Helsinki cluster access
A short user guide for setting up an account at University of Helsinki cluster.
About me
I am a computational astrophysicist studying high-energy astrophysical phenomena around neutron stars and black holes. For my research, I use both theoretical “pen-and-paper work” and large-scale supercomputer simulations.
I am also the Principal Investigator of the European Research Council (ERC) funded research project ILLUMINATOR. The project aims to unravel how neutron stars generate their observed electromagnetic radiation.
I am an Associate Professor of Astrophysics at University of Helsinki and Associate Research Scientist at Columbia Astrophysics Laboratory. Previously, I was a joint Flatiron Research Fellow in Center for Computational Astrophysics, Flatiron Institute and a Postdoctoral Researcher in Columbia University (2020-2023; New York, USA). Before coming to New York, I was a Nordita Fellow in Nordic Institute for Theoretical Physics (2018-2020; Stockholm, Sweden).
You can read more about my research here and on our group page.
In Finnish/Suomeksi:
Olen suomalainen astrofysiikan apulaisprofessori Helsingin yliopistossa. Tutkin pääasiassa suurenergia-astrofysiikan ääri-ilmiöitä, kuten neutronitähtien purkauksia, pulsarien säteilyä, mustien aukkojen kertymäkiekkoja, sekä kosmisia radiopurskeita.
News
- 1.12.2023: Nordic Postdoctoral Plasma Physics (NORPPA) Fellowship 2024 call is now closed. We will inform the applicants about the selection in mid January.
- 2.1.2024: Call for Summer Trainee 2024 positions at the University Helsinki is opening. Stay tuned!
Recent posts
Summer Trainee 2024 positions
Summer Trainee 2024 positions in our group are available for University of Helsinki students.
CGS units
List of CGS units and constants used in especially in astrophysics
Alfven Wave Turbulence
PRL on how Alfven-wave turbulence can heat astrophysical plasmas around black holes and neutron stars.
Relativistic Boris spectrally deferred correction algorithm
In a work led by Kris Smedt we studied the so-called Boris-SDC algorithm for updating particle velocities in kinetic simulations.
Computer vision & turbulence simulations
Together with Maarja Bussov we constructed a new machine learning computer vision algorithm to help us segment turbulence simulations.
Coherent radio emission from magnetized shocks
In our PRL we studied the production of radio waves from magnetized collisionless shocks as a viable FRB emission mechanism.
Kinetic plasma model for orphan gamma-ray flares
Together with Emanuele Sobacchi and Lorenzo Sironi we discuss a new astrophysical model for orphan gamma-ray flares based on reconnection-mediated turbulence
Multimessenger constraints for neutron star matter
In this work, we did a detailed study on how much do we actually know about neutron star equation of state given all the most recent multimessenger constrain...
Combining EM and GW observations to measure neutron star radii
In a Phys. Rev. Letter led by M. Al-Mamun and A. Steiner we combined state-of-the-art EM and GW observations to constrain the size of the neutron radius.
Radiative turbulent flares
We performed new radiative kinetic simulations of reconnection-mediated turbulent flares - these flares are a new way to energize plasmas around neutron star...
Bending of polarized light rays around neutron stars
Together with V. Loktev and T. Salmi we extended our previous work on light bending around neutron stars to account for polarization of the light.
Milli-second pulsar atmospheres
In a work led by T. Salmi we computed new return-current-heated neutron star atmosphere models for millisecond pulsars.
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 s...
Runko: toolbox for plasma simulations
Runko simulation framework is finally available for everybody. Check it out at GitHub!
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.
Exploring helical dynamos with machine learning
Together with Farrukh Nauman we explored helically forced 3D magnetohydrodynamic turbulence simulations with ensemble machine learning techniques.
Quark-matter cores in neutron stars
Our new EOS analysis published in Nature Physics indicates that neutrons stars actually have two distinct phases of matter inside: normal hadronic and a siza...
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.
Bayesian M-R constraints for accreting millisecond pulsars
Together with Tuomo Salmi and Juri Poutanen we studied the possibility of applying Bayesian inference to accreting millisecond pulsar X-ray light curves.
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?...
Constraining the radius of neutron stars with atmosphere model fits
We used new nested hierarchical Bayesian modeling framework to constrain radius of the neutron star in 4U 1702-429 to be R=12.4km. The presented method turns...
Radiation from rapidly rotating neutron stars
Bender is finally here! Together with Pauli Pihajoki, we developed a ray tracing platform for rapidly rotating oblate neutron stars. And yes, it’s open source!
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 result...
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 consta...
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 abou...
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...
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...
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...
Influence of accretion geometry on the spectral evolution during X-ray bursts
In this work we show how the accretion modifies the cooling of X-ray bursts on top of neutron stars. This will then lead to (at least) two different classes ...
Effect of accretion on the NS mass and radius measurements: 4U 1608-52
On this article, published in MNRAS, we show how the accretion can affect the NS mass and radius measurements that are done using the X-ray bursts.