Space Chapter 19 Lives of Stars

Earth’s Most Important Star Stars do not live forever The sun, a medium star, is 93 million miles away from Earth The sun gives us radiant energy for food, warmth and fuel Some of the sun’s energy is stored in the form of fossil fuels, such as coal and oil Another form of energy that comes from the sun is invisible ultraviolet light

A Star is Born A star is made up of a large amount of gas in a small volume of space A nebula, is a large amount of gas and dust spread out in an immense volume All stars begin as a nebula A protostar is the earliest stage of a star’s life

Life times of Stars How long a star lives depends on how much mass it has. Small stars use up their fuel more slowly than large stars, so they have much longer lives. Medium-mass stars live for about 10 billion years Stars that have more mass than the sun have shorter lifetimes

Deaths of Stars When a star runs out of fuel, it becomes a white dwarf, neutron star or black hole. The center shrinks and the outer part expands. White Dwarfs are the blue-white hot core of the star that is left behind Neutron Star are smaller and denser than white dwarfs. After a star explodes, some of the material from the star is left behind. Black hole are the most massive stars and has more than 40 times more mass than the Sun. No light, radio waves or any other form of radiation can ever get out

Life Cycle of a Star

What are the characteristics of a star? Stars differ in… Mass Size Temperature Color Luminosity

Stars in Our Universe The closest star to our solar system is the Alpha Centauri It would take 30,000 boxes of salt to fill all the stars in our galaxy

Star Size The diameters of stars range from as little as 1/10 the Sun’s diameter to hundreds of times larger. The mass of stars can be from less than 1/100 to 20 or more times that of our Sun. Stars over 50 times the Sun’s mass are extremely rare. Our Sun is a medium sized star.

Star Temperature Stars in the sky show tinges of different colors which reveal the stars’ temperatures. Blue stars shine with the hottest temperatures and red stars shine with the coolest temperatures. Our Sun is a yellow star having a surface temperature of about 5,500ºC Stop and Think The hottest flame color in a campfire is? White/Blue

Star Colors A stars color reveals its temperature The hottest stars—over 10,000 degrees Celsius—appear slightly bluer than the sun A Blue-white Rigel is more than 15,000 degrees With a surface temperature of about 5,500 degrees Celsius—appear white The Sun glows white The coolest stars—about 3,200 degrees Celsius—appear reddish in the sky. Betelgeuse (red star on Orion’s shoulder) cool star

The Hertzsprung-Russell Diagram Measures the brightness and surface temperature of stars. More than 90% of all stars are main sequence stars Star colors from Hottest to Coolest: Blue, Blue-White, White, Yellow-White, Yellow, Orange, Red O or blue is the hottest (>25,000oC) M or red is the coolest (3,500-2,000oC)

Star Luminosity/Brightness The brightness of a star depends upon the distance and its luminosity. The amount of light they give off! Brightness depends on size and temperature Stop and Think The star Rigel in Orion is about 60,000 times larger than our Sun. Why does our Sun appear brighter than Rigel? 9/17/2018

1. Main Sequence Stars Upper left stars are Large, hot, luminous 90% of stars occur along the main sequence Middle aged, stable stars Main Sequence runs from upper left to lower right Upper left stars are Large, hot, luminous Ex. Blue Giants Lower right stars are Small, cool, dim Ex. Red Dwarfs 9/17/2018

Upper Right Stars Red Giants & Super Giants (Super Super Giants, too) Large Cool Bright 1% of stars Our sun in 5 billion years will be 2000 times brighter and 100 times larger (large enough to expand past Mars orbit)

Lower Left Stars White Dwarfs (9% of stars) Small Hot Dim