Crab nebula G A S N D U T Carina nebula Cone nebula Orion nebula

Protostar: the first stage in a star’s formation

The Life and Death of Stars 1. Depending on the mass of the star formed from a particular nebula, the star will be Sun-like or massive. - Both types of stars spend most of their lives in this main sequence, converting hydrogen to helium in their cores. 2. When the hydrogen in the core has been used up, the stable-state star shrinks in size, heating the helium core so that it first starts fusing to carbon, then to other elements.

Red Supergiant Star V838 Monocerotis Mira A Red giant As gravity causes the star to contract, further nuclear reactions occur, leading to expansion of the outer layers. In this way, the star becomes larger, turning into a red giant if it is a Sun-like star, or a red supergiant if it is a massive star.

- The final stage in a star’s life occurs when the fusion reaction stops. For a Sun-like star, fusion ends when the core temperature in the star is no long hot enough to keep the reaction going. With no heat input from fusion, the decreasing pressure is unable to prevent gravity from causing the star to collapse slowly on itself. - The Sun-like star continues to shrink, gradually becoming a white dwarf, no large than earth. Eventually, the star will fade completely until it evolves into a cold, dark black dwarf.

- In a massive star, the fusion reaction stops when the star runs out of fuel. The lack of heat input into the core from fusion enables gravity to get the upper hand. The collapse ends suddenly with an outgoing shock wave. This in turn causes the outer part of the star to explode in a catastrophic event known as a supernova. If the star is not destroyed entirely by the explosion, the core is left as a neutron star or a black hole.

Sirius A and White Dwarf Sirius B.

Supernova

- A neutron star is a rapidly spinning object only about 30 km in diameter. A black hold is a highly dense remnant of a star in which gravity is strong that not even light from the radiation going on inside the remnant can escape. NGC 4261