# Are planets and stars things on the same "spectrum"? **URL:** \ **Category:** Factual Questions\ **Created:** [September 18, 2016, 7:09pm UTC](https://boards.straightdope.com/t/are-planets-and-stars-things-on-the-same-spectrum/766295 "2016-09-18T19:09:16Z")\ **Posts on this page:** 3\ **Page:** 2
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [September 19, 2016, 5:22am UTC](https://boards.straightdope.com/t/are-planets-and-stars-things-on-the-same-spectrum/766295/21 "2016-09-19T05:22:10Z")
As noted above, an iron core fusing isn’t just a matter of pressure. You are trying to slam together nuclei that will only deign to do so if you add the energy deficit inherent in the mass change of the resultant nucleus. This is, as a good approximation, not dissimilar to all of the energy released when you took the lighter elements and fused them to get the iron in the first place. Or, is exactly the same energy released when you fission the new heavy elements back to iron. We are talking energies similar to the sum of the entire energy released by the star over many many millions of years, all concentrated into a tiny moment in time as the core of the supernova collapses in a freefall. [The energy is utterly insane](https://what-if.xkcd.com/73/). Indeed “insane” doesn’t seem to be even on the same planet as the word needed to describe the energy. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 19, 2016, 1:18pm UTC](https://boards.straightdope.com/t/are-planets-and-stars-things-on-the-same-spectrum/766295/22 "2016-09-19T13:18:21Z")
> [@](#): > > Quoth **Lumpy** : > > Probably would resemble a white dwarf star, although I don’t know if a stellar core remnant can contain silicon or iron without collapsing into a neutron star. White dwarfs are, in fact, largely iron. And neutron stars, of course, are mostly not made up of any chemical element at all, and what elements they do contain (in their outer layers) are mostly isotopes which would be impossible under less extreme conditions. > [@](#): > > Quoth **watchwolf49** : > > Well, if the Earth absorbed all the mass of Jupiter, it still wouldn’t be enough to start fusion, maybe all four outer planets … but that would wreck land prices in Missouri. To fuse even deuterium (which is significantly easier than ordinary hydrogen) requires 13 times the mass of Jupiter (this is usually used, nowadays, as the cutoff for the definition of a “brown dwarf”). Since there are fewer than 13 outer planets, and since Jupiter is the largest of them, it follows trivially that all of the outer planets combined would not be enough even for the simplest form of fusion. ---
**Author:** ![levdrakon](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@levdrakon](https://boards.straightdope.com/u/levdrakon)\ **Post date:** [September 19, 2016, 2:42pm UTC](https://boards.straightdope.com/t/are-planets-and-stars-things-on-the-same-spectrum/766295/23 "2016-09-19T14:42:14Z")
According to wikipedia, white dwarfs are usually oxygen and carbon, Depending on the initial mass of the star you might get neon and magnesium or a low mass star that can’t fuse helium could become a helium white dwarf. As far as I know, our sun is never going to make iron. > **[White dwarf](https://en.wikipedia.org/wiki/White_dwarf)** > > A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's low luminosity comes from the emission of residual thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the [Previous page](https://boards.straightdope.com/t/are-planets-and-stars-things-on-the-same-spectrum/766295.md?page=1)