National Superconducting
Cyclotron Laboratory

Edward Brown
Edward Brown
Professor of Physics
Theoretical Nuclear Astrophysics
PhD, Physics, University of California, Berkeley 1999
Joined NSCL in February 2004
Phone (517) 884-5620
Fax (517) 432-8802
Office 3266 BPS

Edward Brown

Professional Homepage

Formed in the violent death of a massive star, neutron stars are the most dense objects in nature. Their cores may reach several times the density of an atomic nucleus. As a result, neutron stars are a natural laboratory to study dense matter in bulk. We have observed neutron stars with telescopes, captured neutrinos from the birth of a neutron star, and detected gravitational waves from a neutron star merger. These observations complement laboratory studies of matter at super-nuclear density.

My work connects observations of neutron stars with theoretical and laboratory studies of dense matter. Many neutron stars reside in binaries accrete gas from a binary, solar-like companion. The weight of this accumulated matter compresses the outer layer, or crust, of the neutron star and induces nuclear reactions. These reactions power phenomena over timescales from seconds to years. By modeling these phenomena and comparing with observatons, we can infer properties of dense matter in the neutron star’s crust and core.

Recently, we have set a lower bound on the heat capacity of one neutron star and to inferred the efficiency of neutrino emission from the core of another. We have also calculated, using realistic nuclear physics input, reactions in the crust of accreting neutron stars. These calculations quantified the heating of the neutron star from these reactions, and the results have been used in simulations of the “freezing” of ions into a lattice in the neutron star crust. A surprise from these simulations is that the “ashes” of these bursts chemically separate as they are compressed to high densities. This may explain the inferred high thermal conductivity of the neutron star’s crust.

Cutaway of neutron star

Cutaway of the neutron star in MAXI J0556-332. During accretion, the outermost kilometer of the neutron star—its crust—is heated by compression-induced reactions (inset plot, which shows the temperature within the crust over a span of 500 days).  When accretion halts (at time 0 in the plot), the crust cools.  By monitoring the surface temperature during cooling, Deibel et al. determined that a strong heat source must be located at a relatively shallow depth of approximately 200 meters. 

Selected Publications

Rapid Neutrino Cooling in the Neutron Star MXB 1659-29, E.F. Brown, A. Cumming, F. J. Fattoyev, C.J. Horowitz, D. Page, and S. Reddy, Physical Review Letters, 120, 182701 (2018).

Lower limit on the heat capacity of the neutron star core, A. Cumming, E.F. Brown, F.J. Fattoyev, C.J. Horowitz, D. Page, and S. Reddy, Physical Review C, 95, 025806 (2017)

A Strong Shallow Heat Source In the Accreting Neutron Star MAXI J0556-332,” A. Deibel, A. Cumming, E.F. Brown, and D. Page, Astrophys. Jour. Lett., in press (2015)

Strong neutrino cooling by cycles of electron capture and β- decay in neutron star crusts, H. Schatz et al., Nature, 505, 62 (2014)

The Equation of State from Observed Masses and Radii of Neutron Stars, A. W. Steiner, J. M. Lattimer, and E. F. Brown, Astrophys. J. 722, 33 (2010)

Mapping Crustal Heating with the Cooling Lightcurves of Quasi-Persistent Transients, E. F. Brown and A. Cumming, Astrophys. J. 698, 1020 (2009).

Possible Resonances in the 12C+12C Fusion Rate and Superburst Ignition, R.L. Cooper, A.W. Steiner, and E.F. Brown, Astrophys. Jour., 702, 660 (2009)