# Would ripping the core from a Sun-like star cause it to explode?

I'm well aware that a Sun-like star is incapable of producing a supernova at the end of its life. However, would removing the core or a fraction of it, trigger an explosion from the star collapsing in on itself? Removing, in this case, means actually taking somewhere else, both the mass and energy that may be present. Would the collapse be violent enough to light a more energetic and runaway fusion reaction or produce antimatter as may be the case with a hypernova?

If an explosion occurs how might it compare to an actual supernova?

Don't worry about the mechanism that removes the core; for the sake of the question I'm only concerned with the effect.

• My intuition is that you'd see a fizzle and not an explosion. – ohwilleke Nov 1 '16 at 2:25
• Provided that there is no explosion from the process, I doubt there would be any real noticeable fizzle. Energy from the core of a star under normal circumstances takes a very long time to escape. If I recall correctly, something like a million years. At least exciting is a slow cooling over a period of millions of years. – Joe Kissling Nov 1 '16 at 2:28
• It all depends on how you are ripping it. If you rip it like splitting a melon into two then it probably would cause an explosion from the inner energy suddenly bursting out. If you rip it by sucking the inner core like drinking coconut with a straw then there would be no explosion. – 絢瀬絵里 Nov 1 '16 at 3:25
• Maybe a very interestingly shaped nebula? – Landon Boyd Nov 1 '16 at 4:35
• I highly recommend reading the first chapter of Charles stress's iron sunrise for an answer. – John Meacham Nov 5 '16 at 6:49

Let's think about why a supernova happens in a massive star. You probably know that after a star develops an iron core, further nuclear fusion is not possible on a large scale. Yes, you can produce heavier elements via neutron capture, which indeed happens during supernovae (via the r-process) and inside massive stars (via the s-process), but conditions simply aren't suitable enough to form them at any significant rates inside massive stars, let alone the Sun. Therefore, you no longer have a source of outward pressure in the core (although the outer layers will still be fusing lighter nuclei in shell-burning processes).

Previously, the star was in hydrostatic equilibrium; the outward pressure balanced the inward gravitational force. However, the inner pressure is now gone - as is the case with your coreless Sun - and so the core begins to collapse. What happens next is a little complex; I'm going to quote from an answer I wrote on Astronomy:

1. At high enough densities ($$\rho\sim10^9\text{ g/cm}^3$$), electron capture becomes important, where a proton and electron combine to form a neutron and an electron neutrino: $$e^-+p\to n+\nu_e$$ Simultaneously, beta decay may occur, where a neutron decays to a proton, electron and electron antineutrino: $$n\to p+e^-+\bar{\nu}_e$$ However, beta decay becomes less important than electron capture at this point.
2. Electron capture reduces electron degeneracy pressure in the core, which leads to accelerated core collapse. Degeneracy pressure is important in the cores of many stars, but in extremely massive stars - red supergiants included - it simply isn't enough to stop the collapse.
3. At densities below $$\sim10^{11}\text{ g/cm}^3$$, neutrinos can carry away energy, and the initial burst leaves the star within about ten seconds. However, core collapse quickly leads to much greater densities, and when $$\rho\sim4\times10^{11}\text{ g/cm}^3$$, neutrinos are trapped. They scatter off nuclei, and transfer energy to electrons. Electron-nuclei scattering is also important, and may be dominant at higher energies.
4. At $$\rho\sim2.5\times10^{14}\text{ g/cm}^3$$, the core undergoes a "bounce", and the supernova explosion fully begins. A shock wave propagates into the outer core, and more neutrinos are produced via electron capture.
5. Neutrinos still trapped in/by the stellar remnant are released about ten seconds later. Neutrino pair production, too, leads to rapid cooling. Some of these neutrinos may contribute to a revival of the shockwave.

What if we could quickly stop the densities from reaching high enough that electron capture becomes less important, stalling both accretion and the outward rejuvenating burst of neutrinos? That would provide support against further collapse, and stop the outward shockwave from every forming, because there would be no bounce. In fact, we can do this easily in the case of the Sun, given that we should expect to see a lower core density than in massive stars.

Now, those lower densities mean neutrinos are less likely to interact with the outer layers of the star; thus, they should escape, carrying their energy harmlessly away. This should make the bounce weaker, if it happens at all - another reason I'd argue that the supernova may not occur.

