Astronomy 113Dr. Joseph E. Pesce, Ph.D.
© Dr. Joseph E. Pesce, Ph.D.
Review
https://www.theverge.com/2018/3/10/17104188/melodysheep-time-lapse-universe-earth-formation-watch
© Dr. Joseph E. Pesce, Ph.D.
Semester Recap³Light and Radiation³The Sun³Measuring Stars³Gas Clouds³Star Formation and Evolution³End States of Stars³Our Galaxy and other Galaxies³Cosmology³Life
20-2
© Dr. Joseph E. Pesce, Ph.D.
Nature of Light³Wave? Particle (photon)?³Electromagnetic waves
20-3
© Dr. Joseph E. Pesce, Ph.D.
Wavelength³Waves cycle in space
³Wavelength: distance between crests or troughs
20-4
© Dr. Joseph E. Pesce, Ph.D.
Red/Blue Light³Red light has longer wavelength than blue³Red light has a lower energy than blue
²Remember: Longer wavelengths = lower energy
20-5
© Dr. Joseph E. Pesce, Ph.D.
The Electro-magnetic Spectrum
³Radio³Infrared³Visible³Ultraviolet³Xrays³Gamma-rays
20-6
© Dr. Joseph E. Pesce, Ph.D.
Blackbody Emission20-7
Inte
nsity
Wavelength
Wien’s law
Stefan’s law
© Dr. Joseph E. Pesce, Ph.D.
Spectral Features20-8
© Dr. Joseph E. Pesce, Ph.D.
Bohr Atom20-9
© Dr. Joseph E. Pesce, Ph.D.
Doppler Effect20-10
© Dr. Joseph E. Pesce, Ph.D.
Interior of SunRadiative (= photons) +Convection
�Random walk�: g-ray to visible (Infrared)
1 million yrs
Transport of energy
20-11
© Dr. Joseph E. Pesce, Ph.D.
FusionIn the sun: (600million tons of Hydrogen/sec =
170,000 yrs to consume mass of earth; in 10 billion years….
4 protons: (Hydrogen) + 2 electrons
p+ p+ p+ p+ e- e-
p+
p+n
n
1 helium nucleus
g-ray &
More mass before than after - mass conserved, so �extra� becomes energy (E=mc2) in the form of a photon, the g-ray.
neutrino+
20-12
© Dr. Joseph E. Pesce, Ph.D.
Solar Structure³Core/Interior³Photosphere³Chromosphere³Corona
20-13
© Dr. Joseph E. Pesce, Ph.D.
Activity on the Sun³Sunspots³Flares³Prominences³Solar wind
20-14
© Dr. Joseph E. Pesce, Ph.D.
Distances to Stars³Parallax
20-15
© Dr. Joseph E. Pesce, Ph.D.
Stellar Brightness³Depends on distance and luminosity
²Inverse square law of light
20-16
© Dr. Joseph E. Pesce, Ph.D.
Magnitudes³Apparent magnitude (m)
² Measured on Earth³ Absolute magnitude (M)
² Apparent magnitude of a star if it were at 10pc from Earth² Measure of absolute brightness or luminosity
20-17
© Dr. Joseph E. Pesce, Ph.D.
Color Index³Hot stars emit more blue light than cool stars³Color Index is ratio of blue/red³Color Index is related to surface temperature
20-18
© Dr. Joseph E. Pesce, Ph.D.
Spectral TypesO B A F G K M
³Hot to cool³Bright to faint³Classified by spectra
20-19
© Dr. Joseph E. Pesce, Ph.D.
H-R Diagram20-20
© 2007-2014 Joseph E. Pesce, Ph.D.© Dr. Joseph E. Pesce, Ph.D.
Interstellar Medium20-21
³Gas and dust between stars³Reddens, polarizes, and blocks (extincts) light³Emission nebula and HII regions³HI gas³Hot, warm, cold phases³Giant Molecular Clouds
© Dr. Joseph E. Pesce, Ph.D.
Hydrostatic Equilibrium20-22
³ Hydrostatic Equilibrium² Balance of force of gravity, which tries to
squeeze Sun, and radiative pressure from fusion, which tries to blow apart Sun
© Dr. Joseph E. Pesce, Ph.D.
Star Formation20-23
© Dr. Joseph E. Pesce, Ph.D.
Low-mass Star Evolution20-24
³Post Main Sequence³Core depletion of hydrogen³Hydrogen shell burning³Helium flash and helium core³Helium depletion³Helium shell³Helium shell flashes³Planetary nebula³White dwarf
© Dr. Joseph E. Pesce, Ph.D.
The Evolution of a Low-Mass Star20-25
© Dr. Joseph E. Pesce, Ph.D.
High Mass Stars³5-50 times the mass of the sun
²Last about 1 million years (very short!)²Create elements through iron (fusion)²�Onion skin�²Expand into Red Supergiant²Explode as a supernova²Leave behind neutron stars or black holes
20-26
© Dr. Joseph E. Pesce, Ph.D.
© 2007-2014 Joseph E. Pesce, Ph.D.
Core - Fe
Outer Atmosphere - Hydrogen
Si
Ag
…
Ar
Ne
C
He
Onion-skin nature of High Mass Stars
Not to scale© Dr. Joseph E. Pesce, Ph.D.
Supernova³Type II
²Iron core cannot burn²Mass exceeds Chandrasekhar limit²Core collapses²Core bounces²Star destroyed
³ Type I²White dwarf exceeds Chandrasekhar limit and explodes
20-28
© Dr. Joseph E. Pesce, Ph.D.
