AHPS Unit 1

Continuous spectrum

Unbroken rainbow from a hot, dense source.

Emission spectrum

Bright lines on a dark background, from a hot gas.

Absorption spectrum

Dark lines on a rainbow, from cooler gas in front of a hot source.

How do you find elements in a star?

Match the star's dark absorption lines to the emission lines of known elements.

Why do absorption lines match emission lines?

An element absorbs and emits the same wavelengths.

What did the Big Bang make?

Hydrogen and helium (plus a little lithium).

What happens inside a star?

Nuclear fusion: light nuclei combine into heavier ones and release energy.

How do stars make heavier elements?

Hydrogen fuses to helium, helium to carbon and oxygen, and massive stars go on to iron.

Why does fusion stop at iron?

Fusing iron takes in energy instead of releasing it.

Where do elements heavier than iron come from?

Supernovae and neutron star collisions.

Fate of a low or medium mass star's material

Outer layers form a planetary nebula, leaving a white dwarf.

Fate of a high mass star's material

A supernova scatters it into space, leaving a neutron star or black hole.

Where does the matter from dead stars go?

Into space, where it forms new nebulae, stars, and planets.

H-R diagram axes

Luminosity (up) vs. temperature (hot on left, cool on right).

Spectral classes, hottest to coolest

O, B, A, F, G, K, M.

How do you plot a star on the H-R diagram?

Find its temperature on the x-axis and its luminosity on the y-axis.

Main sequence

Diagonal band where stars fuse hydrogen. Most stars, including the Sun, are here.

Giants and supergiants

Cool or hot but very bright, huge stars at the upper right and top.

White dwarfs

Hot, faint, tiny stars in the lower left.

Why are white dwarfs faint even though they are hot?

They are very small.

Why are red giants bright even though they are cool?

They are very large.

Same temperature, more luminous star: which is bigger?

The more luminous one.

Bigger mass star: brightness and lifespan?

Brighter and shorter lived.

Low mass star life cycle

Nebula, main sequence (very long), white dwarf.

Medium mass star life cycle

Nebula, main sequence, red giant, planetary nebula, white dwarf.

High mass star life cycle

Nebula, main sequence, red supergiant, supernova, neutron star or black hole.

Hydrostatic equilibrium

Gravity pulling in balances pressure pushing out.

What happens when a star runs out of hydrogen?

The core shrinks and heats up, and the outer layers expand into a giant.

Layers of a star, center out

Core, radiative zone, convective zone, photosphere, atmosphere.

What happens in the core?

Fusion.

Luminosity

Total energy a star gives off.

Nebula

Cloud of gas and dust where stars form.

Protostar

A star that is still forming, before fusion starts.

Planetary nebula

Glowing gas shell shed by a dying medium mass star.

Supernova

Explosion that ends a high mass star.

Neutron star

Extremely dense remnant left after a supernova.

Black hole

Remnant so dense that light cannot escape.

White dwarf

Small, dense remnant of a low or medium mass star.