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A dormant overmassive black hole in the early Universe.
Nature
December 2024
NRC Herzberg, Victoria British Columbia, Canada.
Recent observations have found a large number of supermassive black holes already in place in the first few hundred million years after the Big Bang, many of which seem to be overmassive relative to their host galaxy stellar mass when compared with local relation. Several different models have been proposed to explain these findings, ranging from heavy seeds to light seeds experiencing bursts of high accretion rate. Yet, current datasets are unable to differentiate between these various scenarios.
View Article and Find Full Text PDFBattle of the CH motions: aliphatic versus aromatic contributions to astronomical PAH emission and exploration of the aliphatic, aromatic, and ethynyl CH stretches.
Mon Not R Astron Soc
December 2024
NASA Ames Research Center, Astrophysics Branch, Moffett Field, CA 94035, USA.
Strong anharmonic coupling between vibrational states in polycyclic aromatic hydrocarbons (PAH) produces highly mixed vibrational transitions that challenge the current understanding of the nature of the astronomical mid-infrared PAH emission bands. Traditionally, PAH emission bands have been characterized as either aromatic or aliphatic, and this assignment is used to determine the fraction of aliphatic carbon in astronomical sources. In reality, each of the transitions previously utilized for such an attribution is highly mixed with contributions from both aliphatic and aromatic CH motions as well as non-CH motions such as CC stretches.
View Article and Find Full Text PDFIn situ spheroid formation in distant submillimetre-bright galaxies.
Nature
December 2024
European Southern Observatory, Garching bei Munchen, Germany.
Most stars in today's Universe reside within spheroids, which are bulges of spiral galaxies and elliptical galaxies. Their formation is still an unsolved problem. Infrared/submillimetre-bright galaxies at high redshifts have long been suspected to be related to spheroid formation.
View Article and Find Full Text PDFLong-term Doppler imaging of the star XX Trianguli indicates chaotic non-periodic dynamo.
Nat Commun
December 2024
Leibniz-Institute for Astrophysics Potsdam (AIP), D-14482, Potsdam, Germany.
Sunspots are the most well-known manifestations of solar magnetic fields and exhibit a range of phenomena related to the interior dynamo. Starspots are the direct analogs of sunspots on other stars but with the big observational restriction that we usually cannot resolve other star's surfaces. In this paper we employ an indirect surface imaging technique called Doppler imaging and present 99 independent Doppler images of the star XX Trianguli.
View Article and Find Full Text PDFPresolar Grains as Probes of Supernova Nucleosynthesis.
Space Sci Rev
November 2024
Institute for Geochemistry and Petrology, ETH Zürich, 8092 Zurich, Switzerland.
We provide an overview of the isotopic signatures of presolar supernova grains, specifically focusing on Ti-containing grains with robustly inferred supernova origins and their implications for nucleosynthesis and mixing mechanisms in supernovae. Recent technique advancements have enabled the differentiation between radiogenic (from Ti decay) and nonradiogenic Ca excesses in presolar grains, made possible by enhanced spatial resolution of Ca-Ti isotope analyses with the Cameca NanoSIMS (Nano-scale Secondary Ion Mass Spectrometer) instrument. Within the context of presolar supernova grain data, we discuss () the production of Ti in supernovae and the impact of interstellar medium heterogeneities on the galactic chemical evolution of Ca/Ca, () the nucleosynthesis processes of neutron bursts and explosive H-burning in Type II supernovae, and () challenges in identifying the progenitor supernovae for Cr-rich presolar nanospinel grains.
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