
Betelgeuse Remains Steadfast in the Infrared - fhars
http://www.astronomerstelegram.org/?read=13518
======
petschge
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](https://imagebin.ca/v/5DhzHxxS3Eq2) 2:
[https://www.aavso.org/LCGv2/](https://www.aavso.org/LCGv2/) 3:
[https://aavso.org/](https://aavso.org/)

~~~
auxbuss
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](https://arxiv.org/abs/2002.10463)

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

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

~~~
Sharlin
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](https://en.wikipedia.org/wiki/Solar_flare)

------
Jun8
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."

~~~
shadykiller
Does that mean it's not exploding ?

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

~~~
throwaway_tech
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.

~~~
petschge
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.

~~~
SiempreViernes
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.

------
geuis
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...](https://arstechnica.com/science/2020/02/new-image-shows-betelgeuse-
isnt-dimming-evenly/)

~~~
aaroninsf
One person's dust is another's megastructure!

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

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

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

~~~
shagie
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](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.

~~~
atisu
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.

~~~
machello13
You're thinking of a Dyson swarm.

~~~
atisu
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.

~~~
machello13
Huh, TIL. I always thought they were two separate ideas, not that the Dyson
swarm is a type of Dyson sphere.

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

~~~
api
Everyone just needs to say its name three times.

