<p>Other answers are correct; a neutrino pulse is definitely expected as a result of a core-collapse supernova and should occur some hours before a shockwave arrives at the surface.</p>

<p>There essentially would be no visible sign that the star was about to become a supernova and that is because the dynamical timescale of the envelope is relatively long - thus responding slowly with respect to changes in the core. So, even if all support is removed from the centre, the surface can only respond (at best) on a freefall timescale of $\sim (G \rho)^{-1/2}$, where $\rho$ is the average density. If the star is a $10M_{\odot}$ supergiant with a radius of 1 au, then this timescale is tens of <em>days</em>.</p>

<p>Another possibility not mentioned so far is gravitational waves. Assuming that a relatively portable gravitational wave detector was available (!) then you would also expect a sharp gravitational wave pulse on the core collapse timescale (a second or less) that would also presage the supernova blast wave some hours later.</p>

CC BY-SA 3.0
2016-09-23T06:53:17.737Z
With respect to the gravitational wave: Would a non-rotating collapsing star emit gravitational waves? From another discussion I understood (perhaps in error) that rotation was a requirement. Something with quadrupole ...
Peter - Reinstate Monica
CC BY-SA 3.0
2016-09-23T06:58:01.507Z
@PeterA.Schneider Supernovae are fully expected to be GW sources, because there is expected to be asymmetry ( the core will be rotating very fast - see pulsars). eg. http://iopscience.iop.org/article/10.1086/381360/fulltext/59085.text.html
ProfRob
CC BY-SA 3.0
2016-09-23T12:48:28.427Z
@PeterA.Schneider Real supernovae turn out to be highly asymmetric, even when their progenitors display a high degree of spherical symmetry. This asymmetry may be sufficient to produce gravitational waves, although I've not crunched the numbers. Finding the source of this asymmetry is an active topic of research.
Calchas
CC BY-SA 3.0
2016-09-21T16:33:17.227Z
2016-09-21T16:33:17.227Z
ProfRob
<p>As <a href="https://astronomy.stackexchange.com/questions/18423/are-there-observable-changes-in-a-star-about-to-become-supernova-minutes-or-hou#comment28951_18423">Dean said</a>, supernova progenitors typically release neutrinos prior to full core collapse, remnant formation and the ejection of the outer layers of the star. The process - focused here on the neutrinos - goes something like the following:</p>
<ol>
<li>At high enough densities (<span class="math-container">$\rho\sim10^9\text{ g/cm}^3$</span>), <a href="https://en.wikipedia.org/wiki/Electron_capture" rel="noreferrer">electron capture</a> becomes important, where a proton and electron combine to form a neutron and an electron neutrino:
<span class="math-container">$$e^-+p\to n+\nu_e$$</span>
Simultaneously, <a href="https://en.wikipedia.org/wiki/Beta_decay" rel="noreferrer">beta decay</a> may occur, where a neutron decays to a proton, electron and electron antineutrino:
<span class="math-container">$$n\to p+e^-+\bar{\nu}_e$$</span>
However, beta decay becomes less important than electron capture at this point.</li>
<li>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.</li>
<li>At densities below <span class="math-container">$\sim10^{11}\text{ g/cm}^3$</span>, 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 <span class="math-container">$\rho\sim4\times10^{11}\text{ g/cm}^3$</span>, 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.</li>
<li>At <span class="math-container">$\rho\sim2.5\times10^{14}\text{ g/cm}^3$</span>, the core undergoes a &quot;bounce&quot;, and the supernova explosion fully begins. A shock wave propagates into the outer core, and more neutrinos are produced via electron capture.</li>
<li>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.</li>
</ol>
<p>Neutrinos may arrive hours - or possible days, in some circumstances - before the light from the supernova. The former was the case for <a href="https://en.wikipedia.org/wiki/SN_1987A" rel="noreferrer">SN 1987A</a>, the first supernova from which neutrinos were detected.</p>
<h3>References</h3>
<ul>
<li><a href="https://arxiv.org/abs/1503.08095" rel="noreferrer">Balasi et al. (2015)</a></li>
<li><a href="https://arxiv.org/abs/1508.00785" rel="noreferrer">Mirizzi et al. (2015)</a></li>
<li><a href="https://arxiv.org/abs/1205.6003" rel="noreferrer">Scholberg (2012)</a></li>
</ul>

