History's Fastest Jettisoned Gas From Stellar Outburst Discovered Originating From Superstar Eta Carinae

Astronomers have discovered a surprisingly speedy bit of cosmic activity still impressing researchers despite the event being almost 200 years old.  

Approximately 170 years ago, a stellar eruption sped away from our massive (and incredibly unstable) neighboring superstar Eta Carinae. Now, a team from the University of Arizona in conjunction with NASA has determined this event holds the record for the fastest jettisoned gas ever measured from a star -- without the star self-destructing. 

Astronomers Blown Away by Historic Stellar Blast
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— Gemini Observatory (@GeminiObs) August 2, 2018

A star that beat the odds

The energy from the blast would be equivalent to that of a traditional supernova explosion, events that often leave behind only the corpse of a star. However, this double star system stayed relatively intact. 

For the last seven years, University of Arizona's Nathan Smith and the Space Telescope Science Institute's Armin Rest determined how powerful the blast was by looking at echoes of light surrounding Eta Carinae.

Light echoes work similarly to audio echoes. The arriving light signal of the reflection has had a time delay due to the speed of light. So in the case of Eta Carinae, researchers had to wait for the "Great Eruption" of the mid-1800s to echo in the 'modern' era. 

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"A light echo is the next best thing to time travel," Smith said. "That's why light echoes are so beautiful. They give us a chance to unravel the mysteries of a rare stellar eruption that was witnessed 170 years ago, but using our modern telescopes and cameras."

"We can also compare that information about the event itself with the 170-year old remnant nebula that was ejected. This was a behemoth stellar explosion from a very rare monster star, the likes of which has not happened since in our Milky Way Galaxy," added Smith

The second brightest star in the sky

The Great Explosion also allowed Eta Carinae to become the second brightest visible star in the sky. The expelled material is known as a Homunculus, and the remnants remain visible even to amateur telescopes. 

"We see these really high velocities all the time in supernova explosions where the star is obliterated," Smith noted. However, this particular star survived, and the researchers found themselves exploring new territory.

"Something must have dumped a lot of energy into the star in a short amount of time," said Smith. The astronomers hope understanding this event could explain a wide array of observable events that once seemed mysterious.

It could also give astronomers a much better understanding of binary star systems and how they function together. "Understanding the dynamics and environment around the largest stars in our galaxy is one of the most difficult areas of astronomy," said Richard Green, Director of the Division of Astronomical Sciences at NSF, the major funding agency for Gemini.

"Very massive stars live short lives compared to stars like our Sun, but nevertheless catching one in the act of a major evolutionary step is statistically unlikely. That's why a case like Eta Carinae is so critical, and why NSF supports this kind of research," added Green.

Chris Smith served as Head of Mission at the AURA Observatory in Chile, where the astronomers conducted most of their observations. Smith said the discovery is one for the galactic history books.

"I'm thrilled that we can see light echoes coming from an event that John Herschel observed in the middle of the 19th century from South Africa," he said. "Now, over 150 years later we can look back in time, thanks to these light echoes, and unveil the secrets of this supernova wannabe using the modern instrumentation on Gemini to analyze the light in ways Hershel couldn't have even imagined!"

The results of the studies were published in two papers in the journal Monthly Notices of the Royal Astronomical Society.