Light Echo of Eta Carinae Hints The Double Star System Had A Third, Now Dead, Sibling

Eta Carinae might have been a three-star system, but only two of them survived a massive stellar explosion 170 years ago.

Eta Carinae double star system surrounded by the Homunculus Nebula.
NASA, ESA, Hubble SM4 ERO Team

Eta Carinae might have been a three-star system, but only two of them survived a massive stellar explosion 170 years ago.

One of the brightest stars in our galaxy, Eta Carinae may not have always been a binary, reveals a new report from NASA’s Hubble Site. According to recent findings, the massive star explosion that put Eta Carinae on the map may have killed off a third star that was part of the original stellar system.

This puzzling star system — which last month was determined to be the source of cosmic rays that might even make it all the way to Earth, per an Inquisitr report — has long been studied by astronomers looking to find answers to how it came to be.

The massive binary sits 7,500 light-years away from our planet, in the Carina constellation, and is made up of two giant stars weighing 90 and 30 times more than our sun.

The mysterious binary is highly unstable and actually went through a colossal explosion in the 1840s, which made it the second brightest star in the entire night sky for several years. The same event, referred to as the “Great Eruption,” produced the hourglass-shaped dust cloud that envelops Eta Carinae and which has since become known as the Homunculus Nebula, pictured above.

But a new pair of studies published last week in the journal Monthly Notices of the Royal Astronomical Society argue that the double star couldn’t have survived the explosion from 170 years ago unless it there was something else involved in the equation.

The two studies document that the “Great Eruption” of Eta Carinae was almost as powerful as a supernova explosion and should have torn the star system to shreds. However, the binary miraculously survived, and the scientists think they figured out why. Their findings suggest that the two stars made it through the 19th-century explosion by killing off a third sibling and gorging on its energy.

When Eta Carinae erupted, the event released so much energy in space that it ended up hurling into the cosmos enough material to build the sun 10 times over. That material — which now makes up the Homunculus Nebula, notes Space.com — was ejected at incredibly high speeds, 20 times faster than expected.

In fact, according to the Gemini Observatory, the material ejected by Eta Carinae traveled so fast it was enough to cover the distance from here to the moon in just 20 seconds. This was the fastest ejecta astronomers have ever seen, both in Eta Carinae and in other massive stars, shows one of the studies, available on the Hubble Site.

The conclusion comes from recent measurements of the blast, enabled by a phenomenon known as light echo.

“Rather than heading straight toward Earth, some of the light from the outburst rebounded or ‘echoed’ off of interstellar dust, and is just now arriving at Earth,” the Hubble Site explains the light effect that helped uncover new things about Eta Carinae’s past.

Astronomer Nathan Smith of the University of Arizona, who led both studies, also chimed in on strange phenomenon.

“A light echo is the next best thing to time travel. 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.”

After observing the light echo coming from the explosion with the help of three Chile-based telescopes, the Gemini South, the Giant Magellan, and the Blanco telescope at the Cerro Tololo Inter-American Observatory, the scientists uncovered that Eta Carinae survived because “something must have dumped a lot of energy into the star in a short amount of time.”

“We see these really high velocities all the time in supernova explosions where the star is obliterated,” said Smith.

His team believes that this life-saving energy came from a third sibling of the two stars, which Eta Carinae devoured in the few short decades prior to the explosion, explains the second study, which can also be consulted on the Hubble Site.

This “brawl among three rowdy sibling stars” ended up destroying one of the stars and empowering the other two, while also causing the massive explosion that only left two stars standing.

“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,” said Smith.

What’s next in store for the tumultuous Eta Carinae? Most likely a real supernova explosion, sometime within the next half million years, or maybe even sooner, note the researchers.