22 min

With her sights set on the outermost limits of the universe

Already as a child, Kirsten Kraiberg Knudsen loved gazing at the stars. Since then, she has been gazing ever further out into space. As a Wallenberg Academy Fellow, she is studying quasars at the outermost limits of the universe to try to understand how galaxies form and develop.

Kirsten Kraiberg Knudsen

Professor of Astronomy

Wallenberg Academy Fellow/Wallenberg Scholar

Chalmers University of Technology

Research field:
Formation and development of galaxies

Kirsten Kraiberg Knudsen describes herself as a person who doesn’t always have both feet planted firmly on the ground. She likes things that are unclear and difficult to understand at times. Already as a 9 or 10 year old, she began to turn her gaze upward. Initially, it was mostly because she thought it was romantic to gaze at the stars, but quite soon she began to reflect on what was really out there beyond the Earth.

“I remember when Halley’s Comet passed by the Earth in 1986. It was a huge thing for me. That was when I really began to understand that space is much, much larger than the Earth and our own solar system. It was at that moment that my fascination with space was really born, and I decided to become an astronomer.”

The pace is rapid – many words and much laughter – when Kirsten Kraiberg Knudsen tells the story of her journey from Jutland, where she was born, via elementary school and university studies in Copenhagen, a doctoral studentship in the Netherlands, post-doctoral studies in Germany and to the for research position she now holds at Onsala Space Observatory outside Gothenburg. She is the first academic in her family, but one thing that she has taken with her from home is that the chances of getting a job where you have access to new ideas, can be creative, and also have influence, increase if you are prepared to move.

“I would not be happy knowing that I would be doing the same thing every day for the next 50 years. When I write applications for big research grants, I try always to think about where I want to be and what I want to be doing in five years, for example. What are the next step, and the next, and the next? I look to the future and formulate my vision.”

Spiral galaxies and elliptical galaxies

The Milky Way is our galaxy, our home in the universe. It is a big, old galaxy with many billions of stars. The Milky Way is a spiral galaxy with a great deal of gas, and when the gas is compressed, new stars form. There are many other galaxies in the universe: a few that are larger than the Milky Way and others that are smaller; some just like the Milky Way are spiral galaxies; and others are elliptical galaxies that have many old stars but do not have gas, which means that no new stars are formed. Common to all large galaxies is that they have gigantic black holes at their centers.

"First of all, it is personal recognition, secondly I think it is important to provide support for basic research, and thirdly I can now employ more researchers which will give masses of new energy to my research group."

Kirsten Kraiberg Knudsen’s research is about how galaxies form and develop. A crucial question in this research field is how the growth of a galaxy is linked with the growth of its black hole. Does it occur simultaneously, or does the black hole develop first and the galaxy later, or is it the other way round?

Of particular interest for her research are quasars, which are more common far away from the Earth. Far away means that what we see from the Earth today happened long, long ago, when the universe was only a few billion years old. Quasars are extremely luminous, active galactic nuclei with central black holes that grow very rapidly by sucking up enormous amounts of material from their surroundings. The radiation is the result of gas approaching the black hole being heated up and emitting enormous amounts of energy via beaming jets.

“We understand that there’s a lot happening on these occasions, but we are not really sure what is happening. It may be a matter of two things: either gas is being compressed and a mass of new stars are being formed; or the jets take a lot of gas with them out of the galaxy and consequently there is no gas with which to form new stars. We believe that this is a course of events that is important in being able to understand how galaxies form and develop.”

Another way to study how galaxies form and develop is to study the relationship between how many old and new stars there are in different galaxies.

“A question we ask ourselves is whether it is possible to predict why some galaxies become spiral galaxies and others become elliptical galaxies. To use a metaphor, it is like studying children at different ages to understand why adults are the way they are today.”

Radio astronomical data

Kirsten Kraiberg Knudsen’s studies are based on observations from the Atacama Large Millimeter/submillimeter Array (ALMA), which is a new telescope being built in the Chilean desert. The telescope gathers radio astronomical data with wavelengths in the millimeter range, which makes it possible to distinguish between old and new stars, and also enables studies of quasars.

“Our research is important for the simple reason that we are curious about how the universe works. The technological development is important for many other fields, and astronomy contributes, and has always contributed, to how we humans understand and relate to the world around us. It’s also fun: for example, it’s absolutely fantastic when we discover a new galaxy that we haven't seen before.”

Text Anders Esselin
Translation Semantix
Photo Magnus Bergström



Milky Way
Our home galaxy, the Milky Way is an old galaxy, more than 13 billion years, which is almost as old as the universe itself (13.7 billion years). The Milky Way is 100,000 light years wide and our Sun is 25,000 light years away from the center of the Milky Way.

Spiral galaxy
A collection of a relatively large number of stars (10-100 billion), where the majority is in a flat, discus-like state. A spiral galaxy contains a lot of gas, and when the gas is compressed, new stars form.

Elliptical galaxy
A collection of stars whose movements are largely random. Has many old stars but no gas, which means that no new stars are formed.

Radio astronomy
The branch of astronomy that studies radio waves which come to Earth from processes in the universe. Radio waves have a much longer wavelength than the light waves which more conventional optical astronomy studies.

Extremely luminous, remote, active galactic nuclei with central black holes that grow very rapidly by sucking up huge amounts of material from their surroundings.