Quasars and Exoplanets

Question 1

Why are half the stars we observe actually two stars that orbit each other?

How do we know there are two stars?

Answer 1

Many of them are too far away from us to be resolved with telescopes.
However, the lines in their spectra show a binary star system.

Question 2

What is an eclipsing binary star system?

Answer 2

A binary system whose orbital plane lies almost out in our line of sight, so the stars eclipse each other as they orbit.

Question 3

How do you use absorption line spectrum to find the orbital period?

Answer 3

Question 4

What does an apparent magnitude - time graph look like when stars eclipse each other?

Answer 4

Question 5

What are quasars?

Answer 5

Bright radio source that shows large optical red shift

suggesting its very far away.

Question 6

What did quasars show from their emission lines?

Answer 6

elements that astronomers had never seen before

Question 7

What were the emission lines the same as and what has happened to them?

Answer 7

Hydrogen Balmer lines but red shifter enormously

Question 8

The fact that they have Hydrogen Balmer lines but red shifter enormously shows what?

Answer 8

Huge red shift = they’re huge distances away

Question 9

What’s the most distance measurable object?

Answer 9

Quasars

Question 10

What are active galactic nuclei and what is an active galaxy?

Answer 10

Supermassive black holes ejecting huge amounts of material from their nuclei.

Galaxies with supermassive black holes with these active galactic nuclei are called active galaxies.

Question 11

Whats the current consensus about quasars?

Answer 11

Its a galactic nucleus containing a huge black active hole. This supermassive black hole is constantly taking in matter

Question 12

What is an exoplanet?

Answer 12

Any planet not in our solar system

Question 13

Why are exoplanets hard to find?

Answer 13

They orbit stars much brighter than themselves. These brighter stars drown out any light from the light of the exoplanet.

They are too small to distinguish from nearby stars (subtended angle is too small for the resolving power of most telescopes).

Only a few of the largest and hottest exoplanets can be seen directly with specially built telescopes.

Question 14

What’s a method to find exoplanets?

Answer 14

Doppler shift

Question 15

How is Doppler shift used to find exoplanets

Answer 15

Measure the emissions from stars that have been red and blue shifted

Question 16

What effect does an exoplanet have on a star’s orbit?

Answer 16

A wobble

Question 17

Why is a wobble caused?

Answer 17

Both the planet and the star are orbiting around a centre of mass of the system.

The planet is further away and the star is much bigger - the centre of mass is closer to the centre of the star.

Question 18

What does a wobble cause?

Answer 18

Tiny red and blue shifts on the stars emissions

These can be detected

Question 19

What can you find from the red and blue shift?

Answer 19

The minimum mass of the exoplanet.

Question 20

What are the problems with doppler shift to find exoplanets?

Answer 20

The movement needs to be aligned with the observers line of sight.

(can’t detect any shift if the planet orbits the star perpendicular to the line of sight)

Question 21

Describe the transit method

Answer 21

Measures change in apparent magnitude as an exoplanet travels in front of a star

Question 22

How does the transit method work?

Answer 22

Some light is blocked when a exoplanet orbits a star, which leads to sip in light curve observed on earth. radius of planet can be found.

Question 23

What does the amount of dimness of the star’s light depend on?

What measurement can you find from this?

Answer 23

Relative size of the star and orbiting planet.

The bigger the planet relative to the star, the greater the dip in apparent magnitude.

Therefore, you can find the radius of the exoplanet from this.

Question 24

What are the problems with the transit method?

Answer 24

The odds of an exoplanet being perfectly aligned so it passes between the star and observer are very low.

Transit only lasts tiny fractions of it’s whole orbital period = easy to miss

You can only confirm that the already observed planets are there. You can’t rule out the existence of others - if there’s no dip in apparent magnitude, it doesn’t necessarily mean there’s no exoplanets there.