Hubble finds that Betelgeuse's dimming is likely due to ejection of gases | Hacker News Reader

Hubble finds that Betelgeuse's dimming is likely due to ejection of gases

phys.org

150 pointsdnetesn45 comments

> that the old star was about to go supernova

I think the estimate is that Betelgeuse is about 10 million years old, some suggest it is closer to 8 million. Our sun is in its prime with 4.5 billion years.

Glad that stars can have a vastly different life expectancy.

Red dwarfs have to counter less gravity pressure and can be fully convective - they can burn for trillions of years: https://en.wikipedia.org/wiki/Red_dwarf

The absolute magnitude scale is hilarious: logarithmic and inverted. A value lower by 5 means it's 100 times brighter.

The magnitude (absolute or apparent) actually started as an ordinal number: in Italian we still say sometimes first magnitude instead of magnitude 1. Of course that doesn't work too well for the Sun's magnitude of -26.

So, that graph on the GP's link has a total scale of 10^14 times between the smallest and largest point. What is roughly the difference between the energy of electrical and nuclear phenomena.

Every star has the force of gravity that is pressing all the gas to collapse, and heat from fusion that is pushing all the gas apart. These forces are balanced in a stable star: fusion reaction provides the energy that prevents the gas from collapsing. In comparison to our sun, a larger star like Betelgeuse needs to sustain a higher level of fusion to fight off the effects of the higher gravitational force. Larger stars have shorter lifespans because they burn through their fuel faster.

For hydrogen-burning stars, the life expectancy is reciprocal to their mass. As Betelgeuse is much more massive than the Sun, its lifetime is considerably shorter. As it is already a red giant, it is in its last phase before going supernova.

One far day in the future, the Sun is also going to become a red giant, extending out till the Mars orbit. But that is still much smaller than Betelgeuse is right now. Actually it is so large, that its diameter can be directly measured by astronomers.

It's more than reciprocal. Fusion rate and luminosity go up enormously with stellar mass, like m^4 or even higher, so the lifetime goes more like 1/m^4.

Sirius for example is 2x the mass of the sun, but 25x as luminous, therefore 2/25 the lifetime until it runs out of hydrogen.

Please go boom.

yes, please , pretty please, imagine having something as bright as the full moon visible even during the day, decorating our evening skies for a few weeks. oh please happen in my lifetime, please !

Wouldn't we be showered by particles/gamma rays though? I mean... its not only visible light reaching us... but I'm not an astrophysicist

There might be a small increase in background radiation, but B is too far away to do anything dangerous or dramatic.

That would be a fitting end to the year 2020.

700+ light years of inverse square law says we'll get a noticeable ping but nothing remotely harmful.

Also, please happen during wintertime in the northern hemisphere. Covid means I won't be escaping the gloom this year.

I recurrently have these types of dreams:

1. The moon is extremely close to earth, so it covers half of the sky.

2. There's another earth-like planet instead of the moon, also really close.

I love those dreams, they also come in nightmare variety:

1. Planes start falling, then there's a big explosion in the sky and fireballs fall towards the earth.

Does anyone else have these dreams?

The description of your dream made me think of the movie Another Earth. https://www.imdb.com/title/tt1549572/

How long would it last?

Months.

According to this [1] article:

> At the distance of Betelgeuse, by 960 years this shell would be 14 times the diameter of the full moon! At about 95,000 years after detonation, this slow-moving plasma will finally reach the solar system. From then-on, we will be inside the volume of intense x-rays and high-energy particles.

at least from what I can understand (I'm not an astrophysicist), we would have 96k years to leave the solar system or adapt ourselfs to living in a plasma cloud.

[1] https://www.huffpost.com/entry/the-betelgeuse-supernova_b_65...

As the article says, the effect wouldn't affect earth much if at all. At worst, space travel would have to cope with the increased radiation levels.

>From then-on, we will be inside the volume of intense x-rays and high-energy particles.

It goes on saying that the high-energy particles would not be a big deal.

I guess x-rays are a different story.

So saying that "the effect wouldn't affect earth much if at all" probably not correct.

But then again, in a 100k years we probably won't care one way or the other. We will either be super advanced by then or won't exist.

If that were the case, what a fascinating problem for the human race. Imagine knowing we have 95k years to escape the solar system, what would we do? What would it mean for humanity in the next 1000, 5000 and 10000 years?

> what would we do?

Some combination of procrastination and denying the problem exists.

It may already have. The question is is 725 LY far enough away that we don't blow up too?

According to this astronomy.com article, it's well outside the danger zone [0].

This [1] article discusses a closer one that may have been responsible for a mass extinction.

[0] https://astronomy.com/news/2020/02/when-betelgeuse-goes-supe...

[1] https://www.discovermagazine.com/the-sciences/a-nearby-super...

Total layman here but somehow very much not-comforted by seeing it's 724 light-years away. That we might not go extinct seems like a far cry from it being safe. And I have an incredibly hard time believing Earth will be unharmed at such a seemingly astronomically small distance. Don't emitted particles travel at like thousands of miles per second?

Edit: Wikipedia says < 1000 LY would have noticeable effects on life on Earth: https://en.wikipedia.org/wiki/Near-Earth_supernova

There's a world of difference between "we will notice it" and "we have to be worried about it".

