Humans are inherently curiousabout their place in the Universe.

A Spiral Galaxy seen edge on.

We live in an Island Universe

Our galaxy and others are collections of stars of all ages. The birth and death of stars is an ongoing process. Stars are formed by the gravitational collapse of interstellar gas and dust.

The Sombrero Galaxy

The Andromeda Galaxy - our twin at a distance of 2.2 million light-years.

Dark Matter

• Motion of stars in the outer region of our galaxy shows that mass of know matter (stars, IM, etc.) is less than 10% of the mass of the Galaxy.

• Motion of other galaxies within clusters shows need for dark matter.

• Best guess for form of dark matter: exotic matter.

The Rosetta Nebula - hot, glowing hydrogen gas surrounding a cluster of young, hot stars.

The Horsehead Nebula

The Orion Nebula - one ofthe maternity wards of thegalaxy. New stars areforming from interstellargas and dust.

Hubble photo of the star forming region in the Eagle Nebula

The Jewel Box - a young cluster of stars

Evolution of a 1 solar mass star

Protostar - core not hot enough for fusion.

Main sequence - hydrogenfuses to helium in the core.

Red giant - fusion in a shellsurrounding the core. Moreenergy is being generated.Star swells up and cools.Ejects outer regions.

White dwarf -dead star, no fusion. It is just cooling off.

Near the end of its lifethe star will develop a carbon and oxygen core.

The core will not get hot enough to fusecarbon.

The star will pulsateunstably and willeject its outer envelopleaving behind a deadstar that will becomea white dwarf.

The Death of a 1 Solar Mass Star

The Ring Nebula - when a star like our sun dies it ejects its outer regions. A dead white dwarf star is left behind.

The Death of a 15 Solar Mass Star

Near the end of its lifethe star will develop and iron core.

Reactions in the iron core will cause the starto explode (supernova)scattering its contentsinto interstellar space.A dead neutron starwill be left behind.

Elements heavier thaniron will be created in the explosion.

Massive stars produce the elements from carbon to iron through nuclear fusion over their lifetimes. Supernova explosions produce elements heavier than iron and distribute all these heavier elements into the interstellar matter making them available for later generation stars.

Crab Nebula -- supernova explosion

Not only is our galaxy changing with time, the entire Universe is evolving. The space between us and the distance galaxies is increasing with time.

Edwin Hubble with his cat Nikolus Copernicus. (Colliers Magazine, 1949)

Hubble’s Law: For distantgalaxies, the redshift in theirradiation (the amount by which the wavelength of the radiation is increased)is directly proportional to the distance to the galaxy.Published in 1929.

Redshift vs distance

Einstein lecturing on the GTR in Pasadena, California, 1932.

Einstein developed the general theory of relativity (GTR) in 1915.It predicted that space had to be either expanding or contracting.Einstein believed this to be incorrect and changed his theory.

Expansion of Space

• 1916 - Einstein’s general theory of relativity predicts that space must be either expanding or contracting. Einstein does not believe this and tries to “fix” the theory.

• 1920s - Other astronomers and physicists show that all versions of the GTR require either the expansion or contraction of space.

• 1929 - Hubble’s Law.• 1930 - Arthur Eddington explains Hubble’s Law as the

expansion of space as described by the GTR.• 1930 - Einstein calls his not accepting his original theory

“the greatest blunder of my scientific career.”

Clusters of galaxies arerepresented by pieces ofpaper on the balloon.

As the balloon is blownup its surface area (space)increases with time.

The clusters of galaxiesdo not increase in size. They get further apart but do not move throughspace.

The Balloon Model of Expanding Space

1920s - shows that GTR, even with the cosmological constant still requires that space either expand or contract.

1930s - reenters cosmology.First to develop a model basedon GTR of what the universe would have been like in the past.Father of Big Bang.

Most scientists are skeptical in part because LeMaitre is a priest and there are many similiarites between the Big Bang and Genesis.

Abbe George LeMaitre

George Gamow

Gamow with Wolfgang Pauli

1948 - Gamow used newknowledge of nuclear physicsalong with the GTR to describe the early universe.

He assumed (like LeMaitre)that the early universe wasmuch hotter and denser thanit is today and that the expansion of space cooled itand allowed structures to form.

He intended to show how thehot, dense conditions of theearly universe could produce all the chemical elements present in the universe today.

Predictions of the Big Bang model

• The early universe contained only hydrogen and helium. Because of the expansion of space and its cooling effect, nucleosynthesis only occurred between 3 to 4 minutes after the big bang (A.B.B.) and essentially stopped after helium.

• The universe is filled with a background radiation whose temperature is a few degrees above absolute zero. When neutral atoms formed (about 500,000 yrs A.B.B.), the electromagnetic radiation essentially stopped interacting with matter. The expansion of space cooled the radiation from its initial value of about 3000 K to its present low value.

Burbidge, Burbidge, Fowler, and Hoyle show that elements heavier than helium can be produced in the interiors of stars. The explosive deaths of these stars scatter the elements into the space between the stars and make them available forlater generation stars (like our sun).

Arno Penzias and Robert Wilson

Bell Labs’ radio telescope.

Early 1960s - Penzias and Wilsonare hired by Bell Labs to evaluatethe performance of the new radiotelescope to be used in trans-Atlantictelephone communications.

They find a small, unexplained signal regardless of the direction the telescope is pointed. It is notenough to be a problem, but theyare curious.

1964 - They become aware that thenoise in their telescope is the cosmicbackground radiation predicted bythe Big Bang theory.

Early History of the Universe

• T = 0 - Big Bang beginning of a hot, dense universe in expanding space. Expansion cools the universe.

• T = 10-35 sec A.B.B., Temp = 1027 K - Inflationary period. Matter dominates antimatter.

• Temperature is too hot for any structure to exist. Elementary particles - leptons (electrons) and quarks in a sea of photons.

• T = 10-5 sec, Temp = 1012 K - Formation of protons and neutrons from quarks.

• T = 3 to 4 min, Temp = 109 K - Formation of helium nuclei from protons and neutrons. 94% protons (H nuclei) and 6% He nuclei.

• T = 300,000 yrs, Temp = 3000 K - Formation of atoms from electrons and nuclei. Universe becomes neutral and the background radiation is released.

Outline of the History of the Universe

• The universe began about 15 billion years ago - the big bang. The early universe was very hot and dense. The amount of space in the universe increased rapidly with time.

• The expansion of space cooled the universe and made it less dense. As a result, about 1 million years after the big bang, hydrogen and helium atoms formed.

• The force of gravity caused stars and galaxies to form from the hydrogen and helium gas. Some hydrogen and helium was not immediately converted to stars but was left over as interstellar matter.

History (continued)

• The elements heavier than helium were produced by nuclear reactions in the interiors of stars. Explosions of dying high-mass stars scattered these elements into interstellar space and they became part of the interstellar matter.

• Later generations of stars formed from the interstellar matter. Some had earth-like planets.

• The solar system formed about 4.6 billion years ago. • Geological, chemical, and biological evolution led to the

present diversity of life on earth.