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mjda
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Can anyone enlighten me as to why the total thermal energy of a star will increase with time if the star has no nuclear energy source?
Drakkith said:The star will heat up as it contracts, if that is what you mean. The mechanism is called the Kelvin–Helmholtz mechanism, and it converts gravitational potential energy into thermal energy.
snorkack said:The article only specifies the source of heat - not that the heat should increase.
Heat does not always increase - only if the star is mostly ideal gas it does.
snorkack said:...density at centre increases s3=8 times ...
The density was increased 8 times as stated...
But as stated before, the central density was increased just 2 times...
But as stated before, the central density was increased just 8 times.
rootone said:Most stars don't go all the way to iron though.
After the CNO elements are produced. it's game over for stars around the mass of the Sun.
A short puff of a red giant stage, then it's white dwarf time for near eternity unless other objects get involved...
A helium flash is a very brief thermal runaway nuclear fusion of large quantities of helium into carbon through the triple-alpha process in the core of low mass stars (between 0.8 solar masses (M☉) and 2.0 M☉[1]) during their red giant phase (the Sun is predicted to experience a flash 1.2 billion years after it leaves the main sequence).
Android17 said:So does a star heat up when it contracts? Or Contracts when it cools down?
How?Drakkith said:Both, actually. Nuclear fusion muddles the issue a bit,
Drakkith said:Real stars get hot enough to ignite nuclear fusion in there cores
How can gravitational PE be used up? Is it because of the loss of mass as heat? How much mass would a main sequence star lose in its life time? It would be very very small, right? So how gravitational potential gets used up, or are you saying that it comes into equilibrium with other forces like electromagnetic forces between atoms.Drakkith said:which lengthens the amount of time required for the star to contract fully in addition to causing cycles of expansion and contraction in larger stars.
Android17 said:How?
Android17 said:Is it the heat that causing nuclear fusion? Or the fact that gravity is smashing one nucleus into another or a combination of both?
Android17 said:How can gravitational PE be used up? Is it because of the loss of mass as heat?
Android17 said:How much mass would a main sequence star lose in its life time?
Android17 said:So does a star heat up when it contracts? Or Contracts when it cools down?
Heat is energy transferred spontaneously from a hotter to a colder system or body. Heat is energy in transfer, not a property of the system; it is not 'contained' within the boundary of the system. On the other hand, internal energy is a property of a system.
Android17 said:How much mass would a main sequence star lose in its life time?
Yes, the internal kinetic energy is always rising the same, degenerate or ideal, but we only call the internal kinetic energy "thermal energy" if it's not too degenerate. If it's highly degenerate, that energy cannot be lost in the form of heat, even when in thermal contact with the coldness of space, so that's the situation where the "thermal energy" can actually drop. Ironically, that's the more intuitive response to losing heat, but requires quantum mechanics to get it!snorkack said:Bodies whose interiors are largely degenerate, like brown dwarfs, planets and white dwarfs, do produce heat on contraction, but only contract as they cool down (having dissipated the heat produced on contraction).
Be careful here: The energy lost in the form of photons is very, very small. (Well, 1%-ish.) A little is lost in the form of the stellar wind during its main-sequence phase. The major mass loss for stars near the Sun's size and somewhat larger comes near the end, as it sheds its outer layers with a huge wind during the red-giant phase, leaving the core as a white dwarf. This can easily be 1/2 the total mass of the star.Android17 said:How much mass would a main sequence star lose in its life time? It would be very very small, right?
"Stellar Thermal Energy with no Nuclear Source" is a phenomenon in which stars emit heat and light without the presence of nuclear reactions. This is a rare occurrence and is still being studied by scientists.
There are a few theories on how this phenomenon may occur, but it is not fully understood. One theory suggests that the star's intense magnetic fields could be responsible for generating the heat and light, while another theory proposes that it could be due to the star's rotation and turbulence within its core.
It is unlikely that a star could sustain its life solely on stellar thermal energy without nuclear reactions. Nuclear reactions are the primary source of a star's energy and without them, the star would eventually cool and dim.
Yes, there have been a few stars that have been observed to emit thermal energy without a nuclear source. These stars are often referred to as "peculiar stars" and are still being studied to better understand this phenomenon.
The discovery of stellar thermal energy with no nuclear source challenges our current understanding of how stars produce energy. It opens up new avenues for research and could potentially lead to a better understanding of the universe and its processes.