expanding, depleted sun

[jadibartolomeo]

why do stars expand to red giants when they deplete their fuel sournces and then collapse into white dwarfs? i've read so much about how our sun will expand to the diameter of earth's orbit when it runs out of fuel in 5 billion years, but i don't understand why it expands and why it collapses due to this. thanks <img src="/images/icons/smile.gif" />

 

[vogon13]

As the hydrogen fusion ebbs, helium fusion will start in the sun's core.<br /><br />This occurs at a drastically higher temperature and the sun bloats from the higher resulting pressures.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[alokmohan]

Earth will be burnt to a cinder.None t6o observe this.

 

[MeteorWayne]

I see he's not aware of the Restaurant at the end of the Universe <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[michaelmozina]

According to contemporary gas model theory, the sun produces energy by fusing hydrogen into helium. After billions of years, predominantly hydrogen stars eventually "fuse" all their hydrogen atoms in helium atoms. Once all the hydrogen is used up, the sun enters into a "red giant" phase and begins to fuse helium into other heavier elements. This process continues through the various elements until what is left is mostly iron. Because of an iron atom's internal atomic configuration, iron cannot fuse into any other element and gain any energy from it. Once a star reaches this stage of being mostly iron, it tends to go "supernova".<br /> <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[robnissen]

Generally accurate, except that only stars much larger than the sun go supernova.

 

[michaelmozina]

<blockquote><font class="small">In reply to:</font><hr /><p>So, the implication is that there should a lot of gigantic iron ball bearings rolling around in the universe? <p><hr /></p></p></blockquote><br /><br />Well, either that, or the planets and suns that form out of the remnants will tend to contain a lot of iron. <img src="/images/icons/smile.gif" /><br /><br />Rob was correct about the size issue by the way. A small star would not be able to fuse heavier elements into iron and would not tend to go supernova according to current theory. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[nexium]

Class K and G stars are thought to do red giant, then white dwarf without a supernova. Our sun is class G2.<br />This hypothesis is dependent on the assumption that the outer hydrogen plasma does not mix into the core plasma significantly in the million years before the red giant stage. I have no idea how rigorously that assumption can be supported as sometimes, usually or always. If enough core mixing occurs, there will be no red giant phase, nor super nova; The interior will not get hot enough to fuse helium, nor the heavier elements. A mostly helium brown dwarf with almost one solar mass will be the result. It is thought that this will be the fate of M class stars in about 100 billion years. M class stars burn their hydrogen very slowly (mix the outer layers into the core) so we think all class M stars (and most class K stars) are still mainsequence. Please embellish, refute and/or comment. Neil

 

[alokmohan]

"fuse" all their hydrogen atoms in helium atoms?No it happens much before all hydrogen atoms are fused.

 

[alokmohan]

Interesting.Give me the link.

 

[Saiph]

nexium, the lack of core mixing in solar mass stars is pretty solid in the models. It has to do with convection currents and temperature distributions. Near the core, the temperature gradient is to steep to allow convection, so mixing doesn't occur.<br /><br /><br /><br />Also, you won't end up with mostly helium brown dwarfs of one solar mass, even if what you say is true. You'll still have a helium core, under intense pressure, and the remainder of a small star's life cycle will occur. It will swell under a helium flash, undergo core helium fusion, maybe a few other stages, then collapse as a white dwarf.<br /><br />By mixing the envelope hydrogen with the core, all you do is extend the lifespan of the star, specifically the mainsequence stage. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[alokmohan]

In case of stars of mass1.4 times ms that of sun ,we have a neutron stars.But one must be thorough with degeneration nof matter. <br /> Five Ages of the Universe http://www.fathom.com/course/10701055/session3.html<br /> Fathom <br /> <br />Sessions <br />Session 3 <br />Session 2 Session 4 <br /> <br /><br />The Degenerate Era <br /><br /> <br />Hubble Heritage Team <br />Glittering stars and wisps of gas create a breathtaking backdrop for the self-destruction of a massive star, called supernova 1987A, in the Large Magellanic Cloud, a nearby galaxy. Astronomers in the southern hemisphere witnessed the brilliant explosion of this star on Feb. 23, 1987. <br />When stellar evolution comes to an end, we enter the Degenerate Era. Most ordinary stars will be done with the business of nucleosynthesis as stellar bodies. In our inventory of stars, we have about equal numbers of brown dwarfs and white dwarfs, and about three in a thousand black holes and neutron stars. Since the white dwarfs are quite a bit larger than the brown dwarfs (by about a factor of 10 in mass), the vast majority of the actual (baryonic) mass--the protons--are embedded in these white dwarfs. Although a lot of gas is also left behind in this future universe, it's very diffuse and wispy. <br />In sum, what are left in the Degenerate Era are degenerate stellar remnants (degenerate here refers to a quantum mechanical property of dense matter, not to a moral statement about the universe). From cosmological decade 15 to perhaps 37 (1015-1037 years), these degenerate objects are the most important stellar objects in the universe. <br /><br /> <br /> <br /> Five Ages of the Universe <br /> Fathom <br /> <br />Sessions <br />Session 3 <br />Session 2 Session 4 <br /> <br /><br />The Degenerate Era <br /><br /> <br />Hubble Heritage Team <br />Glittering stars and wisps of gas create a breathtaking backdrop for the self-destruction of a massive star, called su