yellow rectangle in the inset indicates the region of the nebula blown up in the main part of the image. Here is a Hubble Space Telescope movie (780 kB MPEG) or equivalently a streaming animation (1.1 MB) of these star forming regions. This animation illustrates the location of these star forming regions in the sky.

The clouds are columns of cool molecular hydrogen and dust that that serve as incubators for new stars. The tallest is almost a light year in length! The finger-like protrusions at the top of the clouds are larger than the solar system and hide embryonic stars that are forming within them.

The pillars are being eroding away by photoevaporation caused by the ultraviolet light from nearby hot stars (approximately 100 young stars can be counted in this part of the nebula). This evaporation uncovers small globules of dense gas buried within the cloud that are termed EGGs ("Evaporating Gaseous Globules"). The finger-like structures at the top of the clouds are produced by the shadows of the EGGs, which protect the gas behind them from the intense UV flux.

The image adjacent left shows a region of star birth in the Triffid Nebula, which is approximately 9000 light years away in the constellation Sagittarius (Ref). There is a hot, young star above and to the right of this image. When it formed, its radiation and stellar wind swept away much of the gas in this region and only low-mass stars are presently forming here. The pillars visible in the image were more dense than their surroundings and thus have survived, though they too are being eroded by the radiation and wind from hot stars. The unusual jet of material that can be seen in the upper left is not well understood, though its source presumably lies hidden in the large left pillar. The red dots are newly formed low-mass stars.


The adjacent IR image from the 8.2 meter telescope of the European Southern Observatory shows a very young open cluster in which the stars are still immersed in the dust from which they were born. This cluster, which is designated RCW38 is about 5000 light years away in the constellation Vela. When we see most open clusters we don't see so much dust because the stars have had time to move away from the nebula in which they formed and to disperse the dust with radiation pressure. In this case the stars are so young that they are still hiding in the dust. In visible light they would be mostly obscured by the dust, but IR penetrates the dust much better and allows the open cluster to be imaged (Ref).



Time to Collapse
to the Main Sequence
Mass
(Solar Units)
Time
(Millions of Years)
0.5 100
1 30
2 8
5 0.7
15 0.16

In the preceding figure, most of the stars lying to the right appear to still be collapsing to the main sequence.

Herbig-Haro Objects

As young stars form, there often still remains substantial accreting matter around them. The new young star has strong solar winds associated with its just-born fusion reactions and matter trying to onto the star is thought to be heated and ejected in jets along the axis of rotation. As this ejected material slams into the gas in the interstellar medium it tends to form nebulosity at the ends of the oppositely directed jets. The following image (Ref) shows a Hubble Space Telescope observation of such a situation in the vicinity of the Orion Nebula (Source).

Such bright patches of nebulosity moving away from protostars and very young stars are called Herbig-Haro Objects. In the above image the young star responsible for the jets and the nebulae at either end of the jets is thought to be hidden in the dark dust cloud in the center of the image. The entire width of this image is about 1 light year.

The following Hubble Space Telescope image shows another jet from a young star (Source). Designated HH-47, this 3 trillion mile long jet originates from a star hidden in a dust cloud near the left edge of the image. The twisted nature of the jet suggests that the star emitting it is wobbling on its rotation axis, perhaps because of interaction with another star. The Herbig-Haro object HH-47 is about 1500 light years away, lying at the edge of the Gum Nebula, which is possibly an ancient supernova remnant.

Catalog of Herbig-Haro objects




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