ILEU astro

Redshift

Light turns red due to the expansion of the universe stretching the waves

Moreso the longer it has been travelling

Fermi’s paradox

Parallax

General relativity proves that

the universe can’t be static, must be expanding

3 key features of the universe

• Homogenous (at a large scale)

• Expanding

• Began hot and dense

Cosmic microwave background

Radiation left over from when the universe began expanding with an explosion

Dark matter

Behaves like baryonic matter but can’t be seen

Dark energy

Doesn’t behave like ordinary matter, also can’t be seen

Hubble’s law

The universe is expanding, galaxies have redshift velocities proportional to distance, so further away galaxies are moving away faster

Main sequence (Hertzsprung-Russell) trend

As temperature increases, luminosity increases

Big stars burn

brightly but briefly

Low mass star fate

Burn out of H₂ → red giant → core collapse to white dwarf + outskirts blow off to planetary nebula

Red giant

Big, cool, He-burning star

White dwarf

Hot ember which cools over time

High mass star fate

Burn until Fe → gas blown off as supernova + super-heavy core becomes neutron star or black hole

Neutron star

• tightly packed neutrons

• rotate on axis and emit beams of radiation, observed as pulsars

Speed of light =

wavelength x frequency

Big Bang nucleosynthesis

In the early universe (secs-mins), photons gaining enough energy to become electrons, nucleons, and atoms

Earth and moon are moving

Apart, due to loss of energy in the orbital system from friction between the sea and land

Escape velocity depends on

temperature of gas and gravitational field at surface

Kepler’s law of harmonies

distance to sun³ is proportional to orbital period²

Necessary for life

• Stability (orbit)

• Surface

• Heavy elements

• Liquid water

• Energy source (ie star)

• Protection (atmosphere or liquid)

• Moon

Why is water important?

• Large and relatively warm liquid range

• Polar = good for cell architecture

Europa

• Water ice and hydrated salts

• H₂O₂ for chem energy

Evidence for past water on Mars

• Landscape features: surface channels like river beds

• Clay minerals which form in water

• Sedimentary-looking rocks

6 methods for finding exoplanets

• Doppler

• Transit

• Astrometry

• Gravitational lensing

• Pulsars (specific case of Doppler)

• Direct imaging

Doppler imaging

Star’s emission spectrum is red/blueshifted as it moves closer/further away, showing orbit with an exoplanet

Astrometry

Movement of star directly observed

Tranist

Change in brightness of star shows exoplanet is passing in front of it

• Can measure period, mass, orbital radius, planet’s size and density

Gravitational lensing

Mass of nearer star bends light from further star; blips indicate exoplanet orbiting further star

• Can calculate exoplanet’s mass

• Unbiased by size and orbital period

Pulsar detection of exoplanets

Specific case of Doppler - any variation in the radiation of a pulsar indicates an exoplanet because they are otherwise so regular

Direct imaging

Directly observing a planet - favours large planets far from star

If star is too big

it doesn’t live long enough for life to evolve (O, B)

If star is too small

there’s not enough light/energy for life

MS star types that could support life

G (sun), K, M (smaller) (97% of total stars)

Problems with nebular collapse model of solar system formation

• Predicts circular orbits, most exoplanets have more eccentric orbits

• Doesn’t allow super-Earths - shouldn’t be enough material in the inner disc

• Doesn’t allow hell planets - they would be part of the star instead of forming separate planets

• Disc/planets don’t always spin same way as stars

How do hot Jupiters form?

Form further out then migrate inwards

Alternative energy sources for life

• Radioactive decay

• Tidal pulsing

Blackbody depends almost entirely on

temperature

Geoindicators

• Liquid (water)

• Complex chemistry

• Atmosphere

Geosignatures

• Atmospheric gases

• Erosion due to biological processes

• Actual civilisation structures

Biosignatures

• Organic macromolecules

• Biogenic substances

• Fossils

Red edge

(biosignature) Change in earth’s spectrum as you switch from looking at oceans to areas of green vegetation

Weak anthropic principle

The universe isn’t specially set up for life - we’re just lucky

Strong anthropic principle

Fundamental parameters are finetuned to support life

Drake’s variables

R_*: stars born per year

f_p: % stars with planets

n_h: Habitable planets per star

f_l: % planets with life

f_i: % life develops intelligence

f_c: % intelligent builds radio telecoms

L: lifetime of telecom civilisations

R*

7

fp

90%

fh

0.3

fl

10%

fi

1%

fc

1% comms chance

L

10 000 000 years