THE SOUTHWORTH PLANETARIUM

70 Falmouth Street      Portland, Maine 04103

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43.6667° N    70.2667° W 

Founded January 1970

2022-2023: XL

Sunrise: 6:35 a.m.

Sunset: 4:16 p.m.

Civil twilight ends: 4:47 p.m.

Sun's host constellation: Libra the Scales

Moon phase: Waning Gibbous (62% illuminated)

Moonrise: 10:12 p.m.

Moonset: 1:10 p.m. (11/16/22)

Julian date: 2459899.21

"Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time." - Thomas Edison

THE DAILY ASTRONOMER Tuesday, November 16, 2022

The Inconvenient Non-Death of Betelgeuse

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Fare thee well, Gaia Girl

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Oh, how the astronomers were excited in 2019-202!  And,  be well assured that when astronomers become excited  storms gather,  space-time quivers, waves toss, sea-foam splatters, goddesses gulp, pandemonium trembles and the most intrepid paladins hasten up trees and then uproot them.  Every member of Earth's thriving stargazer community had diverted their foci to one single star: Betelgeuse, the unfathomably huge red supergiant defining Orion's eastern shoulder.    While this crimson-hued mammoth was never far from our thoughts, it started exhibiting behaviors that commanded everyone's immediate attention.  Its brightness was diminishing rapidly.  As a variable, of course, its luminosity changed constantly, but not like that.    At one point, it dimmed down to sixty percent of its usual brightness.    This startling variability was widely -and logically- believed to have been a precursor to its long-awaited explosion.   We know that the nine-million year old Betelgeuse is close to the end of its life cycle and will soon -within a million years at the outside- perish as a Type II supernova.    Such a supernova would cause Betelgeuse to not only temporarily become the night sky's brightest star, but it would cast shadows on the ground and even be visible during the day.      

So, astronomers gleefully rubbed their hands together, directed their telescopes toward Orion's eastern shoulder and eagerly awaited what they presumed would be the grandest firework any human in recorded history had ever seen. *  And they waited.  And they continued to wait.  The star brightened.  And they waited, albeit with less enthusiasm.   Ultimately, Betelgeuse returned to its usual brightness and remained frustratingly intact.   The waiting ending.  Like crestfallen children excluded from a grand festival, they packed up their telescopes and lumbered home.  

Betelgeuse lives!**

While astronomers now know that they'll have to wait a bit longer to see it erupt into a blindingly brilliant ball of flame, many are wondering what precisely transpired with Betelgeuse when it teased us so with hints of the death that was not to be.    Recently, some astronomers have suggested that an interloping body might have caused at least some of the dimming.    However, this body wouldn't have caused the diminishment by a transit, but instead, by raising a section of Betelgeuse through tidal forces. 

The resultant elevation of its composite material would have caused an effect known as gravity darkening.   As the elevated material draws away from the core, its temperature would decrease and so, too, its energy output, or luminosity.   As a star's luminosity is proportional to the fourth power of its temperature, stellar brightness is highly temperature sensitive.     Astronomers Hailey Aronson, Thomas Baumgarte, and Stuart Shapiro recently published a paper exploring this possibility in the Monthly Notices of the Royal Astronomical Society.  Although this tidal induced gravity darkening could not account for the entire diminishment, they noted that subsequent eruptions could have expelled enough intervening material between Betelgeuse and Earth to cause significant obscuration. 

The identity of this body remains unknown.  It could have been a passing black hole, neutron star or even a renegade planet, defined as a planet that is not attached to any star.   The body could not have been an active star, for such an object would have been readily visible to us.

In short, we might never know what caused Betelgeuse to behave in such an unusual manner as to excite astronomers all over the world.      While the resultant disappointment was particularly embittering, at least the ensuing mystery will keep many astronomers cheerfully engaged for many years to come.

*Other supernovae have been seen, of course, most notably the 1066 event in Taurus.  However, none have occurred as close as Betelgeuse, which is 620 light years away.  

**Mind you, of course, it could have already exploded.  As it is 620 light years from us, information about that explosion -if it has occurred- hasn't yet reached us.    So when we tell you that Betelgeuse "lives," put the "lives" in quotation marks, just as we've done...twice.

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