What seems to us as a star of super giant size on earth may not be the star itself, but the surrounding in which it has to exist. Betelgeuse a mere 650 light-years distant in Orion has been acting as a kind of instrumental comet which will not sustain a note. Its brightness swings and swings upon a common beat of about 400 days but it also passes through a slower beat that extends to nearly 2,100 days. These two clocks have left astronomers perplexed over the decades since both suggest motion and structure in a place that is hard to map, namely the star and its outer billowing atmosphere where gas, dust, magnetic and convective processes may all pose as each other in telescope measurements.
New observations with Hubble and some ground observations reframe that complexity as a simple driver: a close companion star, Siwarha, passing through the outer envelope of Betelgeuse, and carving it out. The team did not depend on a single snapshot, but rather paid attention to the subtle changes of the light and spectral signatures that occurred during almost eight years, which was sufficient to observe repeating patterns that can be attributed to the longer cycle variability. Most obviously of all is a thick, trailing tangle in the surrounding gas a wake formed on the wake of the companion as he passes over before the supergiant during a period of approximately six years. It is a little like a boat sailing through water. The companion star produces the ripple effect in the atmosphere of Betelgeuse which we could actually observe in the data as said by Andrea Dupree. This is our first observation of direct evidence of this wake, or trail of gas, which proves that Betelgeuse actually does have a hidden companion that moulds its aspect and its manners.
The lesson on engineering within astronomy is methodological: the breakthrough is to do less with a particular instrument, and more with coordinated sensing. The ultraviolet and optical stability of Hubble is combined with spectroscopy on the ground to observe variations of the speed and direction of the gas, and long-baseline observation distinguishes long-term cycles of the process, and a single burst. This is the logic that is applied to the diagnosis of complex systems on the earth- many, faulty sensors settle down as final when their signals converge on a common periodic behavior.
Betelgeuse is abnormally helpful in this type of systems test since it is large and sufficiently close to be studied closely. It would have more than 400 million Suns, and its outer air is so large, that an orbiting companion may pass through the matter that is yet actively bound to the star. Even the slightest perturbation in that regime will cause the gas to reorganize into denser streams which alter the same values of brightness that are measured by observers on the Earth. It is also explained why previous concepts, giant convection cells, dust clouds, and the magnetic effect, continued to emerge: all of those processes may still be maintained, but a companion provides a clock-like, self-repeating trigger, which the other processes did not have.
The difference is important to understand dramatic dimming events, such as the 2019-2020 Great Dimming, which was in most discussions most likely being caused by dust ejection. A more general survey of red-supergiant winds adds that Betelgeuse is probably dimmer now because a dust cloud had built up above a cool convection point, an example of events of a short-term nature superimposing on long-term variations without necessarily having a common cause.
Even the companion has been photographed in extreme-resolution. Direct observation and the discovery of a faint close companion of Betelgeuse were possible with techniques of speckle on Gemini North, through the use of the Alopeke instrument, and the same program found it 6 magnitudes weaker in optical light.
To-day, to observe, Betelgeuse has been set in such a manner that the companion may be hard to split off the bright face of the supergiant, but already the policy of observing lies in view of observing: wait till the geometry is better, and then take the measure of the wake again, with more stringent restrictions. A new chance is expected in 2027, but with Betelgeuse, it is not so much of a spectacle, but rather a working laboratory, as the orbital dynamics and atmospheric flow, and periodic bursts of dust will finally be studied as components of the same clockwork.
