Colossal bubble found in Milky Way; astronomers stunned as red supergiant unleashes eruption bigger than anything ever seen in our galaxy

Astronomers in Sweden have found a vast bubble of gas and dust surrounding a red supergiant star, a structure so enormous it dwarfs our entire Solar System thousands of times over.

The bubble, detected by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, spans 1.4 light-years across, roughly 9 trillion miles, and carries as much mass as our Sun. It surrounds a little-known star called DFK 52, buried deep in a stellar cluster near the center of our galaxy.

This is the largest bubble of its kind ever seen in the Milky Way, according to the study published this week in Astronomy & Astrophysics.

A survivor of a cosmic eruption

What makes this discovery remarkable is not just the bubble’s size, but the mystery of its survival story.

Astronomers believe the bubble was blasted out about 4,000 years ago, when DFK 52 shed part of its outer layers in a violent eruption. Normally, such an outburst could be a prelude to a supernova explosion, the spectacular death of a massive star. But somehow, DFK 52 endured.

“The bubble is made of material that used to be part of the star. It must have been ejected in a dramatic event,” said Elvire De Beck, co-author of the study. “In cosmic terms, this happened just a moment ago.”

Why the star is still alive is a puzzle. One explanation is that it may have a hidden stellar companion that helped drive the eruption, much like other unstable giant stars in the galaxy. If so, this would make DFK 52 an even more intriguing target for future research.

How astronomers spotted it

Using ALMA’s ability to capture invisible millimeter-wavelength light, the team traced molecules of carbon monoxide and silicon monoxide drifting in the bubble.

By measuring shifts in the light caused by the Doppler effect, astronomers could see which parts of the bubble were moving toward or away from Earth. The data confirmed the shell is still expanding, with sections traveling at tens of thousands of kilometers per hour.

To put the scale in perspective: If DFK 52 were as close to us as the famous red supergiant Betelgeuse, its bubble would appear nearly as wide in the sky as the full Moon.

A glimpse of the future

Red supergiants are the final stage in the lives of stars that begin their lives with more than eight times the mass of the Sun. They eventually explode as supernovae, scattering newly forged elements like carbon, oxygen, and iron into space, the raw materials for planets and life.

DFK 52’s bubble shows that some stars can lose enormous amounts of mass without immediately going supernova, a finding that challenges long-held theories of stellar evolution.

“If this is typical behavior for red supergiants, we may need to rethink how these stars live and die,” said Siebert.

Astronomers believe DFK 52 could still explode within the next million years, a blink of an eye in cosmic terms, making it a prime candidate for the Milky Way’s next great supernova.

The discovery is more than just a cosmic curiosity. Understanding how stars like DFK 52 shed mass helps scientists learn:

• How galaxies evolve - dying stars enrich the cosmos with heavy elements.
  
• How planets form - material expelled from giants like DFK 52 seeds future star systems.
  
• How stars die - observations like this reveal crucial steps leading up to supernovae.
  

As the ALMA array continues to probe the skies, astronomers are preparing deeper observations to look for a possible companion star and to track how the bubble evolves.