CC BY-SA 3.0
2016-09-21T16:13:11.117Z
Thank you, @HDE. That detailed answer makes me wonder if the core collapse could be accelerated with the introduction of something "new" in the star. In the novel, there is a battle with an unknown hostile alien ship. That ship is disabled and put into a falling trajectory to the star. If there is a way in with that event could shorten the time to explosion, it would add more drama (the core collapse is detected by the characters before expected). I remark that the falling ship is alien and unknown, so there is no problem to include antimatter, strange matter, or wathever needed.
Alfonso de Terán
CC BY-SA 3.0
2016-09-21T17:23:20.073Z
@AlfonsodeTerán, Even assuming some type of unobtainium, it is not believable, even in a fictional environment, that the addition of anything that is on the scale of a spaceship would have sufficient effect when unintentionally falling into a star. The difference in scale is just too vast. Writing it such that it did so would almost certainly destroy my suspension of disbelief if I were reading such a story. Even assuming the ship was powered by a micro-black hole, the time it would take for the singularity to significantly affect the star is longer than what you have been describing.
Makyen
CC BY-SA 3.0
2016-09-21T17:25:14.237Z
@AlfonsodeTerán Mayken's absolutely right. You'd need quite advanced technology to even begin to contemplate having a chance at impacting the evolution of a star like this, if that's even possible. Its effects would be like a drop in the metaphorical bucket.
HDE 226868
CC BY-SA 3.0
2016-09-21T20:05:05.677Z
just for grins... assuming a smallish red giant, and an alien spaceship around 1km, this would be comparable to dropping an 0.1 inch drop into Lake Ontario. Sorry metric rest-of-world.
Spike0xff
CC BY-SA 3.0
2016-09-21T21:06:50.610Z
I thought it would be too far fetched, but I had to ask anyway. Thanks.
Alfonso de Terán
CC BY-SA 3.0
2016-09-21T21:38:42.920Z
@Makyen: Black hole drive ought to do it. I don't want to think about how short of time you have left once dropping a micro black hole into a giant star.
Joshua
CC BY-SA 3.0
2016-09-21T23:47:55.217Z
@Joshua unless the black hole is very much not micro (~$1M_{\odot}$) we're talking years at least. black holes are limited in how fast they can eat by interactions between particles in the accretion disk.
Leliel
CC BY-SA 3.0
2016-09-23T07:02:12.233Z
@Spike0xff If the lake is supercool and the drop is impure it may trigger crystallization. I don't think such phase-shifts occur in stellar cores in reality but as SF one could have hell freeze over...
Peter - Reinstate Monica
CC BY-SA 3.0
2016-09-24T16:05:09.197Z
@PeterA.Schneider A sort of stellar (or cosmological) equivalent of Ice-nine?  That would be quite the weapon.  I don't think Kurt V worked out the exothermics, but for this story the phase transition would have to be deeper than chemical bonds. What about a contagious local change in the zero-pt-energy, or the (usually) frozen physical constants, or the distortion off local space-time caused by the star's mass? (Triggered by the breakdown of the alien ship's drive. Or coffee machine.)
Spike0xff
CC BY-SA 3.0
2016-09-21T15:49:13.743Z
2016-09-21T15:49:13.743Z
2020-06-17T09:47:40.653Z
HDE 226868
<p>A superluminous supernova (aka hypernova) can exhibit a double peak to its brightness and some are theorizing that this may be the norm for a superluminous supernova, though as far as I know it's only actually been observed in one case so far (DES14X3taz).</p>

<p>Anyway, in (at least) this case there was an initial substantial increase in brightness. Then the brightness dropped (a couple of magnitudes) for a few days, then ramped back up to considerably brighter than the initial "bump".</p>

<p>You probably are going to need to be careful about the distances involved. The initial burst of light is already large enough that unless your people are <em>quite</em> a ways away, it'll already be enough to fry them to a crisp.</p>

<p>There is one other point that might be interesting for your novel though. After the explosion, what you probably get is a magnetar--which, as you'd guess from the name, is a star with an <em>extremely</em> strong magnetic field--so strong, in fact, that it's likely to cause all sorts of havoc with anything in the vicinity that depends on anything involving electrical activity--not only electronics, but also probably people's nerves as well.</p>

<p>There is an obvious problem here though: a red supergiant is the right type of star as the progenitor for a "normal" supernova. It's probably <em>not</em> the right type as the progenitor for a superluminous supernova. The progenitor of a supernova is typically something like six or eight solar masses. A superluminous supernova is <em>probably</em> (only a few are known, so it's hard to generalize) something like a couple hundred solar masses. Given the amount of energy released, it <em>has</em> to be quite large anyway.</p>

<p>Reference: <a href="http://arxiv.org/abs/1512.06043" rel="nofollow">Smith, et al (2015)</a></p>

CC BY-SA 3.0
2016-09-22T23:48:58.890Z
2016-09-23T00:08:09.243Z
2016-09-23T00:08:09.243Z
Jerry Coffin
<p>I think your best bet would be detecting neutrinos generated by nuclear burning inside the star (as we do for the Sun). Once the star hits the carbon-burning stage, it's actually putting out more energy in neutrinos than in photons. During the silicon-burning phase, which lasts for a few days and is what creates the degenerate iron core (that collapses once it is massive enough), the neutrino flux increases to about 10<sup>47</sup> erg/s a few seconds before core collapse. (The peak flux <em>during</em> core collapse is about 10<sup>52</sup> to 10<sup>53</sup> erg/s). <a href="https://arxiv.org/pdf/1506.01175v4.pdf" rel="noreferrer">This paper by Asakura et al.</a> estimates that the Japanese KamLAND detector could detect the pre-supernova neutrino flux for stars at distances of <em>several hundred parsecs</em>, and provide advance warning of a core-collapse supernova several hours or even days in advance. Since your characters are <em>in the same system</em> as the star, they'd hardly need a large underground detector to pick up the neutrinos.</p>

