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Record neutron star mass rules out exotics New observations of the binary millisecond pulsar J1614-2230 have identified one of its components as the most massive neutron star for which a precise mass is known — nearly 20% greater than previous highest values. Neutron stars are composed of the densest form of matter known, and millisecond pulsars are rotating neutron stars. The observed range of neutron star masses has hitherto been too narrow to rule out many predictions of 'exotic' non-nucleonic components, but this pulsar weighs in at around two solar masses, ruling out almost all currently proposed equations of state involving exotic hyperon or boson condensates. Neutron stars comprise the densest form of matter known to exist in our Universe, but their composition and properties are uncertain. Measurements of their masses and radii can constrain theoretical predictions of their composition, but so far it has not been possible to rule out many predictions of 'exotic' non-nucleonic components. Here, radio timing observations of the binary millisecond pulsar J1614-2230 are presented, allowing almost all currently proposed hyperon or boson condensate equations of state to be ruled out. Neutron stars are composed of the densest form of matter known to exist in our Universe, the composition and properties of which are still theoretically uncertain. Measurements of the masses or radii of these objects can strongly constrain the neutron star matter equation of state and rule out theoretical models of their composition 1 , 2 . The observed range of neutron star masses, however, has hitherto been too narrow to rule out many predictions of ‘exotic’ non-nucleonic components 3 , 4 , 5 , 6 . The Shapiro delay is a general-relativistic increase in light travel time through the curved space-time near a massive body 7 . For highly inclined (nearly edge-on) binary millisecond radio pulsar systems, this effect allows us to infer the masses of both the neutron star and its binary companion to high precision 8 , 9 . Here we present radio timing observations of the binary millisecond pulsar J1614-2230 10 , 11 that show a strong Shapiro delay signature. We calculate the pulsar mass to be (1.97 ± 0.04) M ⊙ , which rules out almost all currently proposed 2 , 3 , 4 , 5 hyperon or boson condensate equations of state ( M ⊙ , solar mass). Quark matter can support a star this massive only if the quarks are strongly interacting and are therefore not ‘free’ quarks 12 .

The Kepler and TESS space missions significantly expanded our knowledge of what types of stars display flaring activity by recording a vast amount of super-flares from solar-like stars, as well as detecting flares from hotter stars of A-F spectral types. Currently, we know that flaring occurs in the stars as hot as B-type ones. However, the structures of atmospheres of hot B-A stars crucially differ from the ones of late types, and thus the occurrence of flaring in B-A type stars requires some extension of our theoretical views of flare formation and therefore a detailed study of individual objects. Here we present the results of our spectral and photometric study of HD 36030, which is a B9 V star with flares detected by the TESS satellite. The spectra we acquired suggest that the star is in a binary system with a low-mass secondary component, but the light curve lacks any signs of periodic variability related to orbital motion or surface magnetic fields. Because of that, we argue that the flares originate due to magnetic interaction between the components of the system.

Gas accretion onto some massive black holes (MBHs) at the centers of galaxies actively powers luminous emission, but most MBHs are considered dormant. Occasionally, a star passing too near an MBH is torn apart by gravitational forces, leading to a bright tidal disruption flare (TDF). Although the high-energy transient Sw 1644+57 initially displayed none of the theoretically anticipated (nor previously observed) TDF characteristics, we show that observations suggest a sudden accretion event onto a central MBH of mass about 10 6 to 10 7 solar masses. There is evidence for a mildly relativistic outflow, jet collimation, and a spectrum characterized by synchrotron and inverse Compton processes; this leads to a natural analogy of Sw 1644+57 to a temporary smaller-scale blazar.

A stellar interior probed The predictive power of current stellar evolution models is limited by the fact that little is known about the mixing process occurring at the stellar core. In theory, massive stars such as HD 50230 — seven times the mass of the Sun — should be ideal models for seismic probing of the stellar core via the distinct signature they leave in the gravity mode spectrum as it propagates from the core to the stellar surface. These gravity modes have now been detected observationally, in a continuous photometric light curve for HD 50230 collected with the CoRoT satellite. The data make it possible to estimate the extent of the convective core and constrain the location of the chemical transition zone at about 10% of the stellar radius. Measuring the oscillations of a star can allow the various mixing processes in its interior to be disentangled, through the signature they leave on period spacings in the gravity mode spectrum. Here numerous gravity modes in a young star of about seven solar masses are reported: the mean period spacing enables the extent of the convective core to be determined, and the clear periodic deviation from the mean constrains the location of the chemical transition zone — at about 10 per cent of the radius. The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core, preventing precise predictions of stellar evolution 1 . The unknown nature of the mixing processes as well as the extent of the central mixed region is particularly problematic for massive stars 2 . Oscillations in stars with masses a few times that of the Sun offer a unique opportunity to disentangle the nature of various mixing processes, through the distinct signature they leave on period spacings in the gravity mode spectrum 3 . Here we report the detection of numerous gravity modes in a young star with a mass of about seven solar masses. The mean period spacing allows us to estimate the extent of the convective core, and the clear periodic deviation from the mean constrains the location of the chemical transition zone to be at about 10 per cent of the radius and rules out a clear-cut profile.

