Chapter 19 Stars Flashcards
What is a planet definition + (3 characteristics)
Planet is an object in orbit around a star
- has large enough mass for its own gravity to give it a round shape (unlike irregular like asteroids)
- has no fusion reactions (unlike stars)
- has cleared orbit of most other objects (like asteroids)
What is a dwarf planet then (difference to planet)
DONT NEED TO KNOW
Same thing as planet, but only difference is it HASNT CLEARED ITS ORBIT OF MOST OTHER OBJECTS, ( there are objects of comparable size orbiting Pluto)
Thus not a planet
What is a planetary satellite ?
A body in orbit around a planet
For example moon or normal satellite, both
What is a comet
What do all comets do (orbit)
Small irregular bodies made of ICE DUST AND SMALL PIECES OF ROCK
- all comers orbit the SUN
What is a solar system
A system that contains a sun and all other objects that orbit it
What is a galaxy
A collection of stars, interstellar dust and gas
Universe?
All the galaxies with all their energy and mass
What is a nebular
How do they form
Nebulae are just gigantic clouds of dust and gas (mostly hydrogen)
They form over millions of years as tiny particles come together as gravitation attraction of each particle pulls each one closer
What is the formation of a star
1) formation of a protostar
1) nebula forms over millions of years
2) denser regions of a nebula pull in more matter.
-3) they become hotter, as stronger gravity means GPE is converted to KE as they get pulled in
4) this forms a PROTOSTAR= a hot collection of dense dust and gas
What is formation of star
2) fusion of hydrogen
If the protostar manages to become hot and dense enough, this will provide condtions needed for fusion of hydrogen to take place
2) once fusion of hydrogen begins, the protostar goes to a MAIN SEQUENCE STARB
After a protostar, what route will the star take
(What does this depend on)
This depends on its mass, if it’s low mass it will take one route and if it’s high mass another
After a protostar starts fusion what happens for a while for ALL STARS
The star exists in a state of equilibrium
- here the energy released by fusion known as radiation pressure balances the gravitational pull the star does on its outside
- thus the star stays in a period of equilibrium that will last until the HYDROGEN RUNS OUT
What happens once hydrogen in CORE used up for LOW MASS STAR
What does it end being
- the radiation pressure output decreases, so the star collapses under own gravity
- this causes the core to heat up again as GPE converts to KE and the core becomes dense
- now conditions are right for the HYDROGEN IN SHELLS TO START FUSING
- this releases radiation pressure again, which causes the outer layers of star to EXPAND
- as it expands, the layers COOL and becomes RED
The star is now a RED GIANT
What happens to low mass star after it becomes a red giant
What happens to outer layers and what does it become
1) most of the outer layers mass just leaves as planetary nebula in space
2) eventually fusion of hydrogen in shells run out=
- less radiation pressure, collapses on itself again
- all that’s left is the hot core, which is known as a WHITE DWARF
But low mass stats don’t completely collapse…
Why doesn’t the white dwarf COMPLETELY collapse? Explain completely
(Electron degeneracy pressure!)
As atoms collapse due to reduced faction pressure and gravity pulling in, they go closer together
However due to PAULIS EXCLUSION PRINCIPLE, two electrons CANT exist at same energy state (which means the atoms can’t get too close to each other)
AS A RESULT THIS EXERTS AN OUTWARD PRESSURE CALLED THE ELECTRON DEGENERACY PRESSURE
- this counters the gravitational pull which PREVENTS the complete collapse of the white dwarf, but only until a limit
What is the limit to which the white dwarf will not fully collapse called and what is it
Thus why do larger mass stars take a different route
The CHANDRASEKHAR limit
- states that if the core of the white dwarf has mass until 1.44 times the mass of the sun, it will SUSTAIN COLLAPSE BY ELECTRON DEGENERACY
- however if thr mass is more, it will COLLAPSE under gravity
2) this is why larges mass stars take a different path too
What finally ends the life cycle of a low mass star from a white dwarf
Cools down and becomes a black dwarf where not much energy left
That’s it
After a protostar is made, what is the difference in condtions going to be for a more massive star?
What can this change eventually allow for that makes key difference
This time more mass means MORE GPE is converted to a Ke in the core as the nebula forms a protostar
This all means higher temp, and thus FUSION OF HYDROGEN can happen quicker ,
2) and also potentially heavier elements too!!
