Betelgeuse — the second brightest star in the constellation of Orion (the Hunter) — is a red supergiant, one of the biggest stars known, and almost 1000 times larger than our Sun. It is also one of the most luminous stars known, emitting more light than 100 000 Suns.
Betelgeuse is the 12th brightest star in the sky. It is called Alpha Orionis even though it is fainter than Beta Orionis (Rigel). Other names; Betelguex. Betelgeuze, Beteiguex, Al Mankib, Alpha Orionis, HR 2061, HD 39801.
Such extreme properties foretell the demise of a short-lived stellar king. With an age of only a few million years, Betelgeuse is already nearing the end of its life and is soon doomed to explode as a supernova. When it does, the supernova should be seen easily from Earth, even in broad daylight.
Pinned prominently on Orion’s shoulder, the bright red star Betelgeuse hardly seems like a wallflower. But a new study suggests the giant star has been shrinking for more than a decade.
Betelgeuse is nearing the end of its life as a red supergiant. The bright, bloated star is 15 to 20 times more massive than the sun. If it were placed at the centre of the solar system, the star would extend out to the orbit of Jupiter.
But the star’s reach seems to be waning. New observations indicate the giant star has shrunk by more than 15 per cent since 1993. This could be a sign of a long-term oscillation in its size or the star’s first death knells. Or it may just be an artefact of the star’s bumpy surface, which may appear to change in size as the star rotates.
Betelgeuse is enshrouded by vast clouds of gas and dust, so measuring its size is difficult. To cut through this cocoon, astronomers used a set of telescopes that are sensitive to a particular wavelength of the star’s infrared light.
Over a span of 15 years, the star’s diameter seems to have declined from 11.2 to 9.6 AU (1 AU, or astronomical unit, is the distance from the Earth to the sun).
The cause for this reduction is unknown, as it is unclear how red supergiants behave near the end of their lives. The shrinking size could also be evidence of an as-yet-unidentified pulsation in the star.
The surface of Betelgeuse is known to wobble in and out, fed in part by the roiling energy of convection beneath its surface. Two such pulsations are already known – one seems to start anew each year, the other every 6 years.
Since this observation shows a progressive decrease in the size of the star over 15 years with a consistent set of measurements.