Astronomers have made an exciting discovery about what happens when two stars collide and merge, creating something called a “luminous red nova.” Using the James Webb Space Telescope (JWST), they found that this merger results in a massive star, similar to a red supergiant. This event also hints at how such collisions could have provided essential materials for life.
Most cosmic events happen over long periods, taking thousands or even millions of years. However, events like supernova explosions and star mergers occur rapidly—sometimes in just seconds to decades. This gives astronomers a chance to observe them in “real time,” making the study of these events particularly thrilling.
Andrea Reguitti, the leader of the research team at the Istituto Nazionale Di Astrofisica (INAF), highlighted that they’re witnessing the final moments of star systems before their collision. “These pairs of stars are evolving quickly, with changes happening over just a few months,” she explained.
To understand what remains after a luminous red nova fades, Reguitti’s team researched nine such events using archival data. These transients are brighter than classical novas, which occur when a white dwarf pulls in material from a companion star, and less bright than supernovas, which signal the end of massive stars. The stars involved in these mergers vary greatly in size, ranging from less than the mass of the Sun to 50 times more massive.
Among the nine cases studied, only two revealed their full story. One, called AT 2011kp, was spotted 25 million light-years away in 2011, while another, AT 1997bs, surfaced 31 million light-years away in 1997.
“By analyzing old images from major telescopes, we could study the stars before they merged,” Reguitti stated. “But we didn’t know what type of star would remain post-merger.” To reveal the nature of the remnants, the team observed the stars years later, after the merger. When stars merge, they eject a large amount of material, which obscures the view of what’s left behind. This ejected dust can be as much as 300 times the mass of Earth.
The JWST played a crucial role in this research. It captured infrared data in 2023 and 2024, along with visible light images from Hubble and the Spitzer Space Telescope. One of the targets, AT 2011kp, was studied 12 years after its merger, and AT 1997bs was observed 27 years later.
The findings revealed that the remnants resembled a red supergiant star, which could be hundreds of times larger than the Sun. If placed at the center of our solar system, this star would swallow the inner rocky planets and nearly reach Jupiter’s orbit. Despite their size, these stars had lower temperatures than the Sun, around 5,840 to 6,740 degrees Fahrenheit, compared to the Sun’s 10,300 degrees Fahrenheit.
Unexpectedly, the researchers found this new star type wasn’t as hot or compact as they anticipated. Team member Andrea Pastorello remarked, “We expected a star that was hotter and more stable.” The powerful JWST also allowed them to analyze the dust surrounding the new star, revealing it was mostly composed of carbon compounds like graphite, vital for life.
This discovery suggests that luminous red novas might significantly contribute to interstellar dust, potentially supplying the building blocks required for life, including the very carbon that makes up our bodies. “It’s a fresh way to reiterate that we are ‘stardust,'” Reguitti concluded.
This vital research will appear in the journal Astronomy & Astrophysics.
