Alpha Orionis, Betelgeuse for short, is a red supergiant located in the constellation of Orion. It is a very famous star because of a particularly remarkable characteristic: its variable brightness which has perplexed astronomers for centuries. Although there are many convincing hypotheses, no one has ever managed to rigorously prove why this star could shine brightly on a given day, then become much more discreet over the course of a few hundred days, and this following a complex cycle.
A new team has recently looked into the question through a new study that stands out from the others: she favors the hypothesis of the binary systemsuggesting that Betelgeuse might actually be a pair of objects rather than a single star.
A centuries-old mystery
The variability of Betelgeuse is not new: The first evidence of its changing nature dates back to the end of the 16th century.. However, due to the lack of sophisticated instruments, it was not until the 20th century that substantial progress was made… but these new observations only made the problem even more thorny. Not only did the astronomers of the time not find a clear explanation for the phenomenon, but they also found that these variations in brightness were more complex than expected. They follow several distinct cycles, some very short (100 to 200 days) and others taking place over several years.
During this prosperous period, astronomers have put forward a variety of hypotheses, sometimes complementary, to explain these observations. The first is based on a phenomenon already well documented in red giants. Towards the end of their lives, they tend to undergo natural pulsations: the outer layers of the star expand and contract due to variations in temperature and pressure at the core, generating changes in brightness whose frequency could be compatible with the observations of Betelgeuse.
Other astronomers have suggested that it could be other dynamical processes not necessarily related to its age. For example, the star’s surface could be covered in convection cells, turbulent areas whose dynamics could impact the overall brightness of the object. Alternatively, it could also be ejecting vast clouds of dust that may temporarily obscure the star. But again, none of these hypotheses were entirely conclusive.
Tensions escalated further in late winter 2019, when the star suddenly dimmed dramatically. In a few weeks, its brightness dropped by about 40%.This episode has revived the interest of astronomers in another hypothesis: that of the supernova. Indeed, many experts concluded that Betelgeuse was in the twilight of its life, and was about to undergo a cataclysmic explosion in the near future. A few months later, the star finally returned to its average brightness level, leading astronomers to relegate this scenario to the background.
The return of the binary system track with fanfare
For want of anything better, the researchers behind this new study looked at another theory initially formulated in the 1920s: that of the binary system, according to which Betelgeuse would be accompanied by another celestial body whose rotations could periodically mask it. Historically, few people have given much credence to this possibility. And for good reason: despite numerous investigations by a bunch of cutting-edge instruments, no one has ever managed to detect the slightest trace of a second object nearby.
But that doesn’t necessarily mean that this mystery companion doesn’t exist, and that’s what these American and Hungarian researchers sought to prove in their paper. They demonstrated that over the course of its rotations, this object called α Ori B could disperse the dust cloud around its illustrious companion, leading to periodic variations in brightness. This dynamic could be marked enough to explain the great dimming of 2019. They even managed to calculate the theoretical mass of Ori B, which would be around 1.17 solar masses. It would therefore be an object significantly more massive than a planet, perhaps a neutron star.
With all these arguments, Researchers believe that the binary system hypothesis is the most plausible one to explain the variations of Betelgeuseespecially those that occur over the long term.
Still no formal proof
But whatever the case, the mystery will probably persist for some time to come. Even if the elements put forward by the authors fit together relatively well, detecting Ori B will be much easier said than done; it is no coincidence that no one has found any trace of a companion so far. And even if its existence is confirmed one day, it is likely that other hypotheses cited above are also valid, and that Betelgeuse’s behavior is the result of several different factors.
This iconic star is likely to continue to taunt us for many years to come; we can only hope that researchers will discover the end of the story before the fateful supernova, expected within a hundred thousand years!
The study, still in the pre-publication stage, is available ici.
Source: www.journaldugeek.com
