The mass and radius of the neutron star in EXO 1745-248

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186 Scopus citations


Bursting X-ray binaries in globular clusters are ideal sources for measuring neutron star masses and radii, and hence, for determining the equation of state of cold, ultradense matter. We use time-resolved spectroscopic data from EXO 1745-248 during thermonuclear bursts that show strong evidence for photospheric radius expansion to measure the Eddington flux and the apparent surface area of the neutron star. We combine this with the recent measurement of the distance to the globular cluster Terzan 5, where this source resides, to measure the neutron star mass and radius. We find tightly constrained pairs of values for the mass and radius, which are centered around M = 1.4 M and R = 11 km or around M = 1.7 M and R = 9 km. These values favor nucleonic equations of state with symmetry energy that is relatively low and has a weak dependence on density.

Original languageEnglish (US)
Pages (from-to)1775-1779
Number of pages5
JournalAstrophysical Journal
Issue number2
StatePublished - Mar 10 2009


  • X-rays: individual (EXO 1745?248)
  • stars: neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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