Definition of nova, difference between nova and supernova? What is a dwarf nova?


At the end of the 16th century, astronomers Tycho Brahe and Johaness Kepler introduced the term nova stella, which means “new star” in Latin, to describe the transient appearance of new stars on the celestial vault. However, it was not until the developments of astrophysics in the twentieth century that we began to understand what was behind these curious phenomena, colossal thermonuclear explosions with stars, and that we make the distinction between novae and supernovae.

What is the difference between nova and supernova?
Thus, unlike supernovae, novae are explosions that do not lead (or rarely) to the destruction of the progenitor star or that do not produce a neutron star or a black hole. In the case of a nova, it all starts with a white dwarf in a binary system that gathers hydrogen from its companion star, often in the red giant phase, until pressure and surface temperature become sufficient to trigger an explosive thermonuclear fusion reaction.

The brightness of the star is then multiplied by 10,000 for a few days. The process can be repeated: we know for example that RS Ophiuchi exploded six times in a century. The novae are therefore recurrent.

What is a dwarf nova?
Note that what is called a dwarf nova, which is less luminous than a classical nova and a fortiori a supernova, is rather a cataclysmic variable star of the type U Geminorum. In this case, it is mostly variations in brightness due to the accretion process on the white dwarf that are involved and not explosions.

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