Astrobiology - Environment for Life

What is Kepler's First Law?

The orbit of each planet is an ellipse with the sun at one focus

What is Kepler's Second Law?

The radius vector to a planet sweeps out equal areas in equal time

What is Kepler's Third Law?

The square of the period of a planets orbit is proportional to the cube of the semimajor axis of its orbit

What is Newton's First Law?

An object moves at a constant velocity if there is no new force acting on it

What is Newton's Second Law?

Acceleration imparted to a body is proportional to and in the direction of the force applied and inversely proportional to the mass of the body. Force is the cause of a momentum change.

What is Newton's Third Law?

For every force there is an equal and opposite reaction force

What is centripetal force?

A body moving in a circular orbit must have a force towards the centre of its orbit. (speed must be constant but direction is constantly changing).

What is angular momentum?

A body orbiting at radius r with a mass and speed has an angular momentum. Angular momentum of an orbiting body is constant.

What is a semi major axis?

Half of the longest diameter of an elliptical orbit

What is Kepler's Second Law a consequence of?

Conservation of angular motion

What is the Doppler effect?

the relationship between waves, frequency and distance

What are some astronomy applications of the doppler effect?

1. calculate speed at which stars and galaxies are moving away
2. help locate new bodies

What is light?

an electromagnetic wave with an oscillating electric wave

What effect does light have on a charged particle?

will exert an oscillating force

What is the result of an oscillating charged particle and electric field?

light emission

What is a blackbody?

a body that absorbs all light

What happens when a blackbody absorbs light?

it gains energy

What is the temperature of a blackbody proportional to?

the kinetic energy of the electrons

In stars what causes an increase in the kinetic energy of the electrons

nuclear fusion

What is W (Wien's constant) equal to?

2.898x10-3mK

What is σ (Stefan-Boltzmann constant) equal to?

5.67x10-8Wm-2k-4

What is the speed of light?

299, 792, 458m/s (3x10^8m/s)

What is K (Coulomb's constant) equal to?

8.99x10^9 Nm^2C^-2

What H line is the Lyman series?

1

What H line is the Balmer series?

2

What H line is the Paschen series?

3

What H line is the Brackett series?

4

What H line is the Pfund series?

5

What is radiative excitation?

Absorbs a photon with energy equal to the energy difference between two levels. The atom will re-emit the photon after a short period.

What is collisional excitation?

Free particles collide with an atom and transfer some of their kinetic energy. The atom returns to its ground state by emitting a photon.

What happens if an atom gains sufficient energy?

An electron may be liberated and the atom becomes ionised

What is Kirchhoff's First Rule?

A hot, opaque solid, liquid or highly compressed gas emits a continuous spectrum

What is Kirchhoff's Second Rule?

A hot, transparent gas emits a spectrum on emission lines. The lines depends on the elements present.

What is Kirchhoff's Third Rule?

If light from a continuous spectrum passes through a lower temperature transparent gas, the cooler gas causes the appearance of absorption lines.

What happens during the birth of a star?

Collapse of a dense, low pressure molecular cloud

How hot does nuclear fusion need to be to form a star?

Above 10million K

When is the main sequence of a low mass star?

50-150 million years

How is H fused into He in a low mass star?

Proton-proton chain

How is the inward gravitational force balanced in a low mass star?

Outward pressure

How does energy reach the surface in a low mass star?

Radiative diffusion and convection

What is convection important for in stars?

Surface activity (solar flares and coronal mass ejections)

What happens to a low mass star after 10 billion years?

Red Giant Phase

Why does a low mass star enter the red giant phase?

Runs out of H in core

What happens when the H shell in a low mass star becomes very hot?

Ignites fusion - the H shell around the inert He burns

At what temperature does He burning begin in a low mass star?

Above 100 million K

How many He nuclei combine to form a C?

3

What supports the core of the star during He burning?

Degeneracy pressure?

What happens when the rate of He fusion rapidly increases?

He flash

At what temperature does C fusion become possible?

600 million K

How does a low mass star eject its outer layers during its death?

Thermal pulses and stellar wind

At what temperature can solid dust particles form in the outflowing wind of a red giant?

