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The ultraluminous X-ray source M 101 ULX-1 consists of a black hole orbiting a Wolf-Rayet star; optical spectroscopy now shows that the orbital period is 8.2 days, suggesting that the black hole has a mass in the range 5 to 30 solar masses, though the X-ray spectra are unlike what is expected from accretion onto a stellar-mass black hole—accretion must occur from captured stellar wind, which has hitherto been thought to be so inefficient that it could not power an ultraluminous source. Accretion power for an ultraluminous X-ray source Ultraluminous X-ray sources (ULXs), more luminous than known stellar processes but less so than active galactic nuclei, are generally thought to be powered by either intermediate-mass black holes or smaller, stellar-mass black holes radiating at higher rates. Analysis of the optical spectra of M 101 ULX-1, a variable source in the nearby spiral galaxy M 101, suggests that matters may be more complicated. The luminosity of the source at the time of discovery was within the range expected for a ULX harbouring an intermediate-mass black hole. But the optical spectra reported here are consistent with the presence of a stellar-mass black hole, probably with a mass of 20–30 solar masses. The authors suggest that M 101 ULX-1 is driven by a black hole accreting gas from the wind of a companion star, a mechanism that had previously been rejected on the grounds that it was thought too slow for the purpose. There are two proposed explanations for ultraluminous X-ray sources 1 , 2 (ULXs) with luminosities in excess of 10 39  erg s −1 . They could be intermediate-mass black holes (more than 100–1,000 solar masses, ) radiating at sub-maximal (sub-Eddington) rates, as in Galactic black-hole X-ray binaries but with larger, cooler accretion disks 3 , 4 , 5 . Alternatively, they could be stellar-mass black holes radiating at Eddington or super-Eddington rates 2 , 6 . On its discovery, M 101 ULX-1 4 , 7 had a luminosity of 3 × 10 39  erg s −1 and a supersoft thermal disk spectrum with an exceptionally low temperature—uncomplicated by photons energized by a corona of hot electrons—more consistent with the expected appearance of an accreting intermediate-mass black hole 3 , 4 . Here we report optical spectroscopic monitoring of M 101 ULX-1. We confirm the previous suggestion 8 that the system contains a Wolf-Rayet star, and reveal that the orbital period is 8.2 days. The black hole has a minimum mass of 5 , and more probably a mass of 20 −30 , but we argue that it is very unlikely to be an intermediate-mass black hole. Therefore, its exceptionally soft spectra at high Eddington ratios violate the expectations for accretion onto stellar-mass black holes 9 , 10 , 11 . Accretion must occur from captured stellar wind, which has hitherto been thought to be so inefficient that it could not power an ultraluminous source 12 , 13 .

Persistent low-velocity baryonic jets have been detected from a supersoft X-ray source; the low velocity suggests that these jets have not been launched from a white dwarf, and the persistence speaks against the origin being a canonical black hole or neutron star, indicating that a different type of source must be implicated. Supersoft X-ray source hard to explain Persistent low-velocity baryonic jets have been detected from a supersoft X-ray source in the nearby galaxy M81, showing blueshifted broad H? emission lines, characteristic of baryonic jets with relativistic speeds. The combination of relativistic jets and persistently supersoft X-ray spectra is unexpected, and presents a challenge to current theories of supersoft sources and jet formation. One possible explanation is that this source is a long-speculated, supercritically accreting black hole with optically thick outflows. The formation of relativistic jets by an accreting compact object is one of the fundamental mysteries of astrophysics. Although the theory is poorly understood, observations of relativistic jets from systems known as microquasars (compact binary stars) 1 , 2 have led to a well established phenomenology 3 , 4 . Relativistic jets are not expected to be produced by sources with soft or supersoft X-ray spectra, although two such systems are known to produce relatively low-velocity bipolar outflows 5 , 6 . Here we report the optical spectra of an ultraluminous supersoft X-ray source (ULS 7 , 8 ) in the nearby galaxy M81 (M81 ULS-1; refs 9 , 10 ). Unexpectedly, the spectra show blueshifted, broad Hα emission lines, characteristic of baryonic jets with relativistic speeds. These time-variable emission lines have projected velocities of about 17 per cent of the speed of light, and seem to be similar to those from the prototype microquasar SS 433 (refs 11 , 12 ). Such relativistic jets are not expected to be launched from white dwarfs 13 , and an origin from a black hole or a neutron star is hard to reconcile with the persistence of M81 ULS-1’s soft X-rays 10 . Thus the unexpected presence of relativistic jets in a ULS challenges canonical theories of jet formation 3 , 4 , but might be explained by a long-speculated, supercritically accreting black hole with optically thick outflows 14 , 15 , 16 , 17 , 18 , 19 , 20 .

Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic \"core-collapse\" supernova. Such events are usually only detected at least a few days after the star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy Evolution Explorer space telescope reveal a radiative precursor from the supernova shock before the shock reached the surface of the star and show the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve confirm that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a way to probe the physics of core-collapse supernovae and the internal structures of their progenitor stars.

Some stars explode in thermonuclear supernovae, but understanding of why this occurs comes mainly from indirect clues. Now, the progenitor of a member of a strange class of such explosions may have been detected directly. See Letter p.54 A type Iax supernova progenitor SN 2012Z, discovered in the Lick Observatory Supernova Search on 29 January 2012, is a type Iax supernova. Sometimes referred to as 'mini supernovae', these are initially spectroscopically similar to some type-Ia supernovae but diverge with time and are much less energetic and fainter. It is not clear what triggers a type Iax explosion. This paper reports the detection of a progenitor in deep observations of NGC 1309, the host galaxy of SN 2012Z, obtained with the Hubble Space Telescope and including the location of the supernova before its explosion. Its optical properties and similarity to the progenitor of the helium nova V445 Puppis suggest that SN 2012Z was probably an explosion of a white dwarf accreting from a helium-star companion.

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun 1 – 4 . Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star–black-hole binaries 5 , 6 . When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68 − 13 + 11 solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories. Radial-velocity measurements of a Galactic B-type star show a dark companion that seems to be a black hole of about 68 solar masses, in a widely spaced binary system.

Gravitational-wave (GW) observations are revealing the population of compact objects from a new angle. Yet their stellar progenitors remain uncertain because few observational clues on their progenitors exist. Theoretical models typically assume that the progenitor evolution can be approximated with single-star models. We explore how binary evolution affects the pre-supernova (SN) structure of stars, and the resulting distribution of compact object remnants. We focus on the differences in the core properties of single stars and of donor stars that transfer their outer layers in binary systems and become binary-stripped. We show that the final structures of binary-stripped stars that lose their outer layers before the end of core helium burning are systematically different compared to single stars. As a result, we find that binary-stripped stars tend to explode more easily than single stars and preferentially produce neutron stars and fewer black holes, with consequences for GW progenitors.

The 3HE problem inconsistency with regard to the light element production of the Big Bang model is discussed. Computer models of evolving stars showing the discrepancy between the amount of helium-3 predicted and the amount actually observed in the universe are presented.

Variations in the mass loss from single stars have been used to explain the existence of hot subdwarf stars and the existence of single low-mass white dwarfs (LMWDs). Hence remaining uncertainty in mass loss from single red-giant stars is important to the understanding of these problems. However, natural formation channels for hot subdwarfs and single LMWDs have also been proposed which do not rely on unexplained mass loss from single red-giant stars. We outline these, and discuss how the different mechanisms could be distinguished. For example, a formation channel for single LMWDs which involves the break-up of a binary system by a type Ia supernova should produce a population of single LMWDs with a distinct kinematic signature. If that population is found to exist, it could be used to study one of the popular single-degenerate formation channels for type Ia supernovae in a previously impossible way. In addition, we examine the formation of helium-rich sdO stars—which are shown to emerge from one of the previously existing binary formation channels for hot subdwarfs. Both the SN Ia formation mechanism for single LMWDs and the formation channel for He-sdOs are a natural consequence of existing models. Hence if these formation channels do not work at all, then the result is a significant one.