Betelgeuse unusual dimming - what's up?

[Vanadium 50]

Well, monitor all of them.

But what you'd like is spectroscopy.

Instead of hours we might have days in the future.

Well, maybe a day. But suppose you detect the onset of silicon burning. It doesn't help you see the onset of oxygen or neon burning, much less carbon.

 

[Astronuc]

Why is that? Do we expect heavy element fusion to emit lots of neutrinos?

On February 23 1987 detectors deep underground that where designed to detect proton decay suddenly detected a huge number of neutrinos (8 in 5 seconds). Scientist where perplexed by this influx in neutrinos at first until on February 24 a grad student named Ian Shelton announced his observation of a supernova in the Large Magellanic Cloud. This was a core collapse supernova. When the core of a massive star collapses, it crushes the protons and electrons together and neutrinos form.

p + e → n + ν.

The neutrinos pass straight through the collapsing star before the explosion takes place. This is why the neutrinos where detected before the supernova was visibly observed. When the neutrinos leave, they also take energy away from the star and the star continues to collapse and rebounds out in an explosion that can outshine the brightness of the entire galaxy. Neutrinos are very important to the study of supernovas because they provide an early warning signal and allow scientists to be looking in the right direction before the supernova even takes place.

From http://www.astro.wisc.edu/~larson/Webpage/neutrinos.html

Given the proximity of Betelgeuse compared with the SN1987A, I'd expected the number of neutrinos would be much greater from Betelgeuse than from SN1987A.

 

[Vanadium 50]

I'd expected the number of neutrinos would be much greater from Betelgeuse than from SN1987A.

Yes.

But.

We actually saw mostly antineutrinos from SN 1987a. The DUNE experiment will have ~40 kilotons of liquid argon underground, and is sensitive to neutrinos. So even SNe in the LMC will be detected with hundreds of events at DUNE, and because DUNE sees neutrinos it will be a probe of early-time behavior. (Neutrinos come early; Antineutrinos only come late)

 

[mfb]

Why is that? Do we expect heavy element fusion to emit lots of neutrinos?

Not the main fusion reactions directly, but some side reactions produce neutrinos or nuclei doing beta decays, and the overall reaction rates increase massively in the days leading to a supernova. Eventually the temperature gets so hot that the process electron+positron->neutrino+antineutrino becomes relevant (that's also an important process that cools neutron stars initially).
Here is a discussion.

Neutrino detectors can pick up this signal if the star is near enough. Betelgeuse should produce a noticeable signal in Super-Kamiokande (and the larger Hyper-Kamiokande has been approved already). The supernova will flood it with neutrino events afterwards. Slide 21 here has expected warning times. KamLAND might achieve a longer warning time (slide 22). The combination of both should make the signal clearer.

Even dark matter detectors might pick up some neutrinos from the silicon burning phase in the future: Discussion for ARGO

But what you'd like is spectroscopy.

Gaia can detect the temperature, at least. It also does radial velocity measurements. I wonder if a star that varies in size would be registered as change in the radial velocity.

 

[Vanadium 50]

I wonder if a star that varies in size would be registered as change in the radial velocity.

Probably not. Radial motion is 22 km/s. Pulsation period is 200 million seconds. For even large pulsations it's a small effect.

 

[mfb]

Betelgeuse is probably too bright for Gaia anyway, but with the right brightness it can measure ~1 km/s. Some stars are variable with a timescale of just hours.

 

[swampwiz]

This might be the dumbest question I have ever asked here, but would pretty much every observatory in the world that could track it be observing it?

 

[mfb]

If it becomes a supernova? Yes. And every person would do so as well. The estimated rate for supernovae in our galaxy is one per ~50 years. Having one within the working life of current scientists is luck already. Having one just a few hundred light years away? That's the super jackpot.

We'll know about it in advance thanks to the neutrino detectors.

 

[mfb]

Some signs of brightening.

 

[mfb]

The Fall and Rise in Brightness of Betelgeuse

Based on these and additional observations, Betelgeuse has definitely stopped dimming and has started to slowly brighten.

The minimum was 424+-4 days after the previous minimum, perfectly matching the 420-430 day cycles observed before.

 

[Nik_2213]

Does this support hypothesis of 'engulfed planet' circling within the visible 'surface' with ~424 day orbit ??

