
What happens when Betelgeuse explodes? - varmais
https://medium.com/starts-with-a-bang/astroquizzical-what-happens-when-betelgeuse-explodes-c98e4673eaed
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adwn
To get a feel for the tremendous size of that star:
[https://en.wikipedia.org/wiki/File:Star-
sizes.jpg](https://en.wikipedia.org/wiki/File:Star-sizes.jpg)

~~~
jahnu
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 matter is so tenuous that Betelgeuse has often been called
a "red-hot vacuum"."

[https://en.wikipedia.org/wiki/Betelgeuse#Density](https://en.wikipedia.org/wiki/Betelgeuse#Density)

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gunn
Also: "estimates of its mass are poorly constrained, but range from 5 to 30
times that of the Sun". Amazing for having on the order of 16 billion times
its volume.

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jjoonathan
How does that happen? Is its fuel more energetic in some sense or does the
gravity-vs-pressure equilibrium simply favor lower densities for a total mass
of 20M☉?

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nate_meurer
You're right on both counts! Betelgeuse is burning helium now (post main-
sequence). The higher output of helium fusion inflates the outer atmosphere
like a giant floppy balloon.

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d_theorist
"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.

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

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Starwatcher2001
The remnents of the supernova that occurred in 1054 is known as the "Crab
Nebula", AKA M1 on Messier's catalog.

I remember observing this from my back garden some 10 years ago with a small
telescope, but that's quite difficult now due to light polution. It's getting
hard for people to see stars in many big cities, let alone fainter objects.

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agrona
There's a guide (in development) at eyesonthesky.com[1] aimed at newcomers,
who may be using poor telescopes in poor atmospheric and lighting conditions.
I've been following it quite successfully from my back yard in Seattle. It
focuses on the brightest galaxies and nebulae, interesting clusters, and
binary stars.

[1]
[http://eyesonthesky.com/StarCharts/FirstLightGuides.aspx](http://eyesonthesky.com/StarCharts/FirstLightGuides.aspx)

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astletron
"Nighttime will be a different story. The brightness of Betelgeuse’s supernova
is about the same as the quarter moon."

This will last maybe a couple of weeks, but we don't expect it for 100K years.

~~~
themartorana
No, but with billions of stars in our own galaxy, and more beyond, wouldn't
(my misunderstanding of) the probability of witnessing a past supernova event
during one's lifetime be higher than it feels like it is?

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onion2k
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](http://en.wikipedia.org/wiki/Olbers%27_paradox)

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mabbo
> 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](http://en.wikipedia.org/wiki/Ant_on_a_rubber_rope)

~~~
pharke
> ...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](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.

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

~~~
rquantz
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.

~~~
sixdimensional
I agree with you.

I have found that the beauty of the temporary nature of everything (especially
when considered in enormous time scales) highlights the beauty of the here and
now.. and the need to enjoy it. In fact, while some say not to think of the
future and stay in the present, sometimes I find that imagining far into the
future is precisely what brings me back to the importance of and focus on the
present.

Also, there's a feeling of pure awe I get when trying to imagine the
unimaginable scale of the future (for us at least). It's a specific
sensation.. I am not even sure awe is the right word to describe it.

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amoruso
This article reminded me of something I read a few years ago. What is it like
to be really near a supernova? It's a quick read and entertaining too.

Life (Briefly) Near a Supernova:

[http://www.nagt.org/files/nagt/jge/abstracts/Dutch_v53n1.pdf](http://www.nagt.org/files/nagt/jge/abstracts/Dutch_v53n1.pdf)

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dghf
Any risk of a gamma-ray burst affecting Earth?

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Filligree
Not from a supernova. Gamma-ray bursts are a wholly different phenomenon.

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smeyer
Not all supernovae have a GRB and not all GRBs have a supernova, but most long
burst GRBs are thought to be from a supernova, no? I've been out of supernova
research for a few years now, but that's what I recall.

~~~
jgh
Based on my degree in astrophysics from the University of Popular Science
Blogs IIRC they're from quasars or something.

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smeyer
So, I definitely didn't study GRBs in any depth, but based on my increasingly
vague memories from my degree in astrophysics, quasars don't have much to do
with it. All of the major proposed mechanisms I recall for GRBs are on the
scale of a star or two (supernovae, neutron star mergers, and the like)
whereas quasars are a phenomenon involving supermassive black holes in
galactic nuclei. Please, definitely correct me if I'm wrong!

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kijin
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 specific wavelengths that could cause an issue?

[1] [https://en.wikipedia.org/wiki/Near-
Earth_supernova](https://en.wikipedia.org/wiki/Near-Earth_supernova)

~~~
aruggirello
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 sufficient
strength, could permanently damage the retina in your eyes.

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avian
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.

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TazeTSchnitzel
When I read that title, I assumed it had something to do with Douglas Adams.

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lotsofmangos
You are maybe thinking of the Great Collapsing Hrung Disaster that wiped out
all the old Praxibetel communities on Betelgeuse Seven.

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shrikrishna
Starts-With-A-Bang is a must-follow blog collection for anyone mildly
interested in Physics. They're all frequent, up to date, and most importantly,
accurate.

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mkramlich
semi-related: Betty From Betelgeuse is the name of one of the main characters
in my book series The Dread Space Pirate Richard.

I chose Betelgeuse partly as a nod to HHGG and partly for the way it read and
sounded when pronounced aloud. I think of all the star names it is possibly
the most beautiful and memorable.

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robinhoodexe
I'm pretty sure Ford Prefect would be rather disappointed that his home planet
got blown up...

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yourad_io
Don't worry, he won't know for about 600 years. And they can always construct
a new one.

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cgtyoder
_All that said, Betelgeuse isn’t expected to explode for another 100,000 years
or so._

Total click bait title.

