Birth of a Star

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Birth of a Star

• Stars begin as a large spinning cloud of gas and
  dust called a NEBULA

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• PROTOSTARS form within the nebula in pockets of
  matter.

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When a protostar condenses and its temperature
reaches 10,000 C, then nuclear fusion begins.
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When discussing the life and death of stars, we
need to know the size of that star. Is it

• smaller than ½ the size of the Sun (small)
• up to 7 times larger than Sun (average)
• larger than 7 times bigger than the sun (super
  big)

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What is the Life Cycle for average stars like Our
Sun?

• 1. Fuse H to He
• 2. Hang out on main sequence for 90 of
• lifetime
• 3. Fuse all H so cool and contract
• 4. Core temp increases from contraction He fuse
  to C
• 5. Expand outer envelope RED GIANT

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• When this happens, our sun will engulf every
  planet out to Jupiter!

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• 6. Red giant gets hot enough to blow off outer
  layers planetary nebula
• 7. Core remains as a white dwarf, which slowly
  cools to a black dwarf as it radiates the rest of
  its heat into space.

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Life Cycle for super huge stars

• SUPERGIANTS move through life cycle quickly
• 1. Fuse HHeCOSiFe
• 2. Iron core collapses sending out shockwaves
  through the star
• 3. Huge explosion

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• Stars expands and contracts several times and
  then explodes. The violent explosion of a star is
  called a SUPERNOVA,

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• The core continues to collapse until it
  becomes a neutron star. Neutron stars are
  EXTREMELY DENSE .
• ( If you could take a teaspoon of a neutron
  star, it would weigh as much as a car)

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Pulsar

• As the neutron stars spins faster it sends out
  pulses of energy coming from hot spots on its
  surface. The spinning neutron star is called a
  PULSAR.

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• Collapses into one point called a singularity
• Gravitational field so strong nothing escapes not
  even light
• THE BLACK HOLE

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Protostar
Black Dwarf
White Dwarf
Main-Sequence Star
Nebula stellar
Neutron Star or Pulsar
Protostar
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Chapter 25.3 "The Universe"
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? A galaxy is a group of stars, dust, and gases
held together by gravity.
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The Big Bang Theory

• The most widely accepted theory explaining the
  formation of the universe.
• Why? Because it is the only scientifically
  supported theory that we currently have

• Step 1 All matter and energy in the universe was
  once located in a single dense point called a
  singularity.
• Step 2 Then about 13.7 billion years ago a HUGE
  explosion occurred BANG!
• Step 3 Matter and energy were propelled outward
  in all directions as the universe began to
  expand.
• Step 4 Matter began to condense - forming
  galaxies and these galaxies continue to move
  outward today.

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The Expanding Universe
? Hubbles Law
Hubbles law states that the galaxies are
retreating from the Milky Way at a speed that is
proportional to their distance.
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The Expanding Universe
a moving star's light will shift in frequency
in the same way that the whistle on a passing
train changes pitch. - This "Doppler" shift can
be detected by breaking starlight apart into its
component colors, or wavelengths, and looking for
specific chemical "fingerprints" (black lines in
rainbow).
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Red Shift / Blue Shift
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Hubble Classification Scheme

• When telescopes led to the discovery of galaxies,
  astronomers observed many differences.

• In 1926 Edwin Hubble decided to classify the
  galaxies, grouping them according to shape
  creating the Hubble Classification Scheme.

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Types of Galaxies
? Elliptical Galaxies
About 60 percent of galaxies are classified as
elliptical galaxies.
Elliptical galaxies range in shape from round
to oval.
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Types of Galaxies
? Spiral Galaxies
About 30 percent of all galaxies are spiral
galaxies.

• - Disk-shaped with higher concentration of stars
  near their centers
• Many variations
• Arms of stars that rotate - pinwheel

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Hubble Classification Scheme

• What is the difference between a barred spiral
  and a spiral galaxy?
• Barred spirals show the same spiral structure as
  normal spirals, as well as a prominent bar
  through the nucleus.  The spiral arms emerge from
  the end of the bar. 

No Bar
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Types of Galaxies
? Irregular Galaxies
Only 10 percent of the known galaxies have
irregular shapes and are classified as irregular
galaxies.
In addition to shape and size, one of the
major differences among different types of
galaxies is the age of their stars. Irregular
galaxies contain young stars.
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The Milky Way Galaxy
? So what is the Milky Way?
The Milky Way is a large spiral galaxy whose
disk is about 100,000 light-years wide and about
10,000 light-years thick at the nucleus.
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The Milky Way Galaxy
? So what is the Milky Way?
The Milky Way is a large spiral galaxy whose
disk is about 100,000 light-years wide and about
10,000 light-years thick at the nucleus.
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Structure of the Milky Way

• Radio telescopes reveal that the Milky Way has
  at least three distinct spiral arms, with some
  splintering.
• This diagram shows the possibility of five arms
  and the clockwise rotation of the Milky Way.

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The Hubble

• (HST) is a large, space-based observatory
• Launched in 1990
• Hubble orbits Earth every 97 minutes, 360 miles
  above the Earth's surface.
• About the size of a tractor-trailer truck

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Hubble Deep Field
The Hubble Deep Field is an image taken by the
Hubble Space Telescope which reveals hundreds to
thousands of galactic clusters.
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Earth
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