A combination of telescopes reveals hidden star formation in the early universe
Galaxies in the early universe contain more dust and hidden star formation than previously thought. That's what Ivana van Leeuwen concludes in her PhD research, where she combines data from various telescopes to create a more complete picture.
Astronomers often measure star formation in galaxies using ultraviolet light, which originates from young stars. But that does not provide a full picture, Van Leeuwen explains: ‘If there is dust in a galaxy, that light is absorbed. It then appears as if fewer stars are being formed than is actually the case.’
To circumvent this problem, she combined ultraviolet measurements with infrared observations from the ALMA telescope. ‘Dust absorbs ultraviolet light but re-emits it in the infrared. By combining those two wavelengths, you can better determine what is really happening.’
‘The idea that we can look so far back in time remains exciting’
A look at the young universe
Van Leeuwen has always had a wide range of interests – from ancient Egypt to physics. Eventually, she came to Leiden to study astronomy and stayed for her PhD.
Her research focuses on galaxies at extremely great distances. Because their light takes billions of years to reach Earth, they offer a glimpse into the early universe. ‘You are essentially looking back in time and seeing how galaxies form,’ she explains. But it is precisely these distant galaxies that are difficult to study. Because they are so far away from us, they appear very faint and are at the limit of what telescopes can observe.
A wealth of information in the archives
For her research, Van Leeuwen primarily used existing data from the archives of various telescopes – from the ALMA telescope, but also from the Hubble and James Webb space telescopes. ‘Sometimes a dataset contains more information than it was originally intended for,’ says the PhD candidate. Occasionally, that yielded unexpected insights. Some datasets turned out to contain previously unnoticed galaxies.
Part of her PhD consisted of developing new analytical methods. That was challenging, she explains: ‘You have no frame of reference, no scientific articles with a step-by-step plan to follow. That takes more time at the beginning, but it is also very educational.’
More dusty galaxies than expected
The research shows that part of star formation remains hidden behind dust. Remarkably, this also occurs in the early universe, where less dust was expected. ‘These galaxies are young and have had less time to form dust,’ says Van Leeuwen. ‘Yet we see that quite a lot of dust can already be present.’ That result raises new questions about how quickly dust can be produced in a galaxy and how galaxies develop. ‘We are finding more dusty galaxies than we had anticipated.’
From the furthest galaxies to closer to home
After her PhD, Van Leeuwen started working at the KNMI as a space weather specialist. There, she investigates the influence of solar activity on Earth. ‘I really wanted to do something with a more direct link to society,’ she says. ‘I still do a lot of programming, but there is also a policy component involved, for example.’
Nevertheless, her fascination with the universe remains a driving force. ‘The idea that we can look so far back in time remains exciting. And the fact that surprises still emerge only makes the research more interesting.’
PhD supervisors: Rychard Bouwens and Jacqueline Hodge. Van Leeuwen defends her thesis titled 'Hidden star formation in the early Universe' on April 9.
Header photo: The ALMA telescope in Chile with the Milky Way in the background. Dust blocks the light and causes dark spots, similar to the galaxies Van Leeuwen studied.