StarsStarsStarsStars

A Star….A Star….

• Heats and lights the planets in a solar system

• Is a ball of plasma (4th state of matter consisting of ionized particles) held together by its own gravity

• Produces energy by nuclear fusion (4H nuclei 1He nucleus, some matter is converted to energy )– Energy from nuclear fusion is transferred

to the earth (and other places) as:

RADIATION

Characteristics of StarsCharacteristics of Stars

• DISTANCE– Measured in light-years

•The distance which a ray of light would travel in one year

•About 6,000,000,000,000 (6 trillion) miles

•186,282 miles per second

How we tell what stars How we tell what stars are made ofare made of

• Every chemical element has its own unit spectral fingerprint.

• We can study the chemical composition of an astronomical object, like stars by observing its absorption or emission spectrum.

Emission spectrum (top) and absorption spectrum (bottom) of Hydrogen

Characteristics of StarsCharacteristics of Stars

• Magnitude (brightness)– A measure of brightness of celestial

objects•Smaller values represent brighter objects

than larger values

– Apparent magnitude•How bright a star appears to be from Earth

– Absolute magnitude (luminosity)•How bright a star actually is

Characteristics of StarsCharacteristics of Stars

Temperature & ColorThe color of a star indicates its temperature (T)Stars are classified by T in order from brightest to dimmest

O, B, A, F, G, K, M[Oh Be A Fine Girl, Kiss Me]

Blue = Hottest, brightest

Red = Coolest, dimmest

Hertzsprung-Russell Hertzsprung-Russell DiagramDiagram

Main Sequence StarsMain Sequence Stars

• A major grouping of stars that forms a narrow band from the upper left to the lower right when plotted according to luminosity and surface temperature on the Hertzsprung-Russell (HR) diagram

Types of StarsTypes of StarsClassificationClassification

Class Temperature Color

O 20,000- 60,000 K Blue

B 10,000 – 30,000 K Blue-white

A 7,500 – 10,000 K White

F 6,000 – 7,500 K Yellow-white

G 5,000 – 6,000 K Yellow

K 3,500 – 5,000 K Orange

M 2,000 – 3,500 K Red

http://www.answers.com/topic/stellar-classification

Life Cycle of StarsLife Cycle of Stars

http://hea-www.cfa.harvard.edu/CHAMP/EDUCATION/PUBLIC/ICONS/life_cycles.jpg

• The protostar continues to condense, it heats up. Eventually, it reaches a critical mass and nuclear fusion begins.

• Begins the main sequence phase of the star– Most of its life is spent in this phase

• Begin their lives as clouds of dust and gas in a nebula

• Gravity may cause the nebula to contract

• Matter in the gas cloud will condense into a protostar

Life Cycle of StarsLife Cycle of Stars

Life span of a star depends on its size.– Very large, massive stars burn their fuel

much faster than smaller stars– Their main sequence may last only a

few hundred thousand years– Smaller stars will live on for billions of

years because they burn their fuel much more slowly

• Eventually, the star's fuel will begin to run out.

Life Cycle of StarsLife Cycle of Stars

• Most will expand into a red giant

• Massive stars will become red supergiants

• This phase will last until the star exhausts its remaining fuel

• At this point the star will collapse

Life Cycle of StarsLife Cycle of Stars

• Most average stars will blow away their outer atmospheres to form a planetary nebula (but no planets are made or exist here)

• Their cores will remain behind and burn as a white dwarf until they cool down

• What will be left is a dark ball of matter known as a black dwarf

Life Cycle of StarsLife Cycle of Stars

• If the star is massive enough, the collapse will trigger a violent explosion known as a supernova

• If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star

Life Cycle of StarsLife Cycle of Stars

• The matter inside the star will be compressed so tightly that its atoms are compacted into a dense shell of neutrons. If the remaining mass of the star is more than about three times that of the Sun, it will collapse so completely that it will literally disappear from the universe. What is left behind is an intense region of gravity called a black hole

Life Cycle of StarsLife Cycle of Stars

http://www.seasky.org/cosmic/sky7a01.html

Video – How stars create Video – How stars create elementselements

http://www.youtube.com/watch?v=neMEo8ZrwuI