stars
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STARS. Amole Spectra 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 10 15 m Driven by nuclear fusion reactions. - PowerPoint PPT PresentationTRANSCRIPT
STARSAmole
Spectra of Science2013
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 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
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
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
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
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
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
