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star life summary (1 Viewer)
- Thread starter mary^^
- Start date
Hydrogen burning is before helium flash
Nebula -> protostar -> If large enough hydrogen fusion commences and joins main sequence -> hydrogen in core runs out -> core contracts and H in shell starts to fuse -> Shell expands ->Helium flash -> helium in core starts to fuse.
Inside core heavier elements start to form dependent on mass of star.
Death
~1-5 Solar mass; Outer layers shot off as planetary nebula, fusion stops and star slowly cools as a white dwarf -> black dwarf
>5 Core collapses under force of gravity drawing in shells which then explode as a supernova
- Core < 3 solar mass. Gravitational collapse causes neutron degenecy and neutron star forms
-Core > 3 solar mass Collapse continues and results in a black hole.
Nebula -> protostar -> If large enough hydrogen fusion commences and joins main sequence -> hydrogen in core runs out -> core contracts and H in shell starts to fuse -> Shell expands ->Helium flash -> helium in core starts to fuse.
Inside core heavier elements start to form dependent on mass of star.
Death
~1-5 Solar mass; Outer layers shot off as planetary nebula, fusion stops and star slowly cools as a white dwarf -> black dwarf
>5 Core collapses under force of gravity drawing in shells which then explode as a supernova
- Core < 3 solar mass. Gravitational collapse causes neutron degenecy and neutron star forms
-Core > 3 solar mass Collapse continues and results in a black hole.
can u simplify it and explain it dummy style?
jang
is not my real name
r u ruse?
well.. ruse does quanta... but i think there are some that do astro (those that are really interested)
u could be from sefton... they do astro...
or from carlingford...
but yeh, as if u hav reason
well.. ruse does quanta... but i think there are some that do astro (those that are really interested)
u could be from sefton... they do astro...
or from carlingford...
but yeh, as if u hav reason
jang
is not my real name
reasons for them pulsating?! man.. thats some random shit aint it?
i think mainly, they are somehow unstable, their gravitational force inwards is in a disequilibrium with the radiation forces outwards meaning, their size is constantly changing, with pulsating variables- this change is somewhat periodic.
this applies to cepheids, one of the most luminous stellar objects in space. their period on a log scale allows us to predict their absolute M, meaning we can use the distance modulus formula to calculate the distance to the cepheid and hence distant galaxies
i think mainly, they are somehow unstable, their gravitational force inwards is in a disequilibrium with the radiation forces outwards meaning, their size is constantly changing, with pulsating variables- this change is somewhat periodic.
this applies to cepheids, one of the most luminous stellar objects in space. their period on a log scale allows us to predict their absolute M, meaning we can use the distance modulus formula to calculate the distance to the cepheid and hence distant galaxies
jang
is not my real name
hmm then no idea, helper where r u?
OK going way past what is required in the syllabus
Cephids: The fusion of Helium results in the ionisation of some Helium atoms. If a Helium atom is ionised to its second level its opaqueness will increase reducing the luminosity of the star, increasing the temperature causing it to expand as the radiation pressure increases. As it expands it cools, the double ionised Helium returns to a single Helium increasing the luminosity and it contracts because of the decreased radiation pressure.
Red Giants: As the different elements begin to fuse there is an initial decrease in temperature resulting in gravitational collapse and then increase as the heavier element begins to fuse. This results in an increase in radiation pressure and expansion.
Supernova: Osciallations aren't periodic and are caused by thermal winds in the shells
Cephids: The fusion of Helium results in the ionisation of some Helium atoms. If a Helium atom is ionised to its second level its opaqueness will increase reducing the luminosity of the star, increasing the temperature causing it to expand as the radiation pressure increases. As it expands it cools, the double ionised Helium returns to a single Helium increasing the luminosity and it contracts because of the decreased radiation pressure.
Red Giants: As the different elements begin to fuse there is an initial decrease in temperature resulting in gravitational collapse and then increase as the heavier element begins to fuse. This results in an increase in radiation pressure and expansion.
Supernova: Osciallations aren't periodic and are caused by thermal winds in the shells
how bout active and adaptive optics? u know how they use a wavefront sensor between the primary mirror and the final lens or something? then they detect how much the light has been distorted due to atmospheric turbulence, then send info to the computer. does the computer change the shape of a mirror to correct it? and wouldnt this take time so the image that is seen is not real time but delayed? is this true?
Yes they do change the shape of the mirror.
Active optics are only used for slow changes like deformation of the mirror due to its movement. These deformations are slow so the feedback is not going to have major changes to the image. So the time delay will have little effect.
Adaptive optics: For turbulence. This is why they need to resaample at high frequency 1000Hz. It is found that most changes in turbulence are below this frequency so the adjustments is more rapid than the turbulence. It is not 100% but makes a major improvement.
The image is in realtime but the adjustments are a feedback loop.
Active optics are only used for slow changes like deformation of the mirror due to its movement. These deformations are slow so the feedback is not going to have major changes to the image. So the time delay will have little effect.
Adaptive optics: For turbulence. This is why they need to resaample at high frequency 1000Hz. It is found that most changes in turbulence are below this frequency so the adjustments is more rapid than the turbulence. It is not 100% but makes a major improvement.
The image is in realtime but the adjustments are a feedback loop.