Supernovae

What is it?

A supernova is the explosive death of a star. For a few weeks it can shine as brightly as billions of Suns, which is why astronomers can spot them in galaxies millions or even billions of light-years away.

There are two broad routes to a supernova. In a core-collapse supernova, a star more than roughly eight times the Sun's mass runs out of fuel in its core, the core collapses, and the outer layers are blown off. In a Type Ia supernova, a white dwarf (the dense leftover core of a Sun-like star) in a binary system is pushed past a stability limit, either by drawing in matter from a companion or by merging with another white dwarf, and is destroyed in a thermonuclear explosion. The exact details of the Type Ia pathway are still being worked out.

How does it happen?

1. Stage 1

   Massive star or white dwarf in a binary

   The starting point differs by type
2. Stage 2

   Core collapse or runaway fusion

   Balance between gravity and pressure fails
3. Stage 3

   Explosion

   Outer material is thrown out at very high speed
4. Stage 4

   Expanding remnant

   Often with a neutron star or black hole left behind

What do we actually observe?

Brightness

A rapid rise to a peak over roughly one to three weeks, then a slower decline. The shape of this light curve helps classify the event.

Spectrum

Light split into colors shows which elements are present. Whether hydrogen lines appear is one of the main ways types are told apart.

Expanding remnant

Long after the flash, gas shells and filaments keep expanding and glowing, as in the Crab Nebula from the supernova seen in 1054.

Neutrinos

Core-collapse supernovae release a burst of neutrinos. Detectors recorded neutrinos from Supernova 1987A in the Large Magellanic Cloud.

How do scientists detect it?

• Wide-field optical surveys. Surveys such as the Zwicky Transient Facility and ASAS-SN scan large parts of the sky repeatedly and flag new points of light. The Vera C. Rubin Observatory is designed to add far more.
• Spectrographs. Follow-up spectra confirm that a new source is a supernova and identify its type.
• Space telescopes. Hubble, JWST and X-ray and radio observatories study remnants and the surrounding gas.
• Neutrino and gravitational-wave detectors. These can in principle catch a nearby core-collapse supernova before or as the light appears.

• IAU Transient Name Server (new supernova reports)

Why does it matter?

• Stellar evolution: supernovae are the endpoint that tests our models of how stars live and die.
• Element production: explosions and the mergers they leave behind spread elements such as oxygen, calcium and iron into space, where later stars and planets form from them.
• Cosmic distances: calibrated Type Ia supernovae underpin measurements of the universe's expansion.
• Compact objects: core-collapse supernovae are the main known route to neutron stars and stellar-mass black holes.

The SpaceWeatherTracker connection

Supernova remnants are widely thought to accelerate many of the galactic cosmic rays that reach the Solar System. Those particles are modulated by the Sun's magnetic activity, so the same solar cycle SpaceWeatherTracker follows changes how many of them reach Earth's neighborhood.

• Space Weather Dashboard
• The Sun Now

Related phenomena

Primary family: Stellar Explosions & Extreme Stars

• Neutron Stars
• Pulsars
• Magnetars
• Kilonovae
• Gravitational Waves