Just over 650 light-years from Earth, an old, red star lies dying. A new estimate based on Betelgeuse's pulsations suggests that the famous supergiant has only a few decades before it collapses in a final flash of splendour.

By reassessing oscillations in the nearby star's brightness, researchers from Tohoku University in Japan and the University of Geneva in Switzerland have found that they are likely to represent the latest stage of the star's life.
Few stars deserve their own daytime soap opera like the red supergiant Betelgeuse. Learning in 2019 that the suddenly fading star had coughed up something so dark and dusty as to temporarily obscure its brightness, astronomers gathered like trust fund babies awaiting the death of a rich uncle.

Earlier this year, Betelgeuse's usual lustre peaked, shining one and a half times brighter than usual. Once again there was speculation about the fate of the object and whether the changes were a death rattle or the flickers that come with old age.
Betelgeuse, a hot, heavy monster once known as an O-type star, appeared only 10 million years ago, following the burn fast, die young credo.

The years of a bloated red gas cannon, already running low on fuel, are numbered. How many depends on a number of factors.
One of them is its true size, which has been the subject of debate for much of the 20th century. With recent measurements placing it at the more compact end of predictions, the star is likely to have tens of thousands of years before it cools enough to eventually explode.
There are other reasons to think Betelgeuse still has a way to go.
Like many stars, Betelgeuse's outer layers pulsate in a balance of contraction and expansion driven by internal dynamics such as pressure and gravity.

The resulting fluctuations in brightness hum at frequencies that take months or even years to repeat - in Betelgeuse's case, its two most significant periods are about 2,200 and 420 days long.
The shorter period has typically been recognised as the dominant 'rhythm' of this enormous heart, representing an oscillation around its entire circumference known as the star's radial fundamental mode. Critically, calculations based on this relatively rapid expansion and contraction are what we would expect from a slightly smaller and therefore younger O-type star.

But what if there is more to the 2,200-day cycle than meets the eye? The researchers behind this latest study are not so quick to dismiss the much slower pulse as a long secondary period, arguing that the thermodynamics behind the oscillations in bright supergiants like Betelgeuse are a little more complex than in most other stars.
If the star were compressing its atomic nuclei into slightly larger elements, such as carbon, it could achieve a much longer period of radial pulsation. While shorter-period radial modes would make Betelgeuse's radius about 800 to 900 times that of our Sun, the team showed how the longer pulse would be consistent with a radius of about 1,300 times.
This means that as Betelgeuse's mass is concentrated in its core, its outer layers are drifting much further away, consuming fuel fast enough for its engines to stall in decades, not millennia.

Although not yet peer-reviewed, the pre-publication of its calculations and justification is enough to make us somewhat optimistic that we will be able to observe a supernova with modern instruments within our lifetime.
If the model is correct, we could watch Betelgeuse briefly eclipse all other stars before disappearing forever from the constellation shortly after mid-century.

Of course, debate will continue over Betelgeuse's true size and the details of its near-death experience until it finally explodes.
Only then will we view its turbulent existence with fresh eyes, more knowledgeable about stellar dynamics, and like drama-hungry monsters, we will watch with ghoulish glee as we go in search of the next star perched on the brink of destruction.

 

Source: https://www.sciencealert.com/