Nature Astronomy最新文献

Vesta’s large-scale interior structure had previously been constrained primarily using the gravity and shape data from the Dawn mission. However, these data alone still allow a wide range of possibilities for the differentiation state of the body. The moment of inertia is arguably the most diagnostic parameter related to the radial density distribution of a planetary body, making it crucial for assessing the body’s state of internal differentiation. Determining the moment of inertia requires additional measurements of the amplitudes of small rotational motions, such as precession and nutation. Here we report an updated estimate of the moment of inertia of Vesta inferred from Dawn’s Doppler tracking via the Deep Space Network and onboard imaging data. The recovered value for Vesta’s normalized polar moment of inertia is (bar{C}/M{R}^{2}=0.4208pm 0.0047) (where M is the mass of Vesta and R is the reference radius), which is only 6.6% lower than the homogeneous value of 0.4505. This value, combined with the gravity field and global shape, suggests that Vesta’s interior has limited density stratification beneath its howardite–eucrite–diogenite-dominated crust. We propose two possible origin scenarios that are consistent with the observed constraints. In the first scenario, Vesta’s interior did not undergo full differentiation due to late accretion. In the second scenario, Vesta originated as an impact remnant of a larger differentiated body re-accreted with non-chondritic bulk composition produced from a catastrophic impact. Vesta did not experience complete differentiation in either scenario, suggesting that its current state reflects a complex interplay between its accretion timing, thermal evolution, redistribution of ²⁶Al bearing melt and/or impact processes.

The ionized interstellar medium contains astronomical-unit-scale (and below) structures that scatter radio waves from pulsars, resulting in scintillation. Power spectral analysis of scintillation often shows parabolic arcs, with curvatures that encode the locations and kinematics of the pulsar, Earth and interstellar plasma. Here we report the discovery of 25 distinct plasma structures in the direction of the brilliant millisecond pulsar, PSR J0437−4715, in observations obtained with the MeerKAT radio telescope. Four arcs reveal structures within 5,000 au of the pulsar, from a series of shocks induced as the pulsar and its wind interact with the ambient interstellar medium. The measured radial distance and velocity of the main shock allow us to solve the shock geometry and space velocity of the pulsar in three dimensions, whereas the velocity of another structure unexpectedly indicates a back flow from the direction of the shock or pulsar-wind tail. The remaining 21 arcs represent a surprising abundance of structures sustained by turbulence within the Local Bubble, which is a region of the interstellar medium thought to be depleted of gas by a series of supernova explosions about 14 Myr ago. The Local Bubble is cool enough in areas for subastronomical-unit density fluctuations to arise from turbulence.

Protoplanetary disks are traditionally described as finite-mass reservoirs left over by the gravitational collapse of the protostellar core, a view that strongly constrains both disk-evolution and planet-formation models. We propose a different scenario in which protoplanetary disks of pre-main sequence stars are primarily assembled by Bondi–Hoyle accretion from the parent gas cloud. We demonstrate that Bondi–Hoyle accretion can supply not only the mass but also the angular momentum necessary to explain the observed size of protoplanetary disks. Additionally, we predict how the specific angular momentum of protoplanetary disks scales with stellar mass. Our conclusions are based on an analytical derivation of the scaling of the angular momentum in turbulent flows, which we confirmed with a numerical simulation of supersonic turbulence. A key outcome of our analysis is the recognition that density fluctuations in supersonic turbulence—previously overlooked in studies of cloud and core rotation—lead to a significant increase in angular momentum at disk-forming scales. This revised understanding of disk formation and evolution alleviates several long-standing observational discrepancies and compels substantial revisions to current models of disk and planet formation.

This recent JWST image shows a galaxy-scale strong lensing system, consisting of a distant spiral galaxy that is being lensed by a bright, massive elliptical galaxy in the galaxy cluster SMACSJ0028.2-7537. This combined image is composed of four individual images obtained using the JWST’s Near-InfraRed Camera, shown in yellow and red, along with Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys, which are represented in blue. Several blue arcs wrapping around the elliptical galaxy appear to be the distorted light from gas structures of the lensed spiral galaxy, which also includes several bright star clusters. The core of the spiral galaxy appears multiple times around the lensing galaxy, with two bright yellow clumps visible at the six and two o’clock positions, respectively. Thanks to the lensing magnification, we can observe these structures in such detail.

This image was captured by JWST as part of the Strong Lensing and Cluster Evolution (SLICE) survey (PI: Guillaume Mahler/University of Liège), which aims to observe 182 massive galaxy clusters across a redshift range of 0.2 to 1.9. The SLICE team seeks to understand the mass structure of galaxy clusters, including the dark matter distribution. The early results from the SLICE survey (C. Cerny et al. Preprint at https://arxiv.org/abs/2503.17498; 2025) provide observations of 14 massive galaxy clusters with redshifts ranging from 0.25 to 1.06. In this early data analysis, the team modelled the global mass profile of each galaxy cluster to study the inner mass distribution, although the detailed analysis of the strong lensing system in this image is not included in the paper.