1000 - 2000K

What is a white dwarf?

The inert carbon core of a low mass star

What is a planetary nebulae?

When a low mass star ejects its outer layers to form an expanding gas shell. Radiation ionises the gas causing it to glow.

How big are high mass stars?

Above 8 solar masses.

How big are low mass stars?

Less than 2 solar masses

What are the two theories about how high mass stars form?

Same as low mass OR competitive accretion

What is competitive accretion?

1. Star forms the same as a low mass star
2. Star continues to accrete gas until depleted
3. Some stars accrete more efficiently and become high mass stars

How does H fusion occur in high mass stars?

CNO cycle

How many protons form a He in the CNO cycle?

4 (with C catalyst)

When do high mass stars reach the main sequence?

150 000 years

What causes high mass stars to have a higher temperature H core?

Stronger gravity

What do high mass stars become during death?

Super Giants

What does C fusion form?

Heavier elements

What is advanced nuclear burning?

The He nucleus is captured (He capture reaction) to produce heavier elements (C to O).

What happens every time a core depletes the element it is fusing?

Shrinks until hot enough for other fusion reactions

What happens during the final days of a high mass star?

Fe builds up in the Si-burning core

What type of nuclear burning happens in intermediate mass stars?

CNO cycle

Why does an intermediate mass star end up as a white dwarf?

Degeneracy pressure prevents cores becoming hot enough to burn C or O.

Why is iron in the core of a star a problem?

Cannot generate any nuclear energy.

How do elements lighter than Fe gain Energy?

Nuclear fusion

How do elements heavier than Fe gain Energy?

Nuclear fission

What happens to cause the core to collapse in high mass stars?

Gravity pushes electrons past the quantum mechanical limit. Combine with protons to form neutrons and neutrinos are released.

What is formed when the iron core collapses?

Neutron star (a ball of neutrons)

What is a supernova?

The energy released by the collapse of an iron core into a neutron star

What forms if the mass of a neutron star is high enough that gravity overcomes neutron degeneracy pressure?

Black Hole

What prevents further collapse of a neutron star?

Neutron degeneracy pressure

What can be formed in a supernova?

Elements heavier than Fe

Where is most C produced?

Low mass stars

What is the lifetime of a high mass star (10 solar masses)?

10 million years

Why can't Fe fuse?

Lowest mass per nucleon

Where do stars form?

Solar Nebula

What is a solar nebula and how does it form stars?

Cloud of gas and dust that collapses due to its own gravity. Angular momentum causes the cloud to spin faster as it collapses.

In what part of a solar nebula do stars form?

Centre (planets form in the disc)

How do we infer the existence of a formation disc?

Infrared excess

What type of planet forms first?

Gas giants

Why do terrestrial planets form later?

No gas left

What does aerodynamic drag result in in a disc?

Causes solids to collect. If density high enough could form pebbles or planetesimals.

How do grains grow due to streaming instability?

1. Growing grains settle towards midplane
2. Grains collect at certain locations
3. If local solid density is high enough, drag is shut off and the solids can gravitationally collapse to form planetesimals.

What is core growth by pebble accretion?

The gravitational influence of a planetary core and the speed at which a pebble drifts past.

What is escape velocity?

The kinetic energy of the escaping body must be greater than its gravitational potential energy

What is the snow/frost line?

The distance from the star where temperature is less than 170K and H compounds can condense to form ices.

Why are most large planets found past the snow/frost line?

More solid material

What does the final stages of planet formation involve?

oligarchic growth

What is oligarchic growth?

Each body dominates a certain region that grows until it reaches the isolation mass (runs out of planetesimals)

What happens if the embryo mass is larger than the critical mass in a forming planet?

Runaway gas accretion forms a gas giant

After the gas has been depleted, where would you find terrestrial planets forming?

Within the snow/frost line

After the gas has been depleted, where would you find ice giants forming?

Outside snow/frost line

Where would you find short period comets?

The Kuiper Belt

Where would you find long period comets?

the Oort Cloud

Where is the Asteroid Belt?

Between Mars and Jupiter