Nova, definition and study. A-Z index of Cognitio.

In astronomy, a Nova is a huge nuclear explosion caused by the hydrogen accumulation on the surface of a white dwarf that causes the star to become much brighter than usual. The word nova may indicate both the cause of the phenomenon and the star itself at the time of the explosion. A particular type of nova is novoids, characterized by a non-periodic but significant change in brightness. A nova originates from a white dwarf. When it is in a tight binary system, it can subtract matter to its companion by its gravity, especially when the companion crosses the red giant stage and fills his Roche lobe. The captured gas consists mainly of hydrogen and helium, the two most abundant elements of the Universe.

Universe, definition and study. A-Z index of Cognitio.

Universe

The gases deposit on the surface of the white dwarf and are compressed and heated to very high temperatures by the severity of the star. As time goes on, more and more material is accumulated as long as the pressure and the temperature reached are enough to trigger a nuclear fusion reaction that rapidly converts a large part of hydrogen into heavier elements. The enormous energy released by this process literally blows away the rest of the gas from the surface of the white dwarf, and produces a very bright “lightning” but short-lived, destined to go off in a few days. This zeal was what old astronomers called new stars. Studies with the Fermi telescope have shown that nine can radiate gamma rays.

Fermi telescope, definition and study. A-Z index of Cognitio.

Fermi telescope

The novae are distinct in: classic, dwarf and recurring.

In classical novae, the maximum brightness is reached within a few hours during which the nova increases by about 12 magnitudes.

 

Nova classical, definition and study. A-Z index of Cognitio.

Nova classical

 

Dwarf novae are a subclass whose prototype is represented by U Geminorum. The optical flashes have amplitudes of 5 magnitudes repeating at intervals ranging from 120 days to a few years.

Nova dwarf, definition and study. A-Z index of Cognitio.

Nova dwarf

 

The recurring recruits represent a middle ground between the first two: in fact, as the name suggests, they manifested several times, with the difference to the dwarf ones, that the time span between an event and the next is about a dozen years; In addition, the light flash is about eight magnitudes.

Nova, definition and study. A-Z index of Cognitio.

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Nova, definition and study. A-Z index of Cognitio.

Nova