Susanne Aalto
Susanne Aalto, Professor of Radio Astronomy at Onsala Space Observatory. ​​
Photograph: Anna-Lena Lundqvist. 

Susanne Aalto, this year’s William Chalmers lecturer

​How gigantic black holes in the centres of galaxies grow is one of the key questions of life, the universe and everything. And searching for an answer to that question is something that Susanne Aalto, a professor of radio astronomy, devotes her working life to. 
“The black heart of the galaxies – where molecules feed monsters” is the title of this year’s William Chalmers lecture to be given by Aalto, which is derived from studies that her research team is conducting on what is contained at the centre of galaxies. With the aid of the ALMA telescope in Chile and its array of 66 synchronised antennas, they discovered something new in the universe – galaxies whose central parts are so enshrouded in dust and gas that not even an X-ray can pass through them. In visible light they look dull, without any signs of interesting activity. But measurements in the radio spectrum reveal hitherto unknown and very rapid growth behind the dust curtains.
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“What is actually hiding in there? It’s difficult to see since the dust absorbs visible light – it’s rather like looking at a lamp through a blanket. Radio waves can, however, pass through the dust and give us an idea of what is happening in there, but it’s more tricky than I first thought.”

Aalto suspects that it could be rapidly growing black holes. Supermassive black holes are generally assumed to have grown when the universe was considerably younger. But Aalto believes that this can also happen now, but that the growth mainly takes place behind vast quantities of dust.

“Supermassive black holes grow along with their host galaxy. But it’s not that they just swallow up everything that comes their way. The fact is that black holes, like awkward kids at the dinner table, are quite difficult to feed. They control their growth and a lot of matter that flows towards them is flung out in winds or narrow jets. The question is how the enormous galaxy and the tiny black hole – imagine a billion suns tucked away in a thimble – communicate with one another? How does the interaction work when they grow together? This is a key to understanding the development of galaxies, which is in turn an important piece of the puzzle for the development of the entire universe. My dream discovery is to solve this puzzle,” says Aalto.

In order to try to see inside the dust curtains her research team, together with an international team, have developed a method by which they use molecules in the dust as a measuring instrument. The molecules absorb energy-rich infrared light from the interior of the galaxy and then send out corresponding energy in the form of radio waves that can force their way out through the dust. By studying radio waves Aalto and her colleagues have started to piece together the puzzle from the outside to find answers about the processes that have given rise to the energy-rich infrared light. A growing black hole, or perhaps a form of extreme star formation that we have never seen before?

Welcome to the lecture

The William Chalmers Lecture is to be given in Swedish on 4 November at 18.00 in the RuNan conference hall, Students’ Union Building (Kårhus) , Chalmers. You can also follow the presentation live via YouTube. Read more about the lecture and register for it

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Page manager Published: Fri 05 Nov 2021.