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What is the Universe Part 1 Where did our solar system come from? • Stars and planets form from interstellar clouds (nebulae) of gas and dust, mostly made up of hydrogen and helium • We can see these all over the Milky Way galaxy • Clouds begin to condense when gravitational pull of the matter in these clouds grows stronger • This is likely how our solar system came to be Where did our solar system come from? Where did our solar system come from? • Tiny condensed particles of matter from within the interstellar cloud that started it all began to clump and bind a few billion years ago • As the diameters of these objects grew, they became planetesimals • As growth continued, some planetismals were destroyed through meter collisions, but some survived—and became the eight planets of our solar system • The third planetismal from the Sun became our Earth Where did our solar system come from? • Scientists theorize that the first planet to form in our solar system was Jupiter, a gas giant and the fifth planet from the Sun • Jupiter kept growing larger and pulling remaining dust and debris from space into its orbit, as did the other gas giants Where did our solar system come from? • This is likely why the interior planets (including us) remained small and rocky and (initially) without any satellites (moons) • Some debris didn’t get pulled into a planetary orbit and today makes up what is commonly known as an asteroid belt (between Mars and Jupiter) What happened to the “extra” matter? • Some matter did not get pulled into a planetary orbit during the formation of our solar system • Meteor= “space trash” burnt up by our mesosphere • Meteorite=“space trash” that comes in contact with Earth’s surface What happened to the “extra” matter? • Comets= small, icy bodies with highly eccentric orbits around the Sun • Periodic comets= repeatedly orbit in the inner solar system – Ex: Halley comet, last seen in 1986, expected again in 2061 (~75 year period) What is a Galaxy? • Galaxy: Cluster or bunch of billions stars. There are about 100 billion galaxies in the universe. • Our neighboring galaxy, Andromeda, is 2.5 million light years from Earth! • We belong to the local group, a cluster of about 35 galaxies. What is a Galaxy? What does the Milky Way look like? What does the Milky Way look like? 100 billion+ late main sequence and Red Giant stars make up the disk, suggesting that this is the oldest part of the galaxy Sagittarius A, the mass in the center of our galaxy is about 2.6 million times the mass of the sun and it believed to be a super-massive black hole that “glows” because of the hot gas spiraling into it The youngest stars in the galaxy make up the spiral arms, this is where most star Edwin Hubble • Born in small-town Missouri in 1889 • Attended high school in Chicago, excelling at academics and athletics (broke state high jump record, Varsity basketball player and boxer) • Attended college on scholarship, continuing to play sports and earned two degrees in mathematics and astronomy • Went to Oxford University Law School on a Rhodes scholarship, where he did not continue his studies in astronomy, but instead studied law. • He quickly realized that he wasn’t satisfied practicing law and went back to school for his astronomy doctorate Edwin Hubble • As soon as he finished up his third degree, he was drafted during WWI and didn’t begin his career as an astronomer in California until 1917 • First person to… – See other galaxies – Develop a system to classify galaxies – Explain redshifft – Define the Big Bang Theory • Hubble also refined Einstein’s theory of relativity and the two famous scientists got together in 1931 because Einstein was grateful for Hubble correcting his mistakes How do we know the universe is expanding? • Edwin Hubble discovered that most galaxies have redshift in their spectra • Redshift of an object in space depends on distance from Earth • The farther away an object is, the faster it is moving away How does the night sky tell us about the past? • Because many galaxies are so distant, it takes a long time for their light to reach Earth • Ex: When we see sunlight, we are really seeing light the Sun produced eight minutes before Models of the Universe • Big Bang Theory (Edwin Hubble): The universe began as a point and has been expanding ever since • NOT really an explosion, but an expansion • Steady State Theory (Fred Hoyle): New matter has been created such that when objects in space move, new objects fill that void • Conflicts with the law of conservation of matter Big Bang v. Steady State Which theory is right? • BOTH theories have observational tests to support them • BUT evidence weighs in favor of the Big Bang • If the universe began as a highly compressed point (as stated by Big Bang), then high temperature and pressure would have created a great deal of high energy radiation • In 1965, scientists discovered persistent background noise in radio antenna caused by weak radiation • This is believed to be remnant of the Big Bang, as the energy has shifted over time • Steady State supporters have no explanation of this What is going to happen to our universe? 1) Closed Universe (Big Crunch)—expansion will stop and shift to contraction 2) Open Universe—expansion will continue forever 3) Flat Universe (Big Chill)—expansion will slow to a halt in an infinite amount of time, but never contract What is going to happen to our universe? What is going to happen to our universe? • The constant interaction between gravity (pressure in) and expansion (pressure out) will determine what happens • One approach to determining the fate of the universe is to measure how much expansion has already slowed, using redshift of distant galaxies • Latest evidence: expansion has started to speed up again! We don’t know what’s causing it!! • Most evidence points to a flat universe (inflationary model)