NATS 1880 Lecture Notes - Lecture 1: Cosmic Microwave Background, Millisecond Pulsar, Crab Nebula
2 May 2018
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Chapter 3: The Universal Context of Life
Modern Astronomy:
- Begins where Newton left off
- Three important ideas in framing the universal context
o The universe is vast and old
▪ Great potential for life, old age implies time for it to begin and evolve
o The elements of life are widespread
▪ Basic chemical elements that make up Earth and life are present throughout the
universe
o The same physical laws that operate on Earth operate throughout the universe
▪ Neto’s olusio that the las of atue ae the same everywhere is
supported by tests – reasonable to think same process possible on other worlds
- These ideas reinforce the Copernican revolution – We are not the center of the universe
- Cosmic Address:
o Planet in our solar system
o Solar system in our galaxy
o Our galaxy in Local Group
o Local Group in the Local Super-Cluster
o All a part of the universe
- Light year (ly) is the distance a photon of light will travel in a year – 9.46 x 10^12km
- Alpha Centauri
o Closest star system would take 4.3 ly to get to – 50 000km/h and 100 000 years
- Orion Nebula (M42)
o 1500 ly away – seeing the nebula are is was 1500 years ago
- Milky Way is 100 000 ly across and home to about 200 billion stars and dark matter
Modern Sciences:
- The more massive the galaxy, the stronger its gravity and the faster stars should be orbiting
o By studying stellar orbits, astronomers have put together a map of the distribution of
matter in the Milky Way
- The Universe Contains:
o All the matter and energy in existence
o Planets, stars, etc. – 4%
o Dark matter – 28%
o Dark energy or vacuum energy – 68%
▪ Pushing galaxies apart even while their gravity tries to draw them together
▪ Gravity played a key role in assembling galaxies
▪ Evidence has been building for decades
• Does not affect general evolution or study for other life
History:
- Birth of the universe – Big Bang
- Galaxies as cosmic recycling plants – early universe only contained hydrogen and helium, other
elements were made by starts and recycled within galaxies
- Life cycle of stars – born in clouds of gas and dust, explode when they die
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find more resources at oneclass.com
- Earth and life – 4.5 billion years ago, 2% of the original elements converted to heavier elements
Big Bang and the Expanding of the Universe:
- Telescopic observations reveal the entire universe is expanding – average distance between
galaxies are increasing over time
o Individual galaxies and clusters DO NOT expand
- Evidence:
o Detected radiation left over from the Big Bang
▪ Universe was hotter and denser as if it was smaller, producing radiation (light)
▪ Should have left behind a faint glow, known as cosmic microwave background
o Overall chemical composition of the universe
▪ If the Big Bang occurred, it should be ¾ hydrogen and ¼ helium
Stellar Lives and Galactic Recycling:
- Stars are born when gravity compresses the material in a cloud until the center is dense and hot
enough to generate energy by nuclear fusion
o Process of lightweight atomic nuclei smashing together; fuse to make heavier nuclei
o Some mass lost will become energy (E = m x c^2)
- Massive stars die in explosions called supernovae and returned matter mixes to form new stars
Ex. The Crab Nebula
- Eidee e’e ade of stas
o Younger stars (sun) were born with higher proportions of heavy elements
▪ Means they were born from gas clouds containing elements born by earlier
generations of stars
o Overall abundance of chemical elements in the universe today
o Gas from exploding stars
▪ Models of massive stars and their deaths allow astronomers to calculate the
precise makeup expected for these clouds from recently deceased stars
- Importance of stellar manufacturing
o Without it, our universe would not contain the chemical elements of which we are made
o The cloud that birthed the solar system was 98% hydrogen and helium – 2% everything
else which made Earth and small planets
Implications for Life in the Universe
- Stellar and galactic recycling operate throughout the Milky Way as well as similar ones – expect
chemical composition of other star systems to be similar
o Other star systems may have raw materials to build Earth-like planets and life
Scale of Time:
- Cosmic Calendar, where January 1st: Big Bang – December 31st: Present Time
Scale of Size:
- Could be infinite
- Age of the universe places a fundamental limit on the visible portion of the universe
- Known as our observable universe, consisting only of objects that lie within 13.8 billion ly – earth
o Philosophical Implications
▪ Reason to believe universe goes beyond, but no hope of seeing or studying it
▪ By definition, we are at center of the observable universe
find more resources at oneclass.com
find more resources at oneclass.com
Andromeda, our galactic neighbour – we see it as it was 2.5 million years ago
Terrestrial (Earth-Like) Planets:
- Small diameter
- High densities, rock and metal compositions
- Orbit close to the sun (warm surface)
- Thin atmosphere
- Few moons
- No ring system
Jovian/Gas-giant planets:
- Large diameter
- Low densities – gas composition (hydrogen, helium, etc)
- Orbit further from sun (cold surface)
- Thick atmosphere
- Many satellites
- Ring systems
Other
- Dwarf planets, asteroids (minor planets) and comets are common
- All resemble small terrestrial planets with comets having a highe olatile ateials – long tails
Medium and Large Moons:
- Enough self-gravity to be spherical
- A lot of ice
- Formed in orbit around Jovian planets
- Orbit in same direction as planet rotates
Small Moons:
- More numerous than medium/large
- Not enough gravity to be sphere – potato shaped
Formation of Solar System:
- Nebular Theory
o Continues to evolve as new date leads to updates
o Gives us confidence that other worlds can develop
o Planetary formation is a complicated process
- Giant molecular cloud of dust and gas, the solar nebula, begins to spin a collapse - Newts Gravity
- As ateial oes iads, the poto-Sun begins to form at the centre (warm to hot)
- Small planetsimals form and assertion (stickling together) of material commences
- Small, rocky planets form close to the Sun and larger gas planets grow in cooler regions
- “u stats to shie ulea fusio of hdoge ito heliu ad the sola id leas out
remaining gas and dust
Atoms, the building blocks of matter:
- Composed of positively charged nuclei, containing protons and neutrons surrounded by a
negatively charged electron cloud
- Most around us are neutral
- When they lose of gain electrons, they are charged ions
- 92 naturally occurring elements
- Isotopes of an element
o Different number of neutrons but still the same element
- Atomic mass number – mass of protons and neutrons
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
These ideas reinforce the copernican revolution we are not the center of the universe. Cosmic address: planet in our solar system, solar system in our galaxy, our galaxy in local group, local group in the local super-cluster, all a part of the universe. Light year (ly) is the distance a photon of light will travel in a year 9. 46 x 10^12km. Alpha centauri: closest star system would take 4. 3 ly to get to 50 000km/h and 100 000 years. Orion nebula (m42: 1500 ly away seeing the nebula are is was 1500 years ago. Milky way is 100 000 ly across and home to about 200 billion stars and dark matter. The more massive the galaxy, the stronger its gravity and the faster stars should be orbiting: by studying stellar orbits, astronomers have put together a map of the distribution of matter in the milky way. The universe contains: all the matter and energy in existence, planets, stars, etc.
