✨ Luminous red novas: a star merger seen in real time

When two stars collide, their impact can give rise to a brilliant explosion known as a luminous red nova. To determine what stellar object remains after such a merger, astronomers used the James Webb Space Telescope (JWST). Their unexpected observations challenge several previous assumptions.

These stellar mergers are transient events where two stars come together to form a single object, producing a brief but intense burst of light. Unlike other cosmic phenomena that span millennia, luminous red novas unfold in just a few months. This rapidity offers scientists an opportunity to study the phenomenon from start to finish, in real time.


To understand the nature of the remnants of these explosions, researchers examined archived data on nine similar events. Among this selection, only two of them, AT 2011kp and AT 1997bs, could be observed long after the merger, notably thanks to the Hubble and Spitzer telescopes. This step was essential because the dust ejected during the collision initially obscures the newly formed object.

In this context, JWST played a decisive role by capturing infrared images of these objects. Its observations revealed a star resembling a red giant, whose immense size can reach several hundred times that of the Sun. Surprisingly, its surface temperature proved lower than models had suggested, ranging between 3,200 and 3,700 degrees Celsius, well below that of our own star.

Beyond the discovery of this giant star, astronomers also analyzed the composition of the surrounding dust. Their analyses show it is rich in carbon compounds, such as graphite. As these elements are essential for life, this result indicates that such stellar mergers may have contributed to supplying the materials necessary for life's emergence on Earth.

JWST's ability to see through dust clouds allowed observation of the object directly after the initial explosion. These results are set to be published soon in the journal Astronomy & Astrophysics.