Another advantage we may have is that the Sun's core is not degenerate; rather, it is supported by thermal pressure. I suspect this should make it more stable. The analogy I see used a lot, and which I prefer, is that of a thermostat, which was mentioned in the linked notes above. In a star, if the pressure decreases, so does the temperature and fusion rate. The star then collapses a little until it reaches higher densities, increasing fusion rate, temperature and pressure until it is stable once more. I'm guessing that this is what would happen for a coreless Sun. The density would presumably never be high enough for electron capture to occur, and so the shockwave would never happen. You wouldn't have a supernova, because you'd have something to counter the collapse: nuclear fusion.

Here's another little tidbit: electron capture is more likely to happen with free protons than with heavier nuclei (see Balasi et al. (2015)), meaning that if you had plenty of heavy metals in your coreless Sun, perhaps electron capture could happen less dramatically, slowing the core collapse and perhaps preventing the bounce.

Finally, I've been debating whether or not I should mention a helium flash. Again, I have no idea how fusion in the coreless Sun would occur as material moved towards the center, but there's a chance you could see brief runaway fusion (similar to what happens in a helium flash) that would then be damped, albeit a reaction of hydrogen fusion, not helium fusion. I'm still not sure how that would affect the possibility of a bounce.

• From what I am gathering the sun may not be able to create sufficient density to trigger a larger explosion and instead simply relight the fusion process that removing the core took away. And if there is a collapse at all then it may not even occur at a particularly energetic rate. Also in the physics of stars link you posted it stated the core was all that was involved in the collapse, not the whole of the star. And that core alone had a mass greater than the sun. It looks like at best there would be a brightening from the relighting of fusion and/or heat produced in the collapsing shell. – Joe Kissling Nov 1 '16 at 23:20
• @JoeKissling You're correct in all of that. The only reason I consider the outer layers at all is that in a supernova, they're not immediately relevant because it takes so long for them to be effected by the shock waves; other processes in the core happen sooner. Here, however, the layers are the only things at all relevant - the core being gone - and they will fall in towards the core region. – HDE 226868 Nov 1 '16 at 23:27

Solar core is 34% of the Sun mass, so sun will continue to be a star, at some point after the event. It will implode and probably intensify the processes compared to previous conditions and to a comparable star with 66% of the Sun mass. Dynamics of collapsing processes, may lead to ejection of plasma, so it definitely not recommended for planets like our at current state of our technological development.

The core of the Sun is considered to extend from the center to about 0.2 to 0.25 of solar radius

$$U = -G\int_0^R {\frac{(4\pi r^2\rho)(\tfrac{4}{3}\pi r^{3}\rho)}{r}} dr = -G{\frac{16}{3}}\pi^2 \rho^2 \int_0^R {r^4} dr = -G{\frac{16}{15}}{\pi}^2{\rho}^2 R^5$$

From Gravitational binding energy wiki article, but in this case core is out, so is out 0.25R

$$U = -G\int_{0.25R}^R {\frac{(4\pi r^2\rho)(\tfrac{4}{3}\pi r^{3}\rho)}{r}} dr = -G{\frac{16}{3}}\pi^2 \rho^2 \int_{0.25R}^R {r^4} dr = -G{\frac{16}{3}}\pi^2 \rho^2 \cdot \frac{1}{5}(R^5-0.0009765625 \cdot R^5)$$

They assume even distribution for mass, which is definitely not the case, but we will continue assumption farther, let assume that a thing called radius will not change significantly for star with 66% of its original mass (not true but lets hope it is enough true for our purposes)

With these assumptions energy stored as kinetic energy/heat energy/etc as result of this collapse will may be like:

$$0.0009765625 \cdot \frac{0.4356 \cdot 3GM^2}{5R} = \text{9.68176538754e+37 J}$$

That is a Lot, even compared to 3.828e+26 J/s which sun produces, according Sun Fact Sheet

• I'm not sure in any assumption and calculations here, I'm just try to estimate orders of magnitude of orders of magnitude. Looks like it have potential for nasty things.

The question is -- will it be enough? What happens to supernovas is not because they collapse, collapse itself is consequence of what actually happening, and happening changing the fuel they burn. (I do not posses deep knowledge about the processes there, but this is one of them)

Hydrogen burning is a slow process, if we compare it to other types of thermonuclear reactions, as it can be seen in example with thermonuclear bombs, they do not need such extreme conditions as sun have constantly in the core, and they produce more energy per given mass, then sun does per same mass in same time.

Removing core, have potential to slow down burning, as it contains heavy atoms like maybe carbon which maybe helps to catalyze hydrogen burning.

But this potential energy of collapse will heat hydrogen to higher temperatures and maybe compress it in to more dense state for some amount of time, which may not linearly improve speed of hydrogen burning. Which will lead to expansion of matter, slowing down the reaction and create circumstances to collapse again.

