Detection of Binary Stars, Quasars and Exoplanets Flashcards
What is meant by an eclipsing binary star system?
Two stars which orbit each other, and their orbital plane lies almost in our line of sight, meaning the stars eclipse eachother.
How can absorption lines be used to measure a spectroscopic binary systems period?
By viewing how the absorption lines oscillate (one line splitting into two and then combining again). As one star travels away from us, the other travels towards us, hence the blue/red shift - orbital period is the time is takes for the lines to combine back to one line twice.
What do you get if you plot a graph of apparent magnitude against time for an eclipsing binary system?
A graph with frequency dips in apparent magnitude depending on the relative sizes of the orbiting stars.
What are the main characteristics of quasars? (not appearance)
Quasars are extremely far away and extremely powerful.
What are quasars thought to be?
Very powerful galactic nucleus around a huge black hole more than 10^6 times the mass of the Sun.
What is at the centre of all galaxies and what is it called when it ejects huge amounts of material from its nuclei?
A super massive black hole, and it is called an active galactic nucleus if it ejects material from its nuclei.
What is an exoplanet?
Any planet not in our solar system.
What are the 3 main reasons that exoplanets are hard to detect?
- Orbiting stars which are much brighter than them
- Too small to distinguish from nearby stars
- Only a few of the largest and hottest exoplanets that are furthest away from their stars can be seen directly using specially built telescopes
What is the doppler shift method for detecting exoplanets?
- Exoplanet causes star to ‘wobble’ due to gravitational attraction
- This causes tiny red and blue shifts in the star’s emissions which can be detected on Earth
- From this, the minimum mass of the exoplanet can be detected
What is the main problem with the doppler shift method?
The movement needs to be aligned with the observer’s line of sight, or you wouldn’t see and red or blue shift.
What is the transit method for detecting exoplanets?
- Measure of the change in apparent magnitude when an exoplanet passes in front of a star
- Viewed by a dip in the star’s light curve, and can be used to find the radius of the exoplanet
What is the main problem with the transit method?
It’s orbital plane has to be in the line of sight - if it is just orbiting around the star in a visible circle from Earth, there will be no dip in apparent magnitude as it will not pass in front of the star.
