StarsStars

What is a star?What is a star?

•The objects that heat and light the planets in a system

•A star is a ball of plasma held together by its own gravity–Nuclear reactions occur in stars (H He)

–Energy from the nuclear reactions is released as electromagnetic 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

•186,000 miles per second

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 & Color–The color of a star indicates the Temperature of the star

–Stars are classified by Temperature•Decreasing Temperature (bright to dim)

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

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

Types of StarsTypes of StarsClassificationClassification

Class Temperature ColorO 20,000- 60,000 K BlueB 10,000 – 30,000 K Blue-whiteA 7,500 – 10,000 K White F 6,000 – 7,500 K Yellow-whiteG 5,000 – 6,000 K YellowK 3,500 – 5,000 K OrangeM 2,000 – 3,500 K Red

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 diagram

Hertzsprung-Russell DiagramHertzsprung-Russell Diagram

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

Size VideoSize Video• http://www.youtube.com/watch?

v=LsgKp_Vf6wI&list=PL9D64A9B670629B26&index=12

Life Cycle of A Star

Life Cycle of StarsLife Cycle of Stars

Life CycleLife Cycle

•Stars begin their lives as clouds of dust and gas called Nebulae (Greek for cloud)

•Gravity may cause the nebula to begin to contract

Eagle Eagle NebulaNebula

Life Cycle Life Cycle •Matter in the gas cloud will begin to condense into a dense region called a Protostar

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

Star NurseriesStar Nurseries

Life CycleLife Cycle

• After nuclear fusion begins, stars begin the main sequence phase.

•Most of its life is in this phase

The Sun: the nearest Main Sequence star to the Earth. This is an X-ray image from the Yohkoh satelite.

Logo for the Subaru car company.Logo for the Subaru car company.Pleiades or the 7 Sisters

Life CycleLife CycleLife 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 CycleLife Cycle

•It will expand into what is known as 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

BETELGEUSE –RED GIANTBETELGEUSE –RED GIANT• Only a few million years

old, Betelgeuse is already dying. Astronomers predict that it's doomed to explode as a soon, within 1,000 years or so, an event that will be spectacular for Earth's future inhabitants. (Conceivably, it's already happened as Betelgeuse is 640 light-years away!)

Hubble image of Betelgeuse a Red SupergiantHubble image of Betelgeuse a Red Supergiant

Life CycleLife Cycle

•Most average stars will blow away their outer atmospheres to form a planetary nebula

•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

Image of Sirius A and Sirius B taken by the Image of Sirius A and Sirius B taken by the Hubble Space TelescopeHubble Space Telescope

Ant Planetary NebulaAnt Planetary Nebula

Expelled gas streaming away at 1,000 kilometers per second create a strange ant shape

Cats Eye NebulaCats Eye Nebula

Life CycleLife Cycle

•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

Just one teaspoon of a neutron star would have the mass of over 5 x 10Just one teaspoon of a neutron star would have the mass of over 5 x 101212 kilograms.kilograms.

When neutron stars form, they maintain the momentum of the entire star, but now they’re just a few kilometers across. This causes them to spin at tremendous rates, sometimes as fast as hundreds of times a second.

Life CycleLife Cycle• 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