<p>This plot shows an example of neutrino luminosity (for anti-electron neutrinos) versus time for a pre-supernova star (from Asakura et al. 2016, based on Odrzywolek &amp; Heger 2010 and Nakazato et al. 2013); core collapse begins at t = 0s.</p>

<p><a href="https://i.sstatic.net/nF9hR.png" rel="noreferrer"><img src="https://i.sstatic.net/nF9hR.png" alt="Figure 1 from Asakura et al. 2016"></a></p>

<p>By measuring the spectrum of energies for different types of neutrinos and their time evolution, you could probably get a very good idea of how far along the star was, particularly as we can probably assume your characters have much better models for stellar evolution than we currently do. (They'd also want to get accurate measurements of the star's mass, rotation rate, maybe internal structure via astroseismology, etc., in order to fine-tune the stellar-evolution model; these are all things they could do pretty easily.)</p>

<p>The core collapse itself would be signalled by the <em>enormous</em> increase in neutrino flux.</p>

<p><a href="https://what-if.xkcd.com/73/" rel="noreferrer">This "What If" article</a> by Randall Munroe estimates that the neutrino flux from a core-collapse supernova would be <em>lethal</em> to a human being at a distance of around 2 AU. Which, as he points out, could actually be inside of a supergiant star, so your characters would probably be a bit further away than that. But it does show that the neutrino flux would be easily detectable, and that your characters might well get radiation poisoning from it if they were closer than 10 AU. (Of course, you'd want to <em>detect</em> it more directly than just waiting around till you started to feel sick, since that might take longer than the shock wave takes to reach the surface of the star.) This is just to bring home the fact that they wouldn't have any problem detecting the neutrinos....</p>

CC BY-SA 3.0
2016-09-21T15:43:42.187Z
Great answer! @Alfonso It might help your realism to address the fact that neutrinos are notoriously hard to detect. Some simple line implying that neutrino detection capabilities have increased ten-fold for your future-tech would help sell the realism that you can actually detect neutrinos on a small space ship without something like [current neutrino detectors](https://en.wikipedia.org/wiki/Super-Kamiokande) (which are massive).
zephyr
CC BY-SA 3.0
2016-09-21T15:51:43.300Z
Thank you very much, Peter. That's exactly the info I needed.
Alfonso de Terán
CC BY-SA 3.0
2016-09-21T16:37:03.307Z
@zephyr The volume of the neutrino detector can be scaled down by the relative flux of neutrinos you expect. You don't need a large detector to observe the neutrino pulse if you are in orbit around the star that blows up.
ProfRob
CC BY-SA 3.0
2016-09-21T16:39:39.390Z
@RobJeffries Sure, but they'd need to detect these neutrinos before the major burst happens. What's more, who knows how far out the space ship is.
zephyr
CC BY-SA 3.0
2016-09-21T17:01:54.560Z
@zephyr From Table 6 of the paper I linked to, let's say KamLAND can detect pre-SN flux 10 hours before core collapse for a star 150 pc away (after a 48 hour integration). The neutrino flux for a spaceship 100 AU from the star is about 100 billion times higher. So, as Rob Jeffries pointed out, you could use a detector 100 billion times smaller than KamLAND. To cut the integration time to a more practical 1 second, you need a detector 500,000 times smaller than KamLAND: about 2 kg of liquid scintillator. (Assuming no better technology.)
Peter Erwin
CC BY-SA 3.0
2016-09-21T20:13:45.630Z
Even without actual neutron detector, that neutrino flux might deposit enough energy to the star that it would be detectable from stars surface layers, or show as specific kind of noise in other detectors (at least cameras, radars and radios) the ship must have.
hyde
CC BY-SA 3.0
2016-09-21T21:04:47.500Z
The ship is orbiting a planet a few AU from the star surface. From your comments I see it is possible to detect the neutrino burst with wathever sensors has the ship.
Alfonso de Terán
CC BY-SA 3.0
2016-09-22T14:53:44.187Z
@RobJeffries The problem isn't really the volume you need to detect the neutrino flux.  It's the fact that you carry around a neutrino detector in the first place.  Although as noted by hyde the flux might well be large enough to induce noise in other detectors.
Taemyr
CC BY-SA 3.0
2016-09-22T15:54:40.050Z
@Taemyr The immense size of neutrino detectors is because of the sheer amount of stuff you have to have in order for neutrinos to interact with. Neutrino detectors could be much smaller (yes, the volume of detection medium would indeed scale with the neutrino flux). Yes of course the associated electronics etc. wouldn't scale with volume, but neither can we fly a spaceship to a nearby supergiant... The flux might be large enough to kill you. Would that count as a detection..?.
ProfRob
CC BY-SA 3.0
2016-09-22T17:17:07.870Z
@RobJeffries What I mean is that you wouldn't normally carry a small deticated neutrino detector. - Because there are very few situationations where this is useful.  If you knew the star you where visiting was about to go nova you might get one built - the science value could be considerable, and of course the early warning would be useful.  But for a run of the mill starship having a device whose sole purpose is that it goes ding if you are close to a star that is about to go nova is a waste of space, mass and money.  I rate getting killed as noise induced in other detectors.
Taemyr
CC BY-SA 3.0
2016-09-22T22:33:28.663Z
@Taemyr Neutrinos are produced by nuclear reactions, so a neutrino detector might be useful for detecting nearby nuclear reactors (hidden bases or ships?) in addition to its astronomical uses. Alternately, the characters might decide they need to *build* a detector on their ship, given the situation they're in.
Peter Erwin
CC BY-SA 3.0
2016-09-23T16:04:58.600Z
What a great answer.
Fattie
CC BY-SA 4.0
2018-12-29T05:59:34.107Z
@AlfonsodeTerán here is a [amazingly small neutrino detector](https://physics.stackexchange.com/a/350212/83380)! I think you could consider asking a question in Physics SE based on the data in this answer (luminosity 10^45 erg/sec a few hours beforehand) about expected count rate per kg of detector versus distance. The more specific information you add to the question (and link here) the better.
uhoh
CC BY-SA 3.0
2016-09-21T15:31:26.793Z
2016-09-23T11:01:26.783Z
2016-09-23T11:01:26.783Z
Peter Erwin
<p>I am writing a science fiction novel, where a ship is stranded in a single star system (a red supergiant). One of the plot points is the star becoming supernova in several hours, so the characters have to fix their ship before that happens.</p>