How quickly would a gas giant or 'Brown Dwarf' erode thus, and would mass wastage be fast enough to affect orbit period to extent we could detect ?? { Providing prediction, and possible falsification...}

 

[Astronuc]

The Fall and Rise in Brightness of Betelgeuse

The minimum was 424+-4 days after the previous minimum, perfectly matching the 420-430 day cycles observed before.

The article mentions "the red supergiant Betelgeuse has been undergoing an unprecedented decrease in its visual (V) brightness since October 2019." I take that to mean that it is unprecedented since the development of accurate measurements and the recording thereof.

Back on Feb 1, the minimum brightness was expected on 21 (+/-7d) February, 2020.
http://www.astronomerstelegram.org/?read=13439

In the current article, "The star reached a mean light minimum of 1.614 +/- 0.008 mag during 07-13 February 2020," and the previous (shallower: V ~ +0.9 mag) light minimum was observed in mid-December 2018.

So the next dimming is ~10 April 2021, or 425 days from 10 Feb 2020.

Back on Jan 22, https://www.universetoday.com/144694/betelgeuse-is-continuing-to-dim-its-down-to-1-506-magnitude/

I presume the gaps in the luminosity data are during the summer months, between May and July, when Orion is not visible because it appears during the daytime.

I was looking at Betelgeuse a couple of nights ago, and it certainly looks very dim. I wonder if will become brighter than normal, or just recover to a typical maximum.

 

[sophiecentaur]

I heard a suggestion that Betelgeuse's variable luminosity could be due to two variations with different frequencies. The beat between the two could be producing an unusually deep dip. It may be on the way up and perhaps could also get brighter than expected for a while.
I can't help hoping (however irresponsibly) that it will be seen to go Nova in my lifetime. Daytime astrophotography would have an alternative subject for images.

 

[Timboo]

There is a long term graph here:

It doesn't look that unusual. It appears to have got this dim in the 1980s. And presumably many times in the past. It is a variable star. So varying is what it does.

and it looks like the dimming May be over
http://www.astronomerstelegram.org/?read=13512

 

[bahamagreen]

I keep seeing the reassuring "safe distance" from Betelgeuse in the event of supernova. This may be a relief to those worrying the Earth's magnetosphere or atmosphere might be at risk. However, anyone here authoritatively know about supernova neutrinos having an effect on the Sun, and if so, what the very much higher neutrino flux from a close one might do?

Admin - please remove the following if it is not appropriate
The "pop" version suggests ice cores indicating solar variation mapped to the past very distant supernovae show a brief cooling of the Sun followed by a longer warming of the Sun before setting back to normal, these blips effecting the Earth about 100 years later, each instance taking that long to reach the Solar surface from the core... the hook being that the flux and effect from Betelgeuse would be comparatively extremely high... maybe two orders of magnitude.

 

[Vanadium 50]

This keeps getting worse and worse.

1. If you trust the models that say Betelgeuse will supernova withing ~100,000 years, you have to trust the very same models that say it will not supernova within ~2000 years.

2. There is no reason to think dimming is an indicator that a supernova is about to occur. This is particularly true for a periodic oscillation. We're at a periodic minimum now.

3. There is no correlation in ice cores between supernovae and solar temperature. The Japanese ice core work showed the regular 11-year solar cycle on top of three spikes, two of which we see are close in time with known supernova. Maybe the so-called "pop" science writer was confused, but this isn't "pop science". It's nonsense.

 

[Astronuc]

In my previous post, I had pointed out that the article from Astronomer's Telegram indicates the recent dimming is unprecedented. I found a plot posted by AAVSO showing luminosity from 1911 to 2001, and there appears a similar dimming event around 1948 (eyeball estimate from 6 cycles from 1941).
https://www.aavso.org/sites/default/files/images/LTbetelgeuse.jpg
From article: https://www.aavso.org/vsots_alphaori

Costantino Sigismondi (ICRA/Sapienza, ITIS Ferraris, Rome and AAVSO (SGQ)) wrote in a paper, "Betelgeuse, the alpha of Orion, is a semi-regular variable star, supergiant. Its variability was presumably known since the antiquity (Wilk,1999), but Sir John Herschel is the first to point out its variability in modern time (1840). Allen (1899) reports that in 1852, it began the brightest star of the Northern hemisphere. Helen L.Thomas (1948), conversely, affirmed that stellar variability was not a concern of antiquity."

