Unit 3 Part 1 - Universe & Big Bang, Galaxies & Stars

Origins of the Universe

• The Universe is all space, matter, and energy
• Universe is about 13.7 billion years old
• Big Bang Theory: All matter and energy in the Universe started concentrated in a small area, and after an explosion, matter began to organize into subatomic particles and atoms (mostly hydrogen and helium)

Our Universe is Expanding

• Continued to expand and is expanding today
• Evidence: Red-shift in spectra of galaxies and Cosmic Background Radiation coming from all directions in the Universe

Electromagnetic Energy

• Various types of waves transmitting energy through space
• All types travel at the speed of light, which is 3.0 x 10^8 m/s

Wavelength

• Distance between two successive crests or troughs

Frequency

• The number of waves that pass a certain point in a given period of time
• Frequency depends on wavelength: the longer the wavelength, the lower the frequency

The Doppler Effect

• Apparent shift in wavelengths of an electromagnetic wave
• When a light source is moving towards an observer, the shorter wavelengths of light appear blue - called blue-shift
• When a light source is moving away from an observer, the longer wavelengths of light appear red - called red-shift

Galaxy

• A collection of billions of stars and various amounts of gas and dust held together by gravity
• Categorized by shape

Our Milky Way Galaxy

• Spiral shaped and contains over 200 billion stars

Formation and Evolution of Stars

• Stars originate from clouds of gas and dust that swirl, condense and form balls of gases held together by gravity
• Stars form in huge celestial structures called nebulae

Formation and Evolution of Stars (continued)

• From a nebula comes a protostar (early star)
  • Nebula is now spherical
  • Mass, gravity, and temperature increase
• When the mass, temperature, and pressure get high enough, nuclear fusion begins - A STAR IS BORN!
  • Tons of energy radiates out and travels through space as electromagnetic energy

Low & Medium Mass Stars

• Spend most of their lives as main sequence stars
• Further evolution depends on the star's mass
• Expand to red giant
• Burn all fuel, blow up, remaining core = white dwarf
• Example: our Sun

High Mass Stars

• Star remnants that are over 1.5 times the mass of our Sun exist for a shorter time (100,000,000 years) as main sequence stars
• Expand to red supergiant
• Explode as supernova
• High mass = neutron stars
• Very high mass star = black hole

Classification of Stars

• Stars are classified by their Luminosity (brightness) and Temperature
• As temperature increases, star color changes from red (cooler) to blue (hotter)
• 90% of all stars are categorized as main sequence stars
• Stars spend most of their “life” as main sequence stars.