Using data from NASA’s Chandra X-ray Observatory, astronomers are tracking the expansion of the X-ray nebula around Eta Carinae, a luminous binary system that contains two massive stars (one is about 90 times the mass of the Sun and the other is believed to be about 30 times the Sun’s mass). In the middle of the 19th century, Eta Carinae was observed to experience a huge explosion that astronomers have dubbed the ‘Great Eruption.’
Composite images of Eta Carinae. Image credit: NASA / SAO / GSFC / Corcoran et al.
The ‘Great Eruption,’ a giant outburst from the binary system Eta Carinae in the middle of the 19th century, is one of the most impressive Galactic events in the modern history of astronomy.
Starting in 1838, the system brightened by about 4 mag in the visible band (becoming the second-brightest star in the sky, despite its distance of 7,500 light-years) before fading to obscurity.
This event was accompanied by a large ejection of material (between 10 and 45 times the mass of the Sun) which created the bipolar, dusty nebula today known as the Homunculus Nebula.
A bright ring of X-rays around the Homunculus was discovered about 50 years ago and studied in previous Chandra work.
The new movie from Chandra, plus a deep image generated by adding the data together, reveal important hints about Eta Carinae’s volatile history, including rapid expansion of the ring and a previously unknown faint shell of X-rays outside it.
“We’ve interpreted this faint X-ray shell as the blast wave from the Great Eruption in the 1840s,” said Dr. Michael Corcoran, an astronomer at NASA’s Goddard Space Flight Center.
“It tells an important part of Eta Carinae’s backstory that we wouldn’t otherwise have known.”
Because the newly-discovered outer X-ray shell has a similar shape and orientation to the Homunculus Nebula, Dr. Corcoran and his colleagues think both structures have a common origin.
The idea is that material was blasted away from Eta Carinae well before the 1843 Great Eruption — sometime between 1200 and 1800, based on the motion of clumps of gas previously seen in data from the NASA/ESA Hubble Space Telescope.
Later, the fast blast wave from the Great Eruption tore through space, colliding with and heating the clumps to millions of degrees to create the bright X-ray ring. The blast wave has now traveled beyond the bright ring.
“The shape of this faint X-ray shell is a plot twist in my mind,” said Dr. Kenji Hamaguchi, an astronomer at the University of Maryland and NASA’s Goddard Space Flight Center.
“It shows us that the faint shell, the Homunculus, and the bright inner ring likely all come from eruptions from the star system.”
“The story of Eta Carinae just keeps getting more interesting,” said Dr. Nathan Smith, an astronomer at the University of Arizona.
“All evidence is suggesting that Eta Carinae survived a very powerful explosion that would normally obliterate a star.”
“I can’t wait for the next episode of data to find out what other surprises Eta Carinae has in store for us.”
The results appear in the Astrophysical Journal.
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Michael F. Corcoran et al. 2023. The Expansion of the X-Ray Nebula Around η Car. ApJ 937, 122; doi: 10.3847/1538-4357/ac8f27