I can only find the Wilk reference - S. R. Wilk, FURTHER MYTHOLOGICAL EVIDENCE FOR ANCIENT KNOWLEDGE OF VARIABLE STARS, JAAVSO Volume 27, p. 171-174 (1999)

Elizabeth O. Waagen does indicate that the recent dimming event is rather rare.
https://www.aavso.org/aavso-alert-notice-690

 

[mfb]

The "pop" version suggests ice cores indicating solar variation mapped to the past very distant supernovae show a brief cooling of the Sun followed by a longer warming of the Sun before setting back to normal, these blips effecting the Earth about 100 years later, each instance taking that long to reach the Solar surface from the core... the hook being that the flux and effect from Betelgeuse would be comparatively extremely high... maybe two orders of magnitude.

That makes no sense at all. I don't know what you read (and you didn't tell us) but it was nonsense or you completely misunderstood it.

About ~10³⁷ neutrinos would go through the Sun, give or take two orders of magnitude. Less than one in a million of them would interact with anything in the Sun, reactions that change anything (instead of just giving a particle a small kick) would be again orders of magnitude less common.
As comparison: The Sun produces about the same number of neutrinos, 10³⁷, every second. It won't have any impact on the Sun at all.

 

[bahamagreen]

That makes no sense at all. I don't know what you read (and you didn't tell us) but it was nonsense or you completely misunderstood it.

About ~10³⁷ neutrinos would go through the Sun, give or take two orders of magnitude. Less than one in a million of them would interact with anything in the Sun, reactions that change anything (instead of just giving a particle a small kick) would be again orders of magnitude less common.
As comparison: The Sun produces about the same number of neutrinos, 10³⁷, every second. It won't have any impact on the Sun at all.

Regarding flux, I find Dr. Sten Odenwald, NASA Astronomer writing in 2015, updated 2017:

SN 1987A produced a neutrino pulse of 10^58 neutrinos, which was reduced to only 24 detected on Earth due to the inverse-square law at the distance to SN1987A, and the fact that neutrinos interact very weekly with our detector matter. If we were to move this to Betelgeuse, we would get a pulse of 24(168,000/590)^2 = 2 million detected neutrinos!

I read his math to assume 590 is a ly distance to Betelgeuse, the 2 million count scaled with respect to what those original detectors 33 years ago would detect, and assuming the 10^58 figure for both SN 1987A and Betelgeuse.

I'm not sure how to figure what the local flux here would be - is that your 10^37 through the Sun?

 

[mfb]

I used a different approach but the result is the same: 4*10³⁷ if we start with 10⁵⁸ neutrinos. Simple geometry.

 

[Astronuc]

UW, March 6, 2020 - Dimming Betelgeuse likely isn’t cold, just dusty, new study shows
https://www.washington.edu/news/2020/03/06/dimming-betelgeuse-dust/

In a paper accepted to Astrophysical Journal Letters and published on the preprint site arXiv, Emily Levesque, a UW associate professor of astronomy, and Philip Massey, an astronomer with Lowell Observatory, report that observations of Betelgeuse taken Feb. 14 at the Flagstaff, Arizona, observatory allowed them to calculate the average surface temperature of the star. They discovered that Betelgeuse is significantly warmer than expected if the recent dimming were caused by a cooling of the star’s surface.

The new calculations lend support to the theory that Betelgeuse — as many red supergiant stars are prone to do — has likely sloughed off some material from its outer layers.

Betelgeuse Just Isn't That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse
https://arxiv.org/abs/2002.10463

 

[zoki85]

I hope it goes Nova in my lifetime. It would be sight to see. My grandmother used to tell me tales about Orion when I was kid.

 

[Vanadium 50]

I hope it goes Nova in my lifetime.

Unless you will live to be 2000, this is unlikely to happen.

 

[zoki85]

Unless you will live to be 2000, this is unlikely to happen.

