Stars Star- large ball of gas held together by gravity that produces tremendous amounts of energy and shines Sun- our closest star
Star Formation A cloud of gas and dust, called a nebula, begins spinning & heating up. Eventually, it gets hot enough for fusion to take place, and a protostar is born.
Star Formation In the star s core, two hydrogen atoms collide and fuse together to make a new helium atom, releasing huge amounts of energy and making the star expand.
Energy Production in Stars Nuclear fusion- the combining of the nuclei of smaller elements to form the nuclei of larger elements with some of the mass being converted to energy Ex: hydrogen + hydrogen = helium + energy
Sun The sun is a mass of incandescent gas, a gigantic nuclear furnace. Where hydrogen is built into helium at a temperature of millions of degrees.
Typical Star Composition Element Abundance (% of total Abundance number of atoms) (% of total mass) Hydrogen 91.2 71.0 Helium 8.7 27.1 Oxygen 0.078 0.97 Carbon 0.043 0.40 Nitrogen 0.0088 0.096 Silicon 0.0045 0.099 Magnesium 0.0038 0.076 Neon 0.0035 0.058 Iron 0.030 0.014 Sulfur 0.015 0.04
Star Origin and Evolution 1. Stars originate from clouds of gas and dust molecules that clump up due to gravity. 2. When the clump reaches the size of Jupiter, it creates enough energy by nuclear fusion to shine becoming a star. 3. For stars that are about the size of our sun, after main sequence they become giants, white dwarfs, and then black dwarfs. 4. For stars larger than our sun, after main sequence and giant stage, they explode in supernovas, then become either black holes or neutron stars.
Star Classification Luminosity: : the actual brightness of a star; depends on size & temperature Bigger is brighter Hotter is brighter Absolute Magnitude: : a measure of how bright a star would be if all stars were at the same distance from Earth Apparent Magnitude: : a measure of how bright a star appears to be to an observer on Earth Depends on distance closer is brighter
Star Types and Sizes Size- MOST stars are much larger than Earth 1. Main Sequence Stars- average temperature and luminosity stars 90% of stars are main sequence (our sun is one) Majority of a star s lifetime Use up their hydrogen & helium, producing heavier elements Length depends on amount of fuel Massive stars burn faster die faster
Star Types and Sizes 2. Giant or Supergiant (depends on mass) Star has used up its fuel, so energy produced cannot counteract force of gravity & the star s core collapses, while the outer layers expand rapidly Giant - low temperature, high luminosity, red, orange, yellow in color, older than main sequence stars Super Giants- very high luminosity, blue is the largest, explode into a supernova
Star Life Cycle Nebula Main Sequence Star smaller stars larger stars Giant Star Super Giant Star
Star Life Cycle 3. White Dwarf (if <10 solar masses) outer layers from giant stage dissipate, leaving only a small core when finishes burning, becomes black dwarf (dead star) High temperature, low luminosity 4. Supernova (if >10 solar masses) cataclysmic collapse of massive supergiant, creating intense explosion forms iron & heaviest elements in last seconds before becoming either...
Outward Pressure stops when Fe fuses Gravitational Collapse Begins
Star Life Cycle Nebula Main Sequence Star smaller stars larger stars Giant Star Supergiant White Dwarf Supernova
Star Life Cycle 5. Neutron Star (10-20 solar masses) supernova collapses into core 6-20km in diameter, but more massive than our sun so dense, 1 teaspoon weighs a hundred million tons! Occasionally spins to become a pulsar 6. Black hole (20+ solar masses) supernova implodes into a super-tiny, super-massive hole that sucks matter & light towards it
Nebula Main Sequence Star Smaller stars Larger stars Giant Star Supergiant White Dwarf Supernova massive stars Super-massive stars Neutron Star Black Hole
Star Life Cycle Nebula Main Sequence Star smaller stars Giant Star larger stars Supergiant White Dwarf massive stars Supernova super-massive stars Neutron Star Black Hole
Star Types and Sizes
(our Sun now) Life Cycle of a Star
The Luminosity And Temperature of Stars Diagram Hertzsprung-Russell diagram groups stars by temperature and luminosity (also called HR Diagram)
cooler LARGER SMALLER hotter
H-R Diagram As you move up the diagram, the objects become brighter & larger. As you move down the diagram, objects become smaller & dimmer. Moving to the left on this diagram, the temperature increases. Moving right, the temperature decreases
How do we know? SPECTROSCOPY the study of light, breaking it into the spectrum & analyzing the result, giving us the physical properties of a distant object Composition (what elements are in it) Temperature Mass Brightness Movement
Light Spectrum
Spectroscope
Sample Spectra