<p>I have basic knowledge of how it works: Iron generated from nuclear fusion gets accumulated in the core, until it reaches a point when iron fusion starts. As iron fusion is an endothermic reaction, the core is no longer able to generate enough energy to hold against its own gravity and external layers pressure, so it collapses, and explode.</p>

<p>I have read that once the iron fusion starts inside the core, the collapse occurs within minutes, that the collapse itself lasts a few seconds (even less than a second), and that the shockwave takes several hours to reach the surface. Is all that correct?</p>

<p>The thing is that I need the characters to bee able to predict the explosion in a short term. A few hours or even minutes. It would be great if they could be aware of the core collapse and start a countdown.</p>

<p>So, are there any external cue of these events, like changes in luminosity or color? Does the star spectrum change when iron fusion starts, or when the core collapses? I know that the core collapse generates a huge amount of neutrinos. Is this amount so intense that it can be easily detectable? (that is, without a huge detector in an underground facility). Can the amount of iron in the core be estimated from tha star spectrum and size, so the aproximate time of the collapse could be predicted?</p>

CC BY-SA 3.0
2016-09-21T14:37:26.993Z
The earliest warning you could get of an impending core-collapse supernovae would come from neutrinos because they react very-weakly with matter, however this is also why such large detectors are needed to measure their presence so its a catch 22 situation. EM clues are there but they are on much shorter timescales.
Dean
CC BY-SA 3.0
2016-09-21T16:34:06.453Z
I think you could get by with a smaller tub of cleaning fluid if you were in orbit around the star that went supernova!
ProfRob
CC BY-SA 3.0
2016-09-21T17:24:59.093Z
This science of this question is probably fine for this site.  However, the associated story issues and most potential follow-on questions may be more appropriate on [worldbuilding.se].
Makyen
CC BY-SA 3.0
2016-09-21T19:46:14.683Z
@Makyen Actually, on Worldbuilding there is a *highly* related question at [How can we extinguish a supernova?](https://worldbuilding.stackexchange.com/q/16780/29) The title is a little misleading -- it's more about *preventing* the star from going supernova late in the process, than about extinguishing or reducing it once it's started -- but I do think that question will be useful for the OP.
user
CC BY-SA 3.0
2016-09-22T00:48:57.097Z
The Currents of Space.  Isaac Asimov.
Carl Witthoft
CC BY-SA 3.0
2016-09-22T03:39:07.210Z
@Dean A geiger counter will suffice for your neutrino detector in this case.  On the other hand, if you're too close it's simply going to tell you that you're dead:  https://what-if.xkcd.com/73/
Loren Pechtel
CC BY-SA 3.0
2016-09-22T07:58:14.297Z
Related, but I never understood how something collapsing results in an explosion. If it's collapsing doesn't that mean it's getting smaller? How can getting smaller make it explode? Why didn't the explosion happen earlier?
user541686
CC BY-SA 3.0
2016-09-22T09:32:59.320Z
@Mehrdad You should ask that as a separate question. As far as I can see, there are a number of mechanisms. One is that, as the core collapses, it's_moving_ inwards, so it has kinetic energy. When the collapse stops, that energy has to go somewhere. Another is essentially that of a plutonium bomb: as the density increases, fusion reactions that weren't previously feasible become feasible. That's my 300-character summary of [Wikipedia's material on core collapse](https://en.wikipedia.org/wiki/Supernova#Core_collapse). I probably mangled it horribly because I'm _far_ from an expert.
David Richerby
CC BY-SA 3.0
2016-09-22T10:06:50.977Z
@Mehrdad see http://physics.stackexchange.com/questions/63558/why-does-a-supernova-explode but perhaps more specific to your question http://physics.stackexchange.com/questions/194606/what-is-the-process-that-causes-a-collapsing-star-to-bounce-back
