The astronomer Rafael Bachiller reveals to us in this series the most spectacular phenomena of the Cosmos. Pulsating research topics, astronomical adventures and scientific news about the Universe analyzed in depth.
A new study indicates that our neighbor Betelgeuse will explode in the form of a supernova much sooner than previously believed.
red supergiant
Betelgeuse is the second brightest star in the constellation Orion and the ninth brightest in the night sky.. Its unmistakable reddish-orange color comes from the low temperature of its surface that barely reaches 3000 degrees, but despite this low temperature, its luminosity is very great due to its large size.
Location of Betelgeuse in the constellation of Orion
In fact, it is one of the so-called “red supergiants”, very old stars that have already consumed the hydrogen in their central region through nuclear reactions that converted it first into helium and then into carbon.. After the depletion of this nuclear fuel, Betelgeuse became destabilized: the central region gave way under its own weight, began to use carbon as a new fuel and the outer regions swelled to the enormous dimensions that we see now.. Due to instabilities, these outer layers began to pulsate periodically, with a main period of about 420 days.
It is a matter of “a short time” that the star explodes spectacularly to form a supernova. If we look at the closest stars to our solar system, Betelgeuse, located only about 800 light years away, seems to be the first of them all to explode.. But, naturally, when we say 'in a short time' we are referring to astronomical terms, we are not talking about a year or two, but how long are we talking about? Will the human being still be on Earth to be able to see it?
oscillations
Until now, it was thought that Betelgeuse would have to explode within about 100,000 years.. This estimate was based mainly on the oscillation period of the star, which, as has been said, was considered to be 420 days.. That is, every 420 days, the star slightly inflates and deflates, a bit like breathing in and out.. This period implies that the current diameter of Betelgeuse must be about 900 times greater than the diameter of the Sun.
Betelgeuse size measured with ALMA compared to the solar system
But other periods of minor changes superimpose on this period, they are species of overtones that have values of 185, 230 and 2 200 days.. A new study coordinated by astronomer Hideyuki Saio (Univ. from Tohoku, Japan) argues that the main period of Betelgeuse is not 420 days, as we thought until now, but that the main oscillation would be 2,200 days and the rest (185, 230 and 420 days) would be secondary oscillations.. According to this reasoning, the diameter of Betelgeuse would be 1200 times greater than the diameter of the Sun.. The star would be much more supergiant than previously thought, much closer to the end of its life, and therefore closer to exploding as a supernova.
According to Saio and collaborators, Betelgeuse would have fuel in the form of carbon for a few centuries.. When the carbon runs out, the core of the star will collapse again, and
will produce the supernova explosion in just a few tens of years. Therefore, according to this new study, the Betelgeuse explosion would take place in about 1,000 years, a much shorter time than the 100,000 years previously assumed.
Doubts
Betelgeuse is so close that it is possible to measure its size and even obtain rough images of its surface in infrared and radio waves.. After the publication of the work of Saio et al., their conclusions have been questioned by other astronomers.. Specifically, Lázsló Molnár has published a research note in which he argues that the existing measurements of the diameter of Betelgeuse do not fit well with the enormous size that the new study assumes for the star.
This enormous size also raises questions about changes over the 2,200-day period: the star's surface must be expanding and contracting at a rate of 5,400 kilometers per hour, and the stellar diameter must be increasing and contracting by a length about 180 solar diameters in each cycle. These are too large numbers that do not seem to agree with the observations.
However, for the moment, the reasoning of Saio and collaborators cannot be clearly contradicted, and the behavior of this fascinating star will have to continue to be studied, patrolling night after night to record its slightest changes.. In such systematic observations, amateur astronomers play an essential role, specifically the Association of Variable Star Observers (AAVSO) which, as this link shows, has compiled 47,485 observations from 1893 to the present day. days.
The article by Saio et al., entitled “The evolutionary stage of Betelgeuse inferred from its pulsation periods”, has not yet been published in a peer-reviewed journal, but the manuscript can be found here. Lázsló Molnár's research note, entitled “Comment on the Feasibility of Carbon Burning in Betelgeuse”, can be read at this link.
Rafael Bachiller is director of the National Astronomical Observatory (National Geographic Institute) and academic of the Royal Academy of Doctors of Spain.