The elusive 'dark matter' can move out of the centre of a galaxy as a result of star formation, according to a new study by scientists from the University of Surrey, Carnegie Mellon University and ETH Zürich.
This is the first time that scientists have found an observational evidence of the effect known as 'dark matter heating'. They believe the findings could provide new clues on the nature and composition of one of the most mysterious substances in the universe.
Dark matter is an invisible material that is believed to make up about 85 per cent of all the matter in the universe. This hypothetical material is also thought to account for about 25 per cent of the total energy density in the universe.
Its presence has never been observed directly and it is predicted only on the basis of its gravitational effect on other objects in the universe. Most scientists believe that dark matter is ubiquitous in the universe and has had a strong influence on the evolution and structure of the universe.
Some past studies have revealed that at the time of star formation, strong winds can sweep gas and dust away from the centre of the galaxy. This causes a decrease in mass at galaxy's centre which, in turn, decreases the amount of gravitational pull experienced by the remaining dark matter. Due to less gravitational pull, the dark matter acquires energy and moves away from the centre, an effect known as 'dark matter heating'.
In the current research, scientists studied 16 nearby dwarf galaxies with different histories of star formation. The team measured the amount of dark matter at the centres of these galaxies and found that the centres of galaxies that had long ceased forming new stars had higher concentration of dark matter than those that were still forming stars.
The finding supports the theory that the older galaxies show less dark matter heating. On the other hand, younger galaxies continue to create new stars, thus enabling the dark matter to gain energy and move away from the centre.
"We found a truly remarkable relationship between the amount of dark matter at the centres of these tiny dwarfs, and the amount of star formation they have experienced over their lives," said Professor Justin Read, head of the Department of Physics at the University of Surrey, and the lead author of the study.
"The dark matter at the centres of the star-forming dwarfs appears to have been 'heated up' and pushed out."
Based on the findings of the study, the researchers conclude that dark matter is a cold, collisionless fluid that can be kinematically moved around.
The findings of the study are published in the journal Monthly Notices of the Royal Astronomical Society.
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