Anton Petrov has pretty decent coverage of this on his YouTube channel[1].
This type of supernova has been theorized, although to my knowledge not previously observed (due to the mechanics, about 50% of the energy is radiated as visible light, which is why they're so exceptionally bright).
We do have a star near us that is theorized to have undergone a pulsational pair instability supernova in the 19th century: Eta Carinae.
Betelgeuse is a massive star within our galaxy that's relatively close, at 642 light years away. Scientists believe it'll go supernova relatively soon, within 100,000 years.
When it does go supernova, it could be as bright as the moon and still visible during the day.
There are historical reports about supernovae where they were visible during the day for a few weeks. I guess it would look just like another bright star. Makes me wonder what the minimum safe distance is.
See https://en.wikipedia.org/wiki/SN_1006 - "likely the brightest observed stellar event in recorded history." Observed in 1006 AD "across the modern day countries of China, Japan, Iraq, Egypt, and the continent of Europe, and possibly recorded in North American petroglyphs."
If you want to see the shock front move on something like a second timescale, I'm pretty sure you need to be close enough to be in real trouble.
Typical expansion velocity is on the order of 10 000 km/s radially, so you get 20 kkm increase in diameter per second. For safety then, 20 kkm should correspond to a barely perceptual angular change, which wikipedia tells me is around 1 arc minute.
So if you are close enough to just see the shock front move, you have about an hour until it gets to you, and if you want to avoid being overtaken you need to be able to move at ~ 10 kkm/s.
Interesting question. My off-the-top instinct would be to say any explosion that looks bigger than the sun is probably delivering more radiation than the sun and that would be bad news. But that’s without doing any math.
The size of the visible object is determined by it's real size and distance... That's to say, no it will never look big.
But it can look very bright, so it illuminates the sky. It would certainly be interesting to have an object so shiny that it creates a glowing halo around it, but I'm not sure it would be safe to look at that halo.
With a total energy output of 10^44 Joules, it seems odd to exclaim over "500 times brighter!" I guess supernovae all exist in a very narrow band of energies?
Yeah, but that uses carefully calibrated relations with the time evolution at different filters to significantly decrease the the observed spread in luminosity.
Also, here they don't report on a Type Ia supernova (the ones useable as standard candles because we ain't got anything else).
Wouldn't brightness have a cube root relationship to energy, because it radiates into space? That would make it 125 million times more energetic.
Edit: Rereading the article, it seems it's only one order of magnitude higher than a normal explosion? I clearly am out of my depth on this one, because that doesn't make sense to me.
Wouldn't brightness have a cube root relationship to energy, because it radiates into space?
No. The light actually expands in a 2-D wave. So it falls off as the square of distance.
But if we consider 2 sources near each other, they both spread out the same amount by the time they get to us. Therefore there is a linear relationship between energy and apparent brightness. (On top of the inverse square relationship to distance.)
~150 solar masses is the Eddington limit[1] where the outward luminosity pressure becomes greater than the inward gravitational pressure holding the star together. Stars probably cannot grow past this size through normal accretion. However, a few[2] stars have been estimated to have masses much greater than 150 solar masses, up to R136a1 [3] with an estimated 315 solar masses.
This type of supernova has been theorized, although to my knowledge not previously observed (due to the mechanics, about 50% of the energy is radiated as visible light, which is why they're so exceptionally bright).
We do have a star near us that is theorized to have undergone a pulsational pair instability supernova in the 19th century: Eta Carinae.
[1] https://www.youtube.com/watch?v=dhjHs2L4kqw