Neutron Stars: Robust Constraints on Dense Matter from Astrophysics

Neutron stars are remarkable objects.  Their core densities are so large that

the short-ranged strong force leads to immense repulsion between particles,

allowing them to survive despite living on the precipice of gravitational

implosion to black holes.

However, QCD in the cold, high-density regime of neutron star cores is

intractable, so the properties of matter cannot be computed from first principles. 

Instead, observations of neutron stars across the electromagnetic

spectrum and in gravitational waves constrain approximate theories of dense

matter, which typically have poorly understood systematic uncertainties.

In my thesis, I studied how

nonparametric representations of the equation of

state enable more robust constraints on dense-matter and

neutron star astrophysics. Nonparametric methods allow model-agnostic exploration

of the equation of state and help control systematic uncertainty in predictions of neutron star properties.

I will argue, therefore, that nonparametric inference is a natural tool for the data-driven era of high-energy astrophysics, 

and  I will give examples of what we have already learned about dense matter from neutron stars.  

As the focus of this talk, I will discuss in detail what we can hope to

learn by observing everything from the least to the most massive neutron stars, as well as how these

observations constrain existing models of nuclear forces.

This thesis was completed at California Institute of Technology supervised by Katerina Chatziioannou.