Betelgeuse Remains Steadfast in the Infrared | Hacker News Reader

Betelgeuse Remains Steadfast in the Infrared

astronomerstelegram.org

100 pointsfhars52 comments

Have a look at the plot [1] from the excellent plotting tool [2] of the American Association of Variable star observers [3]. You see a strong dip in the U band (U for UV, 365 nm plus or minus 66 nm), B band (B for blue, 445 nm \pm 94 nm) and V band (V for visible, 551 nm \pm 88 nm). But in infrared (only the J band had enough data to make it worth plotting) at 1.22 micro (plus or minus 212 nm) the light curve is really flat.

1: https://imagebin.ca/v/5DhzHxxS3Eq2 2: https://www.aavso.org/LCGv2/ 3: https://aavso.org/

This paper [0] from a couple of days ago (24 Feb 2020) found that Betelgeuse's recent dimming was not caused by a drop in the star's surface temperature.

"We present optical spectrophotometry of the red supergiant Betelgeuse from 2020 February 15, during its recent unprecedented dimming episode. By comparing this spectrum to stellar atmosphere models for cool supergiants, as well as spectrophotometry of other Milky Way red supergiants, we conclude that Betelgeuse has a current effective temperature of 3600 +/- 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse's recent lightcurve evolution, this drop in effective temperature is insufficient to explain Betelgeuse's recent optical dimming. We propose that episodic mass loss and an increase in the amount of large-grain circumstellar dust along our sightline to Betelgeuse is the most likely explanation for its recent photometric evolution."

One of the authors, Emily Levesque, also posted a related twitter thread. [1]

[0] https://arxiv.org/abs/2002.10463

[1] https://twitter.com/emsque/status/1232730880478765057

So... Betelgeuse have "sneezed" in our general direction. Would it be possible to estimate when it going to reach us?

For those of us who aren't astronomers, what does "episodic mass loss" mean?

A large ejection of matter. A sort of an ultra-flare [1], presumably caused by some sort of a massive reconfiguration of the star's magnetic field.

[1] https://en.wikipedia.org/wiki/Solar_flare

From the abstract:

"This suggests that the recent dramatic fading observed at visual wavelengths is due mostly to local surface phenomena, such as changes in dust extinction or molecular opacity along the line of sight through the inner wind and complex atmosphere, and/or surface temperature fluctuations."

Does that mean it's not exploding ?

Super disappointing. Is there still hope to see the supernova in our lifetime ?

Realistically, it is exceedingly unlikely for this to happen in our lifetime. Based on the best estimates we have, it’s most likely ten thousand or more years too early in its red giant phase for this to happen.

Most of the possibility of it happening comes from the error bars in our assumptions about its progress through the red giant phase, and the error bars in our understanding of how red giants collapse. Put another way, it’s not that we think it might happen in our lifetimes, it’s that we’re relatively sure it won’t (but we could be wrong).

Eh... you're mixing apples and oranges. The baseline is that it is super unlikely to happen within a human lifetime. However up until now the recent dimming is exactly the sort of fast event which might precede a supernova. So as of a week or two ago, the Bayesian evidence was that a supernova was about to occur was much, much more likely than the baseline.

It is still more likely to occur in our lifetime than we would have guessed before--these sorts of dust-belching events are likely to happen right before the end. We just can't quantify that likelihood very well because this is the first time we've seen a (pre-)supernova in our stellar neighborhood in modern times.

Best estimates put Betelgeuse at having spent 20,000-140,000 years as a red supergiant, with around 40,000 years being the most likely. We don’t know exactly how many solar masses it is, but under the worst possible conditions (25 solar masses, rotating quickly) we predict that it will persist as a red supergiant for around 300,000 years. For 20 solar masses and rotating, this increases to 500,000 years. Modern models find it most likely to be 15-20 solar masses and non-rotating, in which case it would take even longer to collapse (up to 1,000,000 years from when it began the red supergiant phase).

Even at the oldest it is likely to be, under the best possible conditions for the shortest possible lifespan, it will still likely spend another 150,000 years as a red supergiant before it collapses.

