44

The coordinate system in this image is RA and Dec. It is a coordinate system which uses the Earth's equator (projected onto the sky) as its midline. The inverted U is the Milky Way. The Milky Way is full of dust and gas, and blocks our view of galaxies (and supernovae) behind it. There is enough dust in the plane of the galaxy to block our view in that ...


43

The straightforward answer is, "Yes, we are made of star stuff." Some of it will be from the interior of collapsing stars, some will be from supernovas, some from normal everyday fusion, and some from other processes. The answers from @HDE226868 and @RobJeffries on this question on where heavier elements come from gives good background, including this ...


38

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 ...


31

No, it would not be a problem. Supernovae are not at all like flashbulbs – they brighten over a period of many days and dim again even more slowly. Here are a number of different light curves taken from Wikipedia: The rise is fast on an astronomical scale – several orders of magnitude over a period of roughly ten days – but very slow on a human scale. An ...


27

As HDE 226868 noted in his answer, the Sun is not going to go supernova. That's something only large stars experience at the end of their main sequence life. Our Sun is a dwarf star. It's not big enough to do that. It will instead expand to be a red giant when it burns out the hydrogen at the very core of the Sun. It will continue burning hydrogen as a red ...


19

Sagan's quote is half-correct. While some of these elements are created during or immediately prior to a supernova of some sort, others are either partially or entirely fused during normal stellar nucleosynthesis. Nitrogen falls into the latter category, whereas calcium and iron have one foot in each. On the whole, though, calling these elements "starstuff" ...


19

In order to "blow something up" you need to release more energy than its binding energy and have a way of trapping that energy so it can't escape in another way. At the centre of a core collapse supernovae is a 10 km radius, $1.4 M_{\odot}$ ball of (almost) neutrons. Its gravitational binding energy is $\sim GM^2/R = 5\times 10^{46}$ J. This is almost ...


18

None of those stars can go supernova, so the question is rather moot. If you look at the classifications, the most luminous is Sirius A (an A sequence star even) you can get an idea of its mass. If you look at your source page, and link to the explanation you see that A stars range from 1.4 to 2.1 stellar masses. In order to go supernova though, you need ...


18

If you insist on observing the exploding Betelgeuse at peak brightness, you could potentially damage your eye. The complete answer enters the realm of physiology. Here I'll discuss the astronomical parts: Betelgeuse will explode as a type II supernova, the typical brightness of which is around $M \sim -17$. With a distance of $d\simeq200\,\mathrm{pc}$, its ...


17

Will Sirius B start accreting? Yes, it is doing so now. Sirius A will have a wind and some of that wind will be captured by the white dwarf. The effectiveness of wind capture is a strong function of relative wind speed. An analytic approximation to the accretion rate, known as Bondi-Hoyle accretion, goes as the inverse cube of the relative speed. In its ...


16

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 ...


13

Your question is a bit oversimplified because there are many types of supernovae based on the size and configuration of the star. But I can answer your question about "why iron" by considering what keeps a star from exploding in the first place. In the simplest terms of star formation, when material from an interstellar nebula starts to collapse under its ...


13

It's a matter of size and stellar evolution. There are many, many types of stellar explosions. The University of Arizona has one page that describes these types. generally, a Novs is not what we think of (i.e. a star exploding). That's actually a Type II Supernova. According to that site: Novae are frequently (perhaps always) members of binary systems ...


13

The Sun does not have nearly enough mass to become a supernova. Instead, it will swell to become a red giant, enveloping Mercury, Venus, and possibly Earth. After that, it will shed its outer layers as a planetary nebula, and settle down to become a white dwarf. Wikipedia, apparently, says the exact same things I had though of: The Sun does not have ...


13

Naked eye nova are fairly common, several per year. Here's one. Naked eye supernova are far rarer. SN1987a in the large Magellanic cloud was naked eye visible (vid). From this list, it appears the supernova in 1987 was the most recent naked eye supernova. There was a naked eye gamma ray burst in 2008, but I don't think anyone actually got outside in time to ...


12

Ricky, it is very rapid. The core collapse and initial neutrino burst takes seconds to tens of seconds. We don't normally think about neutrino interactions, but so many are released that even this might be a problem for a nearby habitable planet. It then takes a few hours for the shockwave from the core collapse and bounce to make it out to the surface, ...


