Despite all the optical horsepower afforded by the Hubble Space Telescope and cutting-edge observatories on the ground, astronomers have been able to resolve the disks of only a handful of stars. One of the few successes is Betelgeuse, the enormous red supergiant marking the shoulder of Orion.

Boiling Betelgeuse

This artist’s impression shows the violently boiling surface of the supergiant star Betelgeuse, as revealed by observations with the European Southern Observatory's Very Large Telescope. Distances within the inner solar system appear to scale at right.

ESO / L. Calçada

Astronomers first measured this star's angular diameter in 1920, but I remember getting my first true appreciation for Betelgeuse's size in 1996, when observers released an image of this stellar behemoth taken with the Hubble telescope's Faint Object Camera.

Everything about Betelgeuse is supersize. More than 900 times the Sun's diameter, this star would comfortably engulf the entirety of Mars's orbit and the asteroid belt. It also outshines the Sun by 135,000 times — a dazzling 1st-magnitude beacon despite its distance of some 640 light-years.

And it has practically the largest angular diameter of any star in our sky: about 55 milliarcseconds, depending on what wavelength you use to observe it.

Now two teams of observers have resolved the star as never before, and in doing so they've found that Betelgeuse is throbbing, churning, and spewing shells of its outer layers into the space around it. The new views show that this mass loss, an Earth's worth every year, isn't a nice even flow like our Sun's solar wind. Instead, Betelgeuse is hacking up hairballs of hot gas this way and that at 25,000 miles (40,000 km) per hour.

These spasms aren't a sign of stellar health. Only a few million years old, Betelgeuse is already dying. Astronomers predict that it's doomed to explode as a supernova relatively soon, astronomically speaking, an event that will be spectacular for Earth's future inhabitants.

Betelgeuse resolved with the VLT

The supergiant star Betelgeuse as imaged at near-infrared wavelengths with the NACO adaptive-optics instrument on ESO’s Very Large Telescope. The resolution is 37 milliarcseconds, roughly the size of a tennis ball on the International Space Station (ISS) as seen from the ground. North is up.

ESO / Perre Kervella

The new observations made use of the powerful telescopes atop Cerro Paranal high in the Chilean Andes. In January, Pierre Kervella (Paris Observatory) and six colleagues used an adaptive-optics system on one of the giant eyes of the Very Large Telescope to achieve a resolution of 37 milliarcseconds at near-infrared wavelengths. They've submitted their results to Astronomy & Astrophysics.

A second team, led by Keiichi Ohnaka (Max Planck Institute for Radio Astronomy), coupled the output from three 1.8-meter telescopes at the VLT site to create an near-infrared interferometer with a virtual aperture some 157 feet (48 meters) across. Using this setup's resolution of just 9 milliarcseconds, Ohnaka and his team found that parts of Betelgeuse's atmosphere are heaving up and down violently. Their results will also appear in Astronomy & Astrophysics.

Betelgeuse has long been recognized as a semiregular variable star. In fact, a third team of observers recently reported that its diameter seems to have shrunk by some 15% since 1993.

You can find out more about Orion's hotheaded superstar in press releases here and here.


Image of Enrico the Great

Enrico the Great

August 1, 2009 at 12:43 am

When it goes, it will mess up Orion! My Favorite constellation, visible even from light pollutef NYC!
But, we will get another nebula, how bright will the remnant be???

You must be logged in to post a comment.

Image of WestWitch


August 3, 2009 at 10:42 am

Hi Enrico,

I've read the supernova could potentially be as bright as 4 full moons. If you Google Betelgeuse, a number of articles come up regarding it's activity. Would be interesting to see it happen in our lifetime.

I thought I've noticed this star somewhat dimming over the past few years.

- another astro-junkie

You must be logged in to post a comment.

Image of Patricia del Valle

Patricia del Valle

August 7, 2009 at 10:28 am

Yes, Orion is easy to find. And the info you offer is wonderful. My grandchildren love it and so do I. I've been star-gazing, becoming more involved & informed for many yrs. now--lovely adventure.
Thank you.
My best,

You must be logged in to post a comment.

Image of Jim W.

Jim W.

August 7, 2009 at 12:22 pm

OK, Supernova and 640 light years distance. Gamma rays? This thing is pretty close by astro standards. Are we going to get an unhealthy dose of radiation when it goes or when it gets here? I mean, like you said, it may have already gone off.

You must be logged in to post a comment.

Image of Peter Wilson

Peter Wilson

August 11, 2009 at 10:36 am

Unless it's 400 lightyears away and its spin-axis pointed right at us, believe we'll be okay.

You must be logged in to post a comment.

Image of Billy


August 11, 2009 at 10:41 am

Don't worry Jim, we need to be closer than a couple of hundred light years to be affected by the supernova. we just get to enjoy a fantastic show, whenever it blows that is.

You must be logged in to post a comment.

You must be logged in to post a comment.