I will not wonder if collapsing/expanding cycles will continue for next million of years. How long it will continue will be question of how good will be that system as oscillator.

During that dance solar ejecta will have place, that is for sure, and it will be spectacular to observe from a safe distance.

Will it act really as supernova - probably not, depends, mmm interesting question. I mean sure not any star will, some stars may really become supernova from that, specially if core removal is done in the way to maximize that probability, but others will not.(basically these who may be supernova in a future they can, who will not, they probably will not)

Will this situation lead to some nasty things happening in the star system in a supernova fashion way of bad and good(depends who and for what uses that). Yes, it probably will have some elements of supernova - energy bursts, plasma bursts etc.

Will it be a apocalypse for star system, for planets probably not, for some one on a planet, probably yes.

• Can you explain why you are using those equations? First you appear to be calculating gravitational binding energy, but then it seems that you are saying the 9e37 is potential energy released from the collapsing system. I can't tell what the 9e37 figure is supposed to be. – kingledion Nov 1 '16 at 11:18
• @kingledion yes. Binding energy of a resulting body with mass 0.66M_sun minus binding energy of this body with void instead of core and same mass equals energy converted in to heat/kinetic energy during collapse process. Binding energy answers the question how much energy we should to spend to make this star indistinguishable from interstellar media. In OP's case we have to answer - how much we have to spend just to begin that process and have shell with 0.25R hole instead of core. 9e37J (+-few orders of magnitude) is a energy of the system converted from potential energy into kinetic energy. – MolbOrg Nov 1 '16 at 14:56
• @kingledion or maybe another way, in this case they integrate spherical shell of small thickness, they integrate it over radius of that sphere. at $r<0.25R$ $\rho=0$, for our case, and this is why I have integration from $R$ to $0.25R$ – MolbOrg Nov 1 '16 at 15:04
• @kingledion Just so I am understanding you correctly, the collapse process would release more energy than the remaining gravitational binding energy of the sun after the core is removed? – Joe Kissling Nov 1 '16 at 17:06
• I'm confused as @kingledion is. The mass is instantaneously removed by some unknown process; it's simply gone. What happens next is determined by the structure and mass of the layers outside the core, not the binding energy that disappeared when the core was taken away. I'm also not convinced that it would lead to a supernova; where is the energy to disperse the outer layers coming from? – HDE 226868 Nov 1 '16 at 23:05

It would probably be the same as a regular supernova.

A supernova is caused by the core of the star suddenly collapsing, which can actually happen for a number of reasons (the most well-known type being related to running out of "fuel" and collapsing under gravity), leaving an empty space which the rest of the star "falls into". This infalling matter collides with other infalling matter, rebounds, and the intense forces from this collision blow the star apart.

The reason why normally only large stars experience supernovas is because only large stars have cores massive enough to undergo this kind of rapid gravitational collapse (the other types of supernova also only happen to large stars, but for different reasons). But if you simply removed the core entirely (I'm assuming you're doing this through some kind of hyperspace method and not physically reaching through the star's outer layers to pluck it out), this wouldn't matter. Even a small star like our Sun could suffer the same effects. Perhaps not quite as intense as a large star's supernova, but still a supernova.

There would be no stellar remnant though (neutron star/black hole), since these are the remains of the collapsed core and this star has none.

• Yes, the core is simply winked out of existence either by hyperspace, wormhole, etc. whatever work for you. The key is that it's mass and energy no longer are present. – Joe Kissling Nov 1 '16 at 17:09
• I'm not convinced that the collapse would lead to a supernova. There are mechanisms (namely, thermal pressure generated by fusion) that could counteract it, which don't exist or aren't applicable in a normal massive star before it undergoes a supernova. – HDE 226868 Nov 1 '16 at 23:08
• I must slightly object--the blast will be smaller because there is less mass to go boom. – Loren Pechtel Nov 2 '16 at 5:17
• @HDE226868 And the layers that crash in in a supernova are also capable of fusion. It goes boom anyway because it slams together so hard that it burns very fast rather than over millions or billions of years. – Loren Pechtel Nov 2 '16 at 5:30
• @LorenPechtel Sorry, I wasn't clear enough. It's true that nucleosynthesis happens in the outer layers, but it doesn't occur in a large scale in the core during a supernova; iron fusion is not exactly common. However, for the coreless Sun, you do have fuel that can be fused perfectly fine. – HDE 226868 Nov 2 '16 at 15:05