So why does hydrogen in big star get consumed considerably faster than small star , and thus life cycle shorter
Because bigger mass = bigger temp and dense at core= more hydorgen fusion faster
What happens when hydrogen fusion in the CORE runs out for big stars
What does this end up making the protostar becoming
- radiation pressure decreases, Gravity pull causes star to collapse in on itself
- this increases temp of core, as GPE is converted to KE
- this time the temp increases SO much that fusion of HELIUM CAN NOW TAKE PLACE
- this causes EVEN FURTHER EXAPNSION DUE TO GREATER RADIATION PRESSURE compared to small star
- fusion at shells of hydrogen then take place again , causing further expansion
= eventually this leads to big expansion, and thus SUPER RED GIANT FORMING
What happens within the core once a super red giant is formed
(What eventually happens to core)
The tempertaures so high that fusion of heavier elements in the core and then shells can continue to happen
- what you get is a core of heavier elements closer to centre you get
- however eventually EVERYTHING BECOMES IRON CORE, as you can’t fuse past this
No more fusion takes place
What happens finally in big star when the core is iron and why
What is this called (super…
Iron core = means no more fusion takes place
This leads to unstability of star, no more radiation pressure = THE STAR IMPLODES
Here outer layers bounce into the iron core and out AND THIS CAUSES A SHOCKWAVE THSG SENDS ALL THR MATERIAL INTO SPACE
= this is a SUPERNOVA
What two paths can a red super giant iron core take after supernova occur
Either neutron star
Or black hole
1) how does the iron core of red giant become a neutron star after supernova
What is a neutron star
If the remaining mass of iron core is GREATER THAN CHANRAESKHAR limit, then it will FURTHER COLLAPSE to form a NEUTRON STAR
- this is made almost entirely of neutrons
- very dense and small volume
2) how does iron core of super red giant become a black hole after supernova
What is a black hole and what so special about it
This is if the core mass is about 3M
- even FURTHER collapse happens after neutron star to create mass that has such a string grav field that you need velocity of speed of light to escape it
- nothing can escape it, even photons, and it just ends up being so massive
Summary of life cycle of star
1) formation of star
2) Main sequence star journey
1) dust and gas from space collect together under grav pull to become a nebula
- denser regions cause them to clump together more and higher grav field causes GPE to convert to KE towards centre, increasing temp And density to make a core which is a PROTOSTAR
- once condtions right hydorgen fusion takes place and star is born
2) once main sequence the radiation pressure exerted by fusion balances rhe grav pressure and star exists in state of EQUILIBIRUM for time until hydrogen runs out
Summary of life cycle of stars
3) low mass till black dwarf
3) hydrigen runs out and grav causes star to collapse, increases temp of core as gpe converts to ke, and allows for fusion of hydrogen to take place in shells now
- radiation pressure causes outer layers to expand and cool, forming a RED GIANT
- eventually all hydrogen in star will run out
- will collapse , leaving just the core which is a WHITE DWARF
- everything else ejected as PLANETARY NEBULA
- will maintain this as long as Chandrasekhar limit met (1.44 m of sun), if higher mass it will collapse more (as seen by bigger stars)
- what’s keeping the white dwarf form collapsing is the electron degeneracy pressure, which is caused by electron exclusion principle (two electrons can’t exist in the same energy state )
- finally white dwarf will cool to become black dwarf
Summary of life cycle of stars
4) big mass to black hole / neutron
- hydrigen runs out, collapse happens, increases temp of core, but now as higher mass core much more hotter even before, so conditions are right for even HELIUM IN CORE TO FUSE
- this causes even more rsdisiton pressure and layers ejected more, as hydrogen in core fuse too, forms SUPER RED GIANT
- core so hot that fusion of heavier elements continue to happen to maintain radiation pressure, leaving core where closer you go more heavy elements there is
- however eventually whole core will be iron as CANT fuse past this
- when this happens no more rsdisiton pressure, star collapse in on itself . Layers bound off core into space and all material comoeltley ejected , SUPERNOVA
- finally if mass of iron core remains exceed chanreskahr it collapses further under grav and becomes neutron star, just neutrons, low volume and high dense
- if mass is 3M , then it will collapse even more and become black holes where even light can’t escape
The end
What force needs to be overcome between hydrogen or whatever for fusion to occur
Electrostatic force of repulsion, only overcome with high temps And pressures
HOW ARE ELEMENTS HEAVIER THAN IRON CRESTED THEN?
Through supernova , heavier elements created and ejected
Chacrterisric of a white dwarf (SPEC POINT)
(Mass, dense, volume comparison ?)
Very dense
Mass like our sun
Volume like earth
