A team of researchers have investigated the strength of dark matter scattered across the smallest galaxies in the Universe using stellar kinematics.
The self-interacting dark matter (SIDM) theory is one of the most prominent theories surrounding dark matter. It suggests that dark matter distributions in galactic centres become less dense because of the self-scattering of dark matter. However, supernova explosions, which occur toward the end of a massive star’s life, can also form less dense distributions. Without using stellar kinematics, it is challenging for astrophysics to distinguish whether it is the supernova explosion or the nature of dark matter that causes a less dense distribution of dark matter.
To pinpoint the cause of dark matter distribution, the lead author of the study, Professor Kohei Hayashi, and his team focused on ultra-faint dwarf galaxies. Here a few stars exist, rendering the influences of supernova explosions negligible. The ultra-faint dwarf galaxies are dark matter-dominated and have less active star formation history. Therefore, they are the ideal objects to test the SIDM, as their halo profiles are hardly affected by the baryonic processes.
Results from the dark matter research
The team published their findings in a paper entitled ‘Probing dark matter self-interaction with ultrafaint dwarf galaxies’ in Physical Review D, their results demonstrated that dark matter is dense at the centre of the galaxy, challenging the basic premise of SIDM. Images from the dwarf galaxy Segue 1 revealed high dark matter density at its centre, and that scattering is limited.
Hayashi said: “We discovered that the strength of dark matter is quite small, suggesting that dark matter does not easily scatter together. Our study showed how useful stellar kinematics in ultra-faint dwarf galaxies are for testing existing theories on dark matter. Further observations using next-generation wide-field spectroscopic surveys with the Subaru Prime Focus Spectrograph, will maximise the chance of obtaining dark matter’s smoking gun.”
