About me

I am an astrophysicist focusing on topics like cosmic plasmas, high-energy astrophysical phenomena, and computational physics. I’ve also done some research on computer sciences, statistics, and machine learning. For my research I use tools such as pen & paper and supercomputers.

Currently, I have a joint position as a Postdoctoral Research Scientist in Columbia University and as a Flatiron Research Fellow in Center for Computational Astrophysics, Flatiron Institute (New York, USA). Previously, I was a Nordita Fellow in Nordic Institute for Theoretical Physics (Stockholm, Sweden). I am also an avid open-source science & software advocate — you can find my research and codes freely available from GitHub.

Research

I have a wide range of interdisciplinary research interests. These reflect some of my latest publications:

  • High-energy astrophysics: accretion (accretion disks); compact objects (neutron stars, black holes)
  • Plasma physics: collisionless plasma dynamics; turbulence; particle acceleration
  • Nuclear physics: equation of state of cold ultra-dense neutron matter
  • General relativity: ray tracing
  • Statistics: Bayesian inference; Monte Carlo methods
  • Computer sciences: high performance computing; parallellization paradigms; machine learning; Julia language
  • Mathematics: cellular automata models; topology


Notes on physics

Most of these research notes are done in connection to some publication. If you want to cite these, let me know and I’ll point you to a right paper.

Teaching

Undergraduate/PhD collaborators

  • Tuomo Salmi (host for Nordita PhD visit; MSc and BSc thesis co-supervisor)
  • Maarja Kruuse (host for Nordita PhD visit)
  • John Hope (MSc thesis supervisor)
  • Jere Kuuttila (MSc thesis co-supervisor)
  • Eemeli Annala (PhD collaboration)

Senior collaborators

Recent publications & blog posts

Spreading layers around neutron stars

When an accretion disk around a neutron star touches the star, it can form a so-called spreading layer. In a work led by P. Abolmasov, we designed a new 2D spherical spectral code to simulate the dynamics of these layers. Code is, obviously, calle...

Pulsar-wind heated accretion disks

In a work led by Alexandra Veledina we presented a new model for the transitional millisecond pulsars in terms of wind-heated disks.

Quark-matter cores in neutron stars

Our new EOS analysis indicates that neutrons stars actually have two distinct phases of matter inside: normal hadronic and a sizable quark matter core!

Introduction to Julia

My teaching material for an introductory course on the new high-level, high-performance programming language called Julia is freely available here.

Arcmancer: general purpose ray tracer

In the project led by Pauli Pihajoki, we took ray tracing and numerical differential geometry to the next level. Images of black holes, disks, neutron stars? Can do!

Helium composition in 4U 1820-303

In the work led by Valery Suleimanov, we applied the direct cooling tail method to constrain the atmosphere composition of a neutron star in 1820. Our results show that helium is strongly favored.

Variable spreading layers of neutron stars

In the work led by Jari Kajava, we studied the interface between the neutron star and the accretion disk. This so-called spreading layer seemed not as constant as people have previously assumed!

Dynamic powerlaw method for X-ray bursts

How do X-ray bursts really cool? Is it a single-index powerlaw or maybe an exponential? We investigated this together with our student Jere Kuuttila.

Direct cooling tail method

Here we derived some corrections to our existing cooling tail method. This new method is then applied to a previously measured neutron star, identifying about 500 meter calibration error.

Scientific writing tips

A collection of scientific writing tips for Master students working with their thesis.

Traces of heavy metals in neutron star atmospheres

Some peculiar X-ray bursts are found to have atmospheres that are made almost completely of heavy metals. A radiatively driven wind might then ejects some of the burning ashes into the interstellar space.

UNIX introduction

3 hour introductory lecture material into the world of UNIX.

Equation of state of dense matter from X-ray bursts

Equation of state of the cold dense matter has remained mystery for decades. In this recent work, we set new constraints to the EoS parameters by using X-ray bursts that show signs of passive cooling.

Heavy metal neutron star atmospheres

What happens to the observed spectrum of neutrons stars when the atmosphere is full of heavy metals from the nuclear burning? On this article, published in A&A we test the effects by computing detailed atmosphere models.

Exploration of numerical hydrodynamics

Contains some doodlings I did in the world of hydrodynamics. At some point I became interested in how do fluids actually move so I build my own hydro code to find out.

Cellular Automata

A project I did of Cellular Automata. During my Christmas holidays I did some studies of how self-organizing criticality works. And for that one needs a proper Cellular Automaton code, of course!