Intergalactic Medium & Quasars

The Intergalactic Medium

• Most atoms reside in the intergalactic medium between galaxies, not within the galaxies themselves
• Gravity causes gas to extend from galaxies, drawing new mass into the cosmic network
• Both hydrogen and helium are found in the intergalactic medium

Discovery of Quasars

• Quasars, originally termed "quasi-stellar radio sources," were discovered in the 1950s through detection of mysterious radio waves
• Quasars emit radio waves but appear as point sources, like stars
• Some quasars flicker or emit X-rays
• Quasars move up to 30% of the speed of light
• Rapid movement indicates great distance due to the universe's expansion
• Quasars are the active cores of galaxies billions of light-years away
• Quasars are thousands of times more luminous than the Milky Way

Quasars in the Early Universe

• Millions of quasars have been found at great distances
• Observing distant objects means seeing them as they were in the past
• Quasars were more common in the early universe, peaking 10 billion years ago
• Early galaxies were luminous and violent due to quasars
• The light and radiation from quasars did not originate from stars alone
• Galaxies grow through mergers, but small galaxies should not outshine present-day galaxies
• Supermassive black holes generate enormous energy outputs, powering quasars

How Quasars Generate Energy

• Supermassive black holes at the center of galaxies power quasars
• Light from a quasar emits from a massive gas disc, or "accretion disc," around the black hole
• Black holes convert matter into energy with high efficiency
• Energy released is up to 60 times more than nuclear fusion in a star
• Gravity, not nuclear reactions, releases energy
• Matter accelerates to near light speed when falling into a black hole, carrying immense kinetic energy

Accretion Discs

• Matter forms a disc as it spirals toward the horizon
• Friction heats the disc to tens of thousands of degrees
• The galactic core can release more energy than all its stars combined
• Quasars consume between one and one hundred Earths' worth of gas per minute
• Quasars emitted high amounts of radiation and light because the intergalactic medium was once less dispersed
• Bright quasars feed jets by threading the magnetic field of the surrounding material into a narrow cone
• Particle beams are ejected, traversing the circumgalactic medium and creating matter plumes extending hundreds of thousands of light-years
• Quasars likely only feed for millions of years before halting star formation

Impact on Galaxies

• Quasars overheat galaxies and halt star formation, effectively "killing" them
• Hot gas atoms cannot allow star formation because they move too fast, preventing gravitational collapse
• Cold gas is optimal for star formation
• Quasars deprive galaxies of gas needed for new stars, either by pushing the gas out or overheating it
• The death of a quasar may benefit potentially habitable worlds by preventing new stars that lead to sterilizing supernovae

The Milky Way's Past

• The Milky Way may have been a quasar in the past, which allowed Sagittarius A* to grow
• Galaxies do not preserve their history well
• Sagittarius A* could turn into a quasar in the future
• Merger with Andromeda will result in "double quasars", which results from central black holes being supplied with new gas
• Black holes merge at the center of the new galaxy, stirring up dust and stars