What would happen if our galaxy turned into a quasar?

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Recently, we received the following question from one of the subscribers:

The question is quite interesting, let’s figure it out together, can our galaxy form a quasar in its core, and if so, what will happen to us?

Quasars are actually very rare objects and they are most often found in young galaxies, in the very early stages of their life, when the galaxy is still full of gas. Usually, the material in the galactic disk rotates far from the supermassive black hole at its center. However, from time to time, by coincidence, huge clouds of gas get too close to the black hole, and it tears them apart, while we see a short burst in the galactic core. But this one flash is not a quasar, for a quasar to form, it takes a huge amount of gas constantly falling onto the black hole. In this case, a huge accretion disk is formed near the black hole, from strong friction the matter heats up to hundreds of millions of degrees, and begins to emit the brightest light, eclipsing all the stars of the galaxy taken together. It is such an accretion disk that is called a quasar.

Since the Milky Way is a middle-aged galaxy, it is no longer able to support a quasar in its core, but it is likely that once, at the very beginning of its existence, there was a quasar in the core.

At the moment, a new quasar cannot appear in the center of our galaxy, but it is quite possible that it will appear in 4 billion years. Then the Andromeda galaxy will collide with our galaxy, and if during the collision a supermassive black hole in the center of the Milky Way passes through a huge amount of gas and dust, then its accretion disk will shine brighter than all the stars of the Milky Way combined. A quasar will be born.

According to some reports, the Milky Way passed a short-term quasar stage 6 million years ago. Astronomers say this happened when the Milky Way’s central black hole “swallowed” a huge amount of gas, creating a shockwave. This large-scale event left a gaseous fog, a kind of «bubble» that extends from the core of the Milky Way two-thirds of the way to Earth.

It depends on how much matter the black hole gets. If a medium-sized quasar is located at a distance of 7 thousand sv. years from the Earth, then it will illuminate our planet as a second Sun. We are 23 thousand light-years from the center of our galaxy, which means that the quasar would be nine times less bright than the Sun. At first glance, the difference seems large, but such a quasar will illuminate the planet’s surface well enough. By comparison, the full moon is 400,000 times less bright than the sun.

The light of the quasar is not the most dangerous thing that will reach the Earth. The quasar will emit extremely intense X-ray and gamma rays. Of course, a lot depends on how the relativistic jets will be directed and the fact that galactic dust will slightly obscure us from the quasar, but still the radiation will reach the Earth. In the worst case, if the jets are directed at us or the quasar is huge, this can lead to sterilization of the planet, but in other situations this will only lead to radiation sickness of one degree or another in most living organisms. Potentially, life may well adapt to this.

Author: Alexey Nimchuk. Edited by Fedor Karasenko.

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