Therefore it radiates away net energy its temperature drops, the internal pressure drops and the contraction continues. A new equilibrium is established with a smaller cloud which is hotter than before, especially in comparison with its surrounding environment. At the same time, because the cloud is now smaller, its density must be greater hence its internal pressure has now increased to oppose the collapse. There are indeed some gravity-assist forces around but beyond the scope of this introduction.īut as the cloud collapses, gravitational potential energy is being released which then begins to heat up the gas. How then does the cloud collapse to form stars? If the cloud can be forced (by some kind of gravity-assist force) to shrink just a little bit without the internal pressure rising, then the situation is taken out of balance in favour of gravity and gravity begins to take control. They radiate energy but they also receive energy in the form of electromagnetic radiation from the surrounding environment. This is the case with the interstellar clouds. It can continue to do so until the net loss of energy is zero that is, the energy it radiates of itself is replenished by the radiation it absorbs from its surroundings. As it cools its internal pressure will decrease and therefore the cloud will shrink a bit. The internal pressure counteracts the gravitational forceīut any non-zero temperature body will radiate away a net amount of energy and so will cool. In the same way when you are sitting in a chair, it is the electrons in your clothes which are repelled by the electrons in the chair which prevent you from falling "through" the chair.Īs far as the gas is concerned, at non-zero temperatures (on the Kelvin scale) it always supplies a positive pressure which depends on the density of the gas and its temperature. In a collision between atoms, the electrons which surround the nucleus first come into "contact" like charges repel, and therefore provide an opposing force to gravity. In terms of our gas cloud the force which stops the atoms fusing together is the electromagnetic force. Of the other 3 only the electromagnetic force and the nuclear force participate in providing the sorts of pressure we are considering. We do not have to look very far because there are only 4 forces in nature of which gravity is one. Pressure is a sort of a force (it is the force per unit area) but we need to know what the forces actually are. ![]() The simple answer to the first part is that the gas clouds are prevented from collapsing by their internal pressure exactly the same kind of gas pressure you "put" into the tyres of your car. IMAGE - The Milky Way showing dark nebulae, a reflection nebula and an emission nebula So, why are these clouds stable and then not so stable? What is the force which opposes gravity initially and then later is not able to oppose gravity? Stars are much smaller and considerably more dense so some collapsing mechanism is required. These clouds appear to be quite stable and yet they are also considered to be the clouds from which stars are born. Some we see as just being dark against the general background of light from unresolved stars (dark nebulae). They are not luminous at visible wavelengths but we see them either by light scattered from nearby stars (reflection nebulae) or by light transmitted through them from stars embedded within the clouds (emission nebulae). Here large, diffuse clouds of dust and gas exist. ![]() A place we can start is in interstellar space.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |