Cosmology

Paul Bergeron

Department of Physics and Astronomy,University of Utah, Salt Lake City

April 26, 2018

Today’s Plan

Cosmology

I How to measure distances

I Death of Stars

I Hubble Flow

I Big Bang & CMB

Unit: light-year (ly)

Distance light travels in 1 year.

I 1 foot: 1 light-nanosecond

I Earth-Sun: 8 light-minutes

I Oort Cloud: 1.6 light-years

I Milky Way: 100, 000 light-years

I Observable Universe: 93 billion ly

Today’s Plan

Cosmology

I How to measure distances

I Death of Stars

I Hubble Flow

I Big Bang & CMB

Unit: light-year (ly)

Distance light travels in 1 year.

I 1 foot: 1 light-nanosecond

I Earth-Sun: 8 light-minutes

I Oort Cloud: 1.6 light-years

I Milky Way: 100, 000 light-years

I Observable Universe: 93 billion ly

The Chemical Homogeneity of the Universe

Cecilia Payne-Gaposchkin

Image Credit: Wikimedia Commons

I studied:• stellar composition• variable stars

I smashed astronomy’sglass ceiling

The Most Brilliant Thesis

I temperature-spectra connection

I absorption spectra vary

I Previously: amount of elements

I Showed: ionization statistics

I Concluded:• Earth-like ‘metal’ ratios• But much more Helium• even more Hydrogen

Therefore:The universe is made of hydrogen

Astronomy: ‘metal’ is everything except hydrogen & helium

The Chemical Homogeneity of the Universe

Cecilia Payne-Gaposchkin

Image Credit: Wikimedia Commons

I studied:• stellar composition• variable stars

I smashed astronomy’sglass ceiling

The Most Brilliant Thesis

I temperature-spectra connection

I absorption spectra vary

I Previously: amount of elements

I Showed: ionization statistics

I Concluded:• Earth-like ‘metal’ ratios• But much more Helium• even more Hydrogen

Therefore:The universe is made of hydrogen

Astronomy: ‘metal’ is everything except hydrogen & helium

Measuring the Universe

The Measurement Problem

‘You can’t know the distance to the Moon [and Sun]; you’dneed to go there and stack up a bunch of rulers...’– A Student who doesn’t “believe in all that stuff about the Moon and Sun” (and space)

How It Works

Image Credit: Wikimedia Commons

I Geometry doesn’t lie

I Get trustworthy phenomena

I Calibrate with known distances

I Get new, further phenomena

I Calibrate with known distances

I Rinse and Repeat

Measuring the Universe

The Measurement Problem

‘You can’t know the distance to the Moon [and Sun]; you’dneed to go there and stack up a bunch of rulers...’– A Student who doesn’t “believe in all that stuff about the Moon and Sun” (and space)

How It Works

Image Credit: Wikimedia Commons

I Geometry doesn’t lie

I Get trustworthy phenomena

I Calibrate with known distances

I Get new, further phenomena

I Calibrate with known distances

I Rinse and Repeat

Parallax – Up to 500 ly

Perspective

I The closer the object,the greater the angular shift

I Extremely far objects don’t move

I Closer objects appear to move

Geometry

I Know the Observer’s motion

I Measure the angular motion

I Construct triangles,and use trigonometry

The Shift

Image Credit: Indiana University

Inverse-Square Law

Perspective

I Light emitted is constant

I Spreads out over uniformly: growing sphere (Area: 4πr2)

I Density decreases as the light spreads out

I Apparent Luminosity: Lapparent ∝ Lemitted/r2

The Shift

Image Credits: Institute for Astronomy, University of Hawai‘i Wikimedia Commons

Cepheid Variable Stars – Up to 13 million ly56 million ly for space-based telescopes

What are they?

I Intermediate masses (2-10M�)

I The star pulsates:• The emitted light pulses• The star’s radius pulses Henrietta Swan Leavitt

AIP Emilio Segre Visual Archives

The Physics

I Dense core: Helium fusion

I Hydrogen envelope expands

I Hydrogen burning shuts off

I Light flux decreases

I Envelope schools, contracts

I Fusions turns back on

Sandage & Tammann (1968),

Astrophys. J. 151

Cepheid Variable Stars – Up to 13 million ly56 million ly for space-based telescopes

What are they?

