I found multiple records and different types of measurements, but, considering the error bars, “about 1000 Solar radii” is indeed the estimate for the size of Betelgeuse right now. Which makes it a Class M supergiant. You don’t want to be nearby when it blows.
You don’t want to be nearby when it doesn’t. It is rather bright, plus you might run into Ford Prefect.
Radio measurements of its changing light suggested it was rotating at 5 kilometers (3.1 miles) per second.
The big problem with that is that stars of Betelgeuse’s vintage should, theoretically, have a maximum rotation speed at least two orders of magnitude lower. So, astronomers wonder, what the heck gives?
Well, according to new research, it may have been a big old tricksy-doodle. A team led by astrophysicist Jing-Ze Ma of the Max Planck Institute for Astrophysics in Germany has found that Betelgeuse’s boiling surface could be so riotous that it generates an illusion of fast rotation.
Open access study at:
https://iopscience.iop.org/article/10.3847/2041-8213/ad24fd/pdf
I hadn’t realized there was anything left unknown about Betelgeuse’s rotation. I had thought that that was pretty well pinned down.
I find it baffling when an author (not @PastTense ) describes a rotation rate as a linear speed.
WTF is that supposed to mean?
Doubly so for an amorphous gas ball whose constituent regions are all rotating at different rates.
I was puzzled too and, naturally, the pop science article is no use and its author probably didn’t even woder about it. I was therefore forced to read the first paragraph of the study.
The way I read it is, the linear speed of the surface seems to be the relevant metric. That means large stars with the same linear surface speed would have larger angular velocities (at the surface) but are considered “the same” in terms of the effect being discussed.
The reason for the linear speed could be that it’s determined by studying doppler shifts. This gives you linear speeds. To convert this to angular, you need the star’s radius which is not precisely known. And the rotation is generally not homogenous.
I had assumed there was an observed broadening of spectral adsorption lines that would would, assuming a rotating sphere, provide an estimate of rotation - so indeed Doppler shifts causing the broadening. What is interesting is that the observation below was done in the radio spectrum 340GHz. Which is impressive.
Chasing down the reference for measuring rotation, from the wikipedeia page for Betelgeuse, the abstract includes this:
So the answer is - this is the rotational speed at the equator, assuming the current estimates for distance to the star and the observed angular diameter.
Interesting new theory: it may actually be two stars.
If you train a telescope on Betelgeuse for weeks, you’ll see it dimming, then brightening, then dimming again. These pulsations stretch over roughly 400 days, although the 2020 “Great Dimming” event reveals such periodicity may occasionally go awry. But if you plotted Betelgeuse’s light intensity over years, you’d find these 400-day-long heartbeats superimposed on a much larger, slower heartbeat. Technically called a long secondary period (LSP), this second type of heartbeat lasts about six years, or 2,170 days, in Betelgeuse’s case…
Periodic changes in a star’s brightness typically occur when the star swells and then shrinks, again and again. This happens because gas near the star’s core gets super-heated and rises to the surface, where it expands ― causing the star’s size to increase ― but then cools and settles back towards the interior, shrinking the star. The general consensus among astronomers is that Betelgeuse’s 400-day-long pulsations arise from such cycling. But the cause of the star’s 2,170-day-long LSP had remained elusive, despite several possible theories, including the presence of gigantic dust clouds.
The two star theory is proposed as an explanation of the long secondary period.
Here is the preprint:
I don’t buy it. Stellar companions are not a subtle thing. If Betelgeuse had a companion, we’d have detected it long ago.
The paper addresses the ability to detect a companion ( called Betelbuddy) and suggest it is about 1-2 solar mass and orbiting fairly close , and given the luminosity of Betelgeuse and the max possible temperature of the companion means it would be very difficult to detect. ( section 5.2 of the paper)
If BeetleBuddy existed, wouldn’t we have noticed the periodic dimming well before now?
Yes, the Long Secondary Period has been observed for many years. The Betelbuddy theory is a proposed explanation for this well known phenomenon.
Dimming due to eclipsing has a very distinctive and well-recognized light curve. And I’m not sure how else a companion would cause periodic luminosity changes.
For clarification, does Betelgeuse exhibit this or not?
I just skimmed the paper, but apparently the hypothesis is not a simple eclipsing situation. It involves nearby dust clouds which are affected by the revolution of the hypothesized companion. See section 4.8.3:
Thus we propose a new scenario: a companion whose orbital period sets the timescale of the LSP
and RV fluctuations, and whose presence modulates, removes, eliminates, or changes the optical depth of any
potentially dusty material in its vicinity, rather than
dragging a trailing cloud of dusty material. There are
multiple ways in which this might occur, including, for
example, dynamically perturbing the potential of the
dusty medium or through irradiation.
No. If it did, then it would have been known many decades ago.
So six months after the last post in this topic you resurrected the thread to tell us this.
And you did so on September 11th, exactly five days after the second Beetlejuice movie premiered in theaters.
So, to verify: Yes, there are two Beetlejuices now, and the second one is slightly less radiant than the first, although I actually like Jenna Ortega despite her lack of emotional range, and Winona Ryder and Catherine O’Hara are still smokin’ hot all these decades later.
Astronomers say they have found Betelgeuse’s small companion: a blue A or B star, hot but not yet on the main sequence, orbiting Betelgeuse at about 4 AU. Believed to be the explanation for the six year dimming cycle, caused as it orbits Betelgeuse.
Query: the articles say the companion star has not yet started fusing hydrogen at its core. Then what is it doing as a source of heat and light?