A new N I model atom has been constructed using the energy levels known from laboratory measurements and predicted in N I atomic structure calculations and up-to-date atomic data for calculating the radiative and collisional transition rates. The solar abundance has been determined from N I lines by the synthetic spectrum method with a classical one-dimensional (1D, MARCS) solar model atmosphere and by taking into account the departures from local thermodynamic equilibrium (non-LTE effects). By applying the 3D corrections of Amarsi et al. (2020), we have obtained for the Sun. Based on high-resolution spectra, we have derived the non-LTE nitrogen abundances for 11 unevolved A–F-type stars with reliably determined atmospheric parameters. Non-LTE leads to a strengthening of N I lines, and the non-LTE effects grow with increasing effective temperature. For each of the stars the departures from LTE lead to a decrease in the root-mean-square (rms) abundance error compared to the LTE case. For superficially normal A stars non-LTE removes the enhancements relative to the solar nitrogen abundance obtained in an LTE analysis. The Boo-type star HD 172167 (Vega) also has a nearly solar nitrogen abundance. Four Am stars exhibit a scatter, from a nitrogen underabundance with to a nitrogen overabundance with . The nitrogen abundances for the Sun and superficially normal A stars are consistent within the error limits with the nitrogen abundance in the interstellar gas and early B-type stars.

X-Rated Supernova A link between long γ-ray bursts (GRBs) and supernovae has been established, but whether there is a similar relationship between the weaker and softer X-ray flashes and supernovae is unclear. GRB/XRF 060218, spotted by the Swift satellite on 18 February this year, may supply that missing link. In the first of four papers on this novel burster, Campana et al . report the sighting of the X-ray signature of a shock break-out, possible evidence of a supernova in progress. Pian et al . report the optical discovery of a type Ic supernova 2006aj associated with GRB/XRF 060218. Soderberg et al . report radio and X-ray observations that show that XRF 060218 is 100 times less energetic than, but of a type that is ten times more common than cosmological GRBs. Mazzali et al . modelled the spectra and light curve of SN 2006aj to show that it had a much smaller explosion energy and ejected much less mass than other GRB-supernovae, suggesting that it was produced by a star with a mass was only about 20 times that of the Sun, leaving behind a neutron star, rather than a black hole. Modelling the spectra and light curve of supernova SN 2006aj shows that it had a much smaller explosion energy and ejected much less mass than other gamma-ray burst–supernovae, suggesting that it was produced by a star whose initial mass was only ∼20 solar masses, and which left behind a neutron star, rather than a black hole. Supernovae connected with long-duration γ -ray bursts 1 , 2 , 3 (GRBs) are hyper-energetic explosions resulting from the collapse of very massive stars (∼40  M ⊙ , where M ⊙ is the mass of the Sun) stripped of their outer hydrogen and helium envelopes 4 , 5 , 6 , 7 . A very massive progenitor, collapsing to a black hole, was thought to be a requirement for the launch of a GRB 8 . Here we report the results of modelling the spectra and light curve of SN 2006aj (ref. 9 ), which demonstrate that the supernova had a much smaller explosion energy and ejected much less mass than the other GRB–supernovae, suggesting that it was produced by a star whose initial mass was only ∼20  M ⊙ . A star of this mass is expected to form a neutron star rather than a black hole when its core collapses. The smaller explosion energy of SN 2006aj is matched by the weakness and softness 10 of GRB 060218 (an X-ray flash), and the weakness of the radio flux of the supernova 11 . Our results indicate that the supernova–GRB connection extends to a much broader range of stellar masses than previously thought, possibly involving different physical mechanisms: a ‘collapsar’ (ref. 8 ) for the more massive stars collapsing to a black hole, and magnetic activity of the nascent neutron star 12 for the less massive stars.

