Astrophysics

Question 1

What’s a parsec?

Answer 1

The distance of an object that subtends an angle of one arcsecond to the Earth’s orbital radius.

Question 2

What’s apparent magnitude?

Answer 2

A scale used to show how bright an object appears from Earth. A bigger number means a dimmer object. A difference of one on the scale corresponds to a brightness ratio of the fifth root of 100.

Question 3

What’s the dimmest value visible with the naked eye?

Answer 3

6.

Question 4

Define absolute magnitude.

Answer 4

The apparent magnitude an object would have if it were 10 parsecs from Earth.

Question 5

What’s the difference between the luminosity and intensity of a star?

Answer 5

Luminosity is its total power output. Intensity is a measure of its brightness.

Question 6

What’s the equation for intensity?

Answer 6

I= P/ (4 x pi x (r squared)), where r is the distance from the star.

Question 7

What’s a black body?

Answer 7

An object that absorbs all the radiation incident upon it, and emits perfectly across all wavelengths to produce a smooth black body curve.

Question 8

What does the area under a black body curve represent?

Answer 8

The total power output per square meter.

Question 9

On a black body curve, what’s lambda max?

Answer 9

The wavelength of peak emission.

Question 10

What happens to lambda max and the total area at colder temperatures?

Answer 10

Lambda max is a longer wavelength, and the total area is smaller.

Question 11

What effect does the ozone layer have on our estimation of a star’s temperature?

Answer 11

It absorbs UV from the black body spectrum, so the value for lambda max is a longer wavelength. Therefore our estimate of temperature is lower.

Question 12

What spectral class is the Sun in?

Answer 12

G5.

Question 13

What’s necessary in order to observe hydrogen absorption lines?

Answer 13

The hydrogen must be in the n=2 state, which is achieved by it being at the correct temperature.

Question 14

What causes stellar nebular to be formed?

Answer 14

Dust and clouds in space collapsing inwards due to gravity.

Question 15

Give the life cycle of an average star.

Answer 15

1. Stellar nebular.
2. Protostar
3. Average star
4. Red giant
5. Planetary nebula
6. White dwarf.

Question 16

Give the life cycle of a massive star.

Answer 16

1. Stellar nebular
2. Protostar
3. Massive star
4. Red super giant
5. Supernova
6. Neutron star or black hole.

Question 17

What’s a planetary nebular?

Answer 17

The start of helium fusion causes disturbances that result in the outermost layer of the star to be thrown off.

Question 18

State the different possible outcomes of a white dwarf.

Answer 18

1. If it is less than 0.5 solar masses, it will cool and fade to a brown dwarf.
2. If it is more than 0.5 solar masses, it may draw matter from a companion star (if it’s in a binary star system) until it reaches 1.4 solar masses. At this point, a type 1A supernova will occur.

Question 19

When a red supergiant collapses, what type of supernova occurs?

Answer 19

Type 2.

Question 20

If the core of a supernova is more than 1.4 but less than 2.5 solar masses, what will occur?

Answer 20

A neutron star.

Question 21

If the core of a supernova is more than 2.5 solar masses, what will occur?

Answer 21

A black hole.

Question 22

State 5 properties of a neutron star.

Answer 22

1. Rotate rapidly
2. Extremely dense
3. Have a strong magnetic field
4. Faint
5. Emit pulsars- radio waves in oppositely directed beams that sweep around as the star rotates.

Question 23

What’s a standard candle?

Answer 23

A source with known luminosity.

Question 24

Why is a type 1A supernova a standard candle?

Answer 24

The collapse of a star always occurs at the same mass, so the luminosity of the explosion is always the same.

Question 25

Define supernova.

Answer 25

A star that suddenly and very rapidly increases in absolute magnitude due to an explosion that ejects most of its mass.

Question 26

Where are gamma ray bursts thought to originate from?

Answer 26

Supernovae. If generated in our own galaxy, they could wipe out most life on Earth.

Question 27

State the key features of a supernova light curve.

Answer 27

1. Peak absolute magnitude always occurs at t=0
2. A type 1A is significantly brighter than a type 2, with its peak being at about -19.
3. They hit the x-axis at about 300 days.

Question 28

Define black hole.

Answer 28

An object whose escape velocity is greater than the speed of light, because its gravitational field strength is so high.

Question 29

What’s the event horizon of a black hole?

Answer 29

The boundary or surface where the escape velocity equals the speed of light.

Question 30

What’s the Dopler effect?

Answer 30

Relative motion between an observer and a source produces a shift in apparent wavelength, as perceived by the observer.

Question 31

What are the 3 possible fates of the universe?

Answer 31

1. A closed universe- mass is sufficient to stop expansion, allowing gravity to pull everything back together.
2. A flat universe- mass is just sufficient to slow down expansion at a decreasing rate, but it never quite stops.
3. An open universe- dark energy is sufficient to increase the rate of expansion.

Question 32

What are the units for velocity and distance in Hubble’s law?

Answer 32

Velocity is given in km/s

Distance is given in MPc.

Question 33

What’s an exoplanet and why are they difficult to detect?

Answer 33

An exoplanet is a planet that orbits a star other than our sun. They are difficult to detect because they only reflect the light of the star they orbit, meaning they are very faint.

Question 34

What is the radial velocity method?

Answer 34

Looking for periodic variation in the Doppler shift in the stars’ spectral lines, due to the star and the exoplanet orbiting a common centre of mass.

Question 35

What is the transit method?

Answer 35

Detecting a dimming in a star’s brightness as an exoplanet moves across its disc, perpendicular to our line of sight.