Galaxies & Cosmic Structures

Active Galactic Nuclei

An active galactic nucleus is a galaxy center powered by a feeding supermassive black hole rather than by stars.

Quasars, blazars, Seyfert galaxies and radio galaxies are different faces of the same basic system.

Observe
A galaxy core much brighter than expected from its stars, sometimes with jets.
Measure
Broad emission lines, X-rays and radio jets.
Model
A black hole with an accretion disk, torus of dust, and possible jets.
Explain
Black-hole feeding shapes how galaxies grow.

What is it?

In an active galactic nucleus (AGN), a supermassive black hole actively pulls in gas. The infalling material heats up and radiates strongly. The unified model suggests many AGN types look different mainly because of viewing angle and how much dust hides the center.

Some AGN launch jets that extend far beyond the galaxy. In 2019 the Event Horizon Telescope released the first image of the glowing ring around the black hole at the center of the galaxy M87, which powers a large jet. How AGN feedback regulates star formation in galaxies is an important open question.

How does it happen?

Stage 1
Gas reaches the galaxy's center
Stage 2
Accretion onto the black hole
Stage 3
Radiation and outflows leave the nucleus
Stage 4
Feedback affects the host galaxy

What do we actually observe?

Bright cores: X-ray and optical brightness far beyond stellar emission.
Jets: Narrow streams of plasma seen in radio and X-rays.
Variation: Flickering over hours to years constrains the size of the source.

How do scientists detect it?

X-ray observatories. Chandra and XMM-Newton find nuclear X-ray sources.
Radio interferometers. VLA, VLBI and the Event Horizon Telescope image jets and the region near the black hole.
Gamma-ray telescopes. Fermi observes blazars, jets pointed near Earth.

Why does it matter?

They show how black holes and galaxies grow together.
Their feedback may help regulate star formation.
They are among the brightest steady sources across the universe.

The SpaceWeatherTracker connection

AGN jets and outflows are driven by magnetic fields and plasma. Studying them alongside the Sun's flares and winds shows how much of the same physics works on very different scales.

This is an explainer. SpaceWeatherTracker does not show live data for this phenomenon; see the “Space Phenomena Now” section on the hub for what is currently monitored.

Primary family: Galaxies & Cosmic Structures