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In the past two decades, high-amplitude electromagnetic outbursts have been detected from dormant galaxies and often attributed to the tidal disruption of a star by the central black hole 1 , 2 . X-ray emission from the Seyfert 2 galaxy GSN 069 (2MASX J01190869-3411305) at a redshift of z  = 0.018 was first detected in July 2010 and implies an X-ray brightening by a factor of more than 240 over ROSAT observations performed 16 years earlier 3 , 4 . The emission has smoothly decayed over time since 2010, possibly indicating a long-lived tidal disruption event 5 . The X-ray spectrum is ultra-soft and can be described by accretion disk emission with luminosity proportional to the fourth power of the disk temperature during long-term evolution. Here we report observations of quasi-periodic X-ray eruptions from the nucleus of GSN 069 over the course of 54 days, from December 2018 onwards. During these eruptions, the X-ray count rate increases by up to two orders of magnitude with an event duration of just over an hour and a recurrence time of about nine hours. These eruptions are associated with fast spectral transitions between a cold and a warm phase in the accretion flow around a low-mass black hole (of approximately 4 × 10 5  solar masses) with peak X-ray luminosity of about 5 × 10 42  erg per second. The warm phase has kT (where T is the temperature and k is the Boltzmann constant) of about 120 electronvolts, reminiscent of the typical soft-X-ray excess, an almost universal thermal-like feature in the X-ray spectra of luminous active nuclei 6 – 8 . If the observed properties are not unique to GSN 069, and assuming standard scaling of timescales with black hole mass and accretion properties, typical active galactic nuclei with higher-mass black holes can be expected to exhibit high-amplitude optical to X-ray variability on timescales as short as months or years 9 . Galaxy GSN 069 has unprecedented eruptions of X-ray light every nine hours, which indicate fast transitions between cold and warm states and may shed light on black hole accretion.

A sustained, neutral wind from the outer accretion disk is observed in the transient black hole V404 Cygni during a violent outburst; this unusual wind, which expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin, probably regulates the outburst evolution of the black hole. Accretion regulated by a disk wind in V404 Cygni black hole Teo Muñoz-Darias et al . report observations of a sustained outer accretion disk wind in the stellar-mass black hole in the V404 Cygni binary system that is unlike any seen previously. The outflowing wind is neutral, has a large covering factor and expands at 1% of the speed of light. The luminous, but brief, accretion phases shown by transients with large accretion disks imply that this type of outflow could be a previously unknown factor regulating mass accretion onto black holes. Accretion of matter onto black holes is universally associated with strong radiative feedback 1 and powerful outflows 2 . In particular, black-hole transients 3 have outflows whose properties 4 are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disk encircling the black hole, and collimated radio jets 5 , 6 . Very recently, a distinct optical variability pattern has been reported in the transient stellar-mass black hole V404 Cygni, and interpreted as disrupted mass flow into the inner regions of its large accretion disk 7 . Here we report observations of a sustained outer accretion disk wind in V404 Cyg, which is unlike any seen hitherto. We find that the outflowing wind is neutral, has a large covering factor, expands at one per cent of the speed of light and triggers a nebular phase once accretion drops sharply and the ejecta become optically thin. The large expelled mass (>10 −8 solar masses) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disk was depleted by the wind, detaching the inner regions from the rest of the disk. The luminous, but brief, accretion phases shown by transients with large accretion disks 2 imply that this outflow is probably a fundamental ingredient in regulating mass accretion onto black holes.

A triple supermassive black hole system has been found that shows helical modulation of the large-scale radio jets; this modulation is caused by two of the black holes being tightly coupled as a binary system. Black holes get close in triplets The discovery of a triple supermassive black hole system in a distant (redshift z = 0.39) galaxy provides a rare opportunity to observe what may be the result of galactic mergers. In the four known triple black hole systems, the smallest distance between a pair of black holes is 2.4 kiloparsecs, but the newly discovered triple system includes a 'tight pair' separated by around 140 parsecs. The authors show that the presence of the tight pair is imprinted onto the properties of the large-scale radio jets generated by the black holes, providing a useful way of searching for other tight pairs without the need for extremely high-resolution observations. Six candidate galaxies were surveyed in this study, a 'hit rate' that suggests that tight pairs are more common than was thought. Close-pair binaries are useful targets for gravitational wave studies, so the development of an efficient way of finding them, and the prospect of there being more of them, should stimulate interest in work on predicting the strength of gravitational waves and assist in their eventual detection. Galaxies are believed to evolve through merging 1 , which should lead to some hosting multiple supermassive black holes 2 , 3 , 4 . There are four known triple black hole systems 5 , 6 , 7 , 8 , with the closest black hole pair being 2.4 kiloparsecs apart (the third component in this system is at 3 kiloparsecs) 7 , which is far from the gravitational sphere of influence (about 100 parsecs for a black hole with mass one billion times that of the Sun). Previous searches for compact black hole systems concluded that they were rare 9 , with the tightest binary system having a separation of 7 parsecs (ref. 10 ). Here we report observations of a triple black hole system at redshift z = 0.39, with the closest pair separated by about 140 parsecs and significantly more distant from Earth than any other known binary of comparable orbital separation. The effect of the tight pair is to introduce a rotationally symmetric helical modulation on the structure of the large-scale radio jets, which provides a useful way to search for other tight pairs without needing extremely high resolution observations. As we found this tight pair after searching only six galaxies, we conclude that tight pairs are more common than hitherto believed, which is an important observational constraint for low-frequency gravitational wave experiments 11 , 12 .

Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified ≳10 yr ago. Since then, nearly 40 events have been discovered, although almost all of these have been recovered from archival Chandra and XMM-Newton data. To date, optical sky surveys and follow-up searches have not revealed any multiwavelength counterparts. The Einstein Probe, launched in 2024 January, has started surveying the sky in the soft X-ray regime (0.5–4 keV) and will rapidly increase the sample of FXTs discovered in real time. Here we report the first discovery of both an optical and radio counterpart to a distant FXT, the fourth source publicly released by the Einstein Probe. We discovered a fast-fading optical transient within the 3′ localization radius of EP 240315a with the all-sky optical survey ATLAS, and our follow-up Gemini spectrum provides a redshift, z = 4.859 ± 0.002. Furthermore, we uncovered a radio counterpart in the S band (3.0 GHz) with the MeerKAT radio interferometer. The optical (rest-frame UV) and radio luminosities indicate that the FXT most likely originates from either a long gamma-ray burst or a relativistic tidal disruption event. This may be a fortuitous early mission detection by the Einstein Probe or may signpost a mode of discovery for high-redshift, high-energy transients through soft X-ray surveys, combined with locating multiwavelength counterparts.

The tidal disruption of a star by a supermassive black hole leads to a short-lived thermal flare. Despite extensive searches, radio follow-up observations of known thermal stellar tidal disruption flares (TDFs) have not yet produced a conclusive detection. We present a detection of variable radio emission from a thermal TDF, which we interpret as originating from a newly launched jet. The multiwavelength properties of the source present a natural analogy with accretion-state changes of stellar mass black holes, which suggests that all TDFs could be accompanied by a jet. In the rest frame of the TDF, our radio observations are an order of magnitude more sensitive than nearly all previous upper limits, explaining how these jets, if common, could thus far have escaped detection.

A piece of the action The central engines that drive active galactic nuclei are thought to be supermassive black holes. A long-standing question in astrophysics is whether these central engines vary like Galactic black hole systems when scaled up to 'supermassive' proportions. If they do, it becomes possible to predict how active galactic nuclei should behave on cosmological timescales by studying the brighter and much faster varying Galactic systems. A new study suggests that yes, the accretion process is exactly the same for small and large black holes. Provided, that is, that a correction is made to take account of variations in the rate of the accretion process. Active galactic nuclei vary in a manner similar to Galactic black hole systems when appropriately scaled up by mass, meaning it is possible to determine how active galactic nuclei should behave on cosmological timescales by studying the brighter and much faster varying Galactic systems. A long-standing question is whether active galactic nuclei (AGN) vary like Galactic black hole systems when appropriately scaled up by mass 1 , 2 , 3 . If so, we can then determine how AGN should behave on cosmological timescales by studying the brighter and much faster varying Galactic systems. As X-ray emission is produced very close to the black holes, it provides one of the best diagnostics of their behaviour. A characteristic timescale—which potentially could tell us about the mass of the black hole—is found in the X-ray variations from both AGN and Galactic black holes 1 , 2 , 3 , 4 , 5 , 6 , but whether it is physically meaningful to compare the two has been questioned 7 . Here we report that, after correcting for variations in the accretion rate, the timescales can be physically linked, revealing that the accretion process is exactly the same for small and large black holes. Strong support for this linkage comes, perhaps surprisingly, from the permitted optical emission lines in AGN whose widths (in both broad-line AGN and narrow-emission-line Seyfert 1 galaxies) correlate strongly with the characteristic X-ray timescale, exactly as expected from the AGN black hole masses and accretion rates. So AGN really are just scaled-up Galactic black holes.

