Neutron Stars: Insights into their Formation,

Evolution & Structure from theirMasses and Radii

Feryal OzelUniversity of Arizona

In collaboration with T. Guver, M. Baubock, L. Camarota, P. Wroblewski, A. Santos Villarreal; G. Baym, D. Psaltis, R. Narayan, J. McClintock

Supernovae and Gamma Ray Bursts in Kyoto

Neutron Star Masses Understand stellar evolution & supernova

explosions

Find maximum neutron star mass Dense Matter EoS

GR tests

GW signals

Neutron Star MassesRely on pulsars/neutron stars in binaries

Group by

Data Quality: Number of measurements, type of errors

Source type: Double NS, Recycled NS, NS with High Mass Companion

Total of 6 pairs of double neutron stars (12) and 9 NS+WD systems with precisely measured masses

31 more neutron stars withreasonably well determined masses

NS Mass Measurements

Özel et al. 2012

Current Record Holders: M= 1.97±0.04 M Demorest et al. 2010 M= 2.01±0.04 M Antoniadis et al. 2013

NS Mass Distributions

Özel et al. 2012

NS Mass DistributionsI. Lifetime of accretion/recycling shifts the mean 0.2 M up

II. There is no evidence for the effect of the maximum mass on the distribution

III. Double Neutron Star mass distribution is peculiarly narrow

Why is the DNS distribution so narrow?

Black Hole MassesDetermine velocity amplitude K, orbital period P, mass function f

4U 1543-47

Radi

al V

eloc

ity (k

m s-

1 )

Time (HJD-2,450,600+)

+ Varying levels of data on inclination and mass ratio

from Orosz et al. 1998

Masses of

Stellar Black Holes

Özel, Psaltis, Narayan, & McClintock 2010

Parameters of the Distribution• Cutoff mass ≥ 5 M

• Fast decay at high mass end

• Not dominated by a particular group of sources

Özel et al. 2010

See also Bailyn et al. 1998Farr et al. 2011

Neutron Stars and Black Holes

Özel et al. 2012

Failed Supernovae?

Kochanek 2013Woosley & Heger 2012Lovegrove & Woosley 2013

PROGENITOR MASS

~16-25 M

Failed SNeDirect collapseEject H envelopeBH Mass = He core mass

< 15 M

Successful SNeNo fallbackNS remnant

> 25 M

Significant pre-SN mass loss

NS Radii – What is the Appeal?

Image credit:Chandra X-ray Observatory

The Physics of Cold Ultradense Matter

NS/BHs divisionSupernova mechanismGRB durationsGravitational waves

EoS Mass-Radius RelationP

ρ

The pressure at three fiducial densities capture the characteristics of all equations of state

This reduces ~infinite parameter problem to 3 parameters

Özel & Psaltis 2009, PRD, 80,103003Read et al. 2009, PRD

Özel & Psaltis 2009, PRD ≥ 3 Radius measurements achieve a faithful recovery of the EoS

Data simulatedusing the FPS EoS

Mass-Radius Measurement to EoS:

a formal inversion

Measuring Neutron Star Radii

Complications:

1. The radius and mass measurements are coupled

2. Need sources where we see the neutron star surface, the whole neutron star surface, and nothing but the neutron star surface

Low Mass X-ray BinariesTwo windows onto the neutron star surface

during periods of quiescence and bursts

Modified Julian Date - 50000

AS

M C

ount

s s-1

• Low magnetic fields (B<109 G)• Expectation for uniform emission from surface

Radii from Quiescent LMXBs

in Globular Clusters

Five Chandra observations of U24 in NGC 6397

Guillot et al. 2011

Heinke et al. 2006; Webb & Barret 2007; Guillot et al. 2011

Evolution of Thermonuclear Bursts

Constant, Reproducible Apparent Radii 4U 1728-34

Level of systematic uncertainty < 5% in apparent radii

Two Other Measurements: Distances and Eddington Limit

Frad

Fgrav

Time (s)

Measuring the Eddington Limit4U 1820-30

Guver, Wroblewski, Camarota, & Ozel 2010, ApJ

Pinning Down NS Radii

Globular cluster source EXO 1745-248Özel et al. 2009, ApJ, 693, 1775

Current Radius Measurements Remarkable

agreement in radii between

different spectroscopic

measurements

R ~ 9-12 km

Majority of the 10 radii smaller than

vanilla nuclear EoS

AP4predictions

Can already constrain the neutron star

EoS

The Pressure of Cold Ultradense Matter

Özel, Baym, & Guver 2010, PRD, 82, 101301

Conclusions• Nuclear EoS that fit low-density data too stiff

at high densities

• Indication for new degrees of freedom in NS matter

• NS-BH mass gap and narrow DNS distribution point to new aspects of supernova mechanism

Additional Slides

The Future

a NASA Explorer

an ESA M3 mission

Is the low-mass gap due to a selection effect?

Transient black holes

Follow-up criterion:1 Crab in outburst

If L ~ M, could lead to a low-mass gap

But it is not a selection effect…

Brighter sources are nearby ones

Persistent Sources• Bowen emission line blend technique, @ 4640 A • Applied mostly to neutron star binaries, which are

persistent (Steeghs & Casares 2002)

Steeghs & Casares 2002

Persistent Sources• Bowen emission line blend technique• Applied so far to neutron star binaries, which are

persistent• Can help address if sample of transients

introduces a selection effect

Highest Mass Neutron Star

Measurement of the Shapiro delay in PSR J1614-2230 with the GBT

Demorest et al. 2010

Highest Mass Neutron Star

M= 1.97±0.04 M

SAX J1748.9-2021

Baubock et al. 2012

GR Effects at Moderate Spins

Neutron Star Surface Emission

• Low magnetic fields• Plane parallel atmospheres• Radiative equilibrium

• Non-coherent scattering• Possible heavy elements

from Madej et al. 2004 Majczyna et al 2005

Ozel et al. 2009Suleimanov et al. 2011

Effects of Pile-up on X7 spectrum

Spectra are well-described by Comptonized atmosphere models

Analysis of the Burst Spectra

4U 1636-53626 d.o.f.1712 spectra

Is There A Stiff EoS in 4U 1724-307?The source used by Suleimanov et al. 2011

Redshift MeasurementM/R from spectral lines:

Cottam et al. 2003, Nature

2ME = E0 ( )

R1

These lines do not come from the stellar surface Lin, Ozel, Chakrabarty, Psaltis 2010, ApJ