So I don’t believe your statement to be true. We could be wrong about the mass of Betelgeuse. We could be wrong about its age, its chemical composition, its rate of rotation, etc. We could be wrong about our theories of how red supergiants evolve. Any or all of those could lead us to incorrectly conclude that Betelgeuse won’t go supernova in our lifetime. But by our current cosmological understanding, it’s not that “it could go tomorrow or a hundred thousand years from now”. It’s that we’re pretty sure it won’t go for over a hundred thousand years. But if we’re wrong, it’s technically possible that it could happen tomorrow.

What's the relationship between mass, rotational velocity and what we can observe?

A very complicated one: basically the exact motion and temperature structure of the gas of the star greatly influences the spectrum.

So people run spectral synthesis codes of varying complexity, essentially simulating the entire star, and tweak the parameters to get good agreement between observed and simulated spectra.

how can a star possibly be non rotating?

I was wondering the same, but I saw the GP wrote "rotating quickly" in the first use of "rotating", and so maybe "rotating" became a shorthand in the rest of the post.

"Thus, while Betelgeuse may explode tomorrow or any time in the next few 1e5 yr, the unprecedented current visual faintness is unlikely to be a harbinger of its impending core collapse."

@stouset said it more seriously, but I can try a different take: considering stars like Betelgeuse go supernova only once during their lifetimes, which exceeds ours by many orders of magnitude, the odds of an individual human generation witnessing a cosmic event of any significance from this close are disappointingly low.

Disappointment for some, relief for others. Some of us like our cataclysms comfortably distant. From everybody, one can hope.

Of course there is hope. Lots of stars out there.

With one remaining eye, do not look through telescope at the massive pulse of gamma rays about to strip the magnetosphere and atmosphere from your planet...

Betelgeuse is not that close.

No, but this whole "will I see a supernova in my lifetime" thing is very entertaining, until you go to massive unexpected gamma ray events: Its not the one you "see", its the one you don't see but coming our way from some event a long time ago (I am led to believe these things actually bleed out a bit, so the whole 'be along the axis the two spikes come out at, be very specific about when in the life of the GRB, this condition, that condition' make it all pretty unlikely)

It was, basically, a joke. Nothing you see through an optical telescope by eye is going to burn your retina off a star, excluding the one we orbit.

I did find my vision was degraded looking at Saturn in a 10" reflector: it is surprisingly bright. I was locally blind in the night light, after looking at the moon through binoculars.

Can you share more info (exposure time, etc.) about how that happened? How big was Saturn's shape through the reflector? I wouldnt have expected that to happen!

Degraded purely temporarily. Flashbulb effect in a dark room, lingering phosphene neon-blur overlay for 2-3 minutes. Not damaged forever, retinal burn. Sorry. bad language on my part.

I do not believe you can damage eyes because of reflected sunlight off planets or moons, through a telescope. If somebody can find a fresnel lens fire-starter for moonlight, I'll learn to smoke midnight cigars to light them.

But you definitely can suffer temporary light adaption loss, from the huge difference between what you see in the scope or binoculars, and what you see with full eyes, in the wide. It was 40 years ago, I wouldn't even know what kind of lens was on the eyescope. Saturn was maybe 1/5th of the visual field? Binoculars, 30x or 50x you're already looking at segments of the Moon, not the entire face I think.

The effect of a Betelgeuse supernova on Earth: https://www.huffpost.com/entry/the-betelgeuse-supernova_b_65...

There's always hope.

If you ever see it go supernova, just remember it went supernova 642.5 years ago...or if it actually does go supernova in your lifetime, you unfortunately not see it.

In astronomy we typically date events by observation date, not by date at the remote location. The reason is that distance is often poorly known and the estimates are subject to change over time. Time at the solar system barycenter on the other hand can be determined down to the nanosecond and can be compared very well between different observatories.

I'd say the main reason is that there is no use for the "distance corrected" date. We're all basically in the same place so we can't really mix up the ordering by ignoring the travel time.

Honestly, the best use of this the light delay fact is that you can annoy transient observers by trying to get SN1987A renamed to SN-1678900A or something.

