# Tag Info

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There are essentially two reasons. First, quasars are rare objects, so even though they are homogenously distributed on large scales, the average distance is large. Moreover, the brightest quasars are even rarer, but visible to large distances, so their average distance is even larger. Second, most quasars were most active at redshift $z\sim2$. This is ...

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You have stumbled across a profound observation and almost grasped one of its most important consequences. There are two forms of the so-called cosmological principle. There is the more limited cosmological principle, which to paraphrase, says that the universe will look the same in all directions to any observer anywhere in the universe at the same time (i....

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The quasar gives out light in all directions. The light spreads out in space. Only a very small amount of that light would be pointed exactly in the direction of your telescope. But if a large galaxy or galaxy cluster is between the quasar and us, it bends some of the light towards us, making the quasar brighter (it would also distort the shape, but quasars ...

12

Tricky to say for sure, but I would imagine it comes about from measurements of the luminosity and inference of the black hole mass in such systems. The most extreme objects radiate at the Eddington luminosity, where gravitational forces on matter falling into the black hole are balanced by radiation pressure from the heated material closer in. If ...

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The discussion of the Cosmological Principle above is very relevant, but it is possible that so is a (weak) application of the anthropic principle - in other words if we were in a region of extremely energetic physical phenomena, such as quasars, we would be unlikely to exist - as the evidence suggests that the development of intelligent life takes a ...

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Neutrinos are typically produced in AGN jets through what we refer to as hadronic processes. Protons are accelerated to relativistic speeds and interact with nearby photons. Depending on the particular type of AGN, there are a number of possible sources of these photons: Ambient light within the jet Emission from the accretion disk Photons from the broad ...

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Quasars have a very low density at the present epoch, but were much more common in the past. Their co-moving space density peaks at redshifts of 2-3. The evolving space density of bright quasars. From https://ned.ipac.caltech.edu/level5/Madau/Madau7.html. The fact that the quasar population density evolves was one of the key arguments against steady state ...

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I think you may be mixing up "Energy" and "Power" a little here. Power is the rate of Energy output per time. If Power is the speed, then Energy is the distance travelled. Quasars look like stars, from Earth, they give out a light, and while they do vary a little (or a lot) you would not expect to see new ones forming or existing ones fading away. Gamma ...

7

All quasars are AGN, but not all AGN are quasars. AGN is a terminology that comes later than quasars. Quasars is the term applied at the beginning, when the first objects of this type have been discovered. They were radio-loud and point-like (the so-called quasi-stellar radio sources). This characterization still holds nowadays. Another property is that ...

7

The optical emission lines of quasars do not come from sufficiently close the the central supermassive black hole to be appreciably gravitationally redshifted. If they did arise from gas near the "innermost stable circular orbit", then the maximum gravitational redshift would be about 0.2. In addition, the lines would have a characteristic profile caused by ...

7

Let me see if I can try answering both parts of your question. The key is a combination of two things: 1) Most of the binary BHs in an accretion disk will have their binary orbits in the same plane as the accretion disk, so that "perpendicular to the binary plane" = "perpendicular to the accretion disk"; 2) The most effective form of ...

6

You are right that the stars seen on the sky are within the Milky Way. Only with a large telescope is it possible to resolve individual stars in other galaxies, and only for the nearest ones. I don't know which sources you refer to, by I think perhaps you are confusing the different types of gravitational lensing. I cannot explain them better than the ...

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We could, but there isn't enough energy to make it worthwhile. These types of radiation are referred to as "highly energetic" because each individual particle (or very short burst) has comparatively much energy, but averaged over time, there is far more energy around in the form of sunlight. The highly energetic radiation is more dangerous because even a ...

