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According to this article (A quasar Milky Way six million years ago?), during:

(during) a quasar stage in its evolution (6 million years ago) ... the Milky Way’s central black hole swallowed a huge amount of gas, creating a shock wave that has now crossed 20,000 light-years of space. They say that event left behind a million-degree gaseous fog, a sort of “bubble” that extends from the Milky Way’s core two-thirds of the way to Earth. ... observed, via data from an X-ray spacecraft.

It's traveled 20,000 ly since it was ejected 6Mya and is now 2/3 of the way to Earth. Thus, if my math is correct, it'll intersect with the Earth in 3My.

What then, for the Earth? It'll be weaker due to the Square-cube Law, but it still seems like a lot of X-Rays.

And what's happened to planets around stars within the 20,000 ly radius?

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  • $\begingroup$ The Sun already sits in a bubble in the interstellar medium with those sorts of temperatures. $\endgroup$
    – ProfRob
    Oct 9, 2022 at 17:07
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    $\begingroup$ Consider that the strength of the shockwave diminishes as it expands in all three dimensions. Distances matter a lot. By the time the shockwave reaches us, we'll already have experienced the effects of Betelgeuze gone supernova a mere 500 ly away, and even that won't affect us much. If we're still around as a civilization by that time in the first place. $\endgroup$
    – DevSolar
    Oct 10, 2022 at 17:55

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Probably nothing of practical interest. Keep in mind that the gas in the shock wave in question is much less dense than our Solar wind. The X-rays generated in the shock wave aren't much intense either.

In the Solar system, it may deform the heliopause shock front. Maybe all the way to Neptune orbit.

In the nearby molecular clouds, it may trigger star formation. Depending on the outcome of the star formation process (if it produces some big enough stars), we may get some bright stars in the night sky (as a replacement for the others that already went boom) and some impressive supernovas few million years later.

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In astronomy, we generally use observer time uncorrected for distance (because we usually don't know the distance very well). The 6 Mya is the time that the x-rays from the event arrived at Earth, so initial pulse of x-rays is long gone.

The x-rays from the shock continue to arrive, but they are very weak. The shock is very spread out, so it doesn't get much brighter as it gets closer. Note that x-rays from the Sun are ~100,000 times brighter at Earth than all other astronomical sources of x-rays combined.

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  • $\begingroup$ Since quasars are supposed to be So Powerful (what with the massive jets shooting thousands of light years out of galaxies), it seemed reasonable to wonder how powerful this shock wave is. $\endgroup$
    – RonJohn
    Oct 9, 2022 at 20:59
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    $\begingroup$ @RonJohn Active galactic nuclei have a wide range of luminosities. The super powerful ones like BL Lac are very rare. Weaker ones are much more common. $\endgroup$
    – John Doty
    Oct 10, 2022 at 15:56
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The Fermi Bubble is basically just a huge shockwave from the Sagittarius A* outburst that is speculated to have been quite a powerful quasar a few million years ago.

Now, as John Doty mentioned, the blast of the quasar itself is now some 6 million lightyears away along with the quasar's light since electromagnetic waves travel at the same speed. Fortunately, we have a nice atmosphere that blocked that deadly stuff out when it reached us a long time ago.

So generally, quasars are only a danger if you're in the direct path of the jets, or very close to