That and relative velocity between objects can greatly effect what year they would consider the event happening at in their "past" or "future".

It depends on your frame of reference, there exist frames in which an event and the detection of light from it are simultaneous.

>there exist frames in which an event and the detection of light from it are simultaneous.

At the distance from Earth to Betelgeuse?

This supports recent hypotheses in the last couple weeks that the dimming is from expelled dust. https://arstechnica.com/science/2020/02/new-image-shows-bete...

One person's dust is another's megastructure!

Just fascinating. I spent some time goggling at its absence this weekend, glad to hear it should(?) return to prominence

No mention of a Dyson sphere[1]? I hope we are witnessing the construction of one!

[1] https://en.wikipedia.org/wiki/Dyson_sphere

Assuming using all the mass in the solar system (1.82 10^26 kg), and 1AU, you get something that is about 8-20 cm thick depending on density.

r = 1AU gives a surface of 12.57 square AU (that unit boggles my mind as I write this)

r = 3.5 AU for Betelgeuse and the surface area is 153.94 AU. That 3.5 puts the sphere at the surface of the star.

The 8-20 cm thick surface becomes roughly 0.8 - 2 cm.

Betelgeuse is roughly 100,000 times more luminous than the sun (it is a variable star so I'm using a very round number).

The habitable zone is a function of luminosity only ( https://www.britannica.com/science/habitable-zone ). The approximation then is for the sqrt(L). For 100,000 this is 316. The habitable would be about 320 AU away from the center of Betelgeuse.

This gives the mind boggling large number 1.3 x 10^6 square astronomical units. The thickness of this material on the scale of proteins and Wolfram Alpha says it is about three times the approximate diameter of a carbon nanotube.

---

Hoping to see a Dyson sphere around Betelgeuse would stretch the limits of physics. Or I've got my math off in a few places - which is quite possible.

Just for the record: the Dyson sphere is not an actual solid hollow sphere around a star. Rather it is a swarm of rotating objects orbiting the star.

You're thinking of a Dyson swarm.

The naming is kinda misleading as Freeman Dyson envisioned the "Dyson sphere" as a swarm of objects. Although "sphere" is not technically correct, both swarm and sphere refer to the same thing here: a swarm of objects (e.g., O'Neill cylinders) orbiting a star.

Huh, TIL. I always thought they were two separate ideas, not that the Dyson swarm is a type of Dyson sphere.

Why would a hypothetical Dyson sphere need to be in the habitable zone? I would guess that it should be built as small as the construction materials can tolerate.

Edit: I love that you did napkin math for this, BTW.

We can confidently predict that no one will ever find a Dyson sphere of any description. Anybody equipped to make one would have long since perfected controlled fusion, and spent the time fusing the nearest cold gas giant after mining out the actually frozen ones.

The place to look for aliens is around Neptune. Solar power (like goldilocks planets, and fission) is for extreme primitives.

An actual sphere is implausible and probably impractical. (Unstable, no gravity, no atmosphere). There doesn’t seem to be any reason to orbit artificial structures in the habitable zone.

Around a star that's going supernova in the next 1e+5 years?

No, thanks.

maybe it's stadium seating for a species that doesn't mind a few gamma rays

Or an alien doomsday cult.

Or a shield to protect things nearby from the coming supernova.

A "paranova" is an interesting concept, but it'd probably be more effective to build multiple smaller ones closer to the settled worlds.

We may want to build a smaller scale parasol for Venus so it cools down and can be eventually settled.

IIRC this dimming cycle has been repeating for decades

Actually there is several period detected in the brightness, one being ~420 days (give or take 10 days or so), another is ~2100 days. Several of those having a (nearly) simultaneous minimum might very well explain the stronger than normal dimming we just have seen. The other thing that got some attention is that Betelgeuse did not start to rebrighten January twenty-something -- like expected -- but reached a minimum slightly later, on February 10th or so. The correct conclusion of course is not "it is blowing up" but "we got the period length slightly wrong", closer to 425 days or maybe the period length is not exactly constant.

I'm so disappointed. I really wanted it to explode during my lifetime.

Everyone just needs to say its name three times.

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