AGN feedback is the energy and momentum from an active galactic nucleus that changes the gas in its host galaxy. In Astrophysics I, it is a main way supermassive black holes can regulate star formation and galaxy growth.
AGN feedback is the effect an active galactic nucleus has on the gas around it in Astrophysics I. When a supermassive black hole is actively accreting matter, it can release huge amounts of radiation, fast particles, and jets. That output does not just shine outward, it pushes on surrounding gas and can heat it, stir it up, or even blow some of it out of the galaxy.
The basic idea is a cause-and-effect loop. Gas falls toward the center of a galaxy, feeds the black hole, and powers the AGN. Then the AGN sends energy back into the galaxy and changes the same gas supply that fed it. If the gas gets too hot or too spread out, it cannot collapse into new stars as easily.
That is why AGN feedback is tied to star formation rate. Galaxies need cold, dense gas to form stars. Feedback can keep gas from cooling, or it can remove gas from the central regions where star formation is most active. In that sense, the black hole is not just a passive object sitting in the middle of the galaxy. It can shape the galaxy’s future.
Astrophysics I usually describes two broad feedback modes. In quasar mode, the AGN is very luminous and can drive strong winds while the black hole is rapidly accreting. In radio mode, the AGN launches jets that inflate bubbles in surrounding gas, especially in massive galaxies and galaxy clusters. Both modes transfer energy outward, but they do it in different ways.
You will also see AGN feedback used to explain why some big galaxies have less star formation than their gas supply might suggest. Without feedback, many galaxy-formation models make too many massive, bright galaxies. Adding AGN feedback helps simulations match real observations better because it gives the galaxy a built-in way to regulate itself.
A common misconception is that AGN feedback only destroys star formation. It often suppresses it, but the full picture is broader. By moving and heating gas, it changes where and when stars can form, and in some cases it can compress gas locally and trigger small bursts of star formation nearby.
AGN feedback shows up whenever Astrophysics I connects supermassive black holes to galaxy evolution instead of treating them as separate topics. It is one of the cleanest examples of how a tiny central region, compared with the whole galaxy, can still affect the large-scale structure of that galaxy.
This term also helps explain the mismatch between simple galaxy-growth models and what astronomers actually observe. If you only count gravity and gas supply, massive galaxies should often keep forming stars more aggressively than they do. AGN feedback gives you the missing mechanism for heating, expelling, or redistributing that gas.
It also links several course ideas at once: accretion onto a supermassive black hole, the behavior of gas in galaxies, the star formation rate, and the observed scaling relations between black hole mass and bulge properties. Once you know what feedback does, those correlations stop looking like coincidences and start looking like evidence of coevolution.
In practice, this term is a bridge between observation and modeling. When a simulation includes AGN feedback, it can produce galaxies and clusters that look more like the real universe. That makes it a major piece of the story for why black holes matter far beyond the event horizon.
Keep studying Astrophysics I Unit 12
Visual cheatsheet
view galleryActive Galactic Nucleus (AGN)
AGN feedback comes from the energy output of an AGN itself. If you do not know what makes a galaxy active, the feedback term is just the aftermath without the source. The AGN is the central engine, and feedback is what happens when that engine pushes back on the galaxy around it.
Supermassive Black Hole
The black hole is the object being fed, and its growth powers the activity that drives feedback. In Astrophysics I, this is the link between the tiny central region and galaxy-wide effects. The more material the black hole accretes, the more energy it can return to the surrounding gas.
Star Formation Rate (SFR)
AGN feedback often changes the star formation rate by heating gas or removing it from the star-forming regions. That means SFR is one of the easiest ways to see the effect of feedback in a galaxy. A galaxy with lots of gas but a low SFR is a clue that something is suppressing star formation.
accretion disk
The accretion disk is where gas loses energy before it falls inward, and that process helps power the AGN. The disk is not the feedback itself, but it is part of the chain that produces it. Without accretion, there is no energy reservoir to drive winds, radiation, or jets.
Short-answer questions often ask you to trace the sequence from gas inflow to black hole accretion to heating or expulsion of gas. If you see a graph or simulation image with suppressed star formation in a massive galaxy, AGN feedback is a likely explanation. You may also be asked to compare quasar mode and radio mode, so make sure you can tell radiation-driven winds from jet-driven heating. In a class discussion or lab report, the term usually shows up when you explain why a simulation matches observed galaxy populations better after feedback is included.
An accretion disk is the swirling gas that feeds the black hole, while AGN feedback is the energy and momentum the black hole system sends back out into the galaxy. The disk is the source region, but feedback is the outward impact on surrounding gas.
AGN feedback is the way an active galactic nucleus changes the gas in its host galaxy by heating it, stirring it up, or pushing it out.
It matters because star formation needs cold, dense gas, and feedback can keep that gas from collapsing into new stars.
Quasar mode usually means luminous, rapid accretion with strong winds, while radio mode usually means jets that heat or disturb surrounding gas.
The term helps explain why massive galaxies do not always form stars as quickly as their gas supply might suggest.
In Astrophysics I, AGN feedback is a major example of how supermassive black holes and galaxies evolve together.
AGN feedback is the process where an active galactic nucleus sends energy and momentum into its host galaxy. That energy can heat gas, drive winds, or launch jets that change how easily new stars form. It is one of the main links between black holes and galaxy evolution.
It can keep gas too hot to collapse or move gas out of the central regions where stars usually form. Since star formation needs cold, dense clouds, heated or expelled gas cannot build stars as efficiently. That is why AGN feedback is often connected with quenching.
Quasar mode happens when the black hole is rapidly accreting and the AGN is very luminous, often driving strong winds. Radio mode is usually tied to jets of particles that pump energy into surrounding gas. Both are feedback, but they transfer energy in different ways.
Without it, simulations often make too many massive galaxies with too much star formation. Adding AGN feedback gives the model a way to regulate gas, so the simulated galaxy population matches observations more closely. That is why it shows up in many galaxy-evolution models.