Active galactic nuclei and star formation

Most galaxies host a supermassive black hole (SMBH) at their nucleus. (A supermassive black hole is one whose mass exceeds a million solar-masses.) A key unresolved issue in galaxy formation and evolution is the role these SMBHs play in shaping their galaxies. Most astronomers agree that there must be a strong connection because of the observed correlations between a SMBH's mass and its galaxy's luminosity, stellar mass, and the stellar motions in the galaxy.

These correlations apply both in local galaxies and those at earlier cosmic epochs. But despite progress in studying SMBHs, how they effect their hosts is still not understood. In some suggested scenarios the SMBH suppresses star formation in the galaxy by expelling material. In others, like the merger scenario, the effect is the opposite: the SMBH boosts star formation by helping stir up the interstellar medium. Computer simulations have been undertaken to try to settle these differences, and they tend to show that cold gas flowing in from the intergalactic medium can feed both SMBH and galaxy growth.

Continued...
Source

Credit: NASA, ESA, the Hubble Heritage Team; STScI/AURA)-ESA/Hubble Collaboration and A. Evans University of Virginia, Charlottesville/NRAO/Stony Brook University

The galaxy UGC 5101 contains an active nucleus (AGN), a compact core that emits copious radiation and possible stimulates star formation.

In this Hubble image, the tidal tail at the left suggests that the galaxy is actually a merging pair of galaxies. Astronomers studying how AGN influence their host galaxy's development have concluded that both grow together.

Source / Image Courtesy

This simulation follows the collision of two spiral galaxies that harbor giant black holes. The collision merges the black holes and stirs up gas in both galaxies.

The merged black hole gorges on the feast and lights up, forming an active galactic nucleus called a quasar and creating a 'wind' that blows away much of the galaxy's gas.

This animation provides a close-up look at the behavior of a central black hole in the nucleus of an active galaxy. An accretion disk of infalling material surrounds a central black hole that may be millions or billions of times the mass of our Sun. Some of the superheated material escapes along the black hole's rotation axis.

Powerful magnetic fields keep the material confined to an extragalactic jet. Hubble Space Telescope spectroscopic observations of active galactic nuclei reveal how stellar material is blown back into intergalactic space.

A magnetohydrodynamics simulation of jets emerging from an active galactic nucleus (AGN) powered by the accretion of matter onto a supermassive black hole.

The AGN is in a crosswind, moving at nearly the local speed of sound through a background medium representative of the outskirts of a massive cluster of galaxies.

The rendering shows the fraction of jet material in each computational zone as the crosswind sweeps the jets into tails that are millions of light-years in length over the course of hundreds of millions of years