astro 113 week14 - physics &...

Astronomy 113Dr. Joseph E. Pesce, Ph.D.

Review

https://www.theverge.com/2018/3/10/17104188/melodysheep-time-lapse-universe-earth-formation-watch

Semester Recap³Light and Radiation³The Sun³Measuring Stars³Gas Clouds³Star Formation and Evolution³End States of Stars³Our Galaxy and other Galaxies³Cosmology³Life

Nature of Light³Wave? Particle (photon)?³Electromagnetic waves

Wavelength³Waves cycle in space

³Wavelength: distance between crests or troughs

Red/Blue Light³Red light has longer wavelength than blue³Red light has a lower energy than blue

²Remember: Longer wavelengths = lower energy

The Electro-magnetic Spectrum

³Radio³Infrared³Visible³Ultraviolet³Xrays³Gamma-rays

Blackbody Emission20-7

Wavelength

Wien’s law

Stefan’s law

Spectral Features20-8

Bohr Atom20-9

Doppler Effect20-10

Interior of SunRadiative (= photons) +Convection

�Random walk�: g-ray to visible (Infrared)

1 million yrs

Transport of energy

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-

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+

Solar Structure³Core/Interior³Photosphere³Chromosphere³Corona

Activity on the Sun³Sunspots³Flares³Prominences³Solar wind

Distances to Stars³Parallax

Stellar Brightness³Depends on distance and luminosity

²Inverse square law of light

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

Color Index³Hot stars emit more blue light than cool stars³Color Index is ratio of blue/red³Color Index is related to surface temperature

Spectral TypesO B A F G K M

³Hot to cool³Bright to faint³Classified by spectra

H-R Diagram20-20

Interstellar Medium20-21

³Gas and dust between stars³Reddens, polarizes, and blocks (extincts) light³Emission nebula and HII regions³HI gas³Hot, warm, cold phases³Giant Molecular Clouds

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

Star Formation20-23

Low-mass Star Evolution20-24

³Post Main Sequence³Core depletion of hydrogen³Hydrogen shell burning³Helium flash and helium core³Helium depletion³Helium shell³Helium shell flashes³Planetary nebula³White dwarf

The Evolution of a Low-Mass Star20-25

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

Core - Fe

Outer Atmosphere - Hydrogen

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

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

Pulsars³Magnetized, rotating neutron star

Our Galaxy20-31

Nucleus

BulgeHalo

Rotation Curves

³Plots of orbital velocity versus distance from nucleus

³Gives measure of mass WITHIN each orbit

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

Types of GalaxiesThe Hubble Sequence (1920s)

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

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�)

Cepheid Period-Luminosity Relationship

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

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

Types of AGN³Radio Galaxies³Quasars³BL Lacerta Objects³Seyfert Galaxies

20-405

What Powers

an AGN?

The Cosmological Principle³The universe is isotropic and homogenous³We are not in a special location

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

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

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

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

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

Organic Molecules³Found everywhere in space³Certainly fell on early Earth³Life everywhere?

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

Extrasolar Planets³Everywhere we look (all types of stars)³Every type of planet

²Gas giants²Rocky �earths�

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!

Thank You!

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