Over the past decade, observations of relativistic outflows from outbursting X-ray binaries in the Galactic field have grown significantly. In this work, we present the first detection of moving and decelerating radio-emitting outflows from an X-ray binary in a globular cluster. MAXI J1848−015 is a recently discovered transient X-ray binary in the direction of the globular cluster GLIMPSE-C01. Using observations from the Karl G. Jansky Very Large Array, and a monitoring campaign with the MeerKAT observatory for 500 days, we model the motion of the outflows. This represents some of the most intensive, long-term coverage of relativistically moving X-ray binary outflows to date. We use the proper motions of the outflows from MAXI J1848−015 to constrain the component of the intrinsic jet speed along the line of sight, βintcosθejection , to be =0.19 ± 0.02. Assuming it is located in GLIMPSE-C01, at 3.4 kpc, we determine the intrinsic jet speed, β int = 0.79 ± 0.07, and the inclination angle to the line of sight, θ ejection = 76° ± 2°. This makes the outflows from MAXI J1848−015 somewhat slower than those seen from many other known X-ray binaries. We also constrain the maximum distance to MAXI J1848−015 to be 4.3 kpc. Finally, we discuss the implications of our findings for the nature of the compact object in this system, finding that a black hole primary is a viable (but as-of-yet unconfirmed) explanation for the observed properties of MAXI J1848−015. If future data and/or analysis provide more conclusive evidence that MAXI J1848−015 indeed hosts a black hole, it would be the first black hole X-ray binary in outburst identified in a Galactic globular cluster.

Some types of core-collapse supernovae are known to produce a neutron star (NS). A binary NS merger was recently detected from its gravitational wave emission, but it is unclear how such a tight binary system can be formed. De et al. discovered a core-collapse supernova with unusual properties, including the removal of the outer layers of the star before the explosion. They interpret this as the second supernova in an interacting binary system that already contains one NS. Because the explosion probably produced a second NS (rather than a black hole) in a tight orbit, it could be an example of how binary NS systems form. Science , this issue p. 201 An unusual core-collapse supernova appears to have formed a binary neutron star in a tight orbit. Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 10 50 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.

The sensitivity and field of view of the MeerKAT radio telescope provide excellent opportunities for commensal transient searches. We carry out a commensal transient search in supernova and short gamma-ray burst fields using methodologies established by S. I. Chastain et al. We search for transients in MeerKAT L-band images with integration times of 30 minutes, finding 13 variable sources. We compare these sources to the VLASS and RACS survey data, and examine possible explanations for the variability. Additionally, for one of these sources we examine archival Chandra ACIS data. We find that 12 of these sources are consistent with variability due to interstellar scintillation. The remaining source could possibly have some intrinsic variability. We also split the MeerKAT L band into upper and lower halves, and search for transients in images with an integration time of 8 s. We find a source with a duration of 8–16 s that is highly polarized at the lowest frequencies. This source is spatially coincident with a star detected by the Transiting Exoplanet Survey Satellite. We conclude that this source may be consistent with a stellar flare. Finally, we calculate accurate upper and lower limits on the transient rate using transient simulations.

Black holes in binary systems execute patterns of outburst activity where two characteristic X-ray states are associated with different behaviours observed at radio wavelengths. The hard state is associated with radio emission indicative of a continuously replenished, collimated, relativistic jet, whereas the soft state is rarely associated with radio emission, and never continuously, implying the absence of a quasi-steady jet. Here we report radio observations of the black hole transient MAXI J1820+070 during its 2018 outburst. As the black hole transitioned from the hard to soft state, we observed an isolated radio flare, which, using high-angular-resolution radio observations, we connect with the launch of bipolar relativistic ejecta. This flare occurs as the radio emission of the core jet is suppressed by a factor of over 800. We monitor the evolution of the ejecta over 200 days and to a maximum separation of 10″, during which period it remains detectable due to in situ particle acceleration. Using simultaneous radio observations sensitive to different angular scales, we calculate an accurate estimate of energy content of the approaching ejection. This energy estimate is far larger than that derived from the state transition radio flare, suggesting a systematic underestimate of jet energetics. Radio observations of black hole MAXI J1820+070’s 2018 outburst captured an isolated radio flare that the authors connect with the launch of bipolar relativistic ejecta. Following the oncoming ejecta for more than half a year reveals that black hole jet energetics have been systematically underestimated.