Nature Astronomy最新文献

Organic macromolecular matter is the dominant carrier of volatile elements such as carbon, nitrogen and noble gases in chondrites—the rocky building blocks from which Earth formed. How this macromolecular substance formed in space is unclear. Here we show that its formation could be associated with the presence of dust traps, which are prominent mechanisms for forming planetesimals in planet-forming disks. We demonstrate the existence of heavily irradiated zones in dust traps, where small frozen molecules that coat large quantities of microscopic dust grains could be rapidly converted into macromolecular matter by receiving radiation doses of up to several tens of electronvolts per molecule per year. This allows for the transformation of simple molecules into complex macromolecular matter within several decades. Up to roughly 4% of the total disk ice reservoir can be processed this way and subsequently incorporated into the protoplanetary disk midplane where planetesimals form. This finding shows that planetesimal formation and the production of organic macromolecular matter, which provides the essential elemental building blocks for life, might be linked.

The effects of harmful space radiation are one of the biggest concerns for future lunar explorers. Here, we use a data-validated model, the Radiation Environment and Dose on the Moon (REDMoon), to create mission schedules for different scenarios of lunar bases limited by radiation constraints. We consider habitats at the surface and subsurface of the Moon with different regolith and aluminium shielding using the last two solar cycles (2000–2022) as a baseline. The exposure due to background galactic cosmic rays (GCRs) is about 66% on the lunar surface than in interplanetary space and can even slightly increase beneath the surface before it decreases to a negligible value at about 3 m depth. If the shielding is insufficient, the surface dose during a single solar particle event could sometimes exceed annual GCR exposure, leading to an immediate replacement of the crew. Our work provides radiation-mitigation considerations for future human lunar bases and exploration cost estimates.

A recent addition to the astronomical taxonomy, courtesy of JWST, is a mysterious population of compact, dust-reddened galaxies at redshifts 3 < z < 9, termed ‘Little Red Dots’ (LRDs). Determining the true nature of LRDs could be an important piece of the puzzle of the formation and evolution of the first galaxies, and Tonima Ananna and colleagues analyse X-ray observations to investigate whether their emission is primarily flux from accreting supermassive black holes (SMBHs) in active galactic nuclei, or might be better accounted for by an alternative scenario such as young stars associated with vigorous star formation.

The team uses ultra-deep observations from the Chandra X-ray Observatory to look at LRDs previously identified from JWST infra-red observations, all located behind the lensing galaxy cluster Abell 2744. Individual LRDs are not detected in the X-ray data, allowing the authors to place upper limits of ≲ (1.5−16) × 10⁶ M_⊙ (assuming Eddington-limited accretion) on the masses of supermassive black holes in these galaxies.

Relativistic electron–positron pairs may be generated around black holes or neutron stars. However, exploring properties of such pairs has been limited to theory and simulation studies up to now due to difficulties in laboratory experiments. Recently, Charles Arrowsmith and colleagues reported the generation of high-density, quasi-neutral, relativistic electron–positron pair beams from a relativistic proton beam interaction with a solid target.

In the experiment, a relativistic (440 GeV/c) proton beam at CERN’s Super Proton Synchrotron accelerator interacts with a solid target composed of a low-Z material (graphite) and a high-Z converter (tantalum). In this process the proton beam is converted into pair beams with hadronic and electromagnetic cascades. The energy spectra of the pair beams are measured, and its power-law index is analysed. Other characteristics of the pair beams (for example — beam dimension, number density, beam temperature) are predicted by FLUKA simulations.

The hierarchical model of galaxy evolution suggests that mergers have a substantial impact on the intricate processes that drive stellar assembly within a galaxy. However, accurately measuring the contribution of accretion to a galaxy’s total stellar mass and its balance with in situ star formation poses a persistent challenge, as it is neither directly observable nor easily inferred from observational properties. Using data from MaNGA, we present theory-motivated predictions for the fraction of stellar mass originating from mergers in a statistically significant sample of nearby galaxies. Employing a robust machine learning model trained on mock MaNGA analogues (MaNGIA) obtained from a cosmological simulation (TNG50), we unveil that in situ stellar mass dominates almost across the entire stellar mass spectrum (10⁹ M_⊙ < M_⋆ < 10¹² M_⊙). Only in more massive galaxies (M_⋆ > 10¹¹ M_⊙) does accreted mass become a substantial contributor, reaching up to 35–40% of the total stellar mass. Notably, the ex situ stellar mass in the nearby Universe exhibits notable dependence on galaxy characteristics, with higher accreted fractions favoured being by elliptical, quenched galaxies and slow rotators, as well as galaxies at the centre of more massive dark matter haloes.

Subsurface magnetic reconnection, with its location changing with the depth of the plasma region in the chromosphere (from photosphere to corona), has been observed on the Sun. The authors explored the subsurface structure of active region AR 11504 by analysing the emission lines and their density and temperature dependence.

The figures taken from the work of Deborah Baker and coauthors show the white light continuum images from Hinode’s EUV Imaging Spectrometer, for different days (left panel —14 June 2012 at 00:58 UT and right panel — 15 June 2012 at 00:58 UT). The strength and direction of the horizontal magnetic field is indicated by the arrows. One can see the location of the light bridges in both figures, left panel (around X = −147′′, Y = −292′′), right panel (around X = 64′′, Y = −299′′). The horizontal magnetic field in the light bridge is about 200 G while in the surrounding regions it is up to 1,500 G. These fields are strong enough to produce the I-FIP effect which is supported from the further analysis of the plasma parameters (for example — density and wave amplitude). Overall, these are signatures of episodic heating and reconnection outflows in regions between magnetic flux tubes forming a light bridge and it can be concluded that light bridges are likely locations of the magnetic reconnection.