13.3 Standard Candles Flashcards
What is a cephid star?
Star with varying luminosity over time. It fluctuates between luminosities over periods of time. We can determine its absolute luminosity(max).
How to find d using a Cephid Star?
- Find a cephid star
- measure its period of time
- find luminosity using Leavitt’s TL data.
- measure radiation flux
- use d = (square root)L / 4(PI)F
What other phenomenon can be used as a standard candle?
A supernova explosion.
What are the two standard candles?
Supernovae and cepheid stars.
When do we use standard candles to determine the distance to star/galaxy?
Sometimes stars are to far to exhibit parallax, so we cannot use trigonometric parallax.
What is the method for working out the farthest stars?
Spectral Red Shift
What is the definition for a standard candle?
A distant star of known maximum luminosity.
What are the two problems that showed up when measuring the distances to stars/galaxies?
(1) Galaxies appear to not have enough matter to keep outmost stars orbiting around the centre of the galaxy
(2) Distant galaxies appear to be moving away at an accelerating rate , rather than slowing down as predicted by Newton’s law of gravitation.
What does the 1st problem suggest?
It suggests that 24% of the mass of the near galaxies consists of the unknown - dark matter.
What does the 2nd problem suggest?
It suggests that 71% of our universe consists of a mysterious force that acts against gravity - called dark energy.
How much percent of the universe do we know about?
5%
How much percent of the universe do we not know about ?
95%
What is dark matter?
matter in galaxies that keeps outmost stars orbiting around the centre
What is dark energy?
mysterious force accelerating galaxies away working against gravity
What property can be used to determine the fate the fate of the universe? How to calculate?
Density
Add up all matter (including dark stuff) and divide by area.