ProfRob
CC BY-SA 3.0
2016-09-22T10:13:44.943Z
@RobJeffries, David Richerby: Thank you!! Taking a look at those links right now!
user541686
CC BY-SA 3.0
2016-09-22T10:18:27.663Z
@LorenPechtel As far as i'm aware Geiger counters can only detect Alpha, Beta & Gamma radiation and cant even distinguish between the three. I stand by my statement that neutrinos are such weakly interacting particles you need a lot of mass just to detect them.
Dean
CC BY-SA 3.0
2016-09-22T15:56:39.320Z
@Dean You need a certain number of nuclei to detect a certain *fraction* of neutrinos. It doesn;t matter if that fraction is tiny if you have enough neutrinos. And you do have enough neutrinos in this case. A GM tube detects anything that ionises the inert gas in it. Neutrinos can do this via inverse beta decay. The cross-section is tiny, but as I say, if you have enough neutrinos that doesn't matter.
ProfRob
CC BY-SA 3.0
2016-09-23T10:06:47.323Z
@RobJeffries Yes that is true, but what would the background count rate be that close to a red supergiant? Would you even be able to tell if neutrinos were contributing to your signal?
Dean
CC BY-SA 3.0
2016-09-23T10:54:19.693Z
@Dean Alpha and Beta particles get stopped by the hull of your spaceship. What source of gamma rays were you thinking of?
ProfRob
CC BY-SA 3.0
2016-09-23T11:47:11.493Z
@RobJeffries fair enough, I was assuming the GM tube would be an external sensor, but I guess it makes sense to shield it from outside noise if its just looking for inverse beta decay that occurs in the inert gas inside it. I'm actually rather impressed such a feat is possible, though you wont see me riding a spaceship near a red supergiant!
Dean
CC BY-SA 4.0
2022-06-01T10:59:53.947Z
So what's the name of this novel.
blademan9999
CC BY-SA 4.0
2022-06-06T16:15:07.110Z
@blademan9999 It's has not been published in English. Only in Spanish. Anyway, the name is "Mundo Drek" (Drek World). It's the second book of a saga (or so I try). If you are interested and can read Spanish, you can check http://www.elviajedelargos.com
Alfonso de Terán
<supernova><explosion>
Are there observable changes in a star about to become supernova, minutes or hours before the explosion?
Alfonso de Terán
# Are there observable changes in a star about to become supernova, minutes or hours before the explosion?

(Asked by: username_0 on 2016-09-21)

I am writing a science fiction novel, where a ship is stranded in a single star system (a red supergiant). One of the plot points is the star becoming supernova in several hours, so the characters have to fix their ship before that happens.

I have basic knowledge of how it works: Iron generated from nuclear fusion gets accumulated in the core, until it reaches a point when iron fusion starts. As iron fusion is an endothermic reaction, the core is no longer able to generate enough energy to hold against its own gravity and external layers pressure, so it collapses, and explode.

I have read that once the iron fusion starts inside the core, the collapse occurs within minutes, that the collapse itself lasts a few seconds (even less than a second), and that the shockwave takes several hours to reach the surface. Is all that correct?

The thing is that I need the characters to bee able to predict the explosion in a short term. A few hours or even minutes. It would be great if they could be aware of the core collapse and start a countdown.

So, are there any external cue of these events, like changes in luminosity or color? Does the star spectrum change when iron fusion starts, or when the core collapses? I know that the core collapse generates a huge amount of neutrinos. Is this amount so intense that it can be easily detectable? (that is, without a huge detector in an underground facility). Can the amount of iron in the core be estimated from tha star spectrum and size, so the aproximate time of the collapse could be predicted?

