Miika Pursiainen

I am a Postdoctoral Research Fellow, specialising in understanding peculiar extragalactic transients such as Supernovae (SNe). 

My work largely revolves around understanding how interaction with Circumstellar Material (CSM) affects the observables of the SNe themselves. We know that massive stars (> 8 Solar Masses) often exhibit elevated mass-loss in the last decades/centuries before their explosion as SNe. As the ejecta of the explosion collides with this lost CSM, the kinetic energy of the SN ejecta is converted into radiation, resulting in large diversity in the SNe. Detailed observation of such SNe allow us to decipher how the mass was lost in the first place, and ultimately what kind of star exploded.  

In some situations a confined CSM disk, likely coming from some kind of shedding in a stellar binary system, can be fully swallowed by the SN only to re-emerge much later in the evolution (e.g. Pursiainen et al. 2022; Figure 1). In other cases the CSM can fully enshroud the SN leaving the explosion hidden inside the cocoon (Pursiainen et al. 2023). In some cases you can even have both (Killestein, Pursiainen et al. 2025) implying a very complex mass-loss history! Only by continuous, detailed observations, often starting from within a few days from explosion, can we unravel what these systems are really like. 

One of my specialities is optical polarimetry of extragalactic transients. Much like polarised lenses used in sunglasses or in some 3D cinemas, polarised filters can be used to decipher the geometry of SN explosion, even if they are far too distant to resolve their shape directly. In most case SNe are largely spherical (Pursiainen et al. 2023b), but a number of processes can affect their shape throughout their evolution, such as interaction with aspherical CSM as mentioned above. 

I am also interested in all other kinds of peculiar transients. For instance, during my PhD in the University of Southampton I uncovered the large population of events that evolve faster than standard SNe are expected to (Pursiainen et al. 2018). The study directly contributed to making the fast transients one of the hottest topics in transient astronomy and resulted in a press release. My interest in the topic has since continue, and in 2025 I published a study together with my collaborators on an exceptionally bright and fast transient AT2024wpp – a member of the elusive Cow-like transients (Pursiainen & Killestein et al 2025). Despite evidence for disk-like geometry deep inside the events, the study shows that their relativistic outflows appears to be spherical. You can read more about the study here. 

 

My publications: NASA ADS Library