Betelgeuse, normally one of the brightest stars in the night sky, has dimmed 60% ahead of what some astronomers think of as a potentially imminent supernova.
Betelgeuse is a red supergiant, usually the 10th brightest star in the sky, which is part of the Orion constellation.
It is also one of the largest stars visible to the naked eye and, if placed at the center of our solar system, it will almost certainly gobble up Jupiter.
But for months, scientists have been trying to figure out why its luminosity has dropped to about 40% of what is normally expected.
Some astronomers speculated that the 60% oscillation detected between October last year and this April was related to an impending supernova, cosmologically imminent, that is, within the next 100,000 years.
An international team of astronomers, led by Dr. Thavisha Dharmawardena of the Max Planck Institute for Astronomy, has shown that the attenuation was likely caused by spots of giant stars that cover up to 70% of Betelgeuse’s surface.
“Towards the end of their lives, stars become red giants. As the fuel supply runs out, the processes by which stars release energy change,” explained Dr. Dharmawardena.
This causes the stars to swell and become unstable, pulsating at a rate that can last for hundreds or even thousands of days, causing fluctuations in brightness.
Betelgeuse is so large that the gravitational pull on its surface is not enough to prevent these pulsations from ejecting the outer layers of the star.
The gas that the star exhales then cools and turns into dust, which is how the heaviest elements in the universe are produced.
These high-resolution images show the distribution of brightness in visible light on the Betelgeuse surface. Pic: THAT
Astronomers suspected that a collection of this dust was absorbing Betelgeuse’s light, but that dust did not appear even when the star’s light was studied at different wavelengths.
Dr. Dharmawardena and her collaborators measured Betelgeuse light at a terahertz wavelength, at frequencies thousands of times greater than in visible light.
At this wavelength, the cold dust emitted by the stars generally shines.
“What surprised us was that Betelgeuse became 20% darker even in the sub-millimeter wave range,” said Steve Mairs of the East Asia Observatory, who collaborated on the study.
This was not consistent with what should have been found if the star’s light was absorbed by the dust.
Instead, they reasoned that the star itself must have dimmed, as a result of a reduction in surface temperature.
Using high-resolution images of the star captured in December 2019, the team found areas of variable brightness, indicating the presence of large stars that cover up to 70% of its surface.
“Star spots are common in giant stars, but not on this scale,” said the Max Planck Institute.
“Observations in the coming years will tell us whether Betelgeuse’s sharp decrease in brightness is related to a point cycle. In any case, Betelgeuse will continue to be an exciting object for future studies,” said Dr. Dharmawardena.
