Lecture on Stars

Introduction to Stars

• Stars are compared to fireflies illuminating the sky.
• Stars are born in nebulae, which are clouds of dust and mostly hydrogen gas.

Formation of Stars

• Stars start as protostars or hot cores formed by the collapse of dust and gas.
• As protostars heat up, hydrogen nuclei fuse to create helium.
• Thermonuclear fusion generates a star's heat and energy, causing it to shine.

Classification of Stars

Spectral Classes

• Stars are classified by surface temperature into seven major groups.
• The spectral classes range from M (coolest stars) to O (hottest stars).

Luminosity Classes

• Stars are also classified by their luminosity (amount of light they emit).
• Luminosity classes range from small, less bright white dwarfs to large, extremely bright hypergiants.

The Life Cycle of Stars

• All stars eventually use up their hydrogen fuel and die.

Fate of Less Massive Stars

• Stars like our Sun release their material into space, leaving behind a white dwarf surrounded by a planetary nebula.

Fate of More Massive Stars

• These stars explode in a supernova, leaving a neutron star.

Fate of the Most Massive Stars

• Stars at least three times the mass of the Sun collapse into black holes.

Star Remnants and Life

• Remnants of stars release heavier elements into the universe.
• Star dust forms the building blocks of life itself.