Image nova


Nova means new star. A long time ago novas were thought to be newly-formed stars, because they would suddenly appear and disappear after only a few months. In fact, a nova is an existing star that suddenly increases its luminous intensity becoming thousands of times brighter. Think about the noise made by a train travelling at high speed, as it gets closer its noise increases until it has reached its maximum level of intensity, then as it moves further and further away its noise fades away until it can be heard no longer. This is what happens to a nova, its luminous intensity increases, for a few days, its maximum level is reached and then it fades away once more.

A phase of the mechanism that leads to the appearance of the so-called nova is illustrated.

Astronomers think that the nova phenomenon is actually produced by a double-star system. This is where an evolved and expanded star, typically a red giant - as represented on the right at the top of the figure, is deformed by the gravitational pull exercised on it by its more compact fellow star, normally a white dwarf.

Moving diagonally from the top-right to the bottom-left, a band can be noted between the two stars which resembles a road. This represents the continual flow of gaseous matter that is being dragged by the white dwarf from the red giant. The white dwarf is in the middle of a great disc, represented by a small circle, and it is here that the matter is collected. This gaseous matter rotates around the white dwarf and slowly accumulates on it. This extra matter on the white dwarf continues to accumulate until it has reached the maximum mass possible. An explosive reaction is then produced in the star, and part of the matter it had gained is released. The explosion, which doesn’t destroy the star, suddenly makes the white dwarf brighter and more visible on Earth.

Next page     Back