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Betelgeuse


Wjolcz
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5 hours ago, Brotoro said:

They won't rename the Greek letter designations of the stars in Orion if Betelgeuse explodes. The rule that the stars of a constellation are lettered in order of brightness is not true for all constellations anyway. See Ursa Major, where the Greek letters were assigned in the order the stars appear in the Big Dipper.

Not to mention, Betelgeuse rare is the brightest star in Orion anyways. So most of the time, the designation for Orion is already wrong. Might as well simply skip alpha and keep current designations if Betelgeuse does explode in the near(ish) future.

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8 hours ago, Wjolcz said:

Seems like it isn't getting any dimmer anymore.

The error bars on the measurements are significant. You really should be averaging across several days of data, and the trend on these is still down. Though, it does seem to slow down, yes, so it might have, indeed stopped dimming. We'll know for sure in a few days.

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On 2/5/2020 at 1:49 PM, mikegarrison said:

Maybe more relevant is Niven's story "Inconstant Moon".

That’s the one where the night side of Earth sees the Moon get incredibly bright while at the same time, all communications with the day side get cut off, correct?

13 hours ago, mikegarrison said:

It's always darkest just before the supernova.

... which leads to one hell of a dawn....

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So, the consensus is that most likely we are about 100 000 years from it going kablooey, but what are the error bars on that estimate? Also, what could be the reason for this brightness change? After all, it's very sudden (especially considering that we're on cosmological timescales).

My stellar evolution is a bit rusty, so can somebody shed some light on this please? Do stars change fuel relatively suddenly or do the heavier elements start fusing long before the previous step is finished leading to a more gradual transition?

Could this be one of those fuel transitions, which lead to pressure drop and sudden shrinkage? If so, can we expect a sharp rise and spike in luminosity before it settles back to its usual value?

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3 hours ago, Shpaget said:

So, the consensus is that most likely we are about 100 000 years from it going kablooey

No, I don't think that is consensus. I think the estimate is "any time now", but in stellar time scales that means "any time in about the next 0 - 100 000 years". I know they don't mean "we think there is a ticking clock that is currently reading 100 000".

As to the rest of your question, I thought the super-red-giant phase means the star is already on it's final stellar fuel phase, and there is no further phase to transition to. (But I'm not an astrophysicist, so I suggest you research this rather than believe my recollection.)

OK, no, I guess I was wrong. The super red giant phase means the star is no longer fusing hydrogen in the core. However, the core may still be fusing helium, or it may have transitioned from helium to the heavier elements.

Edited by mikegarrison
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4 hours ago, Shpaget said:

My stellar evolution is a bit rusty, so can somebody shed some light on this please? Do stars change fuel relatively suddenly or do the heavier elements start fusing long before the previous step is finished leading to a more gradual transition?

In red (super)giant branch, at least, it's pretty sudden. The rate at which star burns its fuel is self-regulating based on thermal expansion opposing gravitational collapse. So it can't really ever slow down consumption of any one fuel. As it's starting to run out, the core will decrease in size to maintain the density of fuel for as long as it can burn that fuel. Once it can't, it starts to collapse, until it's dense enough to burn the next fuel. Even at the size of a star, core collapse is pretty quick. I don't know the exact numbers for all stages, but some of the heavier elements burn out within days of the star starting to burn them, just to give you an idea of just how fast it can be.

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51 minutes ago, Scotius said:

LIGO detected a spike or pulse of gravitational waves coming from that area of space during the dimming. But it is unclear if there is any connection to Betelgeuse, or just coincidence.

If you mean the one in January, it was refined to be from a different part of space, IIRC.

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7 hours ago, StrandedonEarth said:

Finally got a chance to see Orion for the fist time in months (it’s been a very wet start to the year). Even though it’s been awhile, yeah,, now that you mention it, Betelgeuse does look dimmer. But I probably wouldn’t have noticed if I wasn’t looking for it. 

You might have missed the lowest point. It looks like it's starting to brighten again. It's hard to say for sure with publicly available data, but it looks like the minimum was a few days ago. It also kind of looks like it might be cooling, because the B band isn't recovering quite as rapidly as V band, but I'm going from single observer on that one, so this is all well within error bars. Can't wait until we get published data on the whole event. Hopefully, there will be more ESO images as well.

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  • 6 months later...

