Astronomers have gained remarkable insights into the mid-19th-century eruption of Eta Carinae, thanks to NASA’s Chandra X-ray Observatory. By analyzing Chandra’s snapshots taken over two decades (1999, 2003, 2009, 2014, and 2020) in collaboration with ESA’s XMM-Newton, they’ve tracked the expansion of this historic stellar event, reaching speeds of up to 4.5 million miles per hour. This collaborative effort underscores how different space observatories can illuminate changes in the universe occurring within human timescales.
Eta Carinae is a binary star system, with one star being a colossal 90 times the mass of the sun, and the other approximately 30 times its mass. In the 1800s, astronomers observed a colossal explosion in Eta Carinae, known as the “Great Eruption,” during which it expelled 10 to 45 times the sun’s mass. This expelled material formed dense spherical gas clouds, now known as the Homunculus Nebula, on either side of the two stars.
About five decades ago, researchers discovered a bright ring of X-rays encircling the Homunculus Nebula, which was previously studied using Chandra data. The new Chandra movie, along with a deep composite image, reveals intriguing details about Eta Carinae’s tumultuous past. Notably, it exposes the rapid expansion of the X-ray ring and an undiscovered faint X-ray shell surrounding it.
Michael Corcoran of NASA’s Goddard Space Flight Center, who led the study, describes this faint X-ray shell as the aftermath of the Great Eruption in the 1840s, providing valuable insights into Eta Carinae’s history.
The hypothesis is that material was ejected from Eta Carinae well before the Great Eruption of 1843, likely between 1200 and 1800, based on the motion of gas clumps observed in data from NASA’s Hubble Space Telescope. Subsequently, the high-speed blast wave from the Great Eruption propagated through space, colliding with and heating these clumps to millions of degrees, forming the bright X-ray ring. Now, this blast wave has extended beyond the initial bright ring.
Co-author Kenji Hamaguchi, a researcher at the University of Maryland, Baltimore County, and NASA Goddard, expressed his fascination, saying, “The shape of this faint X-ray shell is like an unexpected plot twist. It strongly indicates that the faint shell, the Homunculus, and the bright inner ring all originated from dramatic eruptions within the star system.”
Using data from XMM-Newton, the research team observed that the X-ray brightness of Eta Carinae has gradually dimmed over time, corroborating earlier findings from NASA’s Neutron Star Interior Composition Explorer (NICER) telescope aboard the International Space Station. To estimate the brightness of Eta Carinae in X-rays during the Great Eruption, the authors applied a simple model, factoring in the speed of the ejected material derived from the Chandra movie.
By combining this data with an estimation of the ejected gas volume, the researchers concluded that the Great Eruption likely involved two distinct explosions. The initial phase involved a rapid ejection of a small amount of fast, low-density gas, which generated the X-ray blast wave. This was followed by a slower ejection of denser gas that eventually formed the Homunculus Nebula.
Another intriguing theory, proposed by a team led by co-author Nathan Smith from the University of Arizona, suggests that the Great Eruption might have resulted from the merger of two stars in what was initially a triple star system. This merger could also explain the observed ring-like structure in X-rays, as it would cause material to be expelled in a flat plane.
Nathan Smith shared his excitement, stating, “The story of Eta Carinae keeps unfolding in unexpected ways. All the evidence points toward Eta Carinae surviving an immensely powerful explosion that would typically obliterate a star. I eagerly await the next batch of data to uncover more surprises that Eta Carinae has in store for us.”