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The Latin word ‘nebula’, it would simply mean ‘cloud’. The nebula that we are about to talk about, however, is so much more than just a cloud. So what is a nebula?

A nebula is an interstellar cloud in outer space that is made up of dust, hydrogen and helium gas, and plasma. It is formed when portions of the interstellar medium collapse and clump together due to the gravitational attraction of the particles that comprise them.

For those who are not aware of this yet, outer space is not really totally a vacuum (although it may sometimes be approximated as such). Rather, it is made up of gas and dust known collectively as the interstellar medium or ISM. So, it is this dispersed matter that eventually collapses and forms a nebula.
Nebulae, like the Orion Nebula, are often favorite astronomical objects of scientists who want to learn more about stellar or planetary formation. You see, parts of a nebula may clump together some more. The gravitational forces between particles is directly proportional to the their masses, remember?

Thus, the more masses clump together, the greater their gravitational attraction will be to other bodies and particles in their vicinity. As the particles clump further to form larger and more massive structures, they attract more dust and gas. The pressure inside then gets so high that nuclear fusion ensues. This results in the emission of high-energy electromagnetic radiation, which in turn ionizes the outer layers of gas.

Ionized gas is plasma, and so plasma and electromagnetic radiation are now added to the mix. This now becomes the earliest stages of star formation, and is what some scientists are most interested about.
Actually, nebulae are not just the starting points of stellar evolution. Ironically, they can also be the end points. You can think of this as the nebula-star-nebula cycle. Stars that evolve into red giants can lose their outer layers during pulsations in their outer layers, known as their atmospheres. This released matter is typically 97% hydrogen and 3% helium, with a few other trace materials.

It is this released matter that forms what is known as a planetary nebula. The planetary nebula is just one of four major types of nebulae. The other three are H II regions, supernova remnant, and dark nebula.
Some of the more prominent nebulae are the Crab, Eagle, Orion, Pelican, Ring, and Rosette Nebula.

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