Context

Betelgeuse, the red supergiant star that marks the armpit of Orion the Hunter, has been dramatically and mysteriously dimming for the last six months.

About:

• Betelgeuse is a red supergiant star, located an estimated 642 light-years
• Location: It’s usually the 11th brightest star in the sky, taking its position as the right shoulder of Orion. But in the last few months, it’s dimmed down to 38% of its usual brightness, now the 24th brightest star in the sky.

• Variable star: Variations are normal for Betelgeuse, and it’s known to get dimmer and brighter. It’s literally growing and shrinking as the internal temperatures rise and fall pushing the star in and out like a beating heart.
• Convective cells: It has enormous convective cells on its surface that boil creating brighter and dimmer regions, and it’s constantly blowing out dust that can obscure our view for a time.

What’s the reason behind this?

• Astronomers have captured the unprecedented dimming of Betelgeuse Using ESO’s Very Large Telescope (VLT).
• The stunning new images of the star’s surface show not only the fading red supergiant but also how its apparent shape is changing.
• The red supergiant Betelgeuse has recently dimmed quite dramatically because those two periodic cycles are overlapping at minimal brightness.
• Beginning in October 2019, astronomers noticed that the brightness of Betelgeuse suddenly began to change. The star was dimming.
• Once one of the top 10 brightest stars in the sky, its brightness had fallen to 21st place by the end of December 2019. 

Is it going to explode?

• Astronomers have long suspected that the star might explode sometime in the next million years.
• It's also possible that Betelgeuse has already exploded and we just haven't seen it happen; because the star is 600 light-years away, it takes 600 years after something happens on Betelgeuse for light from that event to reach Earth.
• But if and when astronomers do witness the star's explosion, it will be the most astonishing astronomy event of all time. 
• When Betelgeuse explodes, turning into a supernova, it will briefly shine even brighter than the full moon. Then, the star will vanish forever.

What is The Very Large Telescope array (VLT)?

• The Very Large Telescope array (VLT)is the flagship facility for European ground-based astronomy at the beginning of the third Millennium.
• It is the world's most advanced optical instrument, consisting of four Unit Telescopes with main mirrors of 8.2m diameter and four movable 1.8m diameter Auxiliary Telescopes.
• The telescopes can work together, to form a giant ‘interferometer’, the ESO Very Large Telescope Interferometer, allowing astronomers to see details up to 25 times finer than with the individual telescopes.
• The light beams are combined in the VLTI using a complex system of mirrors in underground tunnels where the light paths must be kept equal to distances less than 1/1000 mm over a hundred metres.
• With this kind of precision, the VLTI can reconstruct images with an angular resolution of milliarcseconds, equivalent to distinguishing the two headlights of a car at the distance of the Moon.
• The 8.2m diameter Unit Telescopes can also be used individually.
• With one such telescope, images of celestial objects as faint as magnitude 30 can be obtained in a one-hour exposure.
• This corresponds to seeing objects that are four billion (four thousand million) times fainter than what can be seen with the unaided eye.

Over their lifetimes, red supergiants (like Betelgeuse) create and eject vast amounts of material even before they explode as supernovae. Today’s modern technology has enabled scientists to study these objects, hundreds of light-years away, in unprecedented detail. It gives the opportunity to unravel the mystery of what triggers their mass loss.