Categories: Astronomy

Betelgeuse Is Still Dimming! And We Have the Pictures to Prove It

Near the end of 2019, astronomers watching the red giant Betelgeuse noted how much the star had dimmed, continuing to steadily fade for months. 

It’s a variable star, and it’s known to get dimmer and brighter, but the big surprise is that it’s still continuing to dim, recently passing magnitude 1.56 and still getting dimmer. This is unprecedented in the decades that astronomers have been watching the star.

The world’s biggest telescopes are on the case, and the European Southern Observatory released dramatic new images of Betelguese, resolving features on the star’s surface and surrounding area showing how it’s dramatically changed over the course of 2019. 

Comparison of Betelgeuse from January to December, 2019. Credit: ESO/M. Montargès et al.

I know, I know, you want to know if Betelgeuse is going to detonate as a supernova, and the answer is still: astronomers have no idea, but probably not. It could be any time in the next 100,000 years, and the chances that it happens in our lifetime is incredibly remote. This is probably just a normal variation, and it’ll go back to its regular brightness.

And yes, I understand that anything that’s happening on the surface of Betelgeuse actually happened hundreds of years ago, since the star is about 650 light-years away. But astronomers talk about events based on when they’re observed, not how long it took the light to get here since different observers moving at different velocities relative to an event will measure different amounts of elapsed time.

Telescopes from around the world have been turning their gaze on Betelgeuse, taking this opportunity to see the star at a time when it’s definitely behaving strangely.

Betelgeuse has always been easy to find. 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.

Variations are normal for Betelgeuse. It’s literally growing and shrinking as the internal temperatures rise and fall pushing the star in and out like a beating heart. 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.

An artist’s impression of Betelgeuse, showing the scale of its size and the surrounding dust clouds. Credit: ESO/L. Calçada

A team of European astronomers were lucky enough to have made very detailed observations of the surface of Betelgeuse at the beginning of 2019, using one of the world’s most powerful observatories. This allowed them to check back on the star at the end of the year, seeing huge differences on its surface, and the surrounding cloud of dust shed by the star over eons.

This newest image was captured by the European Southern Observatory’s Very Large Telescope, using its SPHERE instrument, also known as the Spectro-Polarmimetric High-contrast Exoplanet REsearch instrument. 

A quick side note, SPHERE is one of the most exciting instruments operating from the surface of the Earth. It allows astronomers to see the polarized infrared light that comes from newly forming planets orbiting a baby star. But apparently it also allows a high-resolution view of Betelgeuse.

Three planetary disks observed by ESO’s SPHERE instrument. Credit: ESO

Betelgeuse is so close and so big that telescopes here on Earth are able to reveal the surface of the star as a disk, seeing individual features like huge convection cells.

SPHERE’s view of Betelgeuse back in January, 2019. Credit: ESO/M. Montargès et al.

First, let’s take a look at the star as it was seen back in January 2019 using SPHERE. You can see how the star looks like a bright sphere. But then compare this to the image taken a year later in December 2019. You can see there’s a huge bright patch at the top of the star, and then a dimmer region down below.

Betelgeuse in December, 2019. See the dimmer region at the lower portion of the star? Credit: ESO/M. Montargès et al.

If you remember those convective cells on the surface of the Sun as recently seen by the Daniel K. Inouye solar telescope, these are blobs of hot gas carried from deep inside the star to the surface and released into space. On the surface of the Sun, these can be 1,000 km across, releasing the Sun’s heat into space.

But on the surface of Betelgeuse, they can be as big as 60% the size of the entire star. Since the star can be more than a billion kilometers across, these convection cells are hundreds of millions of kilometers across. 

The bright region in this photo might be one of these giant convective cells and the dimmer region might be part of the explanation of why Betelgeuse has dimmed so much. More research will be necessary because there’s another explanation.

Image of Betelgeuse and its surroundings captured by the VISIR instrument. Credit: ESO/P. Kervella/M. Montargès et al., Acknowledgement: Eric Pantin

The other idea that astronomers are working on is that Betelgeuse has belched out a cloud of dust that’s partially obscuring our view. In order to see if this is the case, astronomers used another instrument attached to the Very Large Telescope called the Imager and Spectrometer for mid-Infrared, or VISIR

The purpose of VISIR is to help search for habitable planets around nearby stars like Alpha Centauri, but it also does a great job of revealing details in the environment around Betelgeuse. 

In this image, you can see the infrared light emitted by the dust that was surrounding Betelgeuse in December 2019. They look like flames around the star, but they’re just enormous amounts of material shed by Betelgeuse as it continues through the final stages of its life. 

The VISIR instrument allows astronomers to mask the brightest part of the star, allowing the fainter material to show up. But just for comparison, astronomers put the original Betelgeuse picture back into the middle of the black disk, so you can see its size compared to the surrounding dust. Remember, Betelguese is the size of Jupiter’s orbit in our Solar System, so that’s a huge halo of dust.

Once again, we have no idea if Betelgeuse is going to explode any time soon. The fact that Betelgeuse is dimmer than we’ve seen in modern memory is exciting, the features we can see on the surface of the star and the surrounding dust are exciting. You can go outside, look at Orion and see for yourself how much of a dramatic change it is.

So come on Betelgeuse, explode already.

Source: European Southern Observatory

Fraser Cain

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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