Astronomers analyzed the latest data returned by the Webb Space Telescope and found unexpected surprises. Organic molecules originally thought to be destroyed by the intense high-energy radiation around the black hole at the center of the galaxy are still visible under the mid-infrared camera of the Webb Space Telescope.
A mid-infrared image of NGC 7469 taken by the Webb Space Telescope.
Polycyclic aromatic hydrocarbons (PAHs or PAHs for short) are hydrocarbons with a cyclic structure with more than 100 chemical structural formulas. They are often found in coal and tar deposits in nature, and are often seen in incomplete combustion of organic matter. Many PAHs are Confirmed to be a carcinogen. However, in astronomy, interstellar PAH molecules are affected by the radiation of young stars, and emit specific wavelength spectral lines in multiple infrared bands. They are often used by astronomers to track galaxy star formation activities, or star formation rates near active galactic nuclei (AGN).
▲ Examples of polycyclic aromatic hydrocarbon structures. (Source: US Toxicology Agency ATSDR)
However, astronomers have limited understanding of how PAH molecules are affected by radiation. Previous studies predicted that PAH molecules near the center of active galaxies would be destroyed by the strong radiation of black holes. The camera (MIRI) observed the core regions of three galaxies NGC 6552, NGC 7469 and NGC 7319 and found that these organic molecules can survive in extremely harsh conditions. Even if these PAH molecules survive, the observations still show that the supermassive black hole at the center of a galaxy has a significant effect on the molecular properties. The astronomers found that neutral and large PAH molecules survived in greater proportions, and that the weaker, smaller charged PAH molecules appeared to be more easily destroyed.
▲ The Webb Space Telescope observed the fine structure of the core of NGC 7469 in only 6 arcseconds in the mid-infrared. (Source: A&A)
The discovery has prompted astronomers to re-examine methods for estimating star formation rates using PAH molecules, but it’s not bad news. Thanks to the ultra-high resolution of the Webb Space Telescope, astronomers were able to observe, for the first time, how PAH molecules survive and their specific properties in the core region of a galaxy. This knowledge could help improve PAH’s models that describe the amount of star formation in galaxies and further help us understand how galaxies evolve over time. The detailed results were published in the journal Astronomy & Astrophysics (A&A).
(This article is reproduced with permission from the Taipei Planetarium; source of the first image: Credit: ESA/Hubble & NASA, A. Evans, R. Chandar, CC BY 4.0, via Wikimedia Commons)
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