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Describe what happens in the nebula that turns it into a bok globule. Describe the differences between the nebula and the bok globule in terms of: which has a higher temperature, how is their spectrum different, and what forces are acting on each object.
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To understand the process of how a nebula transforms into a Bok globule, let's first define what each of these objects is.
A nebula is a vast cloud of gas and dust in space. It is often the birthplace of stars and contains a wide range of temperatures, densities, and chemical compositions.
A Bok globule, on the other hand, is a small, dark, and dense region within a molecular cloud that is undergoing gravitational collapse. These globules are typically colder, more compact, and more isolated than the surrounding nebula.
Now, let's look at the differences between a nebula and a Bok globule in terms of temperature, spectrum, and forces acting on them:
1. Temperature:
In general, a nebula has a higher temperature compared to a Bok globule. Nebulas are often heated by nearby stars or energy from other astrophysical processes, which can raise their temperatures to thousands of degrees Kelvin. In contrast, Bok globules are colder and can have temperatures as low as a few degrees above absolute zero.
2. Spectrum:
The spectrum of a nebula is typically characterized by emission lines, which are caused by the ionization of atoms or molecules due to the high energy present in the nebula. These lines can reveal the presence of specific elements or molecules within the nebula. On the other hand, the spectrum of a Bok globule is dominated by absorption lines or features caused by the presence of dust grains that scatter or absorb light. These absorption features can provide information about the composition and physical conditions inside the globule.
3. Forces:
In a nebula, various forces are at play. These include gravitational forces, radiation pressure from stars, stellar winds, and magnetic fields. These forces can shape the nebula, cause gas and dust to move or disperse, and trigger the formation of new stars.
In contrast, a Bok globule is primarily influenced by gravity. The self-gravity of the globule causes it to collapse under its own weight, leading to the formation of a protostar at its core. As the collapse progresses, the dense core becomes more isolated and shielded from external influences.
In summary, a nebula is a vast cloud of gas and dust with higher temperatures, characterized by emission lines in its spectrum and influenced by various forces. In contrast, a Bok globule is a smaller, colder, and denser region within a molecular cloud, with absorption lines in its spectrum, and primarily influenced by gravity as it undergoes collapse.