Brightest possible quasar

[Tom Mazanec]

I understand the Eddington Limit imposes a maximum luminosity to any quasar for a certain black hole mass. I would expect that there is a maximum possible mass quasar...at "billions and billions" of solar masses I would think a black hole would "swallow" its luminous accretion disk, even if it could somehow find the matter it ingest. What is the highest possible luminosity of a quasar given these two factors? Have any been found near this limit?

[Manchurian Taikonaut]

Don't really know the true answer but

I understand a lot of the bulge lumonosity from Quasra or Blazar sources often doesn't shine out in the visible light so much but can be seen through X-ray and Radio Surveys, you don't really find these object with lower red shift and Quasar luminosity, you can have radio-quiet quasar and emission of 10^36-10^38 watts, you'll have to take into account the mass of compact object which can be adding more gas to acccretion & increases the radiation pressure which, and then there is the light psuhing out. Some Blazars have a large blazar multifrequency variability and you must also think about a jet component of the quasar, I think a study has shown that the disc luminosity is often 1 to 20 times related to the jet power. There is often an increase of gamma-ray flux appearing after the first optical/IR peak, there is thought to be a connection between BlackHole Mass of the object the bulgemass of the nucleus and its Near-Infrared luminosity but you'll have to check that out yourself. The quasistellar sources perhaps can have super lumonosity perhaps from 5 to 155,000 times the luminosity of a normal galaxy, but lumonosity has variations perhaps of timescales of days or months. Think about the disc, the near light speed jets sometimes many many parsecs or light years long, think about the blackholes, Galactic collosions, the Galaxy mass, blazars, Seyfert and powerful radio sources in our sky.

Perhaps you can ask someone who knows more about this stuff
picture of jets

http://archive.ncsa.uiuc.edu/Cyberia...CygnusA_lg.jpg
http://www.cosmovisions.com/CygnusA.jpg

[Maddad]

It ought to be easy enough to calculate. Find the most massive galaxies, and then extrapolate their brilliance based on the brilliance of quasars from lightweight ordinary galaxies. If the most massive galaxy is say 1,000 times as much as the galaxies of quasars for which we can measure their mass, then the maximum possible brilliance ought to be a thousand times more.

[Spaceman Spiff]

I understand the Eddington Limit imposes a maximum luminosity to any quasar for a certain black hole mass. I would expect that there is a maximum possible mass quasar...at "billions and billions" of solar masses I would think a black hole would "swallow" its luminous accretion disk, even if it could somehow find the matter it ingest. What is the highest possible luminosity of a quasar given these two factors? Have any been found near this limit?

As you noted, a logical possible limit is the Eddington Luminosity limit. Originally conceived by Sir Arthur for hot (spherical) stars, it simply compares F_radiation less.than.or.equal.to F_gravity. In the current paradigm of quasars, matter is accreted onto a supermassive blackhole in the center of galaxy. Approximately 10% of this matter accretion rate is converted into luminous energy. This leads to:

L < 1.26e38 (M_bh/M_sun){<m>/m_p}/{opacity/k_e} ergs/s

or for those of you who use SI units, the leading coefficient is 1.26e31 Joules/s (Watts). The <m>/m_p is the ratio of the mean mass per nucleus relative to the proton mass (about 1.25 or so for most cosmic abundance mixes), and the {opacity/k_e} term is the ratio between the total opacity of the gas relative to that of pure electron scattering. M_bh/M_sun is the supermassive black hole mass in solar masses.

So do the math. If the most massive smbh is less than about 10^10 solar masses, then the maximum intrinsic quasar luminosity is less than about 2e48 ergs/s (2e41 Watts) or about 5e14 L_sun.

There are quasars whose inferred luminosities apparently exceed this value. In some cases we know that their light flux in our direction has been affected by a line of sight gravitational lens. But it is also possible that the accretion rate can exceed the limit put forth by the simple physical arguments that led to Eddington's luminosity. For example, the accretion onto the smbh is probably not spherical, and various phenomenon (e.g. photon bubbles) can arise within the accretion disk to allow the accretion rate to exceed the Eddington rate by factors of a few. Taking these into account, the maximum expected quasar luminosity could be as high as 10^49 ergs/s or 3e15 L_sun in round numbers.