NASA’s James Webb Space Telescope leaves the world stunned not only with its mesmerising pictures of the cosmos, but also by unravelling mysteries of the universe. The JWST, also called Webb, detected organic molecules in active galaxies swirling around supermassive black holes. In a first-of-its-kind study, researchers at Oxford University investigated tiny dust molecules in the nuclear region of active galaxies, using early observations from Webb. This is the first United Kingdom-led study to use spectroscopic data from Webb’s MIRI. One of the greatest challenges in modern astrophysics is understanding how galaxies form and evolve, something the new study addresses.
The findings were recently published in the journal Astronomy & Astrophysics.
What are polycyclic aromatic hydrocarbons? What role do they play in the cosmos?
Polycyclic aromatic hydrocarbons (PAHs) are tiny dust molecules and among the most widespread organic molecules in the universe. Also, PAHs are important astronomical tools. PAHs are considered to be fundamental building blocks of prebiotic compounds, which may have played an important role in the origin of life. Since PAH molecules produce extremely bright emission bands in the infrared region when they are illuminated by stars, they enable astronomers to not only trace star-formation activity, but also to use them as sensitive barometers of the local physical conditions. In other words, PAHs help astronomers determine physical conditions around the molecules.
ALSO READ | What Are The Stages In The Life Cycle Of A Supermassive Black Hole? Study Gives Answers To Mystery
Webb’s instruments used to study active galaxies
For the first time, Webb’s cutting-edge instruments were used to characterise PAH properties in the nuclear region of three luminous active galaxies. A galaxy hosting an active galactic nucleus is called an active galaxy. An active galactic nucleus is a small region at the centre of some galaxies that is extremely luminous, and emits so much radiation that it can outshine the rest of the galaxy altogether. Active galactic nuclei are now understood to be active supermassive black holes that emit bright jets and winds, and shape their galaxies.
ALSO READ | Astronomers Detect Heaviest Element Ever Found In An Exoplanet Atmosphere
What the study found
The researchers conducted the study using spectroscopic data from Webb’s MIRI, which measures light in the wavelength range of five to 28 microns. After obtaining the data, the researchers compared the observations with theoretical predictions for these molecules.
Previous studies had predicted that PAH molecules would be destroyed in the vicinity of the black hole at the centre of an active galaxy. However, the study found that PAH molecules can actually survive in the black hole at the centre of an active galaxy, even at the regions where very energetic photons could potentially rip these molecules apart. A possible reason why PAH molecules are protected is that they are surrounded by large amounts of molecular gas in the nuclear region.
However, the supermassive black holes at the heart of galaxies had a significant impact on the properties of PAH molecules, even if they were not destroyed. The study found that the proportion of larger and neutral molecules became greater. This suggests that more fragile, small and charged PAH molecules may have been destroyed.
ALSO READ | In A First, James Webb Space Telescope Captures ‘Tree Rings’ From Rare Type Of Star System
What is next?
In a statement released by University of Oxford, Dr García Bernete, one of the authors on the paper, said the scientists will now analyse a larger sample of active galaxies with different properties, enabling them to better understand how PAH molecules survive and which are their specific properties in the nuclear region.
The authors conclude that the results provide evidence that active galactic nuclei have a significant impact on the ionisation state, and probably the size of PAH molecules.