A homogeneous set of calcium and scandium abundances has been obtained for 54 A-type stars with strong metal lines (Am stars) by taking into account the departures from local thermodynamic equilibrium. A correlation of the Ca and Sc abundances with the effective temperature has been revealed, with the Ca and Sc abundances in stars with a surface gravity growing with increasing faster than in stars with . No correlation of the Ca and Sc abundances with the iron abundance and the stellar rotation velocity has been found. Am stars exhibit, on average, a higher value of [Ca/H] than that of [Sc/H] and . However, for K there is a hint at a systematic difference between stars with and . The iron overabundance is, on average, the same in the range . It is shown that when atomic diffusion is taken into account, evolution computations with the MESA code for stellar masses of 1.5–2.2 give surface abundances that are consistent with the Ca and Fe abundances in Am stars in three open clusters with an age greater than 600 Myr. Additional mechanisms for the separation of chemical elements are required to explain the Am phenomenon in young stars in the Pleiades cluster. Published diffusion models have been tested. The turbulent models of Richer et al. (2000) and Hui-Bon-Hoa et al. (2022) are consistent with the observations of Am stars in open clusters at large values of the free parameter : 1000 for Ca and Fe and 500 for Sc. None of the diffusion models corresponding to the mass and age of the Am star Sirius reproduces the abundances of the elements from He to Ni observed in it. The results obtained are important for a better understanding of the chemical peculiarity mechanisms in Am stars.

This study explores the impact of viscous heating on decretion disks around Classical Ae (CAe) stars, with a focus on modeling the disk’s thermal structure. While photoionization is the dominant heating mechanism, viscous dissipation can play an important role in shaping the disk temperature, particularly for cooler CAe subtypes. Our models incorporate viscosity-driven heating and predict that shear heating has a negligible effect for early A-type stars (A0–A1), but it becomes increasingly significant for later spectral types, especially as the viscosity parameter (α) increases. This heating also influences the strength of Hα emission. Furthermore, our models predict a sharp decline in the number of emission-line stars beyond spectral type A2, a trend observed in CAe populations. However, for sufficiently high α values (≥0.3), a higher fraction of emission-line objects is expected even among later subtypes, such as A5, despite the lack of well-characterized CAe stars observed beyond the spectral type A4.

Models of terrestrial planet formation predict that the final stages of planetary assembly—lasting tens of millions of years beyond the dispersal of young protoplanetary disks—are dominated by planetary collisions. It is through these giant impacts that planets like the young Earth grow to their final mass and achieve long-term stable orbital configurations 1 . A key prediction is that these impacts produce debris. So far, the most compelling observational evidence for post-impact debris comes from the planetary system around the nearby 23-million-year-old A-type star HD 172555. This system shows large amounts of fine dust with an unusually steep size distribution and atypical dust composition, previously attributed to either a hypervelocity impact 2 , 3 or a massive asteroid belt 4 . Here we report the spectrally resolved detection of a carbon monoxide gas ring co-orbiting with dusty debris around HD 172555 between about six and nine astronomical units—a region analogous to the outer terrestrial planet region of our Solar System. Taken together, the dust and carbon monoxide detections favour a giant impact between large, volatile-rich bodies. This suggests that planetary-scale collisions, analogous to the Moon-forming impact, can release large amounts of gas as well as debris, and that this gas is observable, providing a window into the composition of young planets. A carbon monoxide gas ring co-orbiting with dusty debris is observed in the outer terrestrial planet region of the star HD 172555, which indicates that a planetary-scale impact took place.

Magnetic fields play a fundamental role for interior and atmospheric properties of M dwarfs and greatly influence terrestrial planets orbiting in the habitable zones of these low-mass stars. Determination of the strength and topology of magnetic fields, both on stellar surfaces and throughout the extended stellar magnetospheres, is a key ingredient for advancing stellar and planetary science. Here, modern methods of magnetic field measurements applied to M-dwarf stars are reviewed, with an emphasis on direct diagnostics based on interpretation of the Zeeman effect signatures in high-resolution intensity and polarisation spectra. Results of the mean field strength measurements derived from Zeeman broadening analyses as well as information on the global magnetic geometries inferred by applying tomographic mapping methods to spectropolarimetric observations are summarised and critically evaluated. The emerging understanding of the complex, multi-scale nature of M-dwarf magnetic fields is discussed in the context of theoretical models of hydromagnetic dynamos and stellar interior structure altered by magnetic fields.