Explore the vast range of titles available.

The final fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf–Rayet stars 1 emit strong and rapidly expanding winds with speeds greater than 1,000 kilometres per second. A fraction of this population is also helium-depleted, with spectra dominated by highly ionized emission lines of carbon and oxygen (types WC/WO). Evidence indicates that the most commonly observed supernova explosions that lack hydrogen and helium (types Ib/Ic) cannot result from massive WC/WO stars 2 , 3 , leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosion 4 . Here we report observations of SN 2019hgp, beginning about a day after the explosion. Its short rise time and rapid decline place it among an emerging population of rapidly evolving transients 5 – 8 . Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen and neon. Narrow absorption features show that this material is expanding at high velocities (greater than 1,500 kilometres per second), requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive Wolf–Rayet stars may be the progenitors of some rapidly evolving transients. Observations of the supernova SN 2019hgp, identified about a day after its explosion, show that it occurred within a nebula of carbon, oxygen and neon, and was probably the explosion of a massive WC/WO star.

The early evolution of a supernova (SN) can reveal information about the environment and the progenitor star. When a star explodes in vacuum, the first photons to escape from its surface appear as a brief, hours-long shock-breakout flare 1 , 2 , followed by a cooling phase of emission. However, for stars exploding within a distribution of dense, optically thick circumstellar material (CSM), the first photons escape from the material beyond the stellar edge and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating 3 . Early serendipitous observations 2 , 4 that lacked ultraviolet (UV) data were unable to determine whether the early emission is heating or cooling and hence the nature of the early explosion event. Here we report UV spectra of the nearby SN 2023ixf in the galaxy Messier 101 (M101). Using the UV data as well as a comprehensive set of further multiwavelength observations, we temporally resolve the emergence of the explosion shock from a thick medium heated by the SN emission. We derive a reliable bolometric light curve that indicates that the shock breaks out from a dense layer with a radius substantially larger than typical supergiants. Using ultraviolet data as well as a comprehensive set of further multiwavelength observations of the supernova 2023ixf, a reliable bolometric light curve is derived that indicates the heating nature of the early emission.

If a star gets too close to a supermassive black hole, it gets ripped apart in a tidal disruption event (TDE). Mattila et al. discovered a transient source in the merging galaxy pair Arp 299, which they interpret as a TDE. The optical light is hidden by dust, but the TDE generated copious infrared emission. Radio observations reveal that a relativistic jet was produced as material fell onto the black hole, with the jet expanding over several years. The results elucidate how jets form around supermassive black holes and suggest that many TDEs may be missed by optical surveys. Science , this issue p. 482 A relativistic radio jet is seen switching on after a star is ripped apart by a black hole. Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 10 52 erg at infrared and radio wavelengths but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH.

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.

With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, which sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF 13dqy = SN 2013fs a mere ∼3 h after explosion. Our rapid follow-up observations, which include multiwavelength photometry and extremely early (beginning at ∼6 h post-explosion) spectra, map the distribution of material in the immediate environment (≲10 15  cm) of the exploding star and establish that it was surrounded by circumstellar material (CSM) that was ejected during the final ∼1 yr prior to explosion at a high rate, around 10 −3 solar masses per year. The complete disappearance of flash-ionized emission lines within the first several days requires that the dense CSM be confined to within ≲10 15  cm, consistent with radio non-detections at 70–100 days. The observations indicate that iPTF 13dqy was a regular type II supernova; thus, the finding that the probable red supergiant progenitor of this common explosion ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars. Type II supernova explosions are common, but our understanding of such events is not complete. Such an event was observed just three hours after the explosion started, providing important information about the early stages.

