# What technologies and sciences are needed to detect a star going supernova?

What technology (at minimum), devices or minimum civilization development is needed, so that an individual member of this civilization would be able to detect that some star is going supernova?

My question is inspired by "The Inner Light" episode of Star Trek Next Generation (though I don't know what civilization development level is presented there).

I just want to know what must be invented by a civilization, to be able to detect this kind of threat?

• never got the impression that the star in "The Inner Light" was in any danger of going supernova any time soon. Jan 5 '15 at 18:38
• how much lead time are you looking for and how close do you want to know? We are watching a couple in our neighborhood that could go anytime between today and the next 10,000 years. Jan 5 '15 at 18:54
• @bowlturner As it was explained (somewhere in the comments), I missed the point of ST episode, that inspired my question. It was not star going to supernova, that was a real threat. It was "pre-supernova" radiation and other changes, that made home planet's surface unhabitable. Jan 5 '15 at 20:05
• well... most people are generally able to notice if their home star is suddenly growing very, very fast. The extreme brightness gives it away, and the heat is another hint that is typically hard to miss. Unfortunately, at this point it is typically very hard to find someone to complain to. Oct 23 '15 at 7:55

When people think of supernovae, they often only think about the visible light emitted during and after the explosion. However, if you restrict yourself to observing in the optical part of the electromagnetic spectrum, you'll lose a whole lot of information. There are a few different astronomical messengers scientists can use to study a supernova.

## Years in advance

In the final stages of their lives, massive stars tend to exhibit violent behavior, such as chaotic episodes of mass loss. The final stages of fusion (neon, oxygen and then silicon) take years down to days to occur, compared to the billions of years during which the Sun fuses hydrogen. Several mechanisms in these late stages could lead to mass loss events. These would be detectable in the optical and infrared bands, appearing as dimming as ejected dust enshrouds the star.

This was one of the reasons it was briefly thought that Betelgeuse could be in its final months of its live when it began dimming this past autumn. While the dimming is likely due to a major mass-loss event, it isn't necessarily due to one of those uber-late-stage mechanisms. In other words, a single large mass loss event isn't evidence of a supernova, but a sustained period of activity could wag its head indicatively.

## Days to hours before

In the hours to days) before a supernova, the progenitor star releases a flood of neutrinos carrying a lot of energy. This burst is detectable, and it's observed before the light from the actual supernova reaches the observer because it's well in advance. We observed neutrino emission from SN 1987A two or three hours before its light reached Earth.

Neutrinos are fairly hard to detect, as they don't interact strongly with matter. Even from SN 1987A, we only detected a handful. To maximize your odds of detecting any of them, you'd need something like the Supernova Early Warning System, a small network of neutrino detectors, all working together. It includes the Super-Kamiokande in Japan and Ice Cube in Antarctica.

Neutrinos can be lethal in large doses, so these neutrinos could serve as an adequate warning sign only if you're far enough away from the supernova - otherwise, you'd just be killed! According to XKCD, you'd want to be at least a few astronomical units away to survive the neutrinos - but then, of course, the actual explosion would kill you a few hours later.

## During the event

You might be surprised to learn that asymmetric supernovae can produce gravitational waves (Ott et al. 2003). There are two possible forms of the gravitational wave signal:

1. A sharp spike followed by high-frequency oscillations, caused by a slow-rotating progenitor star.

2. Oscillating "bounces" of the amplitude caused by expansions and contractions.

Type 1 waves are expected to be stronger, but it appears that both types should be detectable by interferometers like LIGO and Virgo, assuming the sources are within the Milky Way. We're fortunate; their peak frequencies lie in the middle of the frequency range of these instruments. With peak strains of $$h\sim10^{-21}$$ for sources $$\sim10\text{ kpc}$$ away, supernovae on the other side of the galaxy could be detectable. Given that strain scales inversely with distance, the strain of waves from a closer source would be even greater.

## Days, weeks and months later

During the explosion - and in the weeks and months afterward - a supernova will emit visible light, coming from hot, radioactive bits of ejecta moving through space. Astronomers can study the light curve of the event to glean information about the progenitor star and the nature of the explosion. Supernova light curves generally rise rapidly and then fade over time. Scientists can figure out what kind of supernova a supernova is by observing morphological properties of the light curve.

The interesting thing, of course, is that it does take some time for a supernova to reach peak brightness - maybe a few days to a couple weeks. It's possible that the supernova could only prove dangerous at or near that peak brightness, and so the initial increase in luminosity might be enough of a warning sign without being deadly.

Image courtesy of Wikipedia user Lithopsian.

To accurately measure the light curves from a supernova, you'll need sufficiently advanced telescopes working in a range of wavelengths. UV, infrared and visual light are your best bet, and we have many telescopes that study the universe in one or more of these wavelengths.

