Death of Low Mass Stars 8 Solar Masses or less

All stars become a red giant.

All stars will live to be a Red Giant, then… In the core of the Red Giant He is fusing into C. MAJOR Problem!!! Core temps need to reach at least 600 million K for C to ignite into heavier elements (mainly O). Low mass stars cannot do this. Creation of a Planetary Nebula

Planetary Nebula The shell of the star (red giant outer surface) is subject to a series of explosions that eject gas and dust into space (nebula). A star can lose up to 1/2 the original mass. Diameter can be very large (typically 1 ly) Gas expands 30 km/s Usually circular in shape Gas and dust in nebula becomes part of the interstellar medium (ISM). Makes future stars!!!

Ring Nebula (M57) found in Lyra

Ring Nebula again… Hubble

White Dwarf As the surface of the Red Giant expands away, the core is exposed, the White Dwarf. Extremely small, dense and hot. About the size of Earth with a density of kg/m 3 (an object with the volume of 1 grape would have a mass of 1 ton… that’s like the mass of an elephant!!!). Shines from stored heat, no fusion occurs in the core… the star is officially dead :( Usually, but not always, seen in the center of planetary nebulae.

White Dwarf compared to the Sun/Earth

Cat’s Eye Nebula (NGC 6543) found in Draco White Dwarf Planetary Nebula

A white dwarf is a whitish dead star having low luminosity, small size and very great density. These white dwarf stars are intensely hot... but they are cooling. Their interior nuclear fires no longer burn, so they will continue to cool until they fade away. The white dwarfs are circled.

Helix Nebula

Here’s another one!!!!

Black Dwarf Stars Cooled remains of a white dwarf. The resistance of electrons from being squeezed together (electromagnetic repulsion) keeps gravity from compressing it further. Called Electron Degeneracy The black dwarf will continue to exist at temps close to absolute zero forever….

What is a Nova explosion? A star suddenly increasing in brightness, typically by 10,000 times. Caused by an explosion on the surface of a very hot star. Unlike a supernova, a nova explosion does not destroy the star.

Can a low mass star, like the Sun, have a NOVA explosion? Yes, but usually if it is part of a binary star system. Binary Star System- 2 or more stars in orbit about each other held together by their mutual gravitation. MOST “stars” are binary systems. Our closest star is a 3 star system (centauri system).

Accreting White Dwarf

Still answering the question… One star must be a white dwarf, the other has recently become a red giant. The white dwarf will steal some of the expelled matter. Once it reaches the tremendously hot surface it ignites causing a flash.

Nova Explosion in Binary System

What is a Supernova? When a large mass star (8 solar masses or more) EXPLODES destroying the star. Unlike a Nova that does NOT destroy the star Brightest/most energetic event in the Universe (2 nd only to the Big Bang).

Can a small mass star, like the Sun have a supernova explosion? YES!!! ONLY if it’s part of a Binary System. If a white dwarf star has accreted more than 1.5 solar masses, then electron degeneracy cannot stop gravitational collapse. Called a Type I Supernova Type I SN