6

The statement "They're only emitting infrared light" is wrong, or at least poorly phrased. The Ly$\alpha$ forest The Ly$\alpha$ forest (LAF) is caused by the spectrum of the quasar being redshifted along its way; wherever a cloud of neutral hydrogen is located, the part of the spectrum that at that at that position has been redshifted to $\lambda_0 = 1216\,... 5 The solution to your question is surprisingly simple, I think: A quasar that puts out energy around Eddington luminosity or higher, must accrete at a certain rate, corresponding to the energy output. When consulting a lecture and a random paper from the archive on this topic, it is evident that those accretion rates correspond to 1-10 solar masses per ... 5 A quasar is a type of AGN. Its main property is that it's galaxy axis points towards the earth and this way we receive its light and radio signals. That's why they are one of the most energetic AGN. Here you can see a relation of all the AGN types: http://en.wikipedia.org/wiki/Active_galactic_nucleus#Summary 5 The light emitted isn't actually from the black hole itself but the swirling matter that surrounds it called the accretion disk. The light emitted from the accretion disk is far enough to escape from the pull of the quasar. A link from wikipedia sufficiently explains this: Quasars are believed to be powered by accretion of material into supermassive black ... 5 Edit: I found you a very relevant paper! http://arxiv.org/pdf/astro-ph/0007341v1.pdf seems to be solving exactly your problems for sources with arbitrary angular separation$\alpha$. Equations (12) and (14) will give you the comoving distance$\chi_2'$and redshift$z_2'$between them at the epoch when$Q_1$received light from$Q_2$. You will have to solve ... 5 It means the separation between the two objects if they were both at the same distance away. This separation is found by multiplying the angular separation (in radians) by the distance to the objects. Often, the distance to extragalactic objects depends on the assumed value of the Hubble parameter. In this case,$h$is a dimensionless number corresponding ... 5 I assume you're referring to the recent press release about the quasar J043947.08+163415.7, observed recently using Hubble. The paper about the observations details how the authors measured the distance to the quasar, by calculating its redshift, a quantity that describes how the wavelength of light appears to change based on whether the object is moving ... 4 in the early universe there was more diffuse matter in gaseous form available to the black holes. The galaxies were more foggy with diffuse matter and less void, so a BH travelling through a galaxy could catch a continuous cloud of matter as it went along, resulting in huge capture rates. Back then, most gas had not yet collapsed to form stars, there was ... 4 It is unfortunate that the usual poor journalism labels the growth of the black hole as "inexplicable" and then further down in the article refers to some possible explanations. The basic problem is a growth timescale one. Radiation pressure introduces a negative feedback, such that there is a "theoretical" maximum for spherical accretion called the ... 4 Yes, there are many. One of the first, if not the first was the radio lensed quasar B1938+666, in which a near-IR Einstein ring was reported by King et al. (1998). The answer to your real question though is not as straightforward as that. Although lensing should be wavelength independent (according to GR), it is not independent of the size and position of ... 4 There's a pretty comprehensive wikipedia page on the subject. In summary.... Throughout the 2000's conflicting results were published using the same data. The conflict seems to center on the selection effects of the surveys, and the corrections applied to account for them. I did a quick search for 'redshift quantisation' on the Arxiv and found no papers ... 4 I would think that the same reason that a gas disk enhances the growth of planetesimals. Drag from the disk enforces circular, co-planar orbits, which in turn means that objects that get close to each other have small relative velocities. Edit: So what is thought to be going on is a little bit more complex than the simple answer above. The density of massive ... 3 Quasars are not near the Earth. The nearest one is 600 million light years away. Most are much much further. They are so very far away that they appear very dim. The brightest quasar is only visible with a telescope, where it appears like a dim star. The total amount of energy from a quasar per square metre on Earth is minute. It is not a sensible source ... 3 Projected separation is the minimum physical separation of two astronomical objects, as determined from their angular separation and estimated distance.The Parallax shift of a star at a distance of one parsec as seen from the Earth. Not to scale For planets and double stars, this distance is usually given in Astronomical Units. The actual separation of the ... 3 To answer the question "how does science knows what is early and what is late?" in simple terms: We know that the Universe is expanding. Because of this, the light from things further away from us gets "stretched" more, and is redshifted. The bigger the redshift, the further the light has travelled. We can use formulas to work out the distance based on the ... 3 The only physical mechanism I can think of for quasars to have such a large difference in two bands would be at very high redshift ($z\gtrsim6$) where you have the Gunn-Peterson trough completely erasing everything blueward of 912 Å (restframe). But with typical magnitudes of$\sim20$or so at these redshifts, a color of$20\$ that would then mean that the ...

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