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NICER pulse-profile analyses constrain the mass and radius of PSR J0030+0451

Two analyses of NICER X-ray pulse profiles for the millisecond pulsar PSR J0030+0451 inferred its mass, radius and emitting-region geometry. Under their selected models, Riley and colleagues reported an equatorial radius of 12.71 +1.14/−1.19 km and mass of 1.34 +0.15/−0.16 solar masses; Miller and colleagues reported 13.02 +1.24/−1.06 km and 1.44 +0.15/−0.14 solar masses. These quoted marginal uncertainties are 68% credible intervals.

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How do you measure a star you cannot resolve?

A neutron star can be about the size of a city while containing more mass than the Sun. It is far too distant for NICER to photograph its surface directly. Instead, the instrument collects X-rays from a rotating pulsar. As hotter regions move into and out of view, the brightness rises and falls. That changing light curve gives researchers clues about the star and the geometry of its emitting regions.

Turn the light curve into a model

Imagine a lighthouse beam passing an observer again and again. A real pulsar is more complicated: the shape and temperature of its hot regions, the star’s rotation, and the bending of light by gravity affect the observed pulse. The researchers compare candidate light curves with the NICER measurements and use a statistical model to infer ranges for mass and radius. A range describes what the model and data support under the stated assumptions; it is not a photograph of the surface.

Try the arithmetic

In the Riley analysis, a reported radius of 12.71 km with minus 1.19 km and plus 1.14 km gives an illustrative interval of 11.52–13.85 km. In the Miller analysis, 13.02 km minus 1.06 km and plus 1.24 km gives 11.96–14.26 km. The papers describe the quoted intervals as approximately 68% marginal credible intervals. These are not independent telescope detections: both analyses used NICER observations of the same pulsar.

What the result can and cannot tell us

The estimates help researchers compare possible descriptions of dense neutron-star matter. They depend on choices such as the hot-region model, atmosphere, background and instrument calibration. The two analyses use different computational approaches and overlapping personnel, but shared observations mean their agreement is not two separate observing confirmations. A radius interval does not, by itself, select one unique equation of state.

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Ask your agent to find the exact reported mass and radius in each cited version, copy the units and interval convention, and explain which observations are shared. Check its answer against the first pages of the papers. If it cannot locate a figure or separate a model assumption from a measurement, record that uncertainty instead of guessing. This makes a reusable comparison without claiming to repeat the underlying analysis.

Scientific scope

The two analyses use the same NICER observations with overlapping authors and different modelling methods; they are not independent observing confirmations. Inferences depend on the selected hot-spot geometry, atmosphere, calibration, background and distance assumptions. Pulse-profile reconstruction does not directly resolve the stellar surface or establish a unique neutron-star equation of state. The results here are from the two cited preprint versions; their additional online figure sets and later journal versions are outside this summary.

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People and systems

T. E. Riley; A. L. Watts; S. Bogdanov; P. S. Ray; R. M. Ludlam; S. Guillot; Z. Arzoumanian; C. L. Baker; A. V. Bilous; D. Chakrabarty; K. C. Gendreau; A. K. Harding; W. C. G. Ho; J. M. Lattimer; S. M. Morsink; T. E. Strohmayer; M. C. Miller; F. K. Lamb; A. J. Dittmann; S. Mahmoodifar; K. S. Wood; T. Enoto; R. Foster; T. Okajima; G. Prigozhin; Y. Soong

These are source-listed labels from two separate analyses of the same observations, not a joint paper. Each label is bound to a paper on which it appears. Individual effort, author nationality and unresolved cross-record identities are not inferred.

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