12

No, it cannot. A black hole is something vastly different from a star. It's vastly different from anything else. It's not a thing, really, but more like a portion of very distorted spacetime. Nothing escapes from it simply because there is no way out - spacetime is distorted in such a way that all trajectories lead to the center. Now, there is a mechanism ...


11

Interestingly enough, the limit on the time needed for such a change to propagate through the star isn't from the speed of light, but from something called the dynamical timescale, $t_{\text{dyn}}$: $$t_{\text{dyn}}\sim\frac{R}{v}\sim\sqrt{\frac{R^3}{GM}}\simeq\frac{1}{\sqrt{G\bar{\rho}}}$$ where we've assumed that the speed of a pressure wave, $v$ is on the ...


10

Supernova create huge spikes in neutrino emissions. Since neutrinos pass through a stellar mass mostly unimpeded, they're visible up to 3 hours before the shockwave even starts to affect the star's surface. Since neutrinos travel at the speed of light, they will always keep their 3 hour head start. Thus, unless you have a neutrino detector buried a few ...


10

The "iron core" in a supernova is actually the end product of a nuclear statistical equilibrium that begins when the silicon core begins to fuse with alpha particles (helium nuclei). Exothermic reactions are possible right up to Nickel-62 (which is actually the nucleus with the highest binding energy per nucleon). In fact, successive, rapid alpha captures ...


10

Nobody really knows how type Ia supernovae detonate (or deflagrate) - there are a number of possibilities. The "vanilla" possibility is not what you state in your question, it is that the white dwarf accretes sufficient mass that it approaches the Chandrasekhar limit and becomes dense enough in its core to commence carbon burning. However, the emerging ...


10

Actually the peak luminosity for the first binary black hole merger LIGO detected was $3.6 \times 10^{49} \,\text{Watts}$ (source). Whereas the brightest supernova ever recorded was ASASSN-15lh which had a peak luminosity of $2 \times 10^{38} \,\text{Watts}$ (source). In fact the energy radiated by the binary black hole merger during the $0.2 \,\text{s}$ it ...


10

As Dean said, 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: At high enough densities ($\rho\sim10^9\text{ g/cm}^3$), electron capture becomes important, where a proton and ...


10

The odds of a supernova being visible to the naked eye is slim. Adams et al. (2013) estimated that there is a 20% chance that we will be able to see such a supernova within the next 50 years. That should give you an idea of how unlikely this is. The vast majority of supernovae that have been discovered lately have magnitudes ranging from +20 to +16 (check ...


10

There are a variety of models of stars collapsing into black holes without proper supernova explosions. These are often called failed supernovae or direct collapse black holes - although the former seems more common. Failed supernovae can happen if the initial shock wave rebounding from a collapse loses enough energy, causing it to fizzle out. Neutrinos ...


10

There is an accepted answer already, but there is a couple known cases of a star we know has gone supernova, and yet we can still see it. This source describes one such unique circumstance. The star that exploded happened to be in a galaxy that was behind another massive one from our point of view. The alignment was just right such that the light formed ...


10

Although it's a little tricky to say what "bigger" means in this context, the answer is, in most senses, no. A supernova puts out about ten to a hundred times as much energy in the form of light, and hundred or more times as much matter is ejected. (A core-collapse supernova undoubtedly puts out much more energy in the form of neutrinos as well.) What ...


10

The answer is: to a neutron star - possibly; to a black hole, no. The process whereby a neutron star is formed is known as an accretion induced collapse and is being seriously debated, especially in the case of white dwarfs that are born at the upper end of the "natural mass range" for white dwarfs and then accrete more mass as part of a binary system. An ...


9

The Sun will not become a supernova, it will never explode. A star must have about 8 times more mass than the Sun in order to cause a supernova explosion. When it starts to fuse helium, the Sun will become a red giant and expand out to about Earth's orbit and throw out gas to form a beautiful so called planetary nebula. Mercury, Venus and maybe Earth will be ...


9

So from this I can only come to the conclusion that supernovae did in fact happen in the Milky Way in the last two centuries, but that we didn't see any of them. But now I'm confused. I read about supernovae that have happened in galaxies billions of light-years from here that lit up as the brightest source of light in the sky for days. Surely ...


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