Astrophysics Part 2

Square of the period of any planet is proportional to the cube of the semi major axis of its orbit

Created by orbital position. Max shift is when the earth is at opposite sides of the sun. Once angle found, distance is calculated via trigonometry.

Coolest part of the sun. Visible surface that emits all visible light.

< 8 solar masses

> 8 solar masses

Fusion of H begun, low mass spends 99% of lifetime here

Inert He core shrinks down and then the star puffs up.

He begins to fuse in red giant due to a temperature rise.

Occurs after helium flash. Carbon core.

Material of star thrown off by winds, leaving a carbon core.

Dense and degenerate. No more fusion.

White dwarf mass limit

When protons, neutrons and electrons are packed in as tightly as possible, exerting a quantum force

Pre-star formation. Interstella medium collapses down.

Massive and blue

After H core of a high mass star exhausted, core shrinks and heats

Hydrogen shell burning causing high mass star to expand

T ~ 10^8K

Core has expanded after He fusion begins, slowing the fusion rate in a high mass star

After He core exhausted, core shrinks are C fusion begins in core.

Point at which star is doomed. Reactions from here onwards are endothermic

Neutrons are packed so tight that they implode releasing heaps of energy.

Type 2 supernovae powers…

Core collapse supernova

Left by type 2 supernova

M < 3 Solar masses. Detected via pulse radiation or binary system.

M > 3 Solar Masses

Use to detect neutron stars using their fast rotation due to conservation of angular momentum.

Neutron star spinning and releasing radio beams at a constant period

Sends of x-rays after getting hot due to friction of matter from a binary star being pulled into a neutron star.

3 solar masses

Single point of mass as neutron star collapses into a black hole

where escape velocity is speed of light

What we look for when detecting black holes.

Binary not transferring mass

Binary with one roche lobe filled

Both roche lobes filled

White dwarf accreting off donor star via roche lobe overflow

Sudden large increase in brightness, then returns white dwarf to original state.

Used in exceptional circumstances. Needs a large planet with wide separation from parent star.

Only useful for nearby stars as position shifts are very small and accuracy is important. Measures position of star and looks for wobbles

Downside of astrometry

Most sensitive to high mass planets close to the star

Downside of radial velocity

Sensitive to smaller mass planets close to star. Dimming of light tells us about the planet.

Fractional change in flux during transit given by:

Sensitive to all masses, only large distances. Rare events.

Mostly H and He, close to parent star, larger, short orbital period and low density.

More numerous than gas giants.

Flux at surface x cross-sectional area

Methane, liquid water and ozone

Where to search for signs of life

Small planet, with low mass, rocky and close to star

Large, high mass, icy/gaseous and far out

Rocky bodies found in asteroid belt

Ice and rock, found in Kuiper belt

Length of galaxy

Centre of the galaxy

Large region of low density around galaxy

Thin with spiral arms embedded within

Atoms have different spins. When they have slightly more energy, they drop an energy state and release a photon

Doesn’t have strong radiative transitions, hard to detect so we use other molecules to trace it.

Produced by young stars, looks like red glow. Young stars produce UV light that excites atoms.

Heated to high temperatures via starlight which is absorbed a reemitted in the IR

Dust scatters this more easily

What does dust do to light?

Light gets reddened and dimmed as light passes through a cloud.

The difference in colour we observed to that expected for object, called colour excess

colour excess given by…

Non-thermal. High energy electrons are accelerated and spiral in magnetic fields causing this.

Most common source of synchrotron radiation due to very strong magnetic fields

Also known as Free-free emission. From free electrons with free protons in a hot ionised gas, where the proton gets accelerated by electron and releases radiation.

What tells us that the size of Sgr A can’t be more than a light hour in size.

Mass concentrated in centre, with the rotation curve declining as distance increases

Speed stays roughly flat as distance increases after a big jump from zero.

Why the observed rotation curve for the solar system is mostly flat due to not uniform density.

Massive compact halo objects are a type of dark matter. Dead stars and brown dwarfs which are hard to see.

WIMPS – have mass and do not react in a way giving off radiation.

Recycles gas from old stars into new stars. Each generation has heavier elements that previous stars. ISM steadily enriched

Ionsied gas. Caused by supernovae. Atomic hydrogen forms as gas cools and then molecular clouds.

after the molecular cloud stage in the star-gas-star cycle

After star formation in star-gas-star cycle

Supernova and stellar winds do this after the nuclear fusion stage of the star-gas-star cycle

Where do new stars form in our galaxy?