Tru Physics

Quasar

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Tru Physics
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Introduction

A quasar, or a quasi-stellar object (QSO), is an extremely luminous active galactic nucleus (AGN). Quasars are among the most distant objects in the universe, and their extreme brightness is generated by supermassive black holes at the center of galaxies.

The Power Source of a Quasar

The central engine powering quasars is a supermassive black hole. The intense energy output is a result of gravitational energy conversion. When material gets too close to the black hole, it forms an accretion disk around it. As matter spirals into the black hole, it heats up and emits vast quantities of radiation.

Quasar Spectra and Redshift

Quasars are characterized by their unique spectral properties. They have very broad emission lines due to the high-speed movement of the gas near the black hole. Quasars also exhibit a redshift, implying they are moving away from us due to the expansion of the universe. The redshift (z) is calculated using the formula:

z = \dfrac{\lambda_{\text{observed}} - \lambda_{\text{emitted}}}{\lambda_{\text{emitted}}}

where \lambda_{\text{observed}} is the observed wavelength, and \lambda_{\text{emitted}} is the wavelength of the emitted light in the rest frame of the source.

Luminosity and Eddington Limit

The brightness of quasars is often described in terms of luminosity (L), which can reach values of up to 10^{47}\text{ erg/s.} The Eddington luminosity is the maximum luminosity achievable when the force of radiation acting outward balances the gravitational force pulling material inward:

L_{\text{Edd}} = \dfrac{4\pi G M c}{\kappa}

where:

  • L_{\text{Edd}} is the Eddington luminosity,
  • G is the gravitational constant,
  • M is the mass of the black hole,
  • c is the speed of light, and
  • \kappa is the opacity.

Evolution of Quasars

Quasars are most commonly found at large cosmological distances, corresponding to a time when the universe was younger. It’s believed that the abundance of quasars decreases as the universe ages due to the depletion of fuel needed to power the quasar activity.

Conclusion

Quasars provide us with a unique tool for studying the early universe, the physics of supermassive black holes, and the evolution of galaxies. Although their detailed nature continues to be a subject of research, they remain among the most intriguing objects in the cosmos.

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