In Irsic et al. (2023, PRD in press, arXiv: 2309.04533), we have conducted a study on a mysterious type of matter called warm dark matter (WDM). We used data from powerful telescopes (VLT/UVES and Keck/HIRES) to look at light from distant quasars, and we analysed this together with detailed computer simulations of the Universe performed with DiRAC/Cambridge Data Intensive.  The lighter the WDM particle, the larger the smoothing effect on the large-scale structure of the cosmic web. As shown in Fig.1, the WDM simulations with smaller particle mass (2 keV) show a smoother distribution for the gas density in the structures of the cosmic web, compared to models with larger mass (4 keV) or the standard dark matter model of cold dark matter (CDM).  On comparing the quasar absorption data to our computer simulations, we exclude WDM particles with masses >5.7 keV at 2𝜎.   This discovery is an improvement from previous findings, thanks to a combination of a larger and more accurate dataset, and novel modelling techniques. The study helps us understand more about the nature of dark matter, a substance that makes up a significant part of the universe but is still not fully understood by scientists. 

Figure 1: Slices through our DiRAC/Cambridge Data Intensive computer simulations of structure formation (96 million light years on each side) showing the gas density distribution for four different dark matter models including a standard cosmological dark matter model CDM (top left), and several WDM models varying the WDM particle mass from 4 to 2 keV. The lower the WDM particle mass, the smoother the gas density in the simulations. The results are shown at z=4.2, when the Universe had an age of 1.4 billion years, or roughly 10% its current age.