Black Hole Host Galaxy Terminology

Definition of “Host”

In the phrase “black hole and host” (especially in the context of galaxies), the term host almost always refers to the host galaxy—that is, the galaxy which contains the black hole, typically a supermassive black hole at its center.

What “Host” Encompasses

“Host” in this context means:

• The entire galaxy that surrounds and includes the central black hole
• The gravitational and dynamical environment in which the black hole resides
• The stellar, gas, and dark matter components that make up the galaxy

Observable Host Properties

Properties of the host galaxy typically include:

• Stellar mass - Total mass in stars
• Bulge mass - Mass of the central stellar bulge
• Luminosity - Total light output across wavelengths
• Stellar velocity dispersion (σ) - Spread in stellar velocities
• Morphological type - Galaxy classification (elliptical, spiral, etc.)
• Gas content - Amount and distribution of interstellar medium
• Dark matter halo properties - Halo mass and concentration

Standard Usage in Literature

This terminology is standard in extragalactic astronomy, particularly when discussing relationships such as:

• Black hole mass vs. host galaxy bulge mass
• Black hole mass vs. host galaxy velocity dispersion (the M–σ relation)
• Black hole–host coevolution scenarios
• AGN feedback and host galaxy quenching

Relevance to Decoherence Framework

In the context of Decoherence as First Principle, the black hole-host relationship takes on new meaning:

• Both components may emerge from shared gravitational decoherence events
• The co-evolution could reflect synchronized decoherence processes rather than causal feedback
• Scaling relations might represent fundamental decoherence length and time scales

This perspective suggests that black hole-host correlations arise naturally from the decoherence bootstrap process, where both the central compact object and the extended stellar system stabilize together as gravitational pointer states.

Note: Understanding this terminology is essential for interpreting observational studies of supermassive black holes and their galactic environments.