Stars Flashcards
what is the solar thermostat and how does it function
If core temp drops, the fusion rate drops and that leads to lower core pressure, forcing contraction and therefore heating of the core, increasing the fusion rate. If the core temp rises, the fusion rate increases, increasing the core pressure, expanding and therefore cooling the core, dropping the temp.
what is the radiative zone of the sun
Gamma ray photons travel via radiation. This part is so dense and hot that the photons are constantly absorbed and emitted, slowly finding their way to cooler parts.
what is the convection zone of the sun
eventually gas cools a bit more and no longer emits the photons, but absorbs them and the heat travels via convection. the hot rise and cool fall. energy carried as heat in gas.
what is the photosphere
photons can leave the sun at this level as it has cooled. this light is in the visible spectrum.
what is sun granulation, and what are sun spots
sun granulation is convection currents visible on the surface of the sun which change as hot rises and cool sinks. Sunspots are much larger and are cooler spots which trap gas in loops between magnetic fields.
what is the chromosphere
the layer of sun outside the photosphere. Has a low density so we can see through it. hotter than photosphere possibly because magnetic fields transfer head directly into the chromosphere. (temperature rises with altitude.
what is the corona
even further out than the chromosphere, it it hotter than the chromosphere. extremely low density, and produces x waves.
where is solar wind from
solar wind is gas which is released from the corona of the sun. it is mainly protons and electrons
what is the heliosphere
the extension of solar wind, which expands out far beyond the planets
what is the hr diagram
Luminosity vs Temperature (hot to cool, opposite of what you’d think). Plots stars showing what kind they are
luminosity vs brightness
luminosity is the actual energy output of the star, whereas brightness is the apparent brightness to the observer (a lightbulb seems brighter than a star, but not more luminous)
how do you determine luminosity of a star
brightness and the distance to the star
how do you determine the distance to a star
measure the apparent movement of the star over a year, caused by earths actual movement around the sun. using right angles triangle and the angle to the sun, also the distance to the sun (1 AU), the distance can be figured out
if the parallax angle decreases what does that mean about the distance to the object
distance increases
what is the parallax angle
the angle which is changed between earth and a faraway object over a year
how do you determine luminosity of a star
distance ^2 *4pi * apparent brightness =
how do you measure the temperature of stars
1- peak of thermal spectrum (bluer hotter and redder colder)
2- spectral lines show when there are more complex molecules. complex molecules are destroyed in high temperatures and therefore less complex molecules means higher temp.
how do you measure the temperature of stars
1- peak of thermal spectrum (bluer hotter and redder colder)
in a hotter atmosphere would you see more or less absorption lines
less because therefore the molecules have been broken down by the atmosphere. (complex molecules break down in higher temperatures)
how do we classify stars
by surface temperature. O B A F G K M. Arranged from hottest to cool. Hottest everything is ionised, and progressively more molecules can exist
what are the different groups on the HR diagram
Main sequence (y=-x line), about as hot as bright.
Giants, moderately bright for how hot. (above to right of main)
Supergiants, very luminous for how hot they are (top right of diagram)
White dwarves, very dim, but hot.
what does luminosity depend on
temperature and surface area, the larger the brighter and the hotter the brighter (L is proportional to R^2 * T^4, where r is radius, t is temp, l is luminosity).
why are some stars more luminous than but colder than our sun
it is also dependant on the radius because of surface area. therefore the radium might be larger giving it higher luminosity.
how do we find the mass of stars?
For binaries we observe the behaviour of the orbiting star (but can’t work for non binaries). otherwise, location on main sequence tells us mass (further left and up is bigger mass as hotter means more grav pressure).
How does stars mass impact the lifetime
larger mass means shorter lifetimes. Available fuel is greater, but luminosity (lost energy) is much higher
how do we observe the age of stars
observing clusters, as stars in the same cluster formed around the same time, all at the same distance, with a range of different masses. The older the cluster, the shorter the main sequence will be and more dwarves.
What happens to stars on the HR diagram as they age
when they run out of fuel they move off the main sequence. n.b. they don’t move around the sequence, they are fixed on one spot until out of fuel.
what are the forces balancing in gas clouds and how does that form stars?
Gravity vs pressure. therefore if mass is large enough, gravity is greater than pressure and it contracts, heating up until it hits a particular equilibrium.
what is “jeans” mass and what does it say about gas clouds
it is the critical mass of a gas cloud for wether it will collapse or not. If Mcloud < Mjeans, pressure wins no collapse. If vice versa, gravity wins, collapse. Mjeans increases with temp, therefore higher temp higher critical mass to collapse.
how does temperature impact gas clouds
higher temperature, higher the mass needed to collapse
what starts collapses of gas clouds
- supernova shockwave condenses the cloud
- colliding clouds
- galaxy turbulence
- spontaneous cooling of cloud lowers Mjeans
why does a gas cloud spin faster as it collapses
conservation of angular momentum means it will spin faster as radius decreases (think ice skater pulling arms in.
