Milky Way Galaxy

Galaxy A group of stars, dust and gases held together by gravity. 170 billion galaxies in the universe 200 billion stars in a galaxy

Do we have a picture of our galaxy?

Milky Way Galaxy The spiral galaxy our solar system belongs to 100,000 light-years wide 10,000 light-years thick at the nucleus Sun is located within a spiral arm about 28,000 light years from the galactic center

Structure of the Milky Way Galactic Center Supermassive black holes occupy the centers of most galaxies. Sagittarius A A supermassive black hole in the Milky Way’s galactic center. It is the point our galaxy rotates around Spiral Arms Four major spiral arms extend from the center of the Milky Way.

Sagittarius A 2.6 million times the mass of our Sun. Smaller than the solar system.

The Sun orbits the galaxy at a distance of 28,000 light years from the galactic center. The Sun’s orbital period is about 240million years at 220 km/s. The Sun has orbited the galaxy about 20 times in its 5 billion year history.

Local Group Milky Way belongs to this local group of galaxies 10 billion light years end to end

Magellanic Clouds Two satellite galaxies of the Milky Way 160, ,000 light years away Closer than the Andromeda galaxy

Andromeda Galaxy Closest galaxy to the Milky Way 2.5 million light years away

3 billion years from today

4 billion years from today

COSMOLOGY The study of the universe

Big Bang Theory The theory that all matter originated from a hot dense central point about 13.7 billion years ago. Credited to Edwin Hubble ( ).

Big Bang Theory The momentum of the outward expansion of the universe is opposed by the inward force of gravity acting on the matter of the universe to slow that expansion

Big Bang Theory 1.Matter (protons, neutrons, electrons) was created from pure energy. 2.Atomic nuclei formed when the temperature decreased seconds later. 3.Electrons joined with atomic nuclei to form elements 300,000 years later 4.The universe became transparent, allowing light to travel across it forever. 5. The cosmic background radiation confirms the Big Bang theory because its wavelength and temperature match predictions of these early events.

Evidence for the Big Bang 1. Red shifts of distant galaxies Indicate the universe is expanding Wavelength of light waves increases Shifts to the red end of the spectrum Shows that galaxies are moving away from each other 2. Background Radiation Microwave radiation cooled to 3 K Average temperature of the universe is 3K

Hubble’s Law States the galaxies are retreating from the Milky Way The further a galaxy is the faster it is retreating When the rate of expansion of the universe is known, it is possible to calculate the time since the expansion started and determine the age of the universe

Doppler Shift

Measurements of spectral line wavelengths can be used to determine the direction and speed of a star’s motion.

Radio Antenna at Bell Labs Discovered cosmic background radiation in 1965.

Three Possible Fates

Three Possible Fates of the Universe 1. Open Universe The expansion goes on forever (maybe even be speeding up) 2. Flat Universe The expansion becomes so slow that it seems to stop 3. Closed Universe where the expansion stops and all of the mass is pulled back to the original point of origin

Three Possible Fates All three outcomes are based on the premise that the rate of expansion has slowed since the beginning of the universe, but the density of the universe is what is unknown. According to every standard model, the expansion of the universe is slowing down due to gravity. However, there was a surprising discovery that the expansion of the universe is now accelerating. Astronomers have labeled this acceleration dark energy

Dark Matter & Dark Energy Dark matter and dark energy comprise nearly 95% of the universe The nature of dark energy & dark matter is unknown.

Composition of the Universe 70% Dark Energy 25% Dark Matter 4% Free hydrogen & helium 1% Stars (galaxies)

3-D map of the universe.

Edwin Hubble ( )

Hubble Space Telescope (1990-present)

Webb Space Telescope (2015) (4 x the capability of Hubble)

Hubble Space Telescope