Quasars (AQA A Level Physics): Revision Note

Quasars

• Quasars, or quasi-stellar objects, are

Extremely luminous star-like sources of radiation with very high redshifts

• Quasars were first discovered in the 1960s due to their strong radio emissions, but were also notable for their:

  • high luminosities

  • extremely large redshifts

  • small size

Formation of quasars

• After the discovery of supermassive black holes at the centres of galaxies, astronomers were able to determine that quasars are a type of active galactic nucleus, meaning:

  • they are supermassive black holes surrounded by an accretion disc of matter

  • they are found at the centre of extremely distant galaxies

  • when they become active, i.e. when matter falls into them, they become quasars

Structure of a quasar

• As matter falls into the black hole, jets of radiation are emitted from the poles

  • The equivalent of 100 solar masses of matter can fall into a quasar each year

  • The gravitational potential energy of infalling matter is transferred to electromagnetic radiation

  • Now it is known that quasars are strong emitters of all wavelengths, not just radio waves

Redshift of quasars

• Quasars are thought to be some of the most distant measurable objects in the known universe

  • This is evidenced by the extremely large redshifts they show

  • This allows astronomers to see very far back to an early Universe, as it was not long after the Big Bang