Quasars and Exoplanets Flashcards
Why are half the stars we observe actually two stars that orbit each other?
How do we know there are two stars?
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.
What is an eclipsing binary star system?
A binary system whose orbital plane lies almost out in our line of sight, so the stars eclipse each other as they orbit.
How do you use absorption line spectrum to find the orbital period?
What does an apparent magnitude - time graph look like when stars eclipse each other?
What are quasars?
Bright radio source that shows large optical red shift
suggesting its very far away.
What did quasars show from their emission lines?
elements that astronomers had never seen before
What were the emission lines the same as and what has happened to them?
Hydrogen Balmer lines but red shifter enormously
The fact that they have Hydrogen Balmer lines but red shifter enormously shows what?
Huge red shift = they’re huge distances away
What’s the most distance measurable object?
Quasars
What are active galactic nuclei and what is an active galaxy?
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.
Whats the current consensus about quasars?
Its a galactic nucleus containing a huge black active hole. This supermassive black hole is constantly taking in matter
What is an exoplanet?
Any planet not in our solar system
Why are exoplanets hard to find?
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.
What’s a method to find exoplanets?
Doppler shift
How is Doppler shift used to find exoplanets
Measure the emissions from stars that have been red and blue shifted
What effect does an exoplanet have on a star’s orbit?
A wobble
Why is a wobble caused?
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.
What does a wobble cause?
Tiny red and blue shifts on the stars emissions
These can be detected
What can you find from the red and blue shift?
The minimum mass of the exoplanet.
What are the problems with doppler shift to find exoplanets?
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)
Describe the transit method
Measures change in apparent magnitude as an exoplanet travels in front of a star
How does the transit method work?
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.
What does the amount of dimness of the star’s light depend on?
What measurement can you find from this?
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.
What are the problems with the transit method?
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.
