Astrophysics topic test 3 Flashcards

Question

As temp increases, pressure

Answer 1

increases and thermal expansion occurs, expanding the star

Answer 2

decreases, causing star to contract and collapse

Answer 3

1) All stars form from a cloud of dust and hydrogen called a nebula 2) Gravity pulls dust and gas together to form a PROTOSTAR 3) As protostar gets denser as particles collide, temperature increases. At a point, the hydrogen nuclei can now undergo nuclear fusion to form helium nuclei. This gives out lots of energy, keeping the core of the star hot. MAIN SEQUENCE STAR is born 4) Now a long stable period during which OUTWARD PRESSURE caused by THERMAL EXPANSION (from nuclear fusion) balances GRAVITY pulling layers of the star inwards. This lasts several billion years. The heavier the star the shorter its time on main sequence because it must consume lots of fuel to retain luminosity. 5) Eventually hydrogen gas in the core runs out and thermal expansion no longer occurs because no nuclear fusion, therefore gravity is greater than outward pressure and the star is compressed untill it is dense and hot enough that nuclear reactions start again and thermal expansion occurs and outward pressure makes the outer layers of the star expand and well up to form a RED GIANT. It becomes red when the surface cools 6) Once this second stage of reactions has finished, the star becomes unstable and ejects its outer layer of dust and gas to from a PLANETARY NEBULA , leaving behind the hot, dense, solid core - a WHITE DWARF

Answer 4

1 - 4 same 5) when hydrogen in core runs out, and star is compressed due to gravity vs outward pressure / thermal expansion imbalance, the new nuclear reaction form a RED SUPERGIANT 6) From here, big stars glow brightly as they continue to make heavier element s when undergoing more fusion. Expand and contract several times due to thermal expansion vs gravity imbalances. Eventually explode in a SUPERNOVA 7) Exploding supernova throws outer layers of dust and gas into space creating a NEBULA, leaving very dense core called NEUTRON STAR. If neutron star is massive enough, it collapses due to gravity and becomes a BLACK HOLE.

Answer 5

Blue, white, yellow, orange , red

Answer 6

hottest = blue / coldest = red

Answer 7

The hotter the star, the shorter the wavelength of light it will emit

Answer 8

1) Temp 2) Size bigger, hotter = brighter

Answer 9

because star's brightness also depend on distance as well as temp, so close to earth could seem brighter.

Answer 10

a measure of how bright a given star would appear to be if it was a fixed distance from Earth (~3.1 x10^17m).

Answer 11

allows us to compare the brightness of stars without worrying about they distance

Answer 12

OBAFGKM (O = blue, M = red)

Answer 13

frequency, wavelength

Answer 14

When light source is moving away from you, more distance = more energy needed, hence peaks aren't as big as they are when emitted and wavelength increases, so frequency decreases and light appears to be shifted toward the lower frequency end of the visible part of the EM spectrum - red-shifted.

Answer 15

red-shifted

Answer 16

moving away from the earth

Answer 17

Different elements are exposed to the light and because they absorb different frequencies or wavelengths of light, a pattern of dark lines is produced with a dark line at each frequency absorbed This is compared to the light given out from hydrogen + helium gas on earth

Answer 18

change in wavelength / reference wavelength = velocity of a galaxy / speed of light

Answer 19

The wavelength of the light when it was emmited, before it was red-shifted

Answer 20

Absolute magnitude against temperature

Answer 21

Top right, cool but very large, very bright

Answer 22

Bottom left. They are very hot but small, so are dim

Answer 23

diagonally from top left to bottom right . since all roughly same size, a brighter star = higher temp

Answer 24

Red-shift, Microwave radiation (CMB)

Answer 25

More distant galaxies have greater red-shifts than nearer ones, hence they are moving faster and the universe is expanding Something must have set these galaxies into motion - a big explosion - the Big Bang

Answer 26

1) Initially all matter occupied a single point 2) This tiny space was very dense and very hot 3) This single point then "exploded" - the Big Bang . 4) Space started expanding, and the expansion is still going on

Answer 27

CMB radiation is the leftover energy of this initial explosion