Study Tests Modified Gravity Theory Against Black Hole Observations
Researchers developed a theoretical model to predict how accretion disk emissions would appear around black holes in Scalar-Tensor-Vector Gravity (MOG), a modified gravity theory that adds a repulsive fifth force. The model shows that this fifth force would alter thermal emission signatures in ways that could mimic reduced black hole spin. Testing against real X-ray observations of the black hole LMC X-1 found no evidence for the fifth force, constraining the theory's parameters and supporting Einstein's general relativity.
A new theoretical study examines how Scalar-Tensor-Vector Gravity (STVG/MOG)—an alternative gravity theory featuring a repulsive fifth force—would modify the thermal emission from accretion disks surrounding rotating black holes. The researchers derived key orbital and spectral properties for black holes in this modified spacetime, including the innermost stable circular orbit and thermal continuum spectra across various black hole spins and viewing angles. They found that the fifth force would push the innermost stable orbit outward, reduce peak disk temperatures, and soften the thermal spectrum in ways that could be mistaken for lower black hole spin in standard general relativity. To test these predictions, they applied their model to a 69.6-kilosecond XMM-Newton X-ray observation of the black hole binary LMC X-1 and found no significant evidence for the fifth force, constraining the theory's deformation parameter to values consistent with general relativity.
What's missing
The study does not discuss how its constraints on MOG compare quantitatively to limits from other observational tests (e.g., gravitational lensing, pulsar timing, or solar system tests), nor does it address whether independent spin measurements from iron-line reflection spectroscopy have been performed on LMC X-1 to validate the proposed degeneracy-breaking method.
What different sources said
- arXiv astro-phCenter
Probing gravity with non-linear clustering in redshift space
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.