Study Links Obscured Black Hole Accretion to Precessing Jets
Researchers have identified a clear connection between highly obscured accretion systems and mildly relativistic, precessing jets in stellar-mass black hole and neutron star X-ray binaries. The work builds on a prior Nature Astronomy study showing that the fastest jets (Lorentz factor >2) are locked to a fixed axis, likely the black hole spin axis, while slower jets (~0.3c) precess. The findings suggest jet speed and stability are governed by the density of the environment near the launch site, with implications for understanding super-Eddington accretion.
A new paper accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS) presents evidence that highly obscured X-ray binary systems — likely undergoing super-Eddington accretion, either persistently or transiently — are preferentially associated with mildly relativistic jets that precess rather than maintain a fixed direction. The authors, building on earlier work published in Nature Astronomy (Fender & Motta, 2025), argue that the fastest jets, with Lorentz factors greater than 2, are locked to the black hole spin axis and are launched in low-density environments. By contrast, slower jets with velocities around 0.3c, which can originate from both black holes and neutron stars, are found in denser, more obscured environments and tend to precess. The proposed mechanism is mass-loading of the jets near their launch sites: in obscured, super-Eddington systems, denser material close to the jet base slows and destabilizes the outflow. This unified picture ties together jet velocity, directionality, and the accretion environment into a coherent framework for understanding relativistic outflows from compact objects.
What's missing
The proposed mass-loading mechanism is speculative by the authors' own admission.
What different sources said
- arXiv astro-phCenter
The link between obscured accretion and mildly relativistic precessing jets
Related
Gut Bacteria Enzyme Found to Break Down Heat-Processed Food Compounds, Producing Novel Biogenic Amines
Researchers have discovered that an enzyme in common gut bacteria can degrade N-epsilon-carboxymethyllysine (CML), a compound formed during thermal food processing, producing previously unknown biogenic amines. The enzyme, ornithine decarboxylase SpeC from enterobacteria, acts on CML and related modified lysine derivatives through a low-level 'underground' catalytic activity. This finding suggests a previously unrecognized communication axis between thermally processed dietary compounds and gut microbial physiology, with potential implications for host health.
Full-Length Gene Sequencing Reveals Two Distinct Bacterial Communities in Black-Legged Ticks Expanding Into Canada
Researchers used Oxford Nanopore full-length 16S rRNA gene sequencing to characterize the microbiome of Ixodes scapularis black-legged ticks collected in Nova Scotia, Canada, distinguishing between tick-adapted bacteria and environmentally acquired bacteria. The study comes as I. scapularis — the primary vector of Lyme disease — is rapidly expanding northward into Canada due to climate change. The findings suggest that environmentally derived bacteria in tick microbiomes are not mere contamination, which has implications for how tick microbiome data is collected and interpreted across surveillance studies.
Study Identifies Metabolic Link Between Cell Envelope Stress and Biofilm Formation in Bacteria
Researchers have discovered that the metabolite acetyl-CoA directly inhibits enzymes that degrade the bacterial signaling molecule c-di-GMP, connecting cell envelope biosynthesis stress to biofilm formation in Pseudomonas aeruginosa. The study found that sub-inhibitory concentrations of antibiotics targeting early peptidoglycan biosynthesis — but not other antibiotic classes — elevate c-di-GMP levels by reducing phosphodiesterase activity, with acetyl-CoA competing for the enzyme active site. Because the relevant enzyme domain is broadly conserved across bacterial species, this checkpoint mechanism may be widespread and could have implications for understanding antibiotic-induced biofilm responses.