Selected publications

A list of some of the papers of mine that I like the most (in no particular order):

  • Radiative turbulent flares in magnetically-dominated plasmas
    • Detailed study on reconnection-mediated turbulent flares and their radiative properties. These flares can be relevant for explaining plasma energization in neutron star magnetospheres and black hole accretion disks.
  • Radiation from rapidly rotating oblate neutron stars
    • Extensive study on radiation characteristics from rapidly spinning neutron stars. We generalize previous works to include effects from oblate surfaces and quadrupole corrections to the spacetime metric.
  • Evidence for quark matter cores inside neutron stars
    • We show that when results from modern nuclear physics and perturbative QCD limits are combined together, they imply that the most massive neutron stars can have quark matter cores. Importantly, we show that even if there is no quark matter, the core is still made of exotic material that breaks the conformal limit (speed of sound exceeds square root of c/3).
  • Neutron star M-R measurements from atmospheric model fits to X-ray burst cooling tail spectra
    • By using a detailed Bayesian fitting procedure we show that it is possible to measure the neutron star radius very accurately from existing X-ray data. From this analysis we obtained a neutron star radius of 12.4 +- 0.4 km that is amazingly consistent with other measurements, and is still one of the most accurate measurements of NS radius.

Research topics

In general, you can categorize my past work to (roughly) these topics:

Astroplasma physics

Equation of state of ultra-dense matter

Neutron star (astro)physics

X-ray bursts from neutron stars

In addition, there are other miscellaneous topics that I’ve dipped my toes in:

Machine learning

General relativity/ray tracing

Collection of my writings & publications

A full list of my publications is here:

Alfven Wave Turbulence

PRL on how Alfven-wave turbulence can heat astrophysical plasmas around black holes and neutron stars.

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 stars and black holes.

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 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 published in Nature Physics indicates that neutrons stars actually have two distinct phases of matter inside: normal hadronic and a sizable quark matter core!

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.

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.

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.