Supernovae

Supernova remnant N49

Supernovae

When a star reaches the end of its life and burns out the last of its nuclear fuel, it becomes unstable. What happens next depends how much mass the star has.

Stars born with masses many times greater than that of the Sun are predicted to die in violent explosions called supernovae.

A supernova begins with the star collapsing when it can no longer support itself against gravity's inward pressure. After the collapse, it blasts its outer layers into space. The star's core is left behind in the collapsed form of a neutron star or black hole.

Image: A supernova remnant called N49 in the Large Magellanic Cloud (NASA/STScI/UIUC/Y.H.Chu & R.Williams et al.)

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Supernova remnant N49

Introduction

Stars can die in massive explosions.

About Supernovae

A supernova (abbreviated SN, plural SNe after "supernovae") is a stellar explosion that is more energetic than a nova. It is pronounced /ˌsuːpəˈnoʊvə/ with the plural supernovae /ˌsuːpəˈnoʊviː/ or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this interval a supernova can radiate as much energy as the Sun is expected to emit over its entire life span. The explosion expels much or all of a star's material at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant.

Nova means "new" in Latin, referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super-" distinguishes supernovae from ordinary novae which are far less luminous. The word supernova was coined by Walter Baade and Fritz Zwicky in 1931.

Supernovae can be triggered in one of two ways: by the sudden reignition of nuclear fusion in a degenerate star; or by the gravitational collapse of the core of a massive star. A degenerate white dwarf may accumulate sufficient material from a companion, either through accretion or via a merger, to raise its core temperature, ignite carbon fusion, and trigger runaway nuclear fusion, completely disrupting the star. The core of a massive star may undergo sudden gravitational collapse, releasing gravitational potential energy that can create a supernova explosion.

Although no supernova has been observed in the Milky Way since Kepler's Star of 1604 (SN 1604), supernova remnants indicate that on average the event occurs about three times every century in the Milky Way. They play a significant role in enriching the interstellar medium with higher mass elements. Furthermore, the expanding shock waves from supernova explosions can trigger the formation of new stars.

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