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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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Seems like it isn't getting any dimmer anymore.

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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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34 minutes ago, StrandedonEarth said:

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?

Yes, that's the one.

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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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Looks like a giant sunspot.

Has Betelgeuse changed in other frequencies differently? We know it's dimmer in the visual range, but couldn't the same event spike up in radio or X-rays?

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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.

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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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