**Tags:** supernova, explosion

> **Comments:**
> **username_1**: The earliest warning you could get of an impending core-collapse supernovae would come from neutrinos because they react very-weakly with matter, however this is also why such large detectors are needed to measure their presence so its a catch 22 situation. EM clues are there but they are on much shorter timescales.  
> **username_2**: I think you could get by with a smaller tub of cleaning fluid if you were in orbit around the star that went supernova!  
> **username_3**: This science of this question is probably fine for this site.  However, the associated story issues and most potential follow-on questions may be more appropriate on [worldbuilding.se].  
> **username_4**: @username_3 Actually, on Worldbuilding there is a *highly* related question at [How can we extinguish a supernova?](https://worldbuilding.stackexchange.com/q/16780/29) The title is a little misleading -- it's more about *preventing* the star from going supernova late in the process, than about extinguishing or reducing it once it's started -- but I do think that question will be useful for the OP.  
> **username_5**: The Currents of Space.  Isaac Asimov.  
> **username_6**: @username_1 A geiger counter will suffice for your neutrino detector in this case.  On the other hand, if you're too close it's simply going to tell you that you're dead:  https://what-if.xkcd.com/73/  
> **username_7**: Related, but I never understood how something collapsing results in an explosion. If it's collapsing doesn't that mean it's getting smaller? How can getting smaller make it explode? Why didn't the explosion happen earlier?  
> **username_8**: @Mehrdad You should ask that as a separate question. As far as I can see, there are a number of mechanisms. One is that, as the core collapses, it's_moving_ inwards, so it has kinetic energy. When the collapse stops, that energy has to go somewhere. Another is essentially that of a plutonium bomb: as the density increases, fusion reactions that weren't previously feasible become feasible. That's my 300-character summary of [Wikipedia's material on core collapse](https://en.wikipedia.org/wiki/Supernova#Core_collapse). I probably mangled it horribly because I'm _far_ from an expert.  
> **username_2**: @Mehrdad see http://physics.stackexchange.com/questions/63558/why-does-a-supernova-explode but perhaps more specific to your question http://physics.stackexchange.com/questions/194606/what-is-the-process-that-causes-a-collapsing-star-to-bounce-back  
> **username_7**: @RobJeffries, username_8: Thank you!! Taking a look at those links right now!  
> **username_1**: @username_6 As far as i'm aware Geiger counters can only detect Alpha, Beta & Gamma radiation and cant even distinguish between the three. I stand by my statement that neutrinos are such weakly interacting particles you need a lot of mass just to detect them.  
> **username_2**: @username_1 You need a certain number of nuclei to detect a certain *fraction* of neutrinos. It doesn;t matter if that fraction is tiny if you have enough neutrinos. And you do have enough neutrinos in this case. A GM tube detects anything that ionises the inert gas in it. Neutrinos can do this via inverse beta decay. The cross-section is tiny, but as I say, if you have enough neutrinos that doesn't matter.  
> **username_1**: @RobJeffries Yes that is true, but what would the background count rate be that close to a red supergiant? Would you even be able to tell if neutrinos were contributing to your signal?  
> **username_2**: @username_1 Alpha and Beta particles get stopped by the hull of your spaceship. What source of gamma rays were you thinking of?  
> **username_1**: @RobJeffries fair enough, I was assuming the GM tube would be an external sensor, but I guess it makes sense to shield it from outside noise if its just looking for inverse beta decay that occurs in the inert gas inside it. I'm actually rather impressed such a feat is possible, though you wont see me riding a spaceship near a red supergiant!  
> **username_9**: So what's the name of this novel.  
> **username_0**: @username_9 It's has not been published in English. Only in Spanish. Anyway, the name is "Mundo Drek" (Drek World). It's the second book of a saga (or so I try). If you are interested and can read Spanish, you can check http://www.elviajedelargos.com  

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## 4 answers

### Answer by username_17 on 2016-09-21. Score: 45 | Accepted answer

I think your best bet would be detecting neutrinos generated by nuclear burning inside the star (as we do for the Sun). Once the star hits the carbon-burning stage, it's actually putting out more energy in neutrinos than in photons. During the silicon-burning phase, which lasts for a few days and is what creates the degenerate iron core (that collapses once it is massive enough), the neutrino flux increases to about 1047 erg/s a few seconds before core collapse. (The peak flux *during* core collapse is about 1052 to 1053 erg/s). [This paper by Asakura et al.](https://arxiv.org/pdf/1506.01175v4.pdf) estimates that the Japanese KamLAND detector could detect the pre-supernova neutrino flux for stars at distances of *several hundred parsecs*, and provide advance warning of a core-collapse supernova several hours or even days in advance. Since your characters are *in the same system* as the star, they'd hardly need a large underground detector to pick up the neutrinos.

This plot shows an example of neutrino luminosity (for anti-electron neutrinos) versus time for a pre-supernova star (from Asakura et al. 2016, based on Odrzywolek & Heger 2010 and Nakazato et al. 2013); core collapse begins at t = 0s.

[![Figure 1 from Asakura et al. 2016](https://i.sstatic.net/nF9hR.png)](https://i.sstatic.net/nF9hR.png)

By measuring the spectrum of energies for different types of neutrinos and their time evolution, you could probably get a very good idea of how far along the star was, particularly as we can probably assume your characters have much better models for stellar evolution than we currently do. (They'd also want to get accurate measurements of the star's mass, rotation rate, maybe internal structure via astroseismology, etc., in order to fine-tune the stellar-evolution model; these are all things they could do pretty easily.)

The core collapse itself would be signalled by the *enormous* increase in neutrino flux.

[This "What If" article](https://what-if.xkcd.com/73/) by Randall Munroe estimates that the neutrino flux from a core-collapse supernova would be *lethal* to a human being at a distance of around 2 AU. Which, as he points out, could actually be inside of a supergiant star, so your characters would probably be a bit further away than that. But it does show that the neutrino flux would be easily detectable, and that your characters might well get radiation poisoning from it if they were closer than 10 AU. (Of course, you'd want to *detect* it more directly than just waiting around till you started to feel sick, since that might take longer than the shock wave takes to reach the surface of the star.) This is just to bring home the fact that they wouldn't have any problem detecting the neutrinos....

