How large will Antares appear after the supernova?

Stargazing has been quite a treat recently, with the red giant Antares hanging out so close to Jupiter in the sky. I’ve been a big fan of Antares since I saw the size comparison with our own Sun. I’ve read, though, that Antares is ripe and ready to blow any minute now (in cosmological terms, at least).

So, when we’re finally able to see the supernova occur on July 4th, 2025, what exactly will we see? Will the effects be noticeable with the naked eye? Will it appear a lot brighter for a few minutes, then return to normal? Will it appear to be as large or as bright as Jupiter is right now? Will we be inundated with gamma rays? Should I wear sunscreen?

Antares, Betelgeuse, and Spica (also notable in the summer sky) are all supernova candidates, but thankfully far enough away that they’ll only be a fireworks show for us Earthlings and not anything to worry about. When they blow, they’ll probably be easily visible in the daylight (brighter than Jupiter or Venus) though probably not anything more interesting looking than a simple “dot”. It’ll stay very bright for days, not minutes then slowly fade. Perhaps we’ll have a neat nebula in the sky in place of the star when the explosion fades, or maybe nothing at all (naturally they’ll be something there, whether or not you’ll need a telescope to see it is hard to predict). I don’t think astronomers understand supernovae well enough to predict what the aftermath would look like exactly (nor do we have any idea when the stars will pop exactly).

Your thread title and the OP have made me think of something that might be worth another thread to explore, but I’ll gamble that this slight hijack here will serve instead.

I would really feel a tremendous sense of loss if Antares were to blow. But there are other stars, whether supernova candidates or not, that I would hate to see disappear even more. Among them:

Any of the seven Big Dipper stars (8 counting the double double)
Any of the Orion stars
Any of the Pegasus Great Square
Any of the Pleiades
at least a dozen more

These stars are essential for me to locate other stuff in the sky and their loss would be at least as painful as the loss of the World Trade Center Twin Towers. Other earthbound monuments and revered places would hurt to lose, too, but they would most likely come as the result of some stupid terroristic thing or an earthquake or the like. But seeing a favorite star blow up would be a major downer, for sure.

If we were able to see the actual explosion for ourselves with the naked eye, we’d be seeing something that took place long before humans arrived on earth. That’s way too heavy to think about!

Antares is about 600 light years distant (184 pc), the Crab nebula about 6,300 (1931 pc).

Those numbers give an absolute magnitude for the crab supernova of -15.9 to -18.4.
At Antares’ 600 light years distance, that supernova would have a magnitude of -9.5 to -12.1.
The full moon has a brightness of about -12.6 magnitude, so an Antares supernova would produce just about as much light, but from a point source.

Whether we get inundated with gamma rays depends on the spin axis of Antares. High energy jets come off the poles of a star.

Not if you’re talking about a star that’s already a naked-eye object - most of those are well within 1000 light-years, and plenty within 100 ly.

The most likely local candidate for supernova is probably Eta Carinae, which seems to be on the verge of something big and glowy. It’s 7500 light years away, so even that is just about in recorded history.

Of course, you’re right here. I forgot that most (if not all) of the visible stars (as opposed to external galaxies) are within our own galaxy and are thus much closer by in terms of their light’s time of origin than the origin(s) of life here. It’s just that whenever we see whatever out there, including the Sun, it already happened as little as eight minutes ago and as long as billions of years. My error was in having the visible stars be at galaxy distances. Thanks for the catch.

Of course, there are some “comparatively near” supernovae that are at galactic distances and still near enough for the astronomers to wig out over. And IIRC s Doradus is in one of the Magellanic Clouds but has still acted up enough not only to be visible but to outshine mighty Canopus!

All individual stars that are visible are within our own galaxy.

I think you’re conflating two or three different things.

The Large Magellanic Cloud lies within the constellation named Dorado. That’s why a star-producing region within the cloud is called 30 Doradus (also called the Tarantula Nebula). It was indeed originally catalogued as a star, but that was a long time ago. The closest recent supernova, 1987a, appeared there. It was barely visible to the naked eye at a magnitude of 3, but nowhere near as bright as Canopus, with a magnitude of -0.72.

So what you’re saying is, there’s a small but nonzero chance that when Antares blows, one of its poles will be directed at us, and we’ll be firehosed with planet-sterilizing radiation?

Neat. :cool:

Or we all turn green and gain superpowers.

Someone must have already determined the orientation of Antares poles, or at least the orbital plane of its dwarf companion, but I’m not finding it this morning. I’d expect that if a pole were pointed at us, that information would show up under ‘Antares “gamma ray burst”’.

Because of our atmosphere, it most certainly will be much more than a simple “dot”. Stars twinkle, bright stars even more so, scintillating like mad if low on the horizon (appearing to cycle through a bunch of different colors-easily seen in binoculars), and a supernova will likely be something we haven’t seen before. The brightness of a full moon concentrated into a single tiny point? That’s going to look insane, probably flashing like crazy as if from a laser light show.

Of the stars you mentioned, I think that only Betelgeuse and Aldebaran are red giants, so you’re mostly off the hook. On the other hand, Betelgeuse is possibly even closer to bang than is Antares, so only mostly.

I would too. I’d feel a sense of loss if any of the bright stars that I know well were to go supernova.

We’d feel more than a vague sense of loss if either of those went supernova- they’re close enough to have a devastating effect on Earth, especially Sirius at about 8.5 light-years. Vega’s probably close enough to destroy half of our ozone layer by going supernova.

Not in the case of most of our bright stars, actually. All of the 26 brightest stars, a list which includes many of the ones from your list, are within about 2000 light-years of us. The farthest of the Big Dipper stars are a little over a hundred light-years away. Polaris is about 430 light-years from us, as are the Pleiades.

We might get something like the Ordovician-Silurian extinction event, which was one of the worst extinction events in Earth’s history (worse than the Cretaceous-Tertiary event, which killed the dinosaurs). There’s a theory that it was caused by a gamma-ray burst.

I’m not sure they have, actually. Stellar inclinations are tricky to measure, and the orbit of Antares’ companion is not well known (it has a period of about 878 years, which is doubtless part of the problem). It’s especially tricky to measure the inclination of rotation of giant stars like Antares, because their atmospheres are turbulent.

I’m sure not finding it. I figured with that big stellar wind, and a companion, someone would have figured a way to get it. Heck, with Antares angular diameter of 41.3 milliarcsec, a good, modern telescope should be able to resolve spectra from different parts of the disc.
Then again, there’s not all that many telescopes and astronomers in the world.

I don’t get it… I’d think it would be about the coolest thing ever, (from a dabbler in amateur astronomy’s perspective).

You’d see one of the most awe-inspiring things in the cosmos for real and with the naked eye, and understand what you’re seeing. How cool is that? For me, it would make all that astronomy class stuff come to life- rather than an unchanging pinprick of light in the night sky, there would be a change, and not a minor one.

I’m all for it… no sense of loss here.

I would expect that you could get the inclination of any sufficiently-bright star through starspot modelling. I know that one can measure starspots moving across the disk of Betelgeuse, since one of my former professors did so regularly. I wouldn’t expect the situation to be much different for Antares.