Free Astronomy Magazine May-June 2022

23 MAY-JUNE 2022 ASTRO PUBLISHING by supermassive black holes and found at the centre of some galax- ies. These black holes feed on large volumes of cosmic dust and gas. Be- fore it is eaten up, this material spi- rals towards the black hole and huge amounts of energy are re- leased in the process, often outshin- ing all the stars in the galaxy. Astronomers have been curious about AGNs ever since they first spotted these bright objects in the 1950s. Now, thanks to ESO’s VLTI, a team of researchers, led by Violeta Gámez Rosas from Leiden Univer- sity in the Netherlands, have taken a key step towards understanding how they work and what they look like up close. The results are pub- lished in Nature . By making extraordinarily detailed observations of the centre of the galaxy Messier 77, also known as NGC 1068, Gámez Rosas and her team detected a thick ring of cos- mic dust and gas hiding a super- massive black hole. This discovery provides vital evidence to support a 30-year-old theory known as the Unified Model of AGNs. Astronomers know there are differ- ent types of AGN. For example, some release bursts of radio waves while others don’t; certain AGNs shine brightly in visible light, while others, like Messier 77, are more subdued. The Unified Model states that despite their differences, all AGNs have the same basic structure: a supermassive black hole sur- rounded by a thick ring of dust. According to this model, any differ- ence in appearance between AGNs results from the orientation at which we view the black hole and its thick ring from Earth. The type of AGN we see depends on how much the ring obscures the black hole from our view point, com- pletely hiding it in some cases. Astronomers had found some evi- dence to support the Unified Model A ctive galactic nuclei (AGNs) are extremely energetic sources powered by su- permassive black holes. This short video provides insights into these peculiar objects by showcasing a new discovery on the AGN at the centre of the Messier 77 galaxy. [ESO] before, including spotting warm dust at the centre of Messier 77. However, doubts remained about whether this dust could completely hide a black hole and hence explain why this AGN shines less brightly in visible light than others. “The real nature of the dust clouds and their role in both feeding the black hole and determining how it looks when viewed from Earth have been central questions in AGN stud- ies over the last three decades,” ex- plains Gámez Rosas. “Whilst no single result will settle all the ques- tions we have, we have taken a major step in understanding how AGNs work.” The observations were made possi- ble thanks to the Multi AperTure mid-Infrared SpectroScopic Experi- ment (MATISSE) mounted on ESO’s VLTI, located in Chile’s Atacama Desert. MATISSE combined infrared light collected by all four 8.2-metre telescopes of ESO’s Very Large Tele- scope (VLT) using a technique called interferometry. The team used MA- TISSE to scan the centre of Messier 77, located 47 million light-years away in the constellation Cetus. “MATISSE can see a broad range of infrared wavelengths, which lets us see through the dust and accurately measure temperatures. Because the VLTI is in fact a very large interfer- ometer, we have the resolution to see what’s going on even in galax- ies as far away as Messier 77. The images we obtained detail the changes in temperature and ab- sorption of the dust clouds around the black hole,” says co-author Wal- ter Jaffe, a professor at Leiden Uni- versity. Combining the changes in dust temperature (from around room temperature to about 1200 °C) caused by the intense radiation from the black hole with the ab- sorption maps, the team built up a detailed picture of the dust and pinpointed where the black hole must lie. The dust — in a thick inner ring and a more extended disc — with the black hole positioned at its centre supports the Unified Model. The team also used data from the Atacama Large Millimeter/submil- limeter Array, co-owned by ESO,