In 2019, red supergiant star Betelgeuse suddenly dimmed. In fact, the star has a 5.9-year light-cycle minimum period. But, this time, it dramatically to an all-time low.

Betelgeuse is one of the brightest stars in the Earth’s sky and easily can be found on the right shoulder of the constellation Orion. So the dimming, which began in late 2019 and lasted for a few months, was easily noticeable even by backyard observers watching the star change brightness.

This weird, unexpected dimming weird sparked rumors that its death is imminent and it was going to be a supernova.

In fact, Betelguese is really nearing the end of its life. Because of its enormous size, it burns its fuel very rapidly. Red supergiant stars don’t last long, typically only a few hundred thousand years, maybe up to a million. This is actually very short for astronomical timescales. But very long for the human lifespan.

The reason why Betelgeuse dimmed in 2019 is a gigantic mass ejection

But, it seems the red supergiant isn’t dying, yet. Using data from Hubble Space Telescope‘s and several other observatories’ observations, astronomers have concluded that the 2019 dimming was caused by a gigantic Surface Mass Ejection (SME). The ejected material blocked our view and as a result, the supergiant looked dimmed from Earth.

Our Sun also routinely blows off parts of its tenuous outer atmosphere, the corona, in an event known as a Coronal Mass Ejection (CME). But the Betelgeuse Surface Mass Ejection blasted off 400 billion times as much mass as a typical Coronal Mass Ejection!

Why Betelgeuse dimmed
Here’s why Betelgeuse dimmed back n 2019: This four-panel graphic illustrates how the southern region of the rapidly evolving, bright, red supergiant star Betelgeuse may have suddenly become fainter for several months during late 2019 and early 2020. In the first two panels, as seen in ultraviolet light with the Hubble Space Telescope, a bright, hot blob of plasma is ejected from the emergence of a huge convection cell on the star’s surface. In panel three, the outflowing, expelled gas rapidly expands outward. It cools to form an enormous cloud of obscuring dust grains. The final panel reveals the huge dust cloud blocking the light (as seen from Earth) from a quarter of the star’s surface. Illustration credit: NASA, ESA, and E. Wheatley (STScI). Source.

According to scientists, the huge star is still recovering from that gigantic explosion.

Andrea Dupree of the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts says:

“Betelgeuse continues doing some very unusual things right now; the interior is sort of bouncing.”

“We’ve never before seen a huge mass ejection of the surface of a star”, adds Dupree. “We are left with something going on that we don’t completely understand. It’s a totally new phenomenon that we can observe directly and resolve surface details with Hubble. We’re watching stellar evolution in real-time.”

Even more fantastic, the supergiant’s 400-day pulsation rate is now gone, perhaps at least temporarily. For almost 200 years astronomers have measured this rhythm as evident in changes in Betelgeuse’s brightness variations and surface motions. Its disruption attests to the ferocity of the blowout.

Betelgeuse is so huge that if it replaced the Sun at the center of our solar system, its outer surface would extend past the orbit of Jupiter (see: What other stars would look like in the place of the Sun?).

Betelgeuse brightness
This NASA illustration shows changes in the brightness of the red supergiant star Betelgeuse, following the gigantic mass ejection of a large piece of its visible surface. Credits: NASA/ESA/Elizabeth Wheatley (STScI). Source
Sirius in the Earth's sky
Here’s how to find Betelgeuse in the sky: it is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in the constellation of Orion.
Betelgeuse 1995 Hubble image
This photo of Betelgeuse is the first direct image of a star other than the Sun, made with NASA’s Hubble Space Telescope. It was taken in ultraviolet light with the Faint Object Camera on March 3, 1995. The star is so huge that if it replaced the Sun at the center of our solar system, its outer surface would extend past the orbit of Jupiter (scale at lower left). Hubble can resolve the star even though the apparent size is 20,000 times smaller than the width of the full Moon – roughly equivalent to being able to resolve a car’s headlights at a distance of 6,000 miles. Photo: Hubble Space Telescope website

So, when will Betelgeuse go supernova?

The red supergiant’s days are numbered for sure, but remember, astronomical timescales are huge. So Betelgeuse won’t go supernova in our lifetimes, most probably. But, in fact, no one really knows. It could be tomorrow or a few hundred thousand years in the future.

If Betelgeuse goes supernova, will it destroy Earth?

No. It is too far away: current best estimates are on the order of 500-600 light-years from the Sun. Astronomers say we’d have to be within 50 light-years for it to harm us if Betelgeuse goes supernova.

It should be a spectacular view of the Earth’s sky, though. At its peak, it could shine roughly as bright as the Full Moon, maybe even more. Then it should start to fade and become a nebula.

Looking at it, with or without a telescope, would not harm an observer’s eyes.

Video: What will it look like when Betelgeuse goes supernova?

What will it look like when Betelgeuse goes supernova? (4K UHD video)


M. Özgür Nevres
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