Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
32 Cards in this Set
- Front
- Back
|
What are some points on stellar mass and fusion 3 pt |
mass of a main sequence star determines its core pressure and temperature. stars of higher mass have higher core temperature and more rapid fusion making stars more luminous and shorter lived. stars of lower mass have cooler cores and slower fusion rates, this gives them smaller luminosities and longer lifetimes. |
|
|
How does a stars mass affect nuclear fusion? |
mass determines its core pressure of a star and temperature and therefore determines its fusion rate higher mass stars have hotter cores, faster fusion rates, greater luminosities and shorter lifetimes. |
|
|
How long does a star remain on the main sequence? |
as long as it can fuse hydrogen into helium in its core. |
|
|
What is the life track of a star after the main sequence? |
it has stopped or slowed the fusion of hydrogen into helium and becomes larger, redder, and more luminous. |
|
|
What are Red Giants? |
Broken thermostat as the core contacts, h begins fusing to he in a shell around the core luminosity increases because the core thermostat is broken. increasing fusion rate in the shell does not stop the core from contracting. |
|
|
Helium fusion |
does not begin right away because it requires higher temperatures. larger charge leads to greater repulsion between electrons.
fusion of two helium nuclei dosent work. helium fusion must combine three helium nuclei to make carbon.
|
|
|
Helium Flash |
core temperatures rise rapidly when helium fusion begins helium fusion rate skyrockets until thermal pressure takes over and expands the core again. helium buring stars neither shrink or grow because core thermostat is temporarily fixed |
|
|
Life track post helium flash |
red giant shoudl shrink and become less luminous after helium fusion begins in the core. these stars are found on a horizontal branch on teh h-r diagram. |
|
|
How does a low mass star die? |
The helix Nebula is about 7000 light years away and about 5 light years across. it is a planetary nebula arond the exposed core of a dead star about 11000 years after the star expelled its outer layers. |
|
|
What is double shell burning? |
After core helium fusion halts, helium fusies into carbon in a shell around the carbon core, and hydrogen fuses to helium in a shell around the helium layer. this stage never reaches equilibrium. fusion rate periodically spikes upward in a series of thermal pulses. with each spike convectoin dredges carbon up from the core and transpors it to the surface the core left behind is a white dwarf. |
|
|
What happens at the end of fusion? what is the final state for light stars? |
fusion no further in a low mass star because the core temperature never grows hot enough for fusion of heavier elements. sometimes helium will fuse to carbon to make oxygen. two electrons cannot exist in the same state at the same place because electrons resist collapse. the resulting degeneracy pressure supports the white dwarf against gravity, although there is no heat generating fusion any more in the core. |
|
|
what will happen to earth and the sun once the sun leaves the main sequence? |
The suns luminosity will rise to 1000 ties its current level and will be too hot to sustain life on earth. suns radius will grow to nearly the current radius of earth's orbit. |
|
|
what are the stages, in order, of the life cycle of a star? |
protostar contracton of protostar with hydrogen core burning in equilibrium. hydrogen shell begins buring helium core burns double shell burns thermal pulses transition to white dwarf |
|
|
What are the stages of a low mass star? |
hydrogen fusion in core (main sequence) hydrogen fusion in shell around contracting core (red giant) helium fusion in core (horizontal branch, pulsating) double shell burning (red giant) ejection of hydrogen and helium in a planetary nebula leaving behind an inert white dwarf. |
|
|
What do high mass stars do? what is the CNO cycle? |
high mass main sequenc stars fuse h to he at a higher rate using carbon, nitrogen, and oxygen as catalysts. greater core temperature enables hydrogen nuclei to overcome greater repulsion. |
|
|
life stages of a high m ass star |
late lif stages of high mass stars are similar to those of low mass stars hydrogen core fusion hydrogen shell burning supergiant helium core fusion supergiant |
|
|
What elements did the big bang create? how were other elements created? |
Hydrogen 75%, helium 25% traces of Beryllium, lithium, and boron. helium fusion can make carbon in stars CNO cycle in high mass stars can change carbon to nitrogen and oxygen in stars. |
|
|
how can helium fuse with other elements? what does this produce? |
high core temperatures allow helium to fuse with heavier elements helium capture builds carbon into oxygen, neon, magnesium and other elements. |
|
|
What is advanced nuclear bonding? |
core temperatures in stars with less than 8msun allow fusion of elements as heavy as iron. advanced reactions in stars make elements like silicon sulfur calcium and iron it proceeds in a series of nested shells |
|
|
why is iron special? |
nuclear reactions involving iron do not release energy because iron has the lowest mass per nuclear particle. this makes iron a dead end for fusion.
elements heavier than iron are rare because energy is required to make them. |
|
|
Helium capture |
commonly makes even numbered elements |
|
|
How does a high mass star die? |
iron builds up in its core until electron gegeneracy pressure can no longer resist gravity. the core then suddenly collapses, creating a supernova explosion. |
|
|
What happens in a supernova explosion? |
core degeneracy pressure goes away becase electrons combine with protons making neutrons and neutrinos neutrons collapse to the center, forming a neutron star which is stabilized by neutron degeneracy pressure.
|
|
|
how are elements heavier than iron formed? |
energy and neutrons released in supernova enable elements heavier than iron to form. |
|
|
What is a supernova remnant? |
energy released by the collapse of the core drives the star's outer layers into space. the crab nebula is the remnant of the supernova seen in 1054. it is about 6,500 light years away. |
|
|
Role of Mass |
|
|
|
Summary of low mass stars |
main sequence fusion h to he in core red giant h fuses to he in shel around he core helium core burns he fuses to c in core while h fuses to he in shell double shell burning h and he fuse in shells planetary nebula leaves white dwarf behind |
|
|
What are the reason for each life stage of a low mass star? |
core shrinks and heats unti its hot enough for fusion nuclei with larger charge require higher temperature for fusion core thermostat is broken while core is not hot enough for fusion (shell burning). core fusion can't happen if degeneracy pressure keeps core from shrinking |
|
|
What are the stages of a high mass star? |
main sequence h fuses to he in core red supergiant h fuses to he in shell around he core helium core burning he fuses to c in core while h fuse to he in shell multiple shell buringin many elements fuse in shells super noval leaves neurtron star behind |
|
|
How are lives of stars with close companions different? |
algol at onset of mass transfer. when more massive star expands into a red giant it began losing some of its mass to the gravitational pull of its normal, hydrogen core fusion companion. |
|
|
how can things be different in binary star systems? |
matter is close enough that it can flow between subgiant and main sequence star in bianary systems. |
|
|
how does a stars mass determin its life story? |
it determines how high a sars core temperature can rise and therefore determines how quickly a star uses its feul and what kinds of elements it can make.
|