The forum was really cross with me about necroposting when I thought about just bumping the old thread, so here's a new one instead.

Why are we kicking this horse again? Well, just this month paper got published finally explaining why the star dimmed and recovered so rapidly. Case closed, mov...

And then Betelgeuse goes and starts dimming again. This time, completely unexpectedly, not matching the cycle established over years prior even remotely, and the current trend is just as rapid as when you started seeing all the news posts about it at the end of last year.

800px-Betelgeuse_AAVSO_2019.jpg

The star is now rapidly approaching the brightness at which we've seen it at the end of November of last year, when everyone started looking at the skies.

It's a little early to start speculating about why this is happening, but even if it's just another mass ejection, that only raises more questions. If the first one was really due to alignment of circumstances at the right point in star's cycle, why is this happening again, when the star in in completely different part of its cycle? And what amuses me the most is that this happened hundreds of years ago, and the light from second dimming is reaching us just as conclusive paper on first dimming is published. That's some astronomically bad timing.

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20 minutes ago, K^2 said:

The forum was really cross with me about necroposting when I thought about just bumping the old thread, so here's a new one instead.

It's not a problem if the bumping post is on topic and has something to add.

Which this post does....

 

But yeah... Betelgeuse just had some dusty flatulence...

I'm pretty disappointed though.    I really would have liked to kept looking up hoping to see it go one day, although it won't happen in my lifetime.  :(

 

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4 hours ago, Gargamel said:

I'm pretty disappointed though.    I really would have liked to kept looking up hoping to see it go one day, although it won't happen in my lifetime.  :(

I dunno, I always figured that we'd be able to tell it was going to blow around 100 years out marked with weird stuff like this. It could still be the beginning of the end.

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4 hours ago, cubinator said:

I dunno, I always figured that we'd be able to tell it was going to blow around 100 years out marked with weird stuff like this. It could still be the beginning of the end.

I'm not sure that we would. We've never had direct observations, but according to models, a dying star of that size will switch primary fuel it's burning in the core a few times. That is the only real warning we get, as that's a fairly significant event. General consensus is that Betelgeuse is still burning helium in its core and has enough of it to keep going for thousands of years. When it runs out, the core will begin to shrink, until it heats up enough to start fusing heavier elements. This should produce significant enough changes in the star that we see it. And if it does, we will, indeed, know that the supernova is about a century out. But if we miss it ans we only catch the next event, or if we were completely wrong about what Betelgeuse is burning now, we'd be just years out. The final switch to burning silicon is expected to happen less than a year from supernova for Betelgeuse.

The actual final stage where it is definitive is pretty quick. The star burns through the last of its silicon and core begins to cool and shrink. From what I've read, the process is shockingly rapid, taking just months before the core collapses. And because this process begins within the core, I'm not sure we'd even have time to properly register changes in the star's atmosphere.

If it was to happen right now, our first and final definitive warning will come from two experiments. NOvA at Fermilab will register a powerful neutrino flux, automatically triggering thousands of emails to be sent to people watching for it. The other is LIGO detecting something very unusual coming from direction of Orion constellation and updating their Twitter. Correlation will be spotted almost immediately, and we will know that Betelgeuse is going supernova. We will be just hours from the star rapidly gaining brightness. At this point, the core collapse has happened and supernova is on its way.

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10 hours ago, K^2 said:

The forum was really cross with me about necroposting when I thought about just bumping the old thread... 

If they're cross with you again, we moderators will beat them down. 

I've merged the threads to keep the discussion all in one place and let's not have any necromoaning, okay? :D

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29 minutes ago, K^2 said:

The actual final stage where it is definitive is pretty quick.

IIRC from reading back when this first popped up, The transition between fuels is rather quick, with a couple of them burning for a couple weeks, and the last one only lasting a few hours before boom!   Not enough time really for observations to be made, papers to be written and peer reviewed.    The thing will blow up before we can confirm it's about to blow up. 

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22 minutes ago, Gargamel said:

IIRC from reading back when this first popped up, The transition between fuels is rather quick, with a couple of them burning for a couple weeks, and the last one only lasting a few hours before boom!   Not enough time really for observations to be made, papers to be written and peer reviewed.    The thing will blow up before we can confirm it's about to blow up. 

Time enough for the lead scientists to send a text to their colleagues - "Go get your solar glasses. Now!"

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