COSMOLOGY

Question 1

What is the redshift?

Answer 1

If an object moves away from an observer, the wavelength increases and the frequency decreases.

Question 2

What is the blueshift?

Answer 2

If an object moves towards the observer, the wavelength decreases and the frequency increases.

Question 3

What is spectroscopic binary?

Answer 3

Each spectral line splits into two after the stars cross the line of sight, then merge into a single spectral line as the two stars move towards the line of sight. ie: when they cannot be resolved.

Question 4

what did the graph of recession velocity against redshift show?

Answer 4

recession velocity is proportional to the distance from the Earth

Question 5

what does the gradient of recession velocity against redshift show?

Answer 5

Hubble’s constant

Question 6

What is dark energy?

Answer 6

When astronomers calculated the distance to type 1a supernovae they discovered them to be dimmer than expected which suggested that the expansion of the universe is accelerating which is attributed to dark energy.
- Dark energy is energy that has an overall repulsive effect throughout the universe.

Question 7

What does the Big Bang Theory suggest?

Answer 7

over the past 15 billion years or so, the Universe has expanded from an extremely hot and dense point, and is still expanding

Question 8

What is cosmic microwave background radiation?

Answer 8

It is EM radiation from all parts of the universe the spectrum of which follows a black body radiation curve with a peak in the microwave region. This peak corresponds to a temperature of 2.7 K.
- It can be interpreted as the radiation left over from the Big Bang or photons having been stretched to longer wavelengths and lower energies.

Question 9

What is the age of the universe approximately?

Answer 9

1/H0=d/v

Question 10

What must we assume when giving an approximation for the age of the universe?

Answer 10

• Assuming constant speed of galaxies.
• Assuming uncertainty in Ho anyway.
• Ignoring time between BB and galaxy formation.

Question 11

What is a standard candle?

Answer 11

objects of known absolute magnitude.

Question 12

What are the 4 pieces of evidence for the Big Bang?

Answer 12

• cosmic microwave background radiation
  -dark energy via type 1a supernovae
• we’ve not seen any galaxies older than 15 billion years.
  -relative abundance of H & He.

Question 13

Explain relative abundance of H and He as evidence of the Big Bang Theory.

Answer 13

• Big Bang theory suggests that a very brief period of fusion occurred when the Universe was very young, resulting in the production of helium from fusing
  hydrogen.
• The Universe expanded and cooled too rapidly for the creation of larger nuclei, resulting in a relative abundance of H&He spread uniformly throughout the Universe, and a lack of larger elements. This is consistent with observation

Question 14

What are quasars?

Answer 14

one of the most distant and most powerful observable objects

Question 15

Where are quasars assumed to have come from?

Answer 15

It is assumed that it is produced from the matter in the accretion disk around/feeding supermassive black holes at the centre of distant galaxies.

Question 16

What are quasars characterised by?

Answer 16

Lots of radio waves and EM radiation and large red-shifts which means they are far away and old.

Question 17

When do quasars stop?

Answer 17

when a supermassive black hole runs out of nearby stars to feed on. This is what we think happened to the Milky Way.

Question 18

What are exoplanets?

Answer 18

Planets that are not in our solar system ( they do not orbit the sun)
- Many are like gas giants like Jupiter.
- Difficult to observe as they are often obscured by the stars they orbit and tend to be too close together for telescope to resolve them.

Question 19

What is the habitable zone?

Answer 19

The zone where liquid water may exist on a planet because the temperature at the surface needs to be between 273K-373k

Question 20

Why are exoplanets hard to detect?

Answer 20

1] The light from the host star is way brighter than reflected light from the planet.
2] subtends very small angles for telescopes to see.

Question 21

Explain the Radial Velocity Method.

Answer 21

-Periodic doppler shift in light received from star due to star and planet orbiting common centre of mass

Question 22

Explain the Transit method.

Answer 22

-measuring the intensity of light.
-larger the exoplanet, the greater the dip in intensity
-This is where the exoplanet passes infront of the star and blocks out some of the light from the star.
-radius of exoplanet can be found after measuring the dip in intensity.

Question 23

What type of planets are detected in transit method?

Answer 23

only planets with short orbital periods can be detected.