We hope for the best

 

[Astronuc]

Nature, June 16, 2021 - Great Dimming of Betelgeuse explained
https://www.nature.com/articles/d41586-021-01526-6

Observations suggest that an unexpected dimming of the massive star Betelgeuse resulted from dust forming over a cold patch in the star’s southern hemisphere. This finding improves our understanding of such massive stars.

https://www.sciencenews.org/article/betelgeuse-dust-cold-spell-why-giant-star-dimmed

But it seems this is old news -
Hubble Finds That Betelgeuse's Mysterious Dimming Is Due to a Traumatic Outburst
https://www.nasa.gov/feature/goddar...erious-dimming-is-due-to-a-traumatic-outburst

Observations by NASA's Hubble Space Telescope are showing that the unexpected dimming of the supergiant star Betelgeuse was most likely caused by an immense amount of hot material ejected into space, forming a dust cloud that blocked starlight coming from Betelgeuse's surface.

 

[Orodruin]

Nature, June 16, 2021 - Great Dimming of Betelgeuse explained
https://www.nature.com/articles/d41586-021-01526-6

https://www.sciencenews.org/article/betelgeuse-dust-cold-spell-why-giant-star-dimmed

But it seems this is old news -
Hubble Finds That Betelgeuse's Mysterious Dimming Is Due to a Traumatic Outburst
https://www.nasa.gov/feature/goddar...erious-dimming-is-due-to-a-traumatic-outburst

Funny. I was just searching for this thread to post this.

 

[epenguin]

The Times last Thursday reported:

"The “great dimming” of Betelgeuse can be attributed to the sudden formation of an opaque veil of stardust...

images captured by the European Southern Observatory’s Very Large Telescope, which is in the Atacama Desert of northern Chile, together with earlier pictures to show how the surface of the star was changing, particularly its southern region. The surface of Betelgeuse, which is about 643 light years from Earth, alters as vast bubbles of gas move, shrink and swell within the star. The scientists have concluded that some time before the great dimming, the star ejected a large gas bubble. When a patch of its surface cooled shortly afterwards, the temperature decrease was enough for heavier elements, such as silicon, that were contained within the gas to condense into solid particles.

...Andrea Dupree... discovered signs of dense, heated material moving through the star’s atmosphere in the months leading up to the great dimming... With Hubble, we could see the material as it left the star’s surface and moved out through the atmosphere, before the dust formed that caused the star to appear to dim,” Dupree said.

Once the gas bubble was millions of miles from the hot star, it cooled and formed a dust cloud. Betelgeuse returned to its normal brightness by April last year."

https://www.thetimes.co.uk/article/stardust-solves-puzzle-red-giant-betelgeuse-explained-v6mdnd3d8

 

[Orodruin]

The Times last Thursday reported:

"The “great dimming” of Betelgeuse can be attributed to the sudden formation of an opaque veil of stardust...

images captured by the European Southern Observatory’s Very Large Telescope, which is in the Atacama Desert of northern Chile, together with earlier pictures to show how the surface of the star was changing, particularly its southern region. The surface of Betelgeuse, which is about 643 light years from Earth, alters as vast bubbles of gas move, shrink and swell within the star. The scientists have concluded that some time before the great dimming, the star ejected a large gas bubble. When a patch of its surface cooled shortly afterwards, the temperature decrease was enough for heavier elements, such as silicon, that were contained within the gas to condense into solid particles.

...Andrea Dupree... discovered signs of dense, heated material moving through the star’s atmosphere in the months leading up to the great dimming... With Hubble, we could see the material as it left the star’s surface and moved out through the atmosphere, before the dust formed that caused the star to appear to dim,” Dupree said.

Once the gas bubble was millions of miles from the hot star, it cooled and formed a dust cloud. Betelgeuse returned to its normal brightness by April last year."

https://www.thetimes.co.uk/article/stardust-solves-puzzle-red-giant-betelgeuse-explained-v6mdnd3d8

Isn’t this just a popularized account of what was already posted in #55?

 

[DaveC426913]

When a patch of its surface cooled shortly afterwards, the temperature decrease was enough for heavier elements, such as silicon, that were contained within the gas to condense into solid particles.

So we're sayin' ... it snowed.
Silicon.
On a star.

 

[sophiecentaur]

So we're sayin' ... it snowed.
Silicon.
On a star.

Well, why not? It's a funny old world out there and it seems that almost anything goes, if you look hard enough for it.