General / Off-Topic Is Betelgeuse going to blow up?


Just in case people are not clear where Orion is or how to see Betelgeuse-

orion_constellation.jpg


This is the Orion constellation, which is visible throughout the world. I always see the 3 belt stars first, and then the rest appears.
 
The constellation is Orion. Can you see 3 stars in a tight line in the sky where you live? That is the belt of Orion.

The supernova would be bigger than our moon.
Yes, I was more making a joke that the interesting things in the last decade have all happened in the Nth Hemi. Or if it was visible in the Sth, it'd be at 3-5 AM on the Horizon, and I live in a built up area.
 
Presumably the gravitational waves are indications of some violent events (as they commonly happen before a supernova) happening in Betelgeuse.
 
This, and here is an answer about how big/bright it will be seen from earth
https://astronomy.com/news/2020/02/when-betelgeuse-goes-supernova-what-will-it-look-like-from-earth
I've been using a couple of hours to try and calculate just that :)

The article in your link describes the brightness of the supernova as ~half Moon over "more than three months". However, the brightness will be a lot higher in the very early stages, depending on what type of supernova Betelgeuse should decide upon (astronomers haven't decided).

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Note that absolute magnitude is a weird scale. It's logarithmic (orders of magnitude), and the lower the number, the brighter the object (thanks to Hipparchus). The perceived brightness (apparent magnitude) is also dependent on the distance to the object.

I haven't finished my own estimates yet, but I've seen other estimates saying that just after the star explodes, it might be as bright as the Sun during the day. That seems unlikely from my own (rough) calculations, and there are lots of wild speculations out there.

Regarding the nebula the supernova will leave, I also tried doing some estimates, and let me put it like this: It won't cover the whole sky! After the afterglow of the explosion, the nebula will be very bright and rather tiny, even if I cherry pick the velocity of the ejected material (~1/10th the speed of light). The Crab nebula is 10 times further away, and covers 1/10th of a degree of the sky. Moved 10 times closer it would cover roughly 1 degree, which is roughly what you cover with your little finger at a stretched arm length. The Crab nebula is 1000 years old, so the fastest moving ejected material should have moved 100 ly from the explosion by now, but the size of the nebula we can "see" is ~5 ly across, with its radius being half of that.
 
Just take a look at Barnard's Loop. It is believed to have been created approximately 2 million years ago. It is approximately 600 arcminutes in the sky. This is a measure of it's size. The moon is 31 arcminutes in size. This means the moon is about 20 times smaller than Barnard's Loop. That means that in 1/20th of 2 million years it was the size of the Moon. Therefore, ( 2,000,000 / 20 = ) 100,000 years is how long it took to become Moon sized. Betelgeuse is about half the distance, so... roughing the math again, 50,000 years before (if) it's nebula reaches that same size.

Anyone feel free to correct me if I got that wrong, not an expert here, but that's how I understand it.

No, you're not taking distance & perspective into account here. The Moon is tiny (about 2500km in diameter), and only appears large in our sky because it is close (less than 250,000 miles in fact). Barnard's Loop is somewhere in the region of 200 light years across, but because it is proportionately further away, it appears a similar size from our perspective. That doesn't mean it's anywhere near close to the size of the Moon.

Another example is solar eclipses. The Moon is 400 times smaller than the Sun, but because it is also 400x closer to us, it appears the same size and therefore can cover the sun's disc completely if you stand in the right spot at the right time.
 
No, you're not taking distance & perspective into account here. The Moon is tiny (about 2500km in diameter), and only appears large in our sky because it is close (less than 250,000 miles in fact). Barnard's Loop is somewhere in the region of 200 light years across, but because it is proportionately further away, it appears a similar size from our perspective. That doesn't mean it's anywhere near close to the size of the Moon.

Another example is solar eclipses. The Moon is 400 times smaller than the Sun, but because it is also 400x closer to us, it appears the same size and therefore can cover the sun's disc completely if you stand in the right spot at the right time.
He didn't mean literally. He was talking about apparent size.
 
He wasn't talking about their actual sizes though, but their angular diameters as viewed from Earth. His observations are actually quite on point.

Ninja'd! ☝
 
A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly less than 10 to 300 parsecs (30 to 1000 light-years) away[2]) to have noticeable effects on Earth's biosphere.

Historically, each near-Earth supernova explosion has been associated with a global warming of around 3–4 °C (5–7 °F). An estimated 20 supernova explosions have happened within 300 pc of the Earth over the last 11 million years. Type II supernova explosions are expected to occur in active star-forming regions, with 12 such OB associations being located within 650 pc of the Earth. At present, there are six near-Earth supernova candidates within 300 pc.[3]

An interesting thought, could this SuperNova eventually cause us problems?

If it blew up 642.5 years ago tomorrow then tomorrow we will see it start to happen in the night sky, the light and the radiation have been travelling towards Earth for 642.5 years.
 
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Just take a look at Barnard's Loop. It is believed to have been created approximately 2 million years ago. It is approximately 600 arcminutes in the sky. This is a measure of it's size. The moon is 31 arcminutes in size. This means the moon is about 20 times smaller than Barnard's Loop.....

He just did, in fact.
 
He used arcminutes, which are units of apparent size.

Yes I know.

If I say liter we all know I'm talking about volume, and not speed. Right?

If liter had an ever more common definition that is different than the unit it wouldn't be as clear as it is, this is the case of "size" and "apparent size" given "size" by itself almost always denotes physical size.
 

Yaffle

Volunteer Moderator
Waaaay off topic for a moment.

Betelgeus is about 600LY away, so if it does blow up this year it blew up 600 years or so ago. What tense should one use about such events?
 
Yes I know.



If liter had an ever more common definition that is different than the unit it wouldn't be as clear as it is, this is the case of "size" and "apparent size" given "size" by itself almost always denotes physical size.
But arcminutes don't have any other common definition :unsure:
 
Waaaay off topic for a moment.

Betelgeus is about 600LY away, so if it does blow up this year it blew up 600 years or so ago. What tense should one use about such events?

Current tense, or past tense if it's "just" happened from our perspective.

Every time you look into the night sky you are basically looking back in time, potentially many hundreds or even thousands of years with the naked eye in a dark spot. Significantly more with a telescope.

If Betelgeuse (or any star) blows up, it did it a long long time ago. Even if our Sun exploded, and we were somehow miraculously out of range, we wouldn't see it for 8 minutes.
 
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