What is the distance to the farthest known quasar from earth? What are other names for quasars? Can a quasar die? See all questions in Quasars and Galactive Collisions. Impact of this question views around the world. You can reuse this answer Creative Commons License. Galaxies like the Milky Way may once have hosted a quasar that has long been silent. In December , the most distant quasar was found sitting more than 13 billion light-years from Earth.
Quasars this young can reveal information about how galaxies evolved over time. Quasars emit energies of millions, billions, or even trillions of electron volts. This energy exceeds the total of the light of all the stars within a galaxy. The brightest objects in the universe , they shine anywhere from 10 to , times brighter than the Milky Way. For instance, if the ancient quasar 3C , one of the brightest objects in the sky, was located 30 light-years from Earth, it would appear as bright as the sun in the sky.
However, quasar 3C , the first quasar to be identified , is 2. It is one of the closest quasars. Studying quasars has long been a challenge, because of their relationship to the hard-to-measure mass of their supermassive black holes. Dropping things from far away into the much stronger gravity of a black hole is much more effective in turning the energy released by infall into other forms of energy.
Just as the falling book can heat up the air, shake the ground, or produce sound energy that can be heard some distance away, so the energy of material falling toward a black hole can be converted to significant amounts of electromagnetic radiation.
What a black hole has to work with is not textbooks but streams of infalling gas. If a dense blob of gas moves through a thin gas at high speed, it heats up as it slows by friction. As it slows down, kinetic motion energy is turned into heat energy. Just like a spaceship reentering the atmosphere Figure 3 gas approaching a black hole heats up and glows where it meets other gas.
It therefore gets far, far hotter than a spaceship, which reaches no more than about K. Indeed, gas near a supermassive black hole reaches a temperature of about , K, about times hotter than a spaceship returning to Earth. It can even get so hot—millions of degrees—that it radiates X-rays. Figure 3.
Pushing on the air slows down the spacecraft, turning the kinetic energy of the spacecraft into heat. Fast-moving gas falling into a quasar heats up in a similar way. The amount of energy that can be liberated this way is enormous. Quasars are much more efficient than that. Unlike the hydrogen atoms in a bomb or a star, the gas falling into the black hole is not actually losing mass from its atoms to free up the energy; the energy is produced just because the gas is falling closer and closer to the black hole.
This huge energy release explains how a tiny volume like the region around a black hole can release as much power as a whole galaxy. But to radiate all that energy, instead of just falling inside the event horizon with barely a peep, the hot gas must take the time to swirl around the star in the accretion disk and emit some of its energy.
Our own Milky Way black hole is currently quiescent, but it may have been a quasar just a few million years ago Figure 4. Two giant bubbles that extend 25, light-years above and below the galactic center are emitting gamma rays. Were these produced a few million years ago when a significant amount of matter fell into the black hole at the center of the galaxy? Astronomers are still working to understand what remarkable event might have formed these enormous bubbles. Figure 4. Fermi Bubbles in the Galaxy: Giant bubbles shining in gamma-ray light lie above and below the center of the Milky Way Galaxy, as seen by the Fermi satellite.
The gamma-ray and X-ray image is superimposed on a visible-light image of the inner parts of our Galaxy. The bubbles may be evidence that the supermassive black hole at the center of our Galaxy was a quasar a few million years ago.
The physics required to account for the exact way in which the energy of infalling material is converted to radiation near a black hole is far more complicated than our simple discussion suggests. The details of these models are beyond the scope of our book, but they support the basic description presented here.
So far, our model seems to explain the central energy source in quasars and active galaxies. But, as we have seen, there is more to quasars and other active galaxies than the point-like energy source. They can also have long jets that glow with radio waves, light, and sometimes even X-rays, and that extend far beyond the limits of the parent galaxy.
Can we find a way for our black hole and its accretion disk to produce these jets of energetic particles as well? Many different observations have now traced these jets to within 3 to 30 light-years of the parent quasar or galactic nucleus. While the black hole and accretion disk are typically smaller than 1 light-year, we nevertheless presume that if the jets come this close, they probably originate in the vicinity of the black hole.
Another characteristic of the jets we need to explain is that they contain matter moving close to the speed of light. Why are energetic electrons and other particles near a supermassive black hole ejected into jets, and often into two oppositely directed jets, rather than in all directions? Again, we must use theoretical models and supercomputer simulations of what happens when a lot of material whirls inward in a crowded black hole accretion disk.
Although there is no agreement on exactly how jets form, it has become clear that any material escaping from the neighborhood of the black hole has an easier time doing so perpendicular to the disk. Several lines of hydrogen absorption in the visible spectrum have rest wavelengths of nm, nm, nm, and nm. In a spectrum of a distant galaxy, these same lines are observed to have wavelengths of nm, nm, nm, and nm respectively.
What is the redshift of this galaxy? What is the recession speed of this galaxy? The first question astronomers asked was whether quasars obeyed the Hubble law and were really at the large distances implied by their redshifts. If they did not obey the rule that large redshift means large distance, then they could be much closer, and their luminosity could be a lot less. One straightforward way to show that quasars had to obey the Hubble law was to demonstrate that they were actually part of galaxies, and that their redshift was the same as the galaxy that hosted them.
Since ordinary galaxies do obey the Hubble law, anything within them would be subject to the same rules. Observations with the Hubble Space Telescope provided the strongest evidence showing that quasars are located at the centers of galaxies. Hints that this is true had been obtained with ground-based telescopes, but space observations were required to make a convincing case.
The reason is that quasars can outshine their entire galaxies by factors of 10 to or even more. The Hubble Space Telescope, however, is not affected by atmospheric turbulence and can detect the faint glow from some of the galaxies that host quasars Figure 4.
Quasars have been found in the cores of both spiral and elliptical galaxies, and each quasar has the same redshift as its host galaxy. A wide range of studies with the Hubble Space Telescope now clearly demonstrate that quasars are indeed far away. If so, they must be producing a truly impressive amount of energy to be detectable as points of light that are much brighter than their galaxy.
Interestingly, many quasar host galaxies are found to be involved in a collision with a second galaxy, providing, as we shall see, an important clue to the source of their prodigious energy output. Figure 4. The top left image shows a quasar that lies at the heart of a spiral galaxy 1. The bottom left image shows a quasar that lies at the center of an elliptical galaxy some 1.
The middle images show remote pairs of interacting galaxies, one of which harbors a quasar. Each of the right images shows long tails of gas and dust streaming away from a galaxy that contains a quasar. Such tails are produced when one galaxy collides with another. Given their large distances, quasars have to be extremely luminous to be visible to us at all—far brighter than any normal galaxy.
In visible light alone, most are far more energetic than the brightest elliptical galaxies. But, as we saw, quasars also emit energy at X-ray and ultraviolet wavelengths, and some are radio sources as well.
When all their radiation is added together, some QSOs have total luminosities as large as a hundred trillion Suns 10 14 L Sun , which is 10 to times the brightness of luminous elliptical galaxies. Finding a mechanism to produce the large amount of energy emitted by a quasar would be difficult under any circumstances. But there is an additional problem. When astronomers began monitoring quasars carefully, they found that some vary in luminosity on time scales of months, weeks, or even, in some cases, days.
This variation is irregular and can change the brightness of a quasar by a few tens of percent in both its visible light and radio output. Think about what such a change in luminosity means.
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