Shedding light on the dark side of the universe
It must be there. We just cannot see it: mysterious dark matter and dark energy in the universe. Henk Hoekstra is one of the many cosmologists who would love to know what exactly these substances consist of. He has received a European research grant of 1.3 euro million to find out.
Our universe is expanding, and since the end of the 1990s, thanks to a study of distant supernovae, we have known that this process is speeding up. Cosmologists believe this is due to so-called ‘dark energy’ that pushes matter in the universe apart like a kind of anti-gravity. However, at present no one knows what this dark energy is or what causes it.
Hoekstra believes there is clearly something fundamentally wrong in our knowledge of the universe. As the problem of dark energy is relatively new, the experiments that cosmologists can carry out cannot yet lead to a solution for this enigma. The existing instruments therefore have to be improved as quickly as possible. Hoekstra refers to this as a ‘transition stage’ in the study of dark energy.
The effect of a gravitional lens. A large cluster of billions of stars work like a lens, distorting the image. Arcs of light and red and blue colours are the result of this distortion.
With the ERC Grant, a European research grant of EUR 1.3 million, Hoekstra hopes to make progress in terms of experimentation. He is focusing on a relatively new piece of optical technology, the gravitational lens. This is an effect that occurs if you look at an object that is more or less in line with a strong field of gravity. ‘Light is bent by matter in the universe,’ Hoekstra explains. ‘We look at galaxies but as light bends this means that the shape we see is different from the reality.’
The trick is to use observations to determine precisely what this difference, which is very subtle, is. This will say something about the distribution of energy and matter in the universe. And it will not just throw more light on dark energy but also on dark matter, the other secret of the cosmos. The great majority of matter in the universe is invisible to us, but we can tell from the movements of galaxies that it must be there.
Evidence for dark matter: the purple light in this image could be caused by dark matter.
Hoekstra is using the grant to minimise measuring errors in the gravitational lens method: ‘Any number of aspects of it need to be improved. For example, we need to be able to measure the distance to galaxies properly, to determine what galaxies really do look like and to correct for instrumental effects. In five years time I hope that the measurements will be the best that science has to offer at that time.’
It is only then that the search for answers will actually begin. Hoekstra is working on a project to launch a satellite into distant space that will be able to make much better measurements than is possible from the ground, which is how they are currently made. ‘We can use the knowledge that we will gather in the coming years for this project,’ says Hoekstra. Maybe it will then become clear whether our current understanding of gravity in the universe will need to be given a rethink.'