The Life and Death of Stars A Star Is Born Not everyone agrees, but it is generally thought that stars originate from nebulae (clouds of dust and gas). Almost inevitably, a nebula will "collapse" into a single mass or chunk because of the force of its particles' gravity. 1
Star forming region in the nebula NCG 604, in the nearby sprial galaxy M33, as imaged by HST and the Mount Palomar telescope Columns of cool interstellar hydrogen gas and dust in M16, the Eagle Nebula 2
Stellar formation in the Trifid Nebula (M20). NEBULAE ARE WEIRD!! Collision of two gasses ("cometary knots") in the Helix Nebula in the constellation Aquarius 3
The Most Important Factor in Star Evolution There are three general situations: Small/Medium Stars like our Sun Large Stars 10 times the mass of our Sun Very Large Stars 30 times the mass of our Sun MASS! Gravity The more particles that gather together and the closer the particles get to each other, the stronger the force of gravity between them - so the process of "collapse" accelerates and intensifies and becomes more violent as particles collide and particles compress and form a sphere at the nebula's heart. 4
Meanwhile, the compression exerted by the surrounding mass* continues to increase. If enough mass gathers, the force of gravity exceeds the force of repulsion between the hydrogen nuclei and makes these nuclei "fuse". This produces helium and an awful lot of heat - which sustains the hydrogen fusion. HOT! Protostars Baby Stars The Trapezium Theta Orionis The kinetic energy of the particles' activity turns into heat and the sphere starts to glow, so soon it becomes a protostar. (A protostar is a star in its first stage of development.) 5
Small Stars 1 Solar Mass Early Life Gradually turns into hot dense clump that begins producing energy Middle Age Uses nuclear fusion to produce energy for 10 billion years or more Old Age Uses up hydrogen fuel and swells up into a huge, cool red giant Death Gases disperse and the star becomes a small, hot, dense white dwarf White Dwarfs Comparison of ground-based observation of the globular cluster M4 with an HST image showing white dwarfs. (Produced with the Wide-Field Planetary Camera 2, Hubble Space Telescope.) 6
Large Stars 10 Solar Masses Early Life In a fairly short time turns into a hot dense clump that produces large amounts of energy. Middle Age Uses nuclear fusion to produce energy for only a few million years. About 5000 times brighter than our sun. Old Age Uses up hydrogen fuel and swells up into a red supergiant. Death Core collapses inward and causes ejection of gases as SUPERNOVA. Eventually core material packs together as neutron star. Ejected gases form nebulae. Red Supergiant Betelgeuse, the brightest star in the constellation Orion. (Produced with ESA's Faint Object Camera (FOC), Hubble Space Telescope 7
Crab Nebula The "Eskimo" Nebula (NGC 2392). The Eskimo Nebula 8
Neutron Star First direct look, in visible light, at a lone neutron star (RX J185635-3754). (Produced with the Wide- Field Planetary Camera 2, Hubble Space Telescope Very Large Stars 30 Solar Masses + Early Life In a very short time turns into a hot dense clump that produces huge amounts of energy. Middle Age Uses nuclear fusion to produce energy for only about 1 million years. Extremely bright. Old Age Uses up hydrogen fuel and swells up into a red supergiant. Death Core collapses inward and causes ejection of gases as SUPERNOVA. Ejected gases form nebulae. Dense material in core may form BLACK HOLE. 9
Image of the youngest known planetary nebula, the Stingray nebula (Hen-1357). Baby Nebula Hourglass Nebula 10
Black hole candidate in the spiral galaxy M87. (Produced with the Wide-Field Planetary Camera 2, Hubble Space Telescope.) Black hole at the center of a galaxy. (NGC 4438) 11
Black Hole A star, somewhat like our Sun, pictured near a black hole. Material is dragged away from the star and forms an accretion disk as it spirals inwards and finally disappears into the black hole. Very high temperatures near the inner (blue-white) part of the disk create winds (seen in yellow) that spin material off into space. The extreme conditions near the black hole force jets of material (pale blue) to shoot out above and below the accretion disk. Image of the spiral galaxy NGC 4414. 12
Image of the rich galaxy cluster, Abell 2218. The End? Or Just the Beginning? 13