Nova
A stellar explosion on a white dwarf in a binary system.
A nova is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star that slowly fades over weeks or months. All observed novae involve white dwarfs in close binary systems, and they are considered cataclysmic variable stars.
- type
- Astronomical event
- subclasses
- Classical novae, recurrent novae, dwarf novae
- typical frequency_in_Milky_Way
- About 10 per year observed; estimated 25–75 per year
Lore & Background
A nova occurs in a close binary system where a white dwarf accretes matter from a companion star, forming a dense hydrogen atmosphere. When the temperature reaches about 20 million K, runaway fusion ignites, expelling the atmosphere and creating a bright outburst. Classical novae are the most common type, while recurrent novae repeat on cycles of decades or less, as seen in T Coronae Borealis. The rise to peak brightness can be rapid or gradual, and the decline time classifies novae as fast (under 25 days to decay 2 magnitudes) or slow (over 80 days).
Reader's Guide
Novae are significant because they are major sources of lithium enrichment in the Galactic disc, according to recent chemical evolution models. They also contribute elements like helium, carbon, nitrogen, oxygen, neon, and magnesium to the interstellar medium, though their total material contribution is small compared to supernovae or red giants. The study of novae helps astronomers understand binary evolution, accretion processes, and the conditions leading to Type Ia supernovae, which occur when a white dwarf approaches the Chandrasekhar limit.
Did You Know?
- The name 'nova' comes from the Latin 'stella nova,' meaning 'new star.'
- Only about five percent of the accreted mass is fused during a nova outburst.
Frequently Asked Questions
What is a nova?
A nova is a sudden brightening event on a white dwarf star that makes it flash into view as an apparently 'new' star before slowly dimming over weeks or months. It is a surface thermonuclear flare rather than a destructive explosion, leaving the white dwarf intact afterward.
How is a nova different from a supernova?
A nova occurs when a white dwarf in a close binary system accumulates hydrogen from its companion and undergoes a surface eruption, after which the star survives. A supernova is a far more violent event that can completely unmake a star or leave behind a neutron star or black hole.
What triggers a nova?
In a tight binary pair, a white dwarf steadily strips hydrogen-rich gas from its companion until a critical layer builds up on its surface. Once that layer reaches sufficient temperature and pressure, a runaway thermonuclear reaction ignites and hurls the outer material into space.
How often do novae occur in the Milky Way?
Astronomers typically detect about ten novae per year in our galaxy, though the true underlying rate is estimated at roughly 25 to 75 per year because many events go unnoticed. They are grouped into classical, recurrent, and dwarf subtypes depending on their recurrence and energy output.
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