I Intermediate masses (2-10M�)

I The star pulsates:• The emitted light pulses• The star’s radius pulses Henrietta Swan Leavitt

AIP Emilio Segre Visual Archives

The Physics

I Dense core: Helium fusion

I Hydrogen envelope expands

I Hydrogen burning shuts off

I Light flux decreases

I Envelope schools, contracts

I Fusions turns back on

Sandage & Tammann (1968),

Astrophys. J. 151

Stellar InteriorsElemental Envelopes

Image Credit: Wikimedia Commons

I Fusion Requires:• high temperature• high density (presures)

I Fusion Zones:• Stellar Cores• Envelope transitions

Fusion

(Image Credits: Central New York

Observers)

Type II Supernovae

Core Collapse

I Massive stars & 10M�

I Driven by gravity

I Collapse restarts fusion

I Brighter than galaxies

I Energy: photodisintegration

I Rebound: fusion shockwave• heavy elements produced

I Neutrino flux:blows off the outer layers

SN 1987A (HST, NASA) Crab Nebula (HST, NASA)

Type Ia Supernovae – up to 1 billion ly

White-Dwarf Megers

I New mass: fusion restarts

I Significant mass: runaway

I Uniform brightness (almost)• needs spectral corrections

Image Credit: Analyzing the Universe, Rutgers

Accretion Events

I Companion Redgiant

I Strips companion’s

I Novae: critical mass reached

I Repeat:build to supernova limit Image Credit: Analyzing the Universe, Rutgers

Type Ia Supernovae – up to 1 billion ly

White-Dwarf Megers

I New mass: fusion restarts

I Significant mass: runaway

I Uniform brightness (almost)• needs spectral corrections

Image Credit: Analyzing the Universe, Rutgers

Accretion Events

I Companion Redgiant

I Strips companion’s

I Novae: critical mass reached

I Repeat:build to supernova limit Image Credit: Analyzing the Universe, Rutgers

Hubble’s Law – 1 billion ly

v = H0`

What is it?

I Doppler shift:moving shifts light’s frequency

I Far away galaxies are redshifted:• relative motion• galaxies are moving away

I Further the galaxy, greater redshift:• Universe is exanding Image Credit: AIP

Emilio Segre Visual Archives

The Big Bang

If the universe is expanding: play the movie backwards.

What happens?

I Heavy elements go back into supernovae

I Stars unignite & unaccrete

I Galaxies become more amorphous

I Everything comes together

I Everything is gas and light

I densities increase

I Ionization: plasma fills the universeand light can’t propogate

The Big Bang

If the universe is expanding: play the movie backwards.

What happens?

I Heavy elements go back into supernovae

I Stars unignite & unaccrete

I Galaxies become more amorphous

I Everything comes together

I Everything is gas and light

I densities increase

I Ionization: plasma fills the universeand light can’t propogate

The Big Bang

If the universe is expanding: play the movie backwards.

What happens?

I Heavy elements go back into supernovae

I Stars unignite & unaccrete

I Galaxies become more amorphous

I Everything comes together

I Everything is gas and light

I densities increase

I Ionization: plasma fills the universeand light can’t propogate

The Big Bang

If the universe is expanding: play the movie backwards.

What happens?

I Heavy elements go back into supernovae

I Stars unignite & unaccrete

I Galaxies become more amorphous

I Everything comes together

I Everything is gas and light

I densities increase

I Ionization: plasma fills the universeand light can’t propogate

The Big Bang

If the universe is expanding: play the movie backwards.

What happens?

I Heavy elements go back into supernovae

I Stars unignite & unaccrete

I Galaxies become more amorphous

I Everything comes together

I Everything is gas and light

I densities increase

I Ionization: plasma fills the universeand light can’t propogate

Going Forward: There should be an afterglow from the Big Bang.

The Cosmic Microwave Background (WMAP 9 year data, NASA)