• I guess that I can screw my answer then ;) But I'll still maintain that you do not need to go for neutrino dectectors and what not. If your G-type, sun-mass star is trying to kill you by running out of fuel you'll notice million years in advance. Jan 4 '15 at 20:35
• @Ghanima Hey, I liked your answer and upvoted! Yeah, I know, I included much of the first section because it was ways you could figure out that a supernova was occurring. If you're on a planet within a couple dozen AU of your star and you notice a large neutrino flux . . . Not very useful. :P Jan 4 '15 at 20:37
• If we believe the synopsis of the TNG episode in question here, that civilication was not killed by the actual supernova but by effects preceding it by far rendering the planet uninhabitable. They traced the effects back to their sun and figured they would not make it away. Jan 4 '15 at 20:48
• @HDE226868 -- IIRC, a combination of drought, and solar radiation killing the microbes in the soil rendering it sterile. Jan 5 '15 at 12:43
• I liked this answer, but as I read on, two problems occurred to me: One, it's a little all over the place. It could be condensed and focused a bit. Two, it doesn't really answer the question. It seems accurate and well-researched, but it just seems to miss the spirit of the question. Also I was interested in knowing what the time threshold might be for leaving (as I imagine the OP was). Your statement: "unless you have faster-than-light travel, you're screwed if you don't detect this a long time in advance." Maybe you could define "a long time?" Jan 5 '15 at 16:13

For one thing that would be the "scientific method" as to acquire knowledge and investigate phenomena based on empirical observation and measurable evidence - so to say objective rather than subjective.

Other than that, I'd strongly vote for a deep theoretical understanding of the internal workings of a star (that is physics) and to detect the changes in your star, obviously. Optical instruments (so optics and the associated technology chains of glass making, manufacturing of optical elements, e.g. grinding and polishing of lenses, as well as fine mechanical manufacturing for making your instruments). The idea of spectroscopy would be helpful as to measure the changes in emission wavelengths of the star with respect to its lifecycles. Measurable evidence of going supernova besides emission spectra is of course the brightness of the star - its astronomical magnitude. To measure that empirically it's advisable to have had photography invented (which is easier than inventing an electronic photometer).

Most of that hardware should have been available at say ~1850. Although that time lacks the understanding of fusion processes inside the star - kind of vital to the understanding of a supernova.

It's also more than noteworthy that going supernova is not exactly something that happens in no time. We're talking about hundreds of thousands if not millions of years (the heavier the star the faster it lives) from noticeable changes to supernova. That is to say: plenty of time to discover spaceflight and get the hell out of there.

• Great answer, thank you. Willing to accept it, but I'll wait few days to see eventually other answers. About your last comment -- it isn't that obivious. Watch mentioned episode ("The Inner Light of Star Trek Next Generation) or at least read its description at Memory Alpha to see, that it is possible (at least according to script's authors), that your civilisation won't be able to invent spaceflight and fly away. Jan 4 '15 at 18:02
• I am aware of that episode (although some years might have passed since I saw it). Feel free to wait for additional answers. This one could be missing a few points after all. However with respect to the episode it is not up to me to decide which time span is realistic for some changes in the stars radiation levels to make the planet inhabitable. That however could be long before that star really goes supernova. Consider supernova just a plot device with a certain ring to it ;) Jan 4 '15 at 18:23

Ghanima's answer makes the fundamental point that theoretical knowledge is required before the necessary technology is developed. HDE226868's answer is an excellent summary of the process.

There is a problem with the idea of a home star going supernova. A supernova event requires a considerable amount a mass. Further, a star's lifetime is determined by its mass. Here is a table summarizing the relationship between stellar mass and stellar lifetime :

Theory suggests that the minimum mass for a small supernova is about 1.44 solar masses. A core collapsing supernova requires 8 to 9 solar masses.

So a minimum supernova would result from a star with an expected lifespan of about 3 billion years. Consider that our sun is 4.5 billion years old, and that it has taken that long for intelligent life to evolve here on earth. This would seem to imply that a supernova would occur before intelligent life could evolve.

On the other hand, a supernova need not occur on ones home star to have catastrophic effects. Any stars and their planets in the local star group would suffer catastrophe.

• Oh, good, I was hoping someone would bring this up. Nicely written answer. Jan 4 '15 at 21:27
• @HDE226868 I think I sort of knew it, but a quick trawl through wiki helped. The site seems to be doing well. It's my first visit in quite some time.
– NWR
Jan 4 '15 at 21:32
• It is plausible for earth-like intelligent life to evolve on an earth-like planet in a billion years. From the Pre-Cambrian explosion to Archæopteryx took 400 million years. Jan 5 '15 at 17:27
• @Jasper Assuming our solar system is typical, it takes billions of years for a planetary system to evolve, including planet formation, a prolonged period of bombardment by left over debris (meteorites, etc.) and an extended cool down period. Life can only take hold once this process ends. It is hard to imagine a life supporting planetary system forming without this process.
– NWR
Jan 5 '15 at 17:44
• @NickR -- We have fossil evidence of life from about 800 million years after the ignition of the sun. Older fossils were probably destroyed by subduction of oceanic plates. Jan 5 '15 at 19:54