46

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 ...


41

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 ...


40

Supernovae increase in brightness over several days and decrease over months. Thus, whatever you saw, was not a supernova, sorry.


39

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 ...


35

Stars don't "come from" a supernova. Stars come from the interstellar gas in the galaxy, particularly where it is more concentrated into nebulae. This gas is mostly hydrogen and helium, but it is "enriched" with heavier elements from old stars, including from stars that have exploded in supernovae. Over the billions of years since the ...


34

I don't know about your country, but in the United States the major weather services launch instrumented balloons twice a day. They are about 1 or 2 meters in diameter. We often see them in the evening at the observatory, and your description matches. A bright star visible to the unaided eye in the twilight. The balloon and instruments hanging beneath the ...


33

I think the definitive work is that of Hoyle & Fowler (1960). They argued that supernovae were produced by two possible mechanisms - what they called an implosion/explosion or an explosion within degenerate matter. Both of these mechanisms required very high internal temperatures ($>2\times 10^{9}$ K) and they argued that this could only be achieved ...


30

There is a lot of scope to provide a very detailed answer here. The rate depends on what sort of a galaxy you are considering and when, what its star formation rate is (or was) and what its total stellar mass is. A good reference is the Annual Review of Astrophysics article by Maoz et al. (2019). This says that for a Sbc galaxy like the Milky Way, the ...


29

Potentially a short (less than a second) burst of gravitational waves (GWs) would be detected. Much depends on asymmetries in the core collapse, since a spherically (or even axially) symmetric collapse would not produce GWs (e.g. Morozova et al. 2019). However, theoretical models suggest that the GWs start at low frequency (tens of Hz) and are associated ...


28

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 ...


28

The final stages of nucleosynthesis are a statistical equilibrium process. At the same time as nuclei are being built up, photodisintegration is breaking them down. The temperatures required to produce zinc by fusion are high enough that the radiation field is energetic enough to break it up. So there is some present in the mix, but nowhere near as much as ...


27

The most likely scenario is that an asymmetry in the supernova explosion imparts momentum to the proto neutron star at its core. The issue is not settled. A recent study by Verbunt et al. (2017) models the speed distribution of young pulsars as the sum of two Maxwellian distributions, one with an average speed of $\sim 130$ km/s and the other with an ...


27

The low supernova rate in M31 can be directly attributed to the fact that the galaxy's star formation rate is much lower than the Milky Way's. Andromeda is currently in a relatively quiet phase in terms of star formation, currently experiencing rates of $\sim0.40M_{\odot}\;\mathrm{yr}^{-1}$. The Milky Way, on the other hand, has a star formation rate ...


24

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 ...


21

The connection between the dimming and a putative supernova relies on the interpretation that the decrease in luminosity may be due to circumstellar material, ejected in the years/decades/centuries immediately preceding a supernova. There are several mechanisms that could lead to this sort of mass loss (see slides 24-25), including gravity-wave driven ...


19

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 ...


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 "...


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 ...


19

The mean mass of a star in a typical star forming region is about 0.3 solar masses and contains about 1% by mass of elements heavier than helium A typical core-collapse supernova progenitor might have a mass of around 15 solar masses and they will be responsible for dispersing a few (say 3) solar masses of heavy elements into the interstellar medium. i.e. ...


18

Good question - the answer is that stars are not in general well mixed - or rather, the nuclear-burning core is not well-mixed with the rest of the star. That means that a star will finish hydrogen burning even when about 80% of the hydrogen in the star is still available, but is situated outside the core and cannot be mixed into the core (or at least not ...


18

Two things. The abundance of oxygen is a difficult thing to measure in optical spectra - much harder than Mg, Ca, and Si. So these latter are usually used to represent "the alpha elements". There is a strong OI triplet at 777 nm and a much weaker OI forbidden line at 630 nm. But these often give contrary results because they are blended with other ...


17

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 ...


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 ...


14

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 ...


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 ...


13

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 ...


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