Nature Astronomy最新文献

Active galactic nuclei (AGNs) are a key component of galaxy evolution owing to feedback on the host from its supermassive black hole. The morphology of warm inflowing and outflowing dusty material can reveal the nature of the onset of feedback, AGN feeding and the unified model of AGN. Here we use the Large Binocular Telescope Interferometer (LBTI) to image the dense, obscuring disk and extended dusty outflow region of NGC 1068. In Fizeau imaging mode, the LBTI synthesizes the equivalent resolution of a 22.8 m telescope. The 8.7 μm Fizeau images of NGC 1068 have an effective resolution of 47 × 90 mas (3.3 × 6.2 pc) in a 5″ field of view after performing point spread function deconvolution techniques described here. This is the only extragalactic source to be Fizeau imaged using the LBTI, and the images bridge the scales measured with the Very Large Telescope Interferometer (0.5–5 pc) and those of single telescopes such as James Webb Space Telescope and Keck (>15 pc). The images detect and spatially resolve the low surface brightness mid-infrared features in the AGN disk/wind region that are overresolved by the Very Large Telescope Interferometer. The images show strong correlation between mid-infrared dust emission and near-infrared emission of highly excited atomic lines observed by SINFONI. Such LBTI imaging is a precursor to infrared imaging using the upcoming generation of extremely large telescopes, with angular resolutions up to six times better than James Webb Space Telescope, the largest space telescope in orbit.

Long-period radio transients are a new class of astronomical objects characterized by prolonged periods ranging from 18 min to 54 min. They exhibit highly polarized, coherent, beamed radio emission lasting only 10–100 s. The intrinsic nature of these objects is subject to speculation, with highly magnetized white dwarfs and neutron stars being the prevailing candidates. Here we present ASKAP J183950.5−075635.0, boasting the longest known period of this class at 6.45 h. It exhibits emission characteristics of an ordered dipolar magnetic field, with pulsar-like bright main pulses and weaker interpulses offset by about half a period that are indicative of an oblique or orthogonal rotator. This phenomenon, observed in a long-period radio transient, confirms that the radio emission originates from both magnetic poles and that the observed period corresponds to the rotation period. The spectroscopic and polarimetric properties of ASKAP J183950.5−075635.0 are consistent with a neutron star origin, and this object is a crucial piece of evidence in our understanding of long-period radio sources and their links to neutron stars.

The widely accepted accretion scenario of planet formation suggests that the Moon experienced a violent bombardment in its early history. The accretion scenario predicts that a total of ~300 basins with sizes greater than 300 km formed throughout its bombardment history; however, only ~40 basins of this size are identified on the Moon. The cause for this notable discrepancy is unknown. Here we investigate the viscous relaxation of impact basins formed within ~150 Myr after the completion of lunar magma ocean (LMO) solidification, as only impacts that happened afterwards could be retained by the crust. We find that, owing to the high temperature of the lower crust, basins formed within ~100 Myr after the LMO solidification could have been sufficiently relaxed by lower crustal inflow to escape detection in gravitational and topographic data. By contrast, basins formed afterwards should have limited relaxation, as the cooler temperature of the lower crust inhibits the inflow. Our results show that, to have ~40 retained basins, the Moon would have had ~300–1,000 basin-forming impacts throughout its history and the LMO would have solidified ~4.3 Gyr ago. The temperature-dependent viscous relaxation of post-LMO basins provides a realistic explanation for the low number of basins observed on the Moon. The substantial relaxation of early basins suggests that terrestrial planets, which experienced crustal cooling after magma ocean solidification, may have suffered far more impacts than the basin records indicate.

The dynamic properties of molecular clouds are set by the interplay of their self-gravity, turbulence, external pressure and magnetic fields. Extended surveys of Galactic molecular clouds typically find that their kinetic energy (E_k) counterbalances their self-gravitational energy (E_g), setting their virial parameter α_vir = 2E_k/∣E_g∣ ≈ 1. However, past studies either have been biased by the use of optically thick lines or have been limited within the solar neighbourhood and the inner Galaxy (Galactocentric radius R_gc < R_gc,⊙ ≈ 8 kpc). Here we present sensitive mapping observations of optically thin ¹³CO lines towards molecular clouds in the low-metallicity Galactic outer disk (R_gc ~ 9–24 kpc). By combining archival data from the inner Galaxy and four nearby metal-poor dwarf galaxies, we reveal a systematic trend of α_vir, which declines from supervirial dynamic states in metal-rich clouds to extremely subvirial dynamic states in metal-poor clouds. In these metal-poor environments, turbulence alone is insufficient to counterbalance the self-gravity of a cloud. A cloud-volumetric magnetic field may replace turbulence as the dominant cloud-supporting mechanism in low-metallicity conditions, for example, the outermost galactic disks, dwarf galaxies and galaxies in the early Universe, which would then inevitably impact the initial conditions for star formation in such environments.

Exoplanets and smaller bodies have been detected orbiting different kind of stars. However, we do not know of any such objects in planetary nebulae, the short-lived stage of stellar evolution between the asymptotic giant branch and white dwarf phases. The planetary activity (destruction and formation) may be accompanied by dust clouds. Hence, we searched for dust occultation events in planetary nebulae using archival photometric data. We show that the central star of PN WeSb 1 features numerous dimming events with typical durations of a few days to weeks that are up to 3 mag deep. This variability is mainly stochastic with an indication of a 400 d period. The occultations are almost grey, indicating dust grains larger than about 0.1 μm. Based on our follow-up observations, we argue that the central star is a wide binary and that these events are most probably caused by debris from disintegrated small rocky bodies that escaped from the former asymptotic giant branch star to find safe harbour around the companion star. The latter star dominates the optical spectrum enabling us to see the eclipses. This means that planetary systems are present and undergo violent evolution during the planetary nebula stage.

Strong gravitational magnification enables the detection of faint background sources and allows researchers to resolve their internal structures and even identify individual stars in distant galaxies. Highly magnified individual stars are useful in various applications, including studies of stellar populations in distant galaxies and constraining dark matter structures in the lensing plane. However, these applications have been hampered by the small number of individual stars observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of more than 40 microlensed stars in a single galaxy behind Abell 370 at redshift of 0.725 (dubbed ‘the Dragon arc’) when the Universe was half of its current age, using James Webb Space Telescope observations with the time-domain technique. These events were found near the expected lensing critical curves, suggesting that these are magnified stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry, we constrained their stellar types and found that many of them are consistent with red giants or supergiants magnified by factors of hundreds. This finding reveals a high occurrence of microlensing events in the Dragon arc and demonstrates that time-domain observations by the James Webb Space Telescope could lead to the possibility of conducting statistical studies of high-redshift stars.

Cosmic rays (CRs) play a pivotal role in shaping the thermal and dynamical properties of astrophysical environments, such as galaxies and galaxy clusters. Recent observations suggest a stronger confinement of CRs in certain astrophysical systems than predicted by current CR-transport theories. Here, we show that the incorporation of microscale physics into CR-transport models can account for this enhanced CR confinement. We develop a theoretical description of the effect of magnetic microscale fluctuations originating from the mirror instability on macroscopic CR diffusion. We confirm our theory with large-dynamical-range simulations of CR transport in the intracluster medium (ICM) of galaxy clusters and kinetic simulations of CR transport in micromirror fields. We conclude that sub-teraelectronvolt CR confinement in the ICM is far more effective than previously anticipated on the basis of Galactic-transport extrapolations. The transformative impact of micromirrors on CR diffusion provides insights into how microphysics can reciprocally affect macroscopic dynamics and observable structures across a range of astrophysical scales.