STARS

AmoleSpectra of Science

2013

What are Stars?

• A large celestial body of hot gas that emits light

• Greeks grouped stars in patterns called constellations

• Use the unit light-year to measure distances between stars– 9.5 x 1015 m

• Driven by nuclear fusion reactions

Why do Stars look Different from One Another?

• Size• Distance from

Earth• Temperature• Stage of Life Cycle

Characteristics of Stars• Color indicates

temperature– Blue (Short λ) = Hot– Red (Long λ) = Cool– The hotter they are the

faster they burn out

• Magnitude– Brightness– Smaller numbers

represent brightest stars

Classification of Stars• Classified by temperature and brightness• Decreasing Temperature and brightness•

• Oh, Be A Fine Girl, Kiss Me

Classification of Stars

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

H-R Diagram

Nuclear Fusion

• Strong gravitational forces hold stars together

• Energy from fusion creates outward pressure balancing inward pull

• Hydrogen atoms are fused to form helium

Layers of Stars

•Energy moves through layers by radiation and convection

•May take millions of years for energy to work its way through star to surface

•After leaving the surface it enters space traveling at the speed of light, 3 x 108 m/s

Temperatures of the Sun

What Happens When a Star Runs out of H?

• Begins to fuse He• Then, a

succession of heavier elements

• Iron is the most stable; it requires energy verses creating it

• Star begins to die

Life Cycle of Stars

Stellar Nebula• Nebulas are clouds of

dust and gas from which stars are born– Grains of carbon and

silicon

• Matter compresses due to own gravity

• Temperature and pressure slowly increase from compaction

Omega Nebula

Eagle Nebula

Lagoon Nebula

Bubble Nebula

Crescent Nebula

Orion Nebula

Crab Nebula

Adult Star• Actively undergoing

hydrogen fusion• Main Sequence star• Spends most of its

lifetime in this phase• 90% of stars in the

galaxy are in this phase

• An average size like our sun will “burn” much longer than a larger, more massive star

Red Giants and Supergiants• When a star runs out

of hydrogen, it begins to die

• Energy from fusion no longer counteracts gravity, and the core collapses

• Causes outer layers to expand

• Average stars create Red Giants

• Massive stars create Red Supergiants

White and Black Dwarfs• Core runs out of He,

and is no longer able to fuse the remaining heavier elements

• The star blows its outer layer away

• The core remains behind and burns as a white dwarf

• Eventually it cools to become a black dwarf

Little Ghost Nebula

Stingray Nebula

Ring Nebula

Supernova• Massive stars

end in violent explosions that blow away the outer layers of the star

• These stars result in either a neutron star or supernova

Neutron Star• Leftover core has between

1.4 – 3 solar masses

• Collapses so much that protons and electrons combine to form neutrons

• Very dense (a thimbleful weights more than 100 million tons)

• Emit radio waves (pulsars)

Black hole

• Leftover core has a mass greater than 3 solar masses

• Collapses so much that not even light can escape its gravity

Milky Way Black Hole

Death of a Star Simulations

Life Cycle of Stars