> **Comments:**
> **username_18**: Great answer! @username_0 It might help your realism to address the fact that neutrinos are notoriously hard to detect. Some simple line implying that neutrino detection capabilities have increased ten-fold for your future-tech would help sell the realism that you can actually detect neutrinos on a small space ship without something like [current neutrino detectors](https://en.wikipedia.org/wiki/Super-Kamiokande) (which are massive).  
> **username_0**: Thank you very much, username_10. That's exactly the info I needed.  
> **username_2**: @username_18 The volume of the neutrino detector can be scaled down by the relative flux of neutrinos you expect. You don't need a large detector to observe the neutrino pulse if you are in orbit around the star that blows up.  
> **username_18**: @RobJeffries Sure, but they'd need to detect these neutrinos before the major burst happens. What's more, who knows how far out the space ship is.  
> **username_17**: @username_18 From Table 6 of the paper I linked to, let's say KamLAND can detect pre-SN flux 10 hours before core collapse for a star 150 pc away (after a 48 hour integration). The neutrino flux for a spaceship 100 AU from the star is about 100 billion times higher. So, as Rob Jeffries pointed out, you could use a detector 100 billion times smaller than KamLAND. To cut the integration time to a more practical 1 second, you need a detector 500,000 times smaller than KamLAND: about 2 kg of liquid scintillator. (Assuming no better technology.)  
> **username_19**: Even without actual neutron detector, that neutrino flux might deposit enough energy to the star that it would be detectable from stars surface layers, or show as specific kind of noise in other detectors (at least cameras, radars and radios) the ship must have.  
> **username_0**: The ship is orbiting a planet a few AU from the star surface. From your comments I see it is possible to detect the neutrino burst with wathever sensors has the ship.  
> **username_20**: @RobJeffries The problem isn't really the volume you need to detect the neutrino flux.  It's the fact that you carry around a neutrino detector in the first place.  Although as noted by username_19 the flux might well be large enough to induce noise in other detectors.  
> **username_2**: @username_20 The immense size of neutrino detectors is because of the sheer amount of stuff you have to have in order for neutrinos to interact with. Neutrino detectors could be much smaller (yes, the volume of detection medium would indeed scale with the neutrino flux). Yes of course the associated electronics etc. wouldn't scale with volume, but neither can we fly a spaceship to a nearby supergiant... The flux might be large enough to kill you. Would that count as a detection..?.  
> **username_20**: @RobJeffries What I mean is that you wouldn't normally carry a small deticated neutrino detector. - Because there are very few situationations where this is useful.  If you knew the star you where visiting was about to go nova you might get one built - the science value could be considerable, and of course the early warning would be useful.  But for a run of the mill starship having a device whose sole purpose is that it goes ding if you are close to a star that is about to go nova is a waste of space, mass and money.  I rate getting killed as noise induced in other detectors.  
> **username_17**: @username_20 Neutrinos are produced by nuclear reactions, so a neutrino detector might be useful for detecting nearby nuclear reactors (hidden bases or ships?) in addition to its astronomical uses. Alternately, the characters might decide they need to *build* a detector on their ship, given the situation they're in.  
> **username_21**: What a great answer.  
> **username_22**: @username_0 here is a [amazingly small neutrino detector](https://physics.stackexchange.com/a/350212/83380)! I think you could consider asking a question in Physics SE based on the data in this answer (luminosity 10^45 erg/sec a few hours beforehand) about expected count rate per kg of detector versus distance. The more specific information you add to the question (and link here) the better.  

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### Answer by username_2 on 2016-09-21. Score: 20

Other answers are correct; a neutrino pulse is definitely expected as a result of a core-collapse supernova and should occur some hours before a shockwave arrives at the surface.

There essentially would be no visible sign that the star was about to become a supernova and that is because the dynamical timescale of the envelope is relatively long - thus responding slowly with respect to changes in the core. So, even if all support is removed from the centre, the surface can only respond (at best) on a freefall timescale of $\sim (G \rho)^{-1/2}$, where $\rho$ is the average density. If the star is a $10M\_{\odot}$ supergiant with a radius of 1 au, then this timescale is tens of *days*.

Another possibility not mentioned so far is gravitational waves. Assuming that a relatively portable gravitational wave detector was available (!) then you would also expect a sharp gravitational wave pulse on the core collapse timescale (a second or less) that would also presage the supernova blast wave some hours later.

> **Comments:**
> **username_10**: With respect to the gravitational wave: Would a non-rotating collapsing star emit gravitational waves? From another discussion I understood (perhaps in error) that rotation was a requirement. Something with quadrupole ...  
> **username_2**: @PeterA.Schneider Supernovae are fully expected to be GW sources, because there is expected to be asymmetry ( the core will be rotating very fast - see pulsars). eg. http://iopscience.iop.org/article/10.1086/381360/fulltext/59085.text.html  
> **username_11**: @PeterA.Schneider Real supernovae turn out to be highly asymmetric, even when their progenitors display a high degree of spherical symmetry. This asymmetry may be sufficient to produce gravitational waves, although I've not crunched the numbers. Finding the source of this asymmetry is an active topic of research.  

