Insights Blog
-- Browse All Articles --
Physics Articles
Physics Tutorials
Physics Guides
Physics FAQ
Math Articles
Math Tutorials
Math Guides
Math FAQ
Education Articles
Education Guides
Bio/Chem Articles
Technology Guides
Computer Science Tutorials
Forums
Classical Physics
Quantum Physics
Quantum Interpretations
Special and General Relativity
Atomic and Condensed Matter
Nuclear and Particle Physics
Beyond the Standard Model
Cosmology
Astronomy and Astrophysics
Other Physics Topics
Trending
Featured Threads
Log in
Register
What's new
Search
Search
Search titles only
By:
Classical Physics
Quantum Physics
Quantum Interpretations
Special and General Relativity
Atomic and Condensed Matter
Nuclear and Particle Physics
Beyond the Standard Model
Cosmology
Astronomy and Astrophysics
Other Physics Topics
Menu
Log in
Register
Navigation
More options
Contact us
Close Menu
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Forums
Astronomy and Cosmology
Astronomy and Astrophysics
Why does the core collapse happen so fast in a supernova?
Reply to thread
Message
[QUOTE="Drakkith, post: 6825716, member: 272035"] I believe the Kelvin-Helmoltz mechanism merely gives the amount of energy provided by gravity for a star or planet. It was proposed as a possible solution to how the Sun powers itself, though we now know that fusion is the main energy source for the Sun and other stars. I don't think the Kelvin-Helmholtz mechanism itself tells you how fast something contracts. For that you need to know the power output somehow. The key to understanding how collapse happens so fast is to recognize that the normal mechanisms that support are star against gravitational collapse are disrupted or overpowered during a core collapse. There are a variety of ways this happens: electron capture (for example in Super-AGB stars), loss of electron degeneracy pressure (in the collapse of iron/nickel cores) and electron-positron pair instability (in super-massive stars) are some examples. For iron/nickel cores, which are degenerate, the pressures become so high that it is simply more energetically favorable for electrons to be captured by nuclei and the entire mess turning into a sea of neutrons than for the core to remain held up by electron degeneracy pressure. The cause of the collapse here is the removal of electron-electron repulsion from the core. Electrons, being lighter in mass than neutrons, are 'larger' in some sense of the word and will try to stay further apart from other electrons than neutrons will stay apart from other neutrons. So the whole core collapses to a tiny fraction of its original size as the electrons and nuclei turn into neutrons. In super-AGB stars (super-asymptotic giant branch), a similar mechanism to that which occurs in iron/nickel cores occurs with the exception that super-AGB stars have oxygen and neon in their cores. Unlike iron and nickel, oxygen and neon release a lot of energy when they fuse. When the core collapse occurs, the core temperature and density spikes, igniting a runaway fusion reaction that blows the star apart. This collapse is called an electron capture supernova (though it is still a core collapse supernova). In certain super massive stars, the core is primarily held up not by degeneracy pressure from electrons, but by pressure from light itself in the form of gamma rays. These gamma rays can be energetic enough to produce electron-positron pairs that temporarily rob the star of support until they annihilate with each other to produce more gamma rays that then hold up the star. In pair instability supernovas the star undergoes pulsations or fluctuations that cause the production and energy of gamma rays to spike. This increase in energy makes it more likely for the gamma rays to interact with nuclei in the core and produce electron-positron pairs. Then this increase in the production of matter-antimatter pairs robs the star of support, letting the outer layers to collapse inward, exerting more pressure on the core, which compresses it and heats it up, which then causes even more energetic gamma rays to be created, which then creates even more matter-antimatter pairs, etc etc. The whole thing quickly turns into a runaway collapse that blows the whole star apart as oxygen and possibly some heavier elements undergo runaway fusion. The cause of the extremely fast collapse is the sudden loss of support by gamma rays. [/QUOTE]
Insert quotes…
Post reply
Forums
Astronomy and Cosmology
Astronomy and Astrophysics
Why does the core collapse happen so fast in a supernova?
Back
Top