Definition

Quasars (Quasi-Stellar Objects) are extremely luminous active galactic nuclei powered by supermassive black holes at the center of distant galaxies. They emit energy across the electromagnetic spectrum, outshining their host galaxies.

Structure & Components

  • Supermassive Black Hole: Central engine, typically millions to billions of solar masses.
  • Accretion Disk: Surrounds the black hole; infalling matter heats up, emitting radiation.
  • Relativistic Jets: High-speed streams of charged particles ejected perpendicular to the accretion disk.
  • Broad & Narrow Line Regions: Clouds of gas producing distinctive spectral lines.

Diagram

Quasar Structure

Energy Output

  • Luminosity: Up to 1000x the total output of the Milky Way.
  • Radiation: Emitted in radio, optical, ultraviolet, X-ray, and gamma-ray wavelengths.
  • Variability: Brightness can change over days to years.

Formation & Evolution

  1. Galaxy Merger: Collisions funnel gas toward the central black hole.
  2. Accretion: Gas forms a disk, heats up, and emits intense radiation.
  3. Jet Formation: Magnetic fields channel some material into jets.
  4. Quasar Phase: Lasts ~10–100 million years; eventually fades as fuel depletes.

Observational Features

  • Redshift: High redshift values (z > 6) indicate quasars are among the earliest cosmic objects.
  • Spectral Lines: Broad emission lines from fast-moving gas; narrow lines from slower, distant gas.
  • Host Galaxies: Often disturbed or merging systems.

Three Surprising Facts

  1. Quasars Can Outshine Entire Galaxies: Some quasars emit more light than the combined stars of thousands of galaxies.
  2. Quasars Help Map the Universe: Their brightness and distance make them cosmic lighthouses for probing intergalactic material.
  3. Quasar Winds Influence Galaxy Evolution: Powerful outflows can regulate star formation by ejecting gas from galaxies.

Recent Research

  • 2021 Discovery: Astronomers detected the most distant known quasar, J0313-1806, at redshift z=7.64, just 670 million years after the Big Bang (Banados et al., Astrophysical Journal Letters, 2021).
  • Quasar Feedback: New studies show quasar-driven winds can suppress star formation, shaping galaxy growth (Nature, 2022).

Common Misconceptions

  • Quasars Are Stars: False; they are not stars but active galactic nuclei.
  • Quasars Only Exist in the Early Universe: Incorrect; while most are distant, some exist in the nearby universe.
  • All Galaxies Have Quasars: Only galaxies with actively accreting supermassive black holes are quasars.

Future Directions

  • Next-Generation Telescopes: JWST and ELT will study quasars at higher redshifts and finer detail.
  • Quasar Host Galaxy Mapping: Understanding how quasar activity affects galaxy evolution.
  • Black Hole Growth: Investigating how supermassive black holes form so quickly in the early universe.
  • Multi-messenger Astronomy: Combining gravitational waves and electromagnetic signals to study quasar environments.

Quiz Section

  1. What powers a quasar’s luminosity?
  2. Name two observational features of quasars.
  3. How do quasars influence their host galaxies?
  4. True or False: Quasars are the brightest objects in the universe.
  5. What recent discovery was made about quasar J0313-1806?

Additional Notes

  • Quasars are crucial for understanding cosmic reionization and the growth of structure in the universe.
  • Their absorption spectra reveal the composition of intergalactic gas.
  • Quasar variability provides clues about accretion disk physics.

References

  • Bañados, E. et al. (2021). “The discovery of a highly accreting, radio-loud quasar at z = 7.64.” Astrophysical Journal Letters. Link
  • Nature News (2022). “Quasar winds suppress star formation in host galaxies.” Link

End of Revision Sheet