In the mid-1800s, astronomers surveying the night sky in the Southern Hemisphere noticed something strange: For a few years, a previously inconspicuous star named Eta Carinaebegan to grow and brighten, eventually eclipsing all other stars except Sirius, before fading away over the next decade, becoming too faint to see with the naked eye.
What happened to this star? Did 19th century astronomers witness a type of supernova, a star ending its life in a cataclysmic explosion? “Not quite,” replies Megan Kiminki, a doctoral student in the Department of Astrophysics at the University of Arizona. “Eta Carinae is what we call “a supernova impostor”. The star is still there.
The star is famous today and is among the objects in the universe known for their strange beauty. An hourglass-shaped cloud, billowing with glowing gas and dust, engulfs the star and its companion; the Homunculus Nebula, this cloud made up of stellar matter launched into space during the Great Eruption of the 1900s drifts away at more than 3 million kilometers per hour.
Carefully analyzing images captured by Hubble, researchers were surprised to discover that the ‘Great Eruption’ was actually the latest in a series of massive explosions launched since the 13th century. The rate of gas expansion in the outer mantle of the nebula was far too slow and could not be the remnants of the last explosion. By analyzing the outer mantle, the researchers then distinguished two eruptions, one occurring in the middle of the 13th century, and the second in the middle of the 16th century.
“From the first reports of its brightness in the 19th century, to the most recent data obtained by modern telescopes, Eta Carinae continues to thwart us,” explains one of the researchers. “We were looking for the underlying cause of its eruption, and now we find that there were several previous eruptions. It’s a bit like reconstructing the history of a volcano’s eruption by discovering ancient lava flows.
Although the glowing gases of the Homunculus Nebula prevent astronomers from getting a clear look at what is really going on inside, we do know that Eta Carinae is a binary system of two very massive stars orbiting the Earth. other every 5.5 years. Both are much larger than our sun and one of them is nearing the end of its life. By comparison, if you were to replace our Sun with the larger of the two stars, Earth would be swallowed up. March too.
Even today astronomers are trying to understand the cause of these frequent overflows. “We don’t really know what’s going on with Eta Carinae,” explains one of the researchers. “But the fact that the star has exploded at least three times shows us that these flares must be the result of a recurring process, and it is very unlikely that each flare is caused by a different mechanism. »
The fact that the underlying mechanism that caused the 19th century flare was not a one-time event makes the task harder for scientists, but it’s also a critical piece of the puzzle of how very massive stars die. Stars like Eta Carinae apparently refuse to go away quietly in their sleep. We don’t know why yet, but we have some leads.
Eruptions ofEta Carinae give us a unique insight into the last unstable phases of a very massive star’s life. Researchers have recently identified a subclass of supernova explosions that appear to suffer violent eruptions shortly before the final explosion. Eta Carinae may well be our closest example.
Beauty is about a hundred times more massive, a thousand times larger and a million times more luminous than the Sun. An extremely rare monster, as there are only a few dozen per galaxy. This supergiant and unstable star is therefore on the verge of explosion. This will happen tomorrow. But because it takes 7,000 years for light to reach us, a lot could have happened during that time. Eta Carinae may have breathed its last already, but we won’t know for 7,000 years.