Overview of Astronomy AST 200

Astronomy Nature designs the Experiment Nature designs the Experiment Tools Tools 1) Imaging 2) Spectroscopy 3) Computational

Galaxy – Gravitationally bound aggregate of Million to 100 billion stars Million to 100 billion stars Gas and dust (10s of % by mass) Gas and dust (10s of % by mass) Dark Matter Dark Matter

Properties… Masses = million to trillion solar masses Masses = million to trillion solar masses Sizes = 30,000 to 300,000 light years Sizes = 30,000 to 300,000 light years Rotation Period = 10 – 100 million years Rotation Period = 10 – 100 million years Average Separation = 3 million light years Average Separation = 3 million light years

Galaxy Types – Spiral Galaxies Central Bulge – Old Stars Disk – Young Stars, Gas, and Dust Some have bars

Schematic of Spiral Galaxy The Sun is approximately 28,000 light years from the center of our Galaxy

Galaxy Types – Elliptical Galaxies Old Stars Very little Gas and Dust

Galaxy Types – Dwarf Ellipticals Masses = 10 million to 1 billion Solar Masses There are a lot more dwarf elliptical galaxies than there are spiral or normal elliptical galaxies

Galaxy Components - Stars Powered by fusion (hydrogen helium + energy) Stability – balance of inward gravity and outward radiation pressure Importance – heat, light, metal production Lots of low mass stars, fewer high mass stars, & the relative fraction may be the same for every star-forming environment

Hertzsprung-Russell Diagram

Stars (cont) Lifetimes of Stars depend upon Mass (Sun = 10 billion years) Lifetimes of Stars depend upon Mass (Sun = 10 billion years) End State Depends on Mass End State Depends on Mass Average Separation of Stars 3 – 4 light years Average Separation of Stars 3 – 4 light years

End States M star < 8 M solar - White dwarf M star = 8-60 M solar - Neutron star M star > 60 M solar - Black hole

Evolution along the HR Diagram

Galaxy Components - Solar Systems Solar systems consists of objects that are gravitationally bound to stars Our own solar system consists of 8 – 9 planets, comets, and a host of smaller objects comprised of rock and ice Many extrasolar planets have been found recently, indicating that solar systems may be quite common

Formation of Solar System Products Planets Comets, etc

Our Solar System: Terrestrial & Gas Giants

Formation of the Solar System

Extrasolar Planets - Radial Velocities Accuracy needed: ~10s of m s -1 or ~ 20 mph (Video)

Examples -

Galaxy Components – Gas Stars form in molecular clouds Molecular clouds can have masses of up to 1 million solar masses Molecular gas is found in the disk regions of spiral galaxies

Gas, cont. Neutral hydrogen gas extends farther out in galaxies than the stellar disk does We use the motion of the gas to determine galaxy masses…

… and to trace interaction

Components – Black Holes Very massive stars form black holes when they die Very massive stars form black holes when they die But we also find supermassive (million to a billion solar masses) black holes at the centers of galaxies But we also find supermassive (million to a billion solar masses) black holes at the centers of galaxies There is a relationship between the mass of black hole in the center of a galaxy and the mass of stars in the bulge of a galaxy There is a relationship between the mass of black hole in the center of a galaxy and the mass of stars in the bulge of a galaxy

The Center of Our Galaxy

Dark Matter It appears that most (90%) of the mass in the universe is dark – i.e., it doesn’t emit light Evidence – e.g., masses calculated from galaxy rotation curves Distribution in galaxies – spherical What is it? dead stars, black holes + SOMETHING ELSE

Starburst Galaxies & Active Galaxies Some galaxies are observed to be making new stars at 10 – 100 times that of normal spiral galaxies Others are observed to have bright, compact nuclei which appear to be powered by mass accretion onto a central black hole

We believe that activity in extreme starburst galaxies & active galaxies are mostly caused by a galaxy merger event

Clusters of Galaxies Very massive – 100 trillion solar masses

Cosmology – origin and evolution of the universe The universe is expanding – all galaxies are moving away from us The universe was once much hotter – 3K background radiation A lot of work has gone into finding distant galaxies in order to figure out when the first galaxies formed and how they evolve.

Cosmology – origin and evolution of the universe The universe is expanding – all galaxies are moving away from us The universe was once much hotter – 3K background radiation A lot of work has gone into finding distant galaxies in order to figure out when the first galaxies formed and how they evolve. 3K Cosmic Microwave Background

Cosmology – origin and evolution of the universe The universe is expanding – all galaxies are moving away from us The universe was once much hotter – 3K background radiation A lot of work has gone into finding distant galaxies in order to figure out when the first galaxies formed and how they evolve.

Cosmological Parameters Hubble Constant = H 0 Hubble Constant = H 0 Density of Universe =  matter +  DM +   Density of Universe =  matter +  DM +  