At the heart of nebula Tc 1, located 10,000 light-years from us, hides a strange inverted question mark. This curious shape, immortalized by the James Webb Space Telescope, marks the location of a structure that astronomers are still struggling to explain.
This gas cloud is not ordinary: it contains very particular carbon molecules: fullerenes.
Credit: NASA / ESA / CSA / Western University, J. Cami
Fullerenes are gigantic hollow molecules shaped like soccer balls. Their name comes from architect Buckminster Fuller, famous for his geodesic domes. These molecules belong to the family of polycyclic aromatic hydrocarbons, organic compounds considered essential ingredients for life. The James Webb telescope now allows us to observe these structures with unprecedented precision.
Nebula Tc 1 originates from a dying star, similar to our Sun but much older. After exhausting its fuel, the star expelled its outer layers, forming shells of gas and dust. At the center, a glowing core called a white dwarf irradiates these gases and makes them shine. It is near this star that fullerenes were first spotted in 2010 by the Spitzer telescope, but James Webb's images now reveal much finer details.
One question remains: why are these molecules found only in a handful of planetary nebulae? Out of several hundred observed, only about a dozen contain them, and the reasons for this rarity remain unknown. Scientists suspect that the formation of fullerenes requires very specific conditions: an abundance of carbon, little oxygen, and high temperatures.
Another question concerns the infrared emission of fullerenes. No theoretical model correctly predicts their radiation, indicating that physico-chemical processes still escape us. Future analyses, using the James Webb's spectrograph, should explain these mechanisms. Researchers also plan to observe other nebulae containing fullerenes to compare the effect of different radiation fields.
Artistic concept of fullerene molecules in front of the Small Magellanic Cloud, imaged by the Spitzer telescope.
Credit: NASA/JPL-Caltech/MSSS
These observations do not merely reveal fullerenes; they also offer a detailed view of what happens during a star's collapse. Temperature, chemical composition, density, and gas movements are all parameters now measurable.
This first high-resolution image of a planetary nebula paves the way for a better understanding of the evolution of organic molecules in the universe.