- Quasars & Other Active Black Holes
- Galaxy Formation and Evolution
- Galaxy Clusters
- Intergalactic Medium
The nucleus of an active galaxy contains a massive black hole that is vigorously accreting material. In the process, the nucleus typically ejects jets of rapidly moving charged particles that radiate brightly at many wavelengths, in particular radio wavelengths. Active galaxies display a range of dramatically different properties and one categorization uses the radio emission, finding one class that is bright in the radio and a second group that is comparatively faint. Astronomers suspect that the reason for the difference is a different rate of accretion onto the central black hole, but there are other activities that also seem to correlate with the radio emission including nearby star formation, for example, or the age of the galaxy. Astronomers are therefore trying to identify the ones that might be causal.
Feedback from the intergalactic medium onto a galaxy's nucleus has recently been identified as an important driver of galaxy evolution, and the question naturally arises about the role of such feedback in a galaxy’s radio activity and the accompanying effects. CfA astronomers Ralph Kraft and Dan Evans and their colleagues used the Chandra X-Ray Telescope in the first systematic X-ray study of the cluster environment of radio galaxies all dating from the same epoch. The X-ray emission is the key to understanding how the gas accretes onto the black hole.
The team observed fifty-five radio emitting sources spanning a factor of a thousand in radio luminosity, twenty-five of them classified as bright. They found that the bright radio sources show evidence of high accretion from a circumnuclear disk. The faint sources, on the other hand, have a more uncertain mechanism, perhaps the chaotic accretion of cool gas clouds; significantly, their radio emission strength is strongly correlated with the cluster richness and central density, while no such correlations were found for the bright sources. The scientists conclude that there are strong environmental differences between these two classes consistent with thinking that the cluster environment supports the fueling of emission. This evidence has prompted the team to study next the relationships between the gas in the intracluster medium and the other phenomena associated with the two classes.
"The Link between Accretion Mode and Environment in Radio-Loud Active Galaxies," J. Ineson, J. H. Croston, M. J. Hardcastle, R. P. Kraft, D. A. Evans, and M. Jarvis, MNRAS 453, 2682, 2015.
Related News
CfA Astronomers Help Find Most Distant Galaxy Using James Webb Space Telescope
Unexpectedly Massive Black Holes Dominate Small Galaxies in the Distant Universe
Distant Stars Spotted for the First Time in the Vast Magellanic Stream
CfA Scientists Help Reach New Milestone in Quest for Distant Galaxies
Astrophysicists Hunt for Second-Closest Supermassive Black Hole
The Tilt in our Stars: The Shape of the Milky Way's Halo of Stars is Realized
JWST Draws Back Curtain on Universe's Early Galaxies
Dozens of Newly Discovered Gravitational Lenses Could Reveal Ancient Galaxies and the Nature of Dark Matter
A Massive Galaxy Supercluster in the Early Universe
CfA Celebrates Class of 2022 Graduates
Projects
2MASS Redshift Survey
AstroAI
Dark Energy Spectroscopic Instrument (DESI)
GMACS
For Scientists