Supernovae with a difference Two groups working independently report the observation of mildly relativistic outflows from seemingly ordinary type Ibc and type Ic supernovae. Soderberg et al . detected luminous radio emission from the type Ibc supernova SN 2009bb, implying an expansion velocity of 0.85 times the speed of light, and a minimum energy comparable to those of the radio afterglows of nearby γ-ray bursts. Paragi et al . observed mildly relativistic expansion (at 0.6 times the speed of light or more) for a small fraction of the ejecta from the type Ic supernova SN2007gr. These discoveries are relevant to the long-standing question of what makes a small fraction of supernova explosions eject material at relativistic speeds, producing the γ-ray bursts characteristic of the explosion of a massive star. Soderberg et al . conclude that only about 1% of type Ibc supernovae harbour central engines and Paragi et al . that most or all type Ic supernovae produce mildly relativistic jets, but as they account for only a small fraction of the total energy, they are very hard to detect. Long duration γ-ray bursts mark the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. To date, central-engine-driven supernovae have been discovered exclusively through their γ-ray emission, yet it is expected that a larger population goes undetected. The discovery of luminous radio emission from the seemingly ordinary type Ibc supernova SN 2009bb, which requires a substantial relativistic outflow powered by a central engine, is now reported. Long duration γ-ray bursts (GRBs) mark 1 the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. They are distinguished by the production of an energetic and collimated relativistic outflow powered 2 by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested 3 in the pulse of γ-rays and a long-lived radio afterglow. Until now, central-engine-driven supernovae have been discovered exclusively through their γ-ray emission, yet it is expected 4 that a larger population goes undetected because of limited satellite sensitivity or beaming of the collimated emission away from our line of sight. In this framework, the recovery of undetected GRBs may be possible through radio searches 5 , 6 for type Ibc supernovae with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. A comparison with our radio survey of type Ibc supernovae reveals that the fraction harbouring central engines is low, about one per cent, measured independently from, but consistent with, the inferred 7 rate of nearby GRBs. Independently, a second mildly relativistic supernova has been reported 8 .

When a massive star explodes as a supernova, substantial amounts of radioactive elements-primarily Ni-56, Ni-57 and Ti-44 are produced. After the initial from shock heating, the light emitted by the supernova is due to the decay of these elements. However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium. The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellan Cloud. From 1994 to 200l, the ejecta faded owing to radioactive decay of Ti-44 as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejects, enabling us to analyse the structure and chemistry of the vanished star.

Hydrogen-poor superluminous supernovae (SLSN-I) are a class of rare and energetic explosions that have been discovered in untargeted transient surveys in the past decade 1 , 2 . The progenitor stars and the physical mechanism behind their large radiated energies (about 10 51  erg or 10 44  J) are both debated, with one class of models primarily requiring a large rotational energy 3 , 4 and the other requiring very massive progenitors that either convert kinetic energy into radiation through interaction with circumstellar material (CSM) 5 – 8 or engender an explosion caused by pair-instability (loss of photon pressure due to particle–antiparticle production) 9 , 10 . Observing the structure of the CSM around SLSN-I offers a powerful test of some scenarios, although direct observations are scarce 11 , 12 . Here, we present a series of spectroscopic observations of the SLSN-I iPTF16eh, which reveal both absorption and time- and frequency-variable emission in the Mg ii resonance doublet. We show that these observations are naturally explained as a resonance scattering light echo from a circumstellar shell. Modelling the evolution of the emission, we infer a shell radius of 0.1 pc and velocity of 3,300 km s −1 , implying that the shell was ejected three decades before the supernova explosion. These properties match theoretical predictions of shell ejections occurring because of pulsational pair-instability and imply that the progenitor had a helium core mass of about 50–55 M ⊙ , corresponding to an initial mass of about 115 M ⊙ . Probing the pre-explosion environments of hydrogen-poor superluminous supernovae is important for understanding how they exploded. Here, Lunnan et al. infer the presence of a fast-moving circumstellar shell around iPTF16eh through the detection of a resonance-line light echo, which indicates the massive progenitor experienced pulsational pair instability shell ejections.

SN 2010jl was a luminous Type IIn supernova (SN), detected in radio, optical, X-ray and hard X-rays. Here we report on its six-year R- and g-band light curves obtained using the Palomar Transient Factory. The light curve was generated using a pipeline based on the proper image-subtraction method and we discuss the algorithm performances. As noted before, the R-band light curve, up to about 300 days after maximum light is well described by a power-law decline with a power-law index of −0.5. Between day 300 and day 2300 after maximum light, it is consistent with a power-law decline, with a power-law index of about −3.4. The longevity of the light curve suggests that the massive circumstellar material around the progenitor was ejected on timescales of at least tens of years prior to the progenitor explosion.