Betelgeuse is a red supergiant in the constellation Orion. Its mass is about 11 solar masses. The distance to Betelgeuse is about 725 light-years.
At the end of 2019, a group of scientists from Villanova University (USA, Pennsylvania) published observational data that Betelgeuse’s brightness reached a record of low value in the entire history of observations.
This was perceived by many journalists as evidence that Betelgeuse would explode soon, and they did not miss the opportunity to inflate the sensation in fact from scratch.
The real fact is that Betelgeuse is a variable star. This happens due to the cycles of compression and expansion of the star. Thermonuclear reactions in the core of a star warm its outer layers and expand: the brightness of the star increases. Then the outer layers cool and shrink again; the brightness drops, and this cycle repeats many times.
The current drop in Betelgeuse’s brightness, the most significant in the entire history of observations, is not something out of the ordinary. All in all, Betelgeuse’s brightness has been monitored for only a few decades, and something like this has likely happened in the past.
Besides, most of the Betelgeuse radiation is in the infrared range. Changing the luminosity in the optical range says little about the way the total luminosity has changed.
When will it finally explode?
Nobody knows. Maybe tomorrow, maybe in a year, maybe in 100 years, or maybe in 1000 or 10,000 years.
Observations indicate that oxygen and helium have already burned out in the Betelgeuse nucleus and now, apparently, there is a synthesis of heavier elements. This phase can last thousands of years, and scientists cannot say exactly how much time is left for Betelgeuse to end.
Firstly, it is because Betelgeuse is quite far from us and our observational possibilities are limited, and secondly because we have never seen the last stages of a star’s life in such relative proximity to us. In general, we observe supernova explosions regularly, but as a rule, they are at least hundreds of thousands of light-years from us.
Therefore, if we talk about the timing, then for Betelgeuse, it is left less than 100,000 years before the explosion and most likely, less than 10,000 years.
How its explosion will affect the Earth
Betelgeuse, though, is a pretty close star to us, but still, it is too far away for the release of energy during its explosion to somehow harm the earth.
Most likely, several hours or days before the explosion, there will be a record of a powerful neutrino ejection, and then an optical flash will be seen. Within a few weeks, Betelgeuse will become comparable in its luminosity to the Moon and will be visible to the naked eye both day and night.
Betelgeuse luminosity will also increase in other ranges, such as the x-ray and gamma ranges, but firstly, this increase in luminosity will not last long, and secondly, it will still be much less than the radiation of our Sun.
A supernova, which would explode at a distance of 50-100 sv, could pose any real danger. But, fortunately, at such a distance, there are no stars that could explode in the foreseeable future. The closest candidate for the explosion, like a supernova, is IK Pegasi, located at a distance of 150 light-years from Earth.
However, before the explosion of IK Pegasi, at least several hundred million years must pass. Besides, IK Pegasus is moving away from us, so at the time of the explosion, the distance from it to the Sun will be much greater than 150 light-years.