Why is a quasar bright

For the last four years, astronomers have attempted to understand changing-look quasars using the simplest theories possible. At first, that meant finding scenarios that did not require sweeping changes in the accretion disk.

To understand why, it helps to consider the size of these systems. If you could plop a quasar on top of the solar system, the supermassive black hole would swallow the sun, while the accretion disk would stretch out tens of thousands of times farther than Earth. To turn the quasar off, all of that material would have to swirl inward and fall onto the black hole — a process that calculations and even observations suggest should take tens to hundreds of thousands of years.

So astronomers considered other possibilities. But when she and her colleagues tried to model that scenario, they found that only an overly complex situation with multiple clouds could reproduce the observations. It seemed far too unlikely.

To boot, any change would have taken much longer than a few years. Similarly, others have argued that the purported quasars were actually powerful supernovas.

Both possibilities would outshine their host galaxies, much like quasars, and might even emit similar wavelengths of light.

Then the light from these events would fade over the course of a few months to years — thus matching the timescale behind changing-look quasars. So researchers have recently turned back toward quasars. In , Zhenfeng Sheng, an astronomer at the University of Science and Technology of China, and his colleagues examined multiple changing-look quasars in both visible and infrared light. Because of this, any change in the accretion disk will later be echoed within the torus.

Sheng and his colleagues saw just such an echo as did other studies , allowing them to conclude that it must be a sign of a change in the amount of material flowing through the accretion disk.

Just how this sweeping change occurs is still a matter of debate — but many hypotheses have recently emerged. It could be that a quasar does not have to clear its plate completely in order to shut down. One way to understand this is to break up the accretion disk into separate parts: a bright inner region that illuminates an outer dull region. Then if the black hole consumes the inner region a process that could occur in mere months , the inner disk will disappear, and without its bright beacon, the outer disk will grow dark — much like the death of the sun would cause the moon to lose its shine.

Or it could be that the accretion disk changes its shape. It sounds wild, but this year studies of two different quasars found evidence to support this theory based on another echo. In each, the ultraviolet and blue colors fell away first, followed by the green and finally the red. That sequence flows from highest-energy colors to lowest-energy colors. It therefore resembles changes that ripple from the inner disk to the outer disk.

Instead, they think that a cooling front swept out from the supermassive black hole at an incredible clip. The red colors, for example, dropped merely a year after the green colors. While some dust and gas fall into the black hole , other particles are accelerated away from it at near the speed of light.

The particles stream away from the black hole in jets above and below it, transported by one of the most powerful particle accelerators in the universe. Most quasars have been found billions of light-years away. Because it takes light time to travel, studying objects in space functions much like a time machine; we see the object as it was when light left it, billions of years ago.

Thus, the farther away scientists look, the farther back in time they can see. Most of the more than 2, known quasars existed in the early life of the galaxy. 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. Are quasars formed when two black holes combine? Is my assumption right Improve this question. James K Ajay meena Ajay meena 81 1 1 silver badge 7 7 bronze badges. Quasars are different from black holes merging.

Add a comment. Active Oldest Votes. A link from wikipedia sufficiently explains this: Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies.

Improve this answer. CipherBot CipherBot 1, 10 10 silver badges 25 25 bronze badges. The quasar is the whole system consisting of a supermassive black hole, its accretion disk, magnetic fields and what not.

So the light does infact come from the quasar, but not from the black hole. Black holes don't suck, they gravitate The material may come from, for example another star, or in the case of the giant black holes at the centre of many galaxies, from the gas, dust and stars that are found in the cores of galaxies.

James K James K Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Featured on Meta.

Now live: A fully responsive profile. Related