Nova vs. Supernova³Nova
²Explosion on surface of white dwarf²Luminosity = 10,000 x sun²White dwarf survives explosion
³Supernova²Star destroyed²Luminosity = 100 billions x sun²Neutron star or blackhole remains + remnant
20-29
© Dr. Joseph E. Pesce, Ph.D.
Pulsars³Magnetized, rotating neutron star
20-30
© Dr. Joseph E. Pesce, Ph.D.
Our Galaxy20-31
Nucleus
BulgeHalo
Disk
Halo
© Dr. Joseph E. Pesce, Ph.D.
Rotation Curves
³Plots of orbital velocity versus distance from nucleus
³Gives measure of mass WITHIN each orbit
20-32
© Dr. Joseph E. Pesce, Ph.D.
Dark Matter³Matter detected through its gravity
²Has no detectable electromagnetic emission
³Over 90% of the mass of the Galaxy is composed of this dark matter
³Found everywhere we can measure it’s gravitational influence. Universe is full of it
20-33
© Dr. Joseph E. Pesce, Ph.D.
Types of GalaxiesThe Hubble Sequence (1920s)
20-34
© Dr. Joseph E. Pesce, Ph.D.
Stellar Populations in Galaxies³Elliptical galaxies
²Population II stars²Old, red²Very low metal abundance
³Spiral galaxies²Population I stars in spiral arms, Pop II in
bulge & halo²Young, blue stars²Ongoing star formation in arms
20-35
© Dr. Joseph E. Pesce, Ph.D.
Hubble’s Law
vr = Ho * D
³Ho = Hubble Constant = ?
²Need to measure z (easy) and D (hard)
²HST Key Project (observe Cepheids to 200Mly)
³More distant galaxies moving away faster
³Why?
³Universe is expanding (from an �explosion�)
20-36
© Dr. Joseph E. Pesce, Ph.D.
Cepheid Period-Luminosity Relationship
20-37
© Dr. Joseph E. Pesce, Ph.D.
Standard Candles³Objects with known intrinsic luminosity³Luminosity if the same wherever object is³Luminosity is known fairly accurately³Comparing absolute and apparent magnitudes
gives distance³Types
²Cepheids²Supernovae (Type I)²Red Giants²Others
20-38
© Dr. Joseph E. Pesce, Ph.D.
Active Galaxies³The centers of some galaxies are producing
HUGE amounts of energy²About 5% of galaxies
³These are ACTIVE GALAXIES, or ACTIVE GALACTIC NUCLEI (AGN)
³Non-thermal radiation
20-39
© Dr. Joseph E. Pesce, Ph.D.
Types of AGN³Radio Galaxies³Quasars³BL Lacerta Objects³Seyfert Galaxies
20-405
© Dr. Joseph E. Pesce, Ph.D.
What Powers
an AGN?
20-41
© Dr. Joseph E. Pesce, Ph.D.
The Cosmological Principle³The universe is isotropic and homogenous³We are not in a special location
20-42
© Dr. Joseph E. Pesce, Ph.D.
Implications of Hubble’s Law³Hubble’s law must obey the Cosmological
Principle ³Everything is expanding, everywhere³If we go backwards in time, the universe
must be getting ever smaller, denser, and hotter²BIG BANG
20-43
© Dr. Joseph E. Pesce, Ph.D.
Cosmic Microwave Background Radiation
³Predicted by Big Bang Theory³Fossil from early days of universe³First observed by Penzias and Wilson,
confirmed multiple times³Excellent agreement between theory and
observation
20-44
© Dr. Joseph E. Pesce, Ph.D.
Dark Matter & Fate of Universe³Dark matter is important because it adds to
mass of universe³Mass of universe dictates how universe will
end1. Expand forever, at ever decreasing rate (open,
unbound)2. Expand forever at same speed (open, unbound)3. Expansion stops eventually and universe
collapses on itself (closed, bound)³We appear to be in #1 state
20-45
© Dr. Joseph E. Pesce, Ph.D.
Dark Energy³But this doesn’t seem to �matter� much,
because mass/energy dominated by dark energy²Most mass is dark matter²Most energy/mass is dark energy
³Causing expansion to accelerate
20-46
© Dr. Joseph E. Pesce, Ph.D.
The Universe³Started in Big Bang, with Inflation³Matter dominated universe filled with Dark
Energy ³Matter froze out when Universe was 0.0001s
old³All Hydrogen and some Helium (and a
smattering of Li, Be, & B) formed in shortly after the Big Bang
20-47
© Dr. Joseph E. Pesce, Ph.D.
Organic Molecules³Found everywhere in space³Certainly fell on early Earth³Life everywhere?
20-48
© Dr. Joseph E. Pesce, Ph.D.
Solar System³Earth is in habitable zone: ideal temperature
and pressure for liquid water³What about elsewhere?
²Mars had water in past – under surface now ²Europa may have liquid water under surface ice
20-49
© Dr. Joseph E. Pesce, Ph.D.
Extrasolar Planets³Everywhere we look (all types of stars)³Every type of planet
²Gas giants²Rocky �earths�
20-50
© Dr. Joseph E. Pesce, Ph.D.
Extraterrestrial Life³�Lower� forms (e.g., amoeba, bacteria, etc)
²Almost certainly³Intelligent life (e.g., humans)
²Unknown, but maybe less likely³Almost certainly no aliens visiting us now!
20-51
© Dr. Joseph E. Pesce, Ph.D.
Thank You!
© Dr. Joseph E. Pesce, Ph.D.