The dispersive sweep of fast radio bursts (FRBs) has been used to probe the ionized baryon content of the intergalactic medium¹, which is assumed to dominate the total extragalactic dispersion. Although the host-galaxy contributions to the dispersion measure appear to be small for most FRBs², in at least one case there is evidence for an extreme magneto-ionic local environment^3,4 and a compact persistent radio source⁵. Here we report the detection and localization of the repeating FRB 20190520B, which is co-located with a compact, persistent radio source and associated with a dwarf host galaxy of high specific-star-formation rate at a redshift of 0.241 ± 0.001. The estimated host-galaxy dispersion measure of approximately $${903}_{-111}^{+72}$$903 − 111 + 72 parsecs per cubic centimetre, which is nearly an order of magnitude higher than the average of FRB host galaxies^2,6, far exceeds the dispersion-measure contribution of the intergalactic medium. Caution is thus warranted in inferring redshifts for FRBs without accurate host-galaxy identifications.

We present the discovery of 24 pulsars in 15 globular clusters (GCs) using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These include the first pulsar discoveries in M2, M10, and M14. Most of the new systems are either confirmed or likely members of binary systems. M53C and NGC 6517H and I are the only three pulsars confirmed to be isolated. M14A is a black widow pulsar with an orbital period of 5.5 hr and a minimum companion mass of 0.016 M _⊙. M14E is an eclipsing binary pulsar with an orbital period of 20.3 hr. With the other 8 discoveries that have been reported elsewhere, in total 32 GC pulsars have been discovered by FAST so far. In addition, We detected M3A twice. This was enough to determine that it is a black widow pulsar with an orbital period of 3.3 hr and a minimum companion mass of 0.0125 M _⊙.

Accretion of material onto a black hole drags any magnetic fields present inwards, increasing their strength. Theory predicts that sufficiently strong magnetic fields can halt the accretion flow, producing a magnetically arrested disk (MAD). We analyzed archival multiwavelength observations of an outburst from the black hole x-ray binary MAXI J1820+070 in 2018. The radio and optical fluxes were delayed compared with the x-ray flux by about 8 and 17 days, respectively. We interpret this as evidence for the formation of a MAD. In this scenario, the magnetic field is amplified by an expanding corona, forming a MAD around the time of the radio peak. We propose that the optical delay is due to thermal viscous instability in the outer disk.

Spider pulsars are neutron stars that have a companion star in a close orbit. The companion star sheds material to the neutron star, spinning it up to millisecond rotation periods, while the orbit shortens to hours. The companion is eventually ablated and destroyed by the pulsar wind and radiation^1,2. Spider pulsars are key for studying the evolutionary link between accreting X-ray pulsars and isolated millisecond pulsars, pulsar irradiation effects and the birth of massive neutron stars^3–6. Black widow pulsars in extremely compact orbits (as short as 62 minutes⁷) have companions with masses much smaller than 0.1 M_⊙. They may have evolved from redback pulsars with companion masses of about 0.1–0.4 M_⊙ and orbital periods of less than 1 day⁸. If this is true, then there should be a population of millisecond pulsars with moderate-mass companions and very short orbital periods⁹, but, hitherto, no such system was known. Here we report radio observations of the binary millisecond pulsar PSR J1953+1844 (M71E) that show it to have an orbital period of 53.3 minutes and a companion with a mass of around 0.07 M_⊙. It is a faint X-ray source and located 2.5 arcminutes from the centre of the globular cluster M71.

We report the detection of the state transitions and hysteresis effect in the two mini-outbursts of the black hole (BH) transient GRS 1739−278 following its 2014 major outburst. The X-ray spectral evolutions in these two mini-outbursts are similar to the major outburst, in spite of their peak luminosities and the outburst durations are one order of magnitude lower. We found the L_{hard-to − soft} and the L_{peak, soft} of the mini-outbursts also follow the correlation previous found in other X-ray binaries. The L_{hard-to − soft} of the mini-outbursts is still higher than that of the persistent BH binary Cyg X-1, which supports that there is a link between the maximum luminosity a source can reach in the hard state and the corresponding non-stationary accretion represented by substantial rate-of-change in the mass accretion rate during flares/outbursts. The detected luminosity range of these two mini-outbursts is roughly in 3.5× 10⁻⁵– 0.015 (D/7.5 kpc)²(M/8M_⊙) L_Edd. The X-ray spectra of other BH transients at such low luminosities are usually dominated by a power-law component, and an anti-correlation is observed between the photon index and the X-ray luminosity below 1% L_Edd. So the detection of X-ray spectral state transitions indicates that the accretion flow evolution in these two mini-outbursts of GRS 1739−278 are different from other BH systems at such low-luminosity regime.