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What happens when Betelgeuse explodes?

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Re: What happens when Betelgeuse explodes?

#21

Post by pharke »

mabbo wrote: post #19
onion2k wrote: post #16

Earlier quoted context omitted.

Not really. There are a huge number of stars, but most of them are moving away so fast that the light from their death wouldn't ever reach us, and their light would be shifted in to parts of the spectrum we can't see. Similar to Olbers' Paradox - http://en.wikipedia.org/wiki/Olbers%27_paradox

> most of them are moving away so fast that the light from their death wouldn't ever reach us Correct me if I'm wrong, but I believe that's mistaken. Given enough time, even things moving away from us at the speed of light will eventually be seen by us. http://en.wikipedia.org/wiki/Ant_on_a_rubber_rope

> ...galaxies that are more than approximately 4.5 gigaparsecs away from us are expanding away from us faster than light. We can still see such objects because the Universe in the past was expanding more slowly than it is today, so the ancient light being received from these objects is still able to reach us, though if the expansion continues unabated, there will never come a time that we will see the light from such objects being produced today (on a so-called "space-like slice of spacetime") and vice versa because space itself is expanding between Earth and the source faster than any light can be exchanged.

https://en.wikipedia.org/wiki/Metric_expansion_of_space

The rate of expansion of space-time is currently accelerating so the ant on a rubber rope analogy does not hold.

Edit: from the ant on a rubber rope article you linked

> However, the metric expansion of space is accelerating. An ant on a rubber rope whose expansion increases with time is not guaranteed to reach the endpoint.[3] The light from sufficiently distant galaxies may still therefore never reach Earth.

Re: What happens when Betelgeuse explodes?

#23

Post by Steuard »

mabbo wrote: post #19
onion2k wrote: post #16

Earlier quoted context omitted.

Not really. There are a huge number of stars, but most of them are moving away so fast that the light from their death wouldn't ever reach us, and their light would be shifted in to parts of the spectrum we can't see. Similar to Olbers' Paradox - http://en.wikipedia.org/wiki/Olbers%27_paradox

> most of them are moving away so fast that the light from their death wouldn't ever reach us Correct me if I'm wrong, but I believe that's mistaken. Given enough time, even things moving away from us at the speed of light will eventually be seen by us. http://en.wikipedia.org/wiki/Ant_on_a_rubber_rope

This is complicated. Given the accelerating expansion of the universe, there's an eventual "horizon" where light beyond that limit will never manage to get here, simply because the empty space between here and there will expand faster than the light can make up the distance. My understanding is that under current cosmological models, a likely scenario is that eventually (on the order of multiple billion years), everything beyond our local gravitationally-bound group of galaxies (us, Andromeda, and a few hangers-on) will be 100% invisible forever. Kinda makes you wonder what distant-future astronomers might think of the old tales of "galaxy clusters" or "cosmic structure formation".

Re: What happens when Betelgeuse explodes?

#26

Post by whoisthemachine »

d_theorist wrote: post #17

"Betelgeuse is already one of the brightest stars in the night sky, sitting somewhere around the 8th or 9th brightest star in the night sky. (These lists don’t include the Sun, which is somewhat obviously always the brightest object in the sky.)" A good point, although it is fairly rare to see the sun in the night sky these days.

Depending on your definition of "night sky", I would argue it's incredibly easy to see in the night sky!

Re: What happens when Betelgeuse explodes?

#27

Post by avian »

aruggirello wrote: post #18
kijin wrote: post #9

Other than slightly brighter-than-normal nights, will there be any adverse effects on Earth? The wikipedia article on near-Earth supernovae [1] suggests that Betelgeuse will be pretty safe because of its distance. But exactly how safe? What about all the delicate electronics that we've sent up to space? I suppose anything that can withstand a daily dose of solar radiation would probably be okay, but are there any spe…

Actually, a supernova would look like an impossibly tiny point source , much smaller than even your average laser pointer. I'm pretty sure the consequences of this haven't been thoroughly explored yet. I'm not sure the Betelgeuse supernova, at a brightness around that of the full moon, would ignite fires, but I certainly wouldn't want to gaze at it with naked eyes, even at that brightness. IMHO such a light, given su…

I doubt it. Even without knowing exact surface power density that can cause damage to retina, the magnitudes discussed here sound far from dangerous.

You should know that even an impossibly tiny point source will get projected to a spot of finite size on the retina. The eye is not perfect - there is always some optical aberration. Plus, since we're talking about a star, there's also atmospheric distortion to think about.

The chances of light from Betelgeuse igniting a fire are very much zero. We're talking about light intensity about 10x lower than moonlight.

Re: What happens when Betelgeuse explodes?

#29

Post by hellbanner »

jahnu wrote: post #7
adwn wrote: post #5

To get a feel for the tremendous size of that star: https://en.wikipedia.org/wiki/File:Star-sizes.jpg

I feel those images are a little misleading. One might erroneously assume there is a dense surface akin to our star at the outer edge of these massive stars but.. "In the outer reaches of the photosphere the density is extremely low, yet the total mass of the star is believed to be no more than 20 M☉. Consequently, the average density is less than twelve parts per billion (1.119 × 10−8) that of the Sun. Such star mat…

Those images accurately show size, correct? Stars are big.

Re: What happens when Betelgeuse explodes?

#30

Post by rquantz »

nsxwolf wrote: post #22

The transition of the star to nebula will also permanently alter the appearance of the constellation Orion, which is both exciting and sad.

I like the maxim "this too shall pass." It's easy to think of on a generational level - our fathers' generation will disappear, and so will ours. But on the level of a civilization, it becomes both stranger and sadder. Orion is a shape in the sky that humanity has always been able to see (so long as we've lived in the northern hemisphere), and one day, assuming we still grace this planet in 100,000 years, it will no longer resemble the hunter the Greeks imagined. But then, billions of years hence, all the stars will have realigned, the Milky Way will have combined with andromeda. And beyond even that, the energy will so diminish that the bonds of the atoms will release. This too shall pass.
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