Life and Death of Stars - Part 1 Flashcards
What is our galaxy?
- an enormous collection of stars and interstellar matter
- ## contains over 100 billion stars spread through a volume of space close to 100,000 lightyears across
What is our galaxy held together by?
- GRAVITY
What do stars rotate around?
- the galactic centre
- around 250,000 away from Earth
How many stars are there thought to be in our universe?
- around over one quintillion (10 to the power 18) stars
What are some physical quantities of stars?
- luminosity (brightness)
- temperature (colour)
- chemical composition
- size
- mass
What is the photosphere?
- the ‘outer’ layer of the sun
- not such an outer layer, more an area where the internal energy of sun is released back into the atmosphere as visible radiation
- it is the sphere of light that we see on a sunny day
- surface temp = 5800 K
- thickness = 500 km
- has a churning granulated structure with a few dark spots called sun spots
- these also change in size and shape
- the churning, granulated structure is our view of the top of the solar convection
What is the corona?
- can be seen during a total solar eclipse
- extends out ti a distance of several times the radii of the Sun
- can be seen directly when X-ray telescopes are used
What is the chromosphere?
- between the corona and photosphere
- thickness = 1600 km
- more visually transparent than the photosphere
- during a solar eclipse, this is the pink / red ring around the moon
- temperature = 6000-10,000 K
Describe the interior of the Sun
- divided into 3 different regions
- based on how energy / heat is transferred at various points
- CONVECTION ZONE
- RADIATION ZONE
- SOLAR CORE
Interior of the Sun - Convection zone
- immediately below the photosphere
- causes the granular look of the photosphere
- heat is transferred here by convection
- hot material flows up to the surface
- cool material sinks down to the larger depths
Interior of the Sun - Radiation zone
- below the convection zone
- solar energy is transported from the core to the outer parts by radiation
Interior of the Sun - Solar Core
- the very heart of the Sun
- where the nuclear reactions which provide it with its energy occurs
- energy is also transported by radiation here but very slowly
What is luminosity?
- the amount of energy radiated by a star
Sun’s luminosity = 4 x 10 to the power 26 W
What is the solar constant?
- the amount of solar energy that reaches the surface of th Earth’s atmosphere every second
- is 1400 W m(-2)
- about 50-70% of this energy reaches the Earth’s surface
- the rest is absorbed by the atmosphere or reflected away by clouds
What is nuclear fusion?
- the way in which the Sun creates its energy
- the combination of light atomic nuclei into heavier ones
- two nuclei combine to create a third
- the mass of this third nuclei is always less than the total of the first two
- the lost mass has been converted into energy
- given by the equation E = mc(2)
What is nucleosynthesis?
- the building of elements through the process of nuclear fusion
Properties of the Sun
Radius = 7 x 10 to the power 8 m Mass = 2 x 10 to the power 30 kg Average density = 1410 kg m(-3) Surface gravity = 274 m s(-2) Time for rotation = 25 days (at equator) Surface temperature = 5780 K Luminosity = 3.9 x 10 to the power 26 W
Comparing the Sun with other stars - SIZE
- stars vary greatly in terms of size
- go from a few hundredth of a solar radius to several hundreds of a solar radius
Comparing the Sun with other stars - MASS
- there is no way to determine the mass of a single distant star
- the only way is to calculate stellar mass is to measure its gravitational effect on some other object
- this other object - often another star or a planet
- binary star system - two stars orbit each other
- its possible to work out their mutual gravitational attraction
- since this attraction is dependent on the masses of those stars, we can then work out the masses of those stars
Comparing the Sun with other stars - LUMINOSITY
- use luminosity and surface temperature to classify stars in the same way height & weight are used to classify humans
- therefore we can say that luminosity and surface temperature are connected
Hertzprung-Russell diagrams
- diagrams plotting the luminosities of stars against their surface temperatures
What is the main sequence?
- on H-R diagrams a band, containing a large concentration of stars, running from top-left to bottom-right
- Sun and the majority of it’s neighbours live on it
- temperatures = 3000 to 30,000 K
- luminosities = 10(-4) to 10(4) solar units
- radii of stars also varies
What is the Stefan-Boltzmann Law?
- the radiation emitted by a star is governed by this law which states that ‘the energy emitted per unit area per unit time increases as the fourth power of the star’s surface temperature’
- star’s luminosity is this energy multiplied by its surface area
luminosity is proportional to radius(2) x temperature(4)
What are blue giants?
- found at the end of the main sequence
- large, hot and blue stars