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The mysteries of exoplanets and supermassive black holes: two Vici grants for Leiden Observatory

One unravels the origin of the largest black holes in the universe, the other investigates the influence of stellar wind on the atmosphere of exoplanets. Both Elena Maria Rossi and Aline Vidotto receive a Vici grant for their research into the mysteries of the universe. ‘I have no idea yet how we can explain this mystery.’

Elena Maria Rossi – What a flash of light reveals about the evolution of the universe

Rossi is on a quest to unravel the origin of supermassive black holes. ‘The largest black holes in the universe,’ she says. ‘They are at least a million times heavier than the sun. Only with extreme physical conditions could we explain their existence.’ Scientists use their imagination to come up with various scenarios, but which of the proposed scenarios is the one that actually occurs in nature? That's what Rossi wants to find out.

Elena Rossi

Supermassive holes versus galaxies

In this way, she hopes to learn more about the evolution of galaxies: the building blocks of our universe. Rossi: ‘Supermassive black holes play a crucial role in shaping galaxies. That’s why it’s important for us to understand how they form and evolve.’

Did they start big or did they grow enormously?

Does Rossi have a suspicion yet? ‘No! It's quite a deep mystery because the number of observations of these very first black holes is very scarce. You have to look back to the distant past of the universe.’ Some observations suggest that supermassive black holes were already gigantic from the start due to the direct collapse of gas in newly forming galaxies. ‘But it's unclear if those are just rare cases. Perhaps common supermassive black holes form in different ways.’

A flashy computer model is the biggest challenge

Rossi hopes to get hints by focusing on the ‘smaller’ cases: supermassive black holes that haven't grown as much as others. She does this by studying flares: light flashes coming from stars being torn apart and devoured by black holes. These light flashes tell us something about the mass of the black hole. For instance, a heavier black hole produces brighter flashes that also last longer. ‘The biggest challenge will be building accurate models to translate the light flashes we measure into mass. This requires advanced computer simulations, but fortunately, I have the required experience to incorporate all the relevant physics into such simulations. And I can rely on the NWO supercomputer Snellius for the necessary computing capacity.’

Aline Vidotto – Leaking atmospheres, how does that work?

Vidotto also faces challenging computer work. She will investigate the effect of stellar wind on the atmospheres of exoplanets. ‘Exoplanets are constantly exposed to stellar radiation and particles,’ she explains. ‘Especially for planets orbiting close to their parent star, this can cause their atmosphere to ‘leak’. Stellar radiation heats up the atmosphere, causing it to expand and making it more likely to escape. Stellar outflows, on the other hand, can cause pressure confinement that keeps the atmosphere in place. Together, these two processes determine how much atmosphere leaks away.’

Aline Vidotto

No atmosphere? So what?

Understanding these processes is important because an atmosphere can play a key role in the 'life' of a planet. Vidotto explains: ‘For some planets, the presence of an atmosphere can influence it’s potential to develop and host life. The loss of atmosphere can affect how fast they rotate. And that, in turn, affects the magnetic field.’ In extreme cases, a atmospheric escape can even lead to the complete loss of an atmosphere. ‘This could turn planets that were once gas giants into barren cores.’

Does Earth's atmosphere leak as well?

Yes, Earth’s atmosphere also leaks to space, but at a much lower rate than the planets Vidotto is studying in this project. No need to worry!

Using observations to their full potential

Vidotto will focus on planets orbiting very close to their parent star. ‘We already have some data showing that their atmospheres are leaking. Currently, most models of leaking atmospheres rely on only a few types of elements, mostly hydrogen and helium atoms. But the new measurements we are making with state-of-the-art observatories and instruments collect much more data. So, we are not yet fully tapping into the full potential of these new measurements.’ With this project, Vidotto and her colleagues aim to create a new 3D model that also considers other atoms besides hydrogen and helium.

Model of a leaking atmosphere on a magnetised close-in exoplanet. Credits: Carolan et al. 2021

A significant modeling task

The astronomers will model the various chemical elements separately. ‘We want to understand how different types of gas behave in the atmospheres of planets,’ Vidotto says. ‘So, the model must take into account things like magnetic fields and the outflow of matter and radiation from stars. By comparing the results of our model with observations, we hope to learn more about these leaking atmospheres of exoplanets.’

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