Betelgeuse will explode in a faint Type II-P supernova, which is the least dangerous type. The thing to really be worried about with supernova are gamma ray bursts, which require low metallicity stars of at least 120 solar masses. Betelgeuse is a high metallicity star with about 15 solar masses. So it's nowhere even in the ballpark of producing a gamma ray burst.

Look at this graph:

https://upload.wikimedia.org/wikipedia/commons/5/5a/Comparat...

Betelgeuse will be the blue line that peaks the lowest and plateaus out. (the P is Type II-P stands for "plateau") This is a logarithmic plot, so the brightest supernova are like 40 times as bright as Betelgeuse's supernova will be. Furthermore, this is just visual light; in terms of gamma rays, while normal supernova are bright in gamma rays, gamma ray bursts are many orders of magnitude brighter.

When Betelgeuse goes supernova, no species will go extinct, no crops will fail, no uptick in cancer will happen. It might dork up some migration patterns and mess with particularly precarious food chains, but the effects will be minor, especially compared to the catastrophic damage humanity is doing to the environment.

> There's a world of difference between "we will notice it" and "we have to be worried about it".

The phrase I was referring to was "have noticeable effects on Earth's biosphere", not "we will notice it". The article explains:

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.

That seems like quite a bit more just seeing something in the sky or seeing a few species get their migration patterns messed up. And re: gamma ray bursts, I do agree they would be bad if they occurred, but you might notice I didn't mention them either. My first worry was about fast-moving particles, which you didn't mention anything about. Why would those not be problematic?

You might very well be right about Betelgeuse specifically, but I'm guessing you're relying on more information because I just can't deduce it from the information I'm seeing.

I am speaking specifically about Betelgeuse. I do not believe it's possible for Betelgeuse to cause 3-4C global temperature increase.

Assume Betelgeuse explodes in a typical Type II-P supernova. This will give it an absolute magnitude in the ballpark of -16.5, call it an even -17. Betelgeuse is approximately 220 parsecs away, which would give an apparent magnitude of 5*(log10(220) - 1) - 17 = -10.3. The full moon is -12.9, so is approximately 10 times as bright.

Specifically regarding energetic particles, the amount of material blown out at relativistic speeds from a II-P supernova is negligible. The high energy interactions happen way inside the star's envelope. The high energy stuff all gets absorbed and re-emitted as lower energy light. The plateau in the light curve of a Type II-P supernova is caused because the outer layers are completely opaque and are trapping energy in the interior.

That's actually the reason I keep contrasting Type II-P with gamma ray bursts. In those events, the outer layers have been stripped away, and we have a direct view on the high energy interactions happening in and around the collapsing core. There is no material to block it, so everything about it is more intense; there are vastly more high energy particles spilling out as cosmic rays, the peak brightness is much brighter, and the light that is emitted is much hotter.

Basically, supernova are fundamentally different from each other. They're a family of phenomena, not just one thing. A gamma ray burst directed at Earth will be catastrophic at 1000ly; (which is why the article talks about supernova up to 1000ly) a Type II-P supernova at 10ly will be comparably catastrophic, but simply won't register at 700ly.

I see, thank you!

You should be comforted by the fact that there's not a damn thing we can do about it either way, so there's no point in worry about it.

Is there really nothing though? Would some kind of a bunker not help? Like imagine 50m-100m underground? Not sure how much matter it might take to stop fast-moving particles (or all the dangerous forms of associated radiation).

Given a high enough tech level and a sufficient handle on the associated ethics, you could [digitize your population and restore it afterwards](http://localroger.com/revelation-passage/borden3.html)

It would not be difficult. Nuclear reactors could provide power almost indefinitely. Greenhouses could maintain plant life. Animals could be bred and slaughtered. A quick survey would have to be made of all the suitable mine sites in the country, but I shouldn't be surprised if several hundred thousand of our people could be accommodated. Every nation would undoubtedly follow suit.

There is no risk for the Earth due to Betelgeuse. At worst, space travel will be impacted, but we would have 100k years to prepare for that after it blows up.

Based on this https://en.wikipedia.org/wiki/Near-Earth_supernova it seems like we'd probably be safe, although there's not a lot of specific information about Betelgeuse so perhaps not. The global temperature increase mentioned in the first paragraph is pretty significant and added on top of the imminent anthropogenic climate change maybe don't buy green bananas for the next hundred years or so.

Oh no it hasn't, not in our frame of reference.

Imagine the scientific gains by observing a nearby supernova event “live” (you know what I mean). I heard most likely is that it would become either a neutron star/ pulsar or black hole depending on retained material in the innermost region following the supernova.

Awesome to have an explanation now. Recently watched this video, and this reason was one of the suggestions for explanation: https://www.youtube.com/watch?v=5bvuwTuGnkc

Ah, the language of science in our times, a universe described as "violent" and "traumatic".

I noticed that weirdness as well. Replaced with representative language from the article body.

dupe: https://news.ycombinator.com/item?id=24148796

> dupe: https://news.ycombinator.com/item?id=24148796

I found this out recently: HN doesn't have a programmatic de-duping system the way Reddit does, so they permit multiple submissions of the same link and don't dedupe until one gets traction.

If a link has already had some amount of discussion on it and it's resubmitted soon after, that's when they de-dupe.

Correct. Described, along with much else, in the recently expanded FAQ: https://news.ycombinator.com/newsfaq.html.

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