Are any of the stars you see in the night sky already dead?
Probably not.
Individual stars visible to the naked eye on a good night are all within a few thousand light years (*maybe* tens of thousands, depending), & stars live on average many millions or billions of years. They’re likely all okay!
Of the individual stars we can see, there’s only one (Betelgeuse) known to be close to the end of its stellar lifetime and by “close” I mean it could go supernova any millennium now. Of course we all hope it goes soon because that would be amazing to see! (And no it won’t hurt us when it happens.)
Another weirdly sticky idea about star death: I often hear “in the future when the Sun explodes…”
The Sun isn’t going to explode! It’s not massive enough for supernova. In 5-ish billion yrs it’ll swell up & slough off its outer layers & probably destroy Earth but it’ll be like a gentle incineration
It’s okay the Sun’s luminosity will increase dramatically in the run-up to the red giant phase and should effectively sterilize the surface of the Earth in only like a billion years or so
Unless we build a Dyson Sphere to capture the energy it emits propelling us at hyper light speed in a great circular path through Space/Time to reach Earth in the year 1,000,000 BCE and mate with apes, thus producing our ancestors!
Plus you'd need to wait until it's already a dead white dwarf cinder. If you added that mass now it would just be blown off during the sun's final windy death.
While it’s true 1.4 solar mass is the Chandrasekhar mass you need to be much more massive to go supernova (~ 10 solar masses). You need to be hot enough to burn till Iron and 1.4 solar mass stars are not hot enough.
Yeah I realized I needed to clarify that after I posted it -- if you added 0.4 solar masses AFTER the Sun became a white dwarf, that should do it, but not before
given it would likely enter the solar system coplanar with the orbits of the planets, wouldn't we likely have issues well before it reached the center?
How much damage would that do crashing into the sun in the first place? Presumably rather less than star death, but I'm guessing it could be an existential threat for flimsy carbon-based lifeforms clinging onto the shell of a nearby planet.
I thought I'd heard something about "by a billion years from now, the Sun will have swollen or something enough that Earth's temperatures are uninhabitable"?
