January 2nd 2013 Objective Warm-Up Students will know how galaxies are classified in order to identify the various types What is the name of the galaxy that contains the sun, the earth and the known planets? What is bigger: the solar system or a galaxy? What is the name of our galaxy?

What is a Galaxy? A dense group of stars, dark matter, dust and gas held together by gravity. Dark matter- matter that produces no detectable light or other form of energy, but can be detected through its gravitational pull on visible stars and gas.

Galaxies: Small galaxies Contain only about a million stars Dust and gas Milky Way galaxy Contains several hundred billion stars Dark Matter -90% of the total mass of the galaxy Large galaxies Contain more than one trillion stars At the center (heart) of most galaxies there is a supermassive black hole

Formation of Galaxies Theory 1: Theory 2: Galaxies were formed when vast clouds of dust and gas collapsed under their own gravitational pull, allowing stars to form Theory 2: The young universe contained many small “lumps” of matter which clumped together to form galaxies. Hubble space telescope has gathered images to support this theory Most of the early galaxies were spirals but over time many spirals merged to form elliptical

Galaxies They are still being formed!

Galaxy Mergers Larger galaxies consume smaller galaxies. Most bright galaxies are formed from the merger of two or more smaller galaxies. Galaxies are very massive which means they also have a strong gravitational pull. This force can cause galaxies to attach themselves to one another and merge over time Few hundred million to a few billion years to complete

Results of Galaxy Mergers When two or more large spiral galaxies merge they form elliptical galaxies containing more than a trillion stars. Trigger intense bursts of new star formation Create gigantic black holes Galaxy Collision

Types of Galaxies: Shape Classification Spiral Galaxy Most beautiful type of galaxy Examples: Milky way, Andromeda(M31) Flat disks of stars with bright bulges at the center Spiral arms wrap around the bulge Arms are a result of density waves which influence matter as they pass. Color of the spiral arms depend on the new born stars and their characteristics. Dark spaces between the arms contain older stars, which are not as bright

Types of Galaxies: Shape Classification Spiral Barred Galaxies Stars in the center form a bar The arms of the spiral shoot out from the end of the bar The Milky Way galaxy is a spiral bar galaxy

Types of Galaxies: Shape Classification Elliptical Look like fat, fuzzy footballs Stars wrap completely around the galaxy’s heart in all directions Largest galaxies in the universe are elliptical in shape Contain more than a trillion stars Span more than one million light years

Types of Galaxies: Shape Classification Irregular Galaxies This category has a mixture of shapes- anything that is not a spiral or elliptical No identifiable form Usually the smallest galaxies are irregular in shape Contain about one million stars Irregular galaxies are hypothesized to be the building blocks that came together to form the first larger galaxies

Types of Galaxies: Energy Classification Active Galaxies Observing these galaxies in the X- ray, ultraviolet, infrared and radio wavelengths, they appear to be giving off enormous amounts of energy 4 Classifications of Active galaxies Seyfert galaxies Have broad spectra indicating cores of hot, low-density ionized gas. Radio galaxies Nuclei emit jets of high-velocity gas above and below the galaxy -- the jets interact with magnetic fields and emit radio signals. Quasars Most energetic objects in the universe. Blazars  Jet emanating from the galaxy.

Types of Galaxies: Energy Classification Normal Galaxies most of the light comes from the stars in visible wavelengths and is evenly distributed throughout the galaxy

Closure What is the most common way for classifying galaxies? Classify one of the galaxies from the activity. Explain why it is classified that way.

Objective: You will use the different types of galaxies and their characteristics in order to explain the major systems within the universe and earth’s place in it. Warm-Up: Classify the following galaxies by shape 1 2 3 4 A B C

The Milky Way Galaxy The Milky Way galaxy consists of a bulge of stars in the core, probably a thick bar of stars flanking the core, and bright spiral arms wrapping around the core.

The Milky Way Galaxy Size and structure of our galaxy Our solar system Spiral galaxy Thin flat disk 100,000 light-years in diameter 2,000 light years thick Milky Way disk The disk is surrounded by a halo of about 200 globular star clusters Objects near the center of the galaxy move faster Contains between 200 billion and 400 billion stars A black hole (~ 4 million times more massive than our sun) at the center of the galaxy Our solar system 27,000 light years from the center

The Local Group The Milky Way Galaxy is part of a larger cosmic neighborhood- a collection of more than 35 galaxies known as the local group. These galaxies move through space as a single unit, bound by mutual gravitational pull. Largest and heaviest members of the Local Group Milky Way Galaxy Large collection of satellite galaxies Largest and best known satellite galaxies Large and small Magellanic Clouds 200,000 light years away Andromeda Galaxy (M31) 2.5 million light years away

In about 4 billion years Astronomers predict that in several billion years, the Milky way galaxy and Andromeda will merge to form a galactic giant

Hubble’s Law An observational effect of the expansion is that the farther a galaxy is from you, the faster it appears to be receding (Red shift in spectral line). This creates a relationship between the recessional velocity and distance. This phenomenon is known as Hubble's Law Recessional Velocity = Hubble's Constant X Distance V = Ho D   V is the observed velocity of the galaxy away from us, usually in km/sec Ho is Hubble's Constant, in km/sec/Mpc (Ho = 73 km/sec/Mpc). D is the distance to the galaxy in Mpc

Closure: Explain where Earth is located in the universe. Be specific to include local group, location in the galaxy to the solar system. When looking at the relationship between velocity and distance based on Hubble’s law, galaxies that are farther away are moving (faster or slower)?