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### Answer by username_12 on 2016-09-21. Score: 11

As [username_1 said](https://astronomy.stackexchange.com/questions/18423/are-there-observable-changes-in-a-star-about-to-become-supernova-minutes-or-hou#comment28951_18423), supernova progenitors typically release neutrinos prior to full core collapse, remnant formation and the ejection of the outer layers of the star. The process - focused here on the neutrinos - goes something like the following:

1. At high enough densities ($\rho\sim10^9\text{ g/cm}^3$), [electron capture](https://en.wikipedia.org/wiki/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](https://en.wikipedia.org/wiki/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.

Neutrinos may arrive hours - or possible days, in some circumstances - before the light from the supernova. The former was the case for [SN 1987A](https://en.wikipedia.org/wiki/SN_1987A), the first supernova from which neutrinos were detected.

### References

* [Balasi et al. (2015)](https://arxiv.org/abs/1503.08095)
* [Mirizzi et al. (2015)](https://arxiv.org/abs/1508.00785)
* [Scholberg (2012)](https://arxiv.org/abs/1205.6003)

> **Comments:**
> **username_0**: Thank you, @HDE. That detailed answer makes me wonder if the core collapse could be accelerated with the introduction of something "new" in the star. In the novel, there is a battle with an unknown hostile alien ship. That ship is disabled and put into a falling trajectory to the star. If there is a way in with that event could shorten the time to explosion, it would add more drama (the core collapse is detected by the characters before expected). I remark that the falling ship is alien and unknown, so there is no problem to include antimatter, strange matter, or wathever needed.  
> **username_3**: @username_0, Even assuming some type of unobtainium, it is not believable, even in a fictional environment, that the addition of anything that is on the scale of a spaceship would have sufficient effect when unintentionally falling into a star. The difference in scale is just too vast. Writing it such that it did so would almost certainly destroy my suspension of disbelief if I were reading such a story. Even assuming the ship was powered by a micro-black hole, the time it would take for the singularity to significantly affect the star is longer than what you have been describing.  
> **username_12**: @username_0 Mayken's absolutely right. You'd need quite advanced technology to even begin to contemplate having a chance at impacting the evolution of a star like this, if that's even possible. Its effects would be like a drop in the metaphorical bucket.  
> **username_13**: just for grins... assuming a smallish red giant, and an alien spaceship around 1km, this would be comparable to dropping an 0.1 inch drop into Lake Ontario. Sorry metric rest-of-world.  
> **username_0**: I thought it would be too far fetched, but I had to ask anyway. Thanks.  
> **username_14**: @username_3: Black hole drive ought to do it. I don't want to think about how short of time you have left once dropping a micro black hole into a giant star.  
> **username_15**: @username_14 unless the black hole is very much not micro (~$1M_{\odot}$) we're talking years at least. black holes are limited in how fast they can eat by interactions between particles in the accretion disk.  
> **username_10**: @username_13 If the lake is supercool and the drop is impure it may trigger crystallization. I don't think such phase-shifts occur in stellar cores in reality but as SF one could have hell freeze over...  
> **username_13**: @PeterA.Schneider A sort of stellar (or cosmological) equivalent of Ice-nine?  That would be quite the weapon.  I don't think Kurt V worked out the exothermics, but for this story the phase transition would have to be deeper than chemical bonds. What about a contagious local change in the zero-pt-energy, or the (usually) frozen physical constants, or the distortion off local space-time caused by the star's mass? (Triggered by the breakdown of the alien ship's drive. Or coffee machine.)  

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### Answer by username_16 on 2016-09-22. Score: 1

A superluminous supernova (aka hypernova) can exhibit a double peak to its brightness and some are theorizing that this may be the norm for a superluminous supernova, though as far as I know it's only actually been observed in one case so far (DES14X3taz).

Anyway, in (at least) this case there was an initial substantial increase in brightness. Then the brightness dropped (a couple of magnitudes) for a few days, then ramped back up to considerably brighter than the initial "bump".

You probably are going to need to be careful about the distances involved. The initial burst of light is already large enough that unless your people are *quite* a ways away, it'll already be enough to fry them to a crisp.

There is one other point that might be interesting for your novel though. After the explosion, what you probably get is a magnetar--which, as you'd guess from the name, is a star with an *extremely* strong magnetic field--so strong, in fact, that it's likely to cause all sorts of havoc with anything in the vicinity that depends on anything involving electrical activity--not only electronics, but also probably people's nerves as well.

There is an obvious problem here though: a red supergiant is the right type of star as the progenitor for a "normal" supernova. It's probably *not* the right type as the progenitor for a superluminous supernova. The progenitor of a supernova is typically something like six or eight solar masses. A superluminous supernova is *probably* (only a few are known, so it's hard to generalize) something like a couple hundred solar masses. Given the amount of energy released, it *has* to be quite large anyway.

Reference: [Smith, et al (2015)](http://arxiv.org/abs/1512.06043)


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