Fhapter 19 Stars Flashcards
What is a planet
Object that orbits a stars
- has cleared its atmosphere of most things in orbit like asteroids
- has high enough grab field to give it a round shape
- has NO FUSION REACTIONS LEFT ( unlike stars)
Planetarybsatlritesn
These are anythign that orbits a planrt like moons or satellited
Comets
These are collection of dust and ice and rock , which orbit thr SUN
Solar system
Includes the sun and all the planets and objectd in jtd irbit ( comets, moomens etc)
Galaxies
Include all the stars and objects, interstellar dust and hsd
Universe
All the matter, energy and space time available conssits of our universe
These stars will have their own galaxies and solar systems
Nebulaloe
This is collection of dust that attracts itself to each other over time. The tiny gravational force of attraction from the particles cause them to clump up together, to form a collection of dust and GAS. HYDROGEN GAS
How is a peotodtar made
As the nebulae becomes more and more massive, grvaitnal energy from psrticles is transferred to ke as the particles become closer. In a more dense region, this starts to form a hot core , and thus a protostar is msde
As soon as the core is hot enough for fusion to take place, the star is born and enters its main sewuence
Why must their be high temlergsured and pressures for fusion to occur?
Fusion occurs when the nuclei get close enough for thr strong nuclear force attrvstice rsnge . At these small distances the electrostatic force of repulsion from protons in the nuckeud is so strong, and thus high temperatures and pressures are needed so nuclei have enough energy to overcome this force of attraction, and get close enough to fuse
What happens when the star is in its main sequence?
As hydrogen fused, this releases energy outwards. The photons preoduce create a RADIAITON PRESSURE, and also gas pressure . This works to counter to gavrwrionsl force of atrevstion due to the mass of the star on the outer layers .
While there is enough hydrogen and hydrogen is fusing, this is sustained, and the Starr is in a STEADY STATE FOR A LONG TIME
so the hrvaronal force acts to compress the star. It this is countered by gas and radiation pressured produced due to fusion
Why do bigger masses have a lower period as mains rauende compared to lower?
Bigger mass stars have higher temperature and pressure cores, due to more gpe being converted into ke as particles accelerate to its centre . Higher tempegured and pressure means fusion of hydrogen happens fsdter, and so it runs out of its store quicker. Therefore it has a lower time as main sewuende
How do low mass stars thrn become red giants after fusion of hydrogen runs out
- fusion of hydrogen runs out, so radiation and gas pressure drops
- therefore gravational pull is now bigger force than the pressure
- so the star begins to compress
- this makes the core of the star much hotter as it compresses
- which allows for fusion of hydrogen to take place in the shells of the core, due to right conditions
- the pressure produced by this expands the layers of the star
- eventually they cool down and become red in colour as a result
Thus red giant
Then what happens once hydrogen in shells run out?
Once hydrogen in shells run out , there is no longer any radisjton pressures
- by this time most of the outer layers have been eejected as planetary nebulae
- but now thr rgvatwitnal force of attraction is greater then outward oressure, the core of the Starr which is what’s left begins to compress
- if it has mass of less than 1.44M, it remains stable as a WHITE DWARF
- which then cools and becomes a black dwarf
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How can the core end up sd a stable liece of mass, when there is no pressure?
There is .
- as the core compressed, a certain ELECTRON DEGENERACY pressure is extended outwards
- this is produced due to do Pauli exclusion principe. Which stated that electrons can’t exist at the same energy state
- therefore as the core compressed, the electrons exert a pressure otjwards , which counters the force from gravational attraction
- for masses less than 1.44M , the electron degeneracy pressures Is enough to counter the grab pull, and thus remain as a stable white dwarf
However for masses ABOVE 1.44M, the grav force is TOO strong and the electron degeneracy pressure is not enough to counter. Other things happen, but the core is only 1.4d m and abive if it’s a big mass tar that becomes a super red giant anyways
This limit is called the CHANDRESHAKR limit
Features of a white dwarf
Extremely hot due to small size and, photons still emitting from before
However no more fusion, therefore luminosity is minimum
Small and high density m high mass, but masses are generally less than 1.44M obviously
What happens for a high amss star 10M plus afternintiwllyruns out of hydrogen
Runs out if hydirgen, the gravational pull then is bigger than radiajton pressured.
This causes the star to compress , which increase the temperature of th encore
Yet because the star is so massive, this means the core becomes hot enough for fusion of heavier stars to occur , with the hottest part being the middle.
As a result , pressure generated from this caused expansion of the outer layers, creating a super red giant
Here, the core keeps fussing until the whole core becomes iron, as this is the most stable element , with the highest binding energy.
What happens when all the hydrogen is finally used up, as well as ENITRE CORE iron?
Once entire core iron, no more fusion can take place
- no more ourtwar pressure, so the force due to gravity rapidly compressed the outer layers
- these rebound of the core and are ejected into the soace as part of a SUPERNOVA ! An IMPOLOSION , then Supernova that is a shockwave ejection alm layers
Describe the superoniva again
What about fusion
Once entire core is fused to iron, the gavtisotnal force pulls on layers leading to implosion which REBOUND of the core and into space as a supernova, ejecting all the layers
At this point, fusion of heavier elemetsoccur … things more than iron
What can happen to the super red gian core after supernova
1) if thr mass is between 1.44 and 3, As this exceeds the chandeskha r limit, the core continued to compress, until it forms a neutron star
- this is extreme,y low volume but high density such that it is massive.
2) if Mass if core event bigger than 3M, it compressed to become a black hole
X black hole is so massive that the grvatjnal pull means photons can’t even escape, and thus an escape velocity greater than the speed of light is needed.
