In recent years, the number of pulsars with secure mass measurements has increased to a level that allows us to probe the underlying neutron star (NS) mass distribution in detail. We critically review the radio pulsar mass measurements. For the first time, we are able to analyze a sizable population of NSs with a flexible modeling approach that can effectively accommodate a skewed underlying distribution and asymmetric measurement errors. We find that NSs that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. NSs in double neutron star and neutron star-white dwarf systems show consistent respective peaks at 1.33 M ⊙ and 1.55 M ⊙ suggesting significant mass accretion (∆m ≈ 0.22 M ⊙ ) has occurred during the spin-up phase. The width of the mass distribution implied by double NS systems is indicative of a tight initial mass function while the inferred mass range is significantly wider for NSs that have gone through recycling. We find a mass cutoff at ∼ 2.1 M ⊙ for NSs with white dwarf companions which establishes a firm lower bound for the maximum NS mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for NS matter. The lack of truncation close to the maximum mass cutoff along with the skewed nature of the inferred mass distribution both enforce the suggestion that the 2.1 M ⊙ limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare super-massive NSs is possible.

Intermediate mass black holes play a critical role in understanding the evolutionary connection between stellar mass and supermassive black holes 1 . However, to date the existence of these species of black holes remains ambiguous and their formation process is therefore unknown 2 . It has been long suspected that black holes with masses 10 2 − 10 4 M should form and reside in dense stellar systems [3][4][5][6] . Therefore, dedicated observational campaigns have targeted globular cluster for many decades searching for signatures of these elusive objects. All candidates found in these targeted searches appear radio dim and do not have the X-ray to radio flux ratio predicted by the fundamental plane for accreting black holes 7 . Based on the lack of an electromagnetic counterpart upper limits of 2060M and 470M have been placed on the mass of a putative black hole in 47 Tucanae (NGC 104) from radio and X-ray observations respectively 8,9 . Here we show there is evidence for a central black hole in 47 Tuc with a mass of M• ∼ 2300M +1500 −850 when the dynamical state of the globular cluster is probed with pulsars. The existence of an intermediate mass black hole in the centre of one of the densest clusters with no detectable electromagnetic counterpart suggests that the black hole is not accreting at a sufficient rate and therefore contrary to expectations is gas starved. This intermediate mass black hole might be a member of electromagnetically invisible population of black holes that are the elusive seeds leading to the formation of supermassive black holes in galaxies.An intermediate mass black hole (IMBH) strongly affects the spatial distribution of stars in globular clusters (GCs). Massive stars sink into the centre more efficiently during relaxation in order to achieve energy equipartition. As a consequence, as stars sink closer to the centre they are scattered by the black hole which heats up the core. This process quenches mass segregation (Figure 1). Over the lifetime of a cluster, dynamical processes such as energy equipartition and twobody relaxation therefore contribute to the outward propagation of an integrated dynamical effect beyond the black hole's radius of direct influence. We find that this dynamical signature is efficiently propagated outward into the cluster. In relation to this effect, the distributions of pulsar accelerations for any projected distance from the centre show distinct features also sensitive to an IMBH. There are currently 25 millisecond pulsars detected within the cluster 47 Tuc. 19 of these have phase resolved timing solutions [10][11][12] (See Extended Data Table 1) which we use to infer spatial accelerations caused by the gravitational potential of the cluster 13 . Pulsar acceleration measurements together with N -body simulations provide stringent constraints on the mass of the central black hole in one of the most massive clusters (MGC ∼0.7 × 10 6 M ) with a compact core 14 .IMBHs have distinct imprints on how massive stars dynamically settle three-dimensionally after the c...

The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new γ -ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of Γ = 1.51 +0.05 −0.04 with an exponential cutoff at E c = 2.9 ± 0.1 GeV. Spectral fits with generalized cutoffs of the form e −(E/E c ) b require b 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.

Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 milliseconds and a period derivative of 3.614 × 10–13 seconds per second. Its characteristic age of 104 years is comparable to that estimated for the SNR. We speculate that most unidentified Galactic gamma-ray sources associated with star-forming regions and SNRs are such young pulsars