Betelgeuse - The next supernovae ?

One of the brightest stars on the sky - Betelgeuse - seems to loose its brightness. Experts are uncertain if that phenomenom is just a normal anomalie or the next big supernovae.

Hard Facts

Betelgeuse, also known as alpha Orionis or shoulder star of Orion, is the 2nd brightest star in the constellation of Orion.

The Herzsprung-Russell diagram classifies it as a red supergiant.

As a red supergiant, Betelgeuse belongs to the class of variable stars. It is assigned to the semi-variable stars of the SRc. With stars of this type, the brightness varies in certain periods from 30 to several thousand days. In Betelgeuse, the brightness varies in several periods of different lengths and strengths.

On average, Betelgeuse has 55,000 times the luminosity (= brightness) of the sun, making it the 7th brightest star on our sky.

With a mass of 20 solar masses and a radius of 950 to 1200 sun radii, Betelgeuse is also significantly larger than the sun. To make these sizes a little more conceivable: if Betelgeuse were placed in our solar system instead of the sun, the star would spread approximately to the Jupiter orbit.

Due to its size, Betelgeuse is not nearly as old as our sun, while our sun will be around 9 billion years old and still have about half of it. Betelgeuse is likely to be just over 10 million years old.

Betelgeuse is around 640 +/- 150 light-years from Earth, although one is very uncertain about this value because the calculation is very difficult. In contrast to many other stars, Betelgeuse does not appear in telescopes as a point light source, but because of its size and its proximity to the solar system, as a small disk-shaped light source. As a result, Betelgeuse is larger than its annual parallax when viewed from Earth. The annual parallax describes the change in its position that a star moves through our starry sky over the course of a year. Since almost all of a star's properties depend on its distance from Earth, this blurring continues, of course, so that despite its proximity and size, we actually know relatively little about Betelgeuse. And can only make limited statements about the development status of the star.

Current

Betelgeuse has darkened unusually strongly since October 2019, since then the star has lost a total of 75% of its luminosity and is therefore no longer the 6th / 7th Brightest star in our night sky, but only the 21st brightest. Scientists have worked out 2 theories to explain this phenomenon.

The first theory, hyped by the media in particular, is that Betelgeuse is much more advanced than previously thought, and this enormous obscuration is a first sign that the star is becoming more unstable and may be on the verge of a supernova. This theory is supported by recently measured unusual gravitational waves, the origin of which could be near Betelgeuse. However, this theory speaks against the fact that stars in front of a supernova become larger and brighter instead of smaller and darker. The origin of the gravitational waves is only suspected in the relative proximity of Betelgeuse, Betelgeuse itself is not in the suspected area of ​​origin. And ultimately, an impending supernova would release a multitude of neutrinos, which would be measured accordingly in the IceCube, which has not yet happened. A supernova would have only minor consequences for our earth, the critical distance is a good 200 LJ, as a reminder Betelgeuse is around 500 - 800 LJ away from us. Nevertheless, one could observe the supernova in the sky, also during the day, Betelgeuse would reach the brightness of a crescent moon for over 2 weeks before the neutron star remains.

The second much more probable theory states that two periods of brightness of Betelgeuse simply overlap and thus darken the star strongly. In theory, two of these periods should actually overlap at the moment, but such a strong and fast darkening is very unusual. According to the 2nd theory, Betelgeuse should become brighter again at the end of February. Of course, there is also the question of whether a spontaneous darkening of 25% can also occur in our sun, after all, life depends on the sun not shining too weak and not too strong. Yes, the brightness of the sun is also subject to very slight fluctuations, which, however, can be justified quite differently than with Betelgeuse. While the fluctuations in the sun are mainly due to sunspots, the difference in Betelgeuse's apparent brightness in our starry sky mainly depends on its size, which fluctuates very strongly. Betelgeuse has more than a billion times the volume of the sun's mass, but "only" 20 times the mass of our sun. This "stretching" of matter makes the surface of the star very unstable, so that the star becomes larger and smaller in certain periods.