SAM MORRELL


ASTROPHYSICIST

My Research

My current research involves understanding the fundamental properties of low-mass stars. Despite the fact that these stars the key ingredients to the modern slew of exoplanet discovery and characterisation missions, they are still remarkably poorly understood. Using cutting edge observations from the second data release of the Gaia mission, and a whole slew of photometry from a variety of all-sky surveys, we are working on trying to understand what we do and don't understand about the physics that drives them.

Of particular interest to me is understanding the  apparent radius inflation in this class of star when compared directly to a model of equal luminosity. This discrepancy is commonly noted in M dwarf stars at all stages of evolution, but there still remain some important open questions:

  • How large is the radius discrepancy between these stars and the models?
  • Is the effect in some way linked to convective inhibition, driven by stellar magnetic fields?
  • Can the effect be described entirely by star spots and photospheric opacities?
  • What is the underlying physics driving this divergence from models?
  • What is the true effect of this discrepancy on star- and planet-formation timescales?

We are currently working on publications in this area and they will be shared here when they are avaliable.

Interstellar Dust or Protoplanetary Grain

Throughout my masters project I worked as part of a team, under the supervision of Tim Naylor, in the Astrophysics group at the University of Exeter. The research entailed studying interstellar dust grains and the way they interact with incident light. It's commonly noted in a plethora of publications on the topic that this effect is strongly dependent on the wavelength of the incident light. This correlation has the net effect of making observed colours of targets appear redder than they should when observing through dust. Due to the scattering and absorption effect of this dust the light that travels through it is also noticeably reduced in intensity. Our research has involved carefully studying this effect in order to develop mathematical models which describe the wavelength dependence adequately enough to remove its effect.

Why Dust is a Problem

Nearly everywhere you look within the Milky Way, our host galaxy, there are almost imperceptible dust grains. Because they've been well studied and we believe we understand them quite well, they pose little trouble for modern astrophysics. However, the problem comes in denser regions such as gas clouds. Due to the much cooler temperature, a result of the shielding effect of the cloud, it's thought that dust grains have a fundamentally different composition to their diffuse counterparts. This would suggest that existing theory pertaining to dust in the Interstellar Medium (ISM) would be inaccurate. This does indeed appear to be the case.

We should also consider that most current research interests in astrophysics are focusing on these denser regions. Fields such as star formation require un-reddened observations in order to conduct thorough investigations, and as of yet reliable methods to remove dust from these observations are sadly lacking. It's for both of these reasons that the research interest in this topic is of interest.