Quasars show range of Luminosities ?

[Widdekind]

Apparent Magnitude (m):

[math]m = M_{\odot} - \frac{5}{2} log_{10} \left( \frac{F}{F_{\odot, 10pc}} \right)[/math]

 

[math]M_{\odot} = 4.76[/math]

 

[math]F_{\odot, 10pc} = \frac{L_{\odot}}{4 \pi \; 10pc^{2}}[/math]

 

Received Flux (F), across cosmological distances:

[math]F = \frac{L}{4 \pi \left( w \left( 1 + z \right) \right)^{2}}[/math]

 

Present distance (w), equivalent to the comoving coordinate, of an observed object, at a given Redshift (z), in a Flat universe ([math]\Omega_{0} = 1[/math]):

[math]w = \frac{2 \; c}{H_{0}} \left( 1 - \frac{1}{\sqrt{1+z}} \right)[/math]

 

[math]H_{0} \approx 75 \; km \; s^{-1} \; Mpc^{-1}[/math]

 

From these relations, we can calculate the Apparent Magnitude (m), of quasars of fixed Luminosity (L), at varying Redshifts (z). On the following figure, lines of constant Luminosity have been overlain atop the plot of Redshift vs. Apparent Magnitude for known quasars. Beginning with the upper left line, Luminosities displayed are [math]10^{14} \; L_{\odot}[/math], [math]10^{13} \; L_{\odot}[/math], ..., [math]10^{8} \; L_{\odot}[/math]:

 

 

CONCLUSIONS:

 

At any given epoch, quasars' intrinsic Luminosities vary over roughly three orders-of-magnitude. And, quasars appear to brighten from z=3 to z=2, before steadily dimming, by about three orders-of-magnitude, from z=2 to z=0.03, after which quasars have faded from view.

 

Quasar numbers also follow a similar evolution, rapidly increasing in comoving density, before fading from view:

Thus, as quasars "powered up" across the cosmos, they became both (1) more numerous; and (2) more Luminous. Likewise, as quasars faded from view, they became both (1) rarer; and (2) dimmer.

 

Note that no quasars were ever brighter than about [math]10^{14} L_{\odot}[/math], nor were any ever dimmer than about [math]10^{9} L_{\odot}[/math]. And, in the quasars' Redshift vs. Apparent Magnitude plot, their appears to be the hint of a linear feature running nearly parallel to the [math]10^{11} L_{\odot}[/math] contour — perhaps representing the stablest, and longest-lived, sub-population of quasars ??

 

 

 

SOURCES:

 

• Carroll & Ostlie. Introduction to Modern Astrophysics, pp. 89,1289-ff.
  
• Jayant V. Narlikar. Seven Wonders of the Cosmos, pg. 307.
  
• Martin Rees. New Perspectives in Astrophysical Cosmology, pg. ~100.
  

Edited September 4, 2009 by Widdekind

[Airbrush]

Would this suggest that quasars brighted at meal time? Does that mean their accretion disks deliver fuel to the supermassive black hole at irregular intervals?

 

BTW, do you have an opinion of what powers quasars? Is it simply gas and dust getting heated to Trillions of degrees or is matter-antimatter being created and annihilated?

[granpa]

thank you. great thread.

[insane_alien]

so your conlusion is that different quasars have different luminosities? well who'd have thunk it.

 

i'd be far more astounded if they had identical luminosities because thats something you wouldn't expect.

[J.C.MacSwell]

so your conlusion is that different quasars have different luminosities? well who'd have thunk it.

 

i'd be far more astounded if they had identical luminosities because thats something you wouldn't expect.

 

I think it is as much to do with "when and how many", which is interesting.

[granpa]

I'd love to see how that compares to GRB numbers and luminosities.

[Airbrush]

I believe the intense luminosity of quasars comes from the inner edge of the accretion disk, along with it spinning at high rps and something incredible going on near the poles. The jets are something else. If the jets were the brightest thing of a quasar it would not resemble the point source we see, but rather a band of luminosity. However, the cloud of gas and dust in the accretion disk conceals what is going on, and blocks the path, and only the polar regions allow light to escape. Do the radio waves penetrate the gas and dust, along with gamma and X-rays, anything else? Maybe quasars appear as point sources because the most intense energy release and luminosity that escapes from the black hole is very near both poles of the quasar. Since the distance between the two poles is extremely relatively short, we see what looks like a star at such great distance, hence the name quasi stellar radio source.

 

I am still not clear on what generates so much power. According to wikipedia the reaction is about 20 times as energetic as nuclear fusion, but that seems low. What do you think?