The Planck satellite’s highly precise measurements of the temperature and polarization properties of the cosmic microwave background (CMB) have provided detailed information about the cosmological model, but other features of the CMB remain largely inaccessible due to the low frequencies at which their signals appear. One such feature is its spectral distortion from a perfect blackbody, which is governed by Compton scattering of photons to increasing distances during recombination and, as such, contains imprints of primordial density structure. David Zegeye and colleagues propose the use of the Square Kilometer Array (SKA) to measure these spectral distortions, and demonstrate SKA’s future effectiveness as a probe of primordial non-Gaussianity.

The authors use a Fisher matrix approach to simulate the angular cross power spectra of a spectral distortion signal, as might be obtained with SKA’s medium-frequency array in single-dish mode, with temperature and polarization measurements from the upcoming CMB space mission LiteBIRD. Accounting for multiple Galactic and extragalactic foreground contaminants in the SKA wavelength window and adopting a careful calibration strategy, they show that the two instruments will provide highly complementary measurements, with their most realistic setup forecast to improve current constraints of the local primordial non-Gaussianity f_NL at this spatial scale by a factor of ~30.

Amazing Worlds of Science Fiction and Science Fact

• Keith Cooper

Thirty years ago, our understanding of the Universe changed in a subtle and profound way. For as long as humans have looked to the skies, we have peopled them with intelligent life, both deeply alien and just like ourselves. Finally, in 1995, astronomers discovered the first world circling a main sequence star other than the Sun — an exoplanet. Over the three decades since, as survey missions such as Kepler and TESS have revealed thousands of exoplanets, the reality has dawned that many are very different from those we expected — although the discovery of Earth-like worlds now hovers tantalizingly within reach.

Although the Perseus cluster has often been regarded as an archetypical relaxed galaxy cluster, several lines of evidence, including ancient, large-scale cold fronts, asymmetric plasma morphology, filamentary galaxy distribution and so on, provide a conflicting view of its dynamical state, suggesting that the cluster might have experienced a major merger. However, the absence of a clear merging companion identified so far hampers our understanding of the evolutionary track of the Perseus cluster consistent with these observational features. Here, through careful weak-lensing analysis, we successfully identified the missing subcluster halo (total mass ({M}_{200}={1.70}_{-0.59}^{+0.73}times {10}^{14},{M}_{odot })) at the >5σ level centred on NGC 1264, which is located ~430 kpc west of the Perseus main cluster core. Moreover, a significant (>3σ) mass bridge, which is also traced by the cluster member galaxies, is detected between the Perseus main and subclusters, which serves as direct evidence of gravitational interaction. With idealized numerical simulations, we demonstrate that an ~3:1 off-axis major merger can create the cold front observed ~700 kpc east of the main cluster core and generate the observed mass bridge through multiple core crossings. This discovery resolves the long-standing puzzle of Perseus’s dynamical state.

Barnard’s Star is one of the closest and most studied M dwarfs, and various attempts have been undertaken to determine whether it hosts planets. Despite these efforts, the first exoplanetary detection came only in 2024 by radial velocity data from the ESPRESSO spectrograph on the VLT (J. I. González Hernández et al. Astron. Astrophys. 690, A79; 2024). The same study found three other unconfirmed signals. Armed with this knowledge, Ritvik Basant and colleagues revisited the system.

The authors analyse data obtained by another spectrograph, MAROON-X at Gemini North, first separately then jointly with the ESPRESSO data, allowing the detection of radial velocity signals less than 50 cm s^–1. They confirm the presence of four planets in a very compact configuration: the innermost planet has a period of 2.34 days and the outermost one of 6.74 days. Remarkably, all have very small minimum masses, between 0.19 and 0.34 M_⊕.

The stellar demographics of the central Milky Way have remained somewhat unclear due to observational challenges posed by high interstellar extinction. To provide a comprehensive picture of this region, Danny Horta Darrington, Michael Petersen and Jorge Peñarrubia have conducted a population study of metal-rich red giants ([Fe/H] > –0.8) in the inner Galaxy (r < 5 kpc) from APOGEE and Gaia DR3. They identified three populations co-existing spatially: inner disk stars, the bar, and a spheroidal ‘knot’, suggesting a close connection between the inner Galaxy and the Galactic bar.

While these populations are statistically distinct in the dynamic distribution, they share similar chemical composition and age characteristics, suggesting a common star formation history. The ‘knot’, composed of old stars with a spheroidal distribution, resembles most characteristics of a classical bulge, except for its broad metallicity range from –0.8 to super-solar metallicity. The authors suggest that this discrepancy could arise from a different formation pathway for the ‘knot’: secular evolution. This is the mechanism believed to have formed the Milky Way bar; as opposed to the major merger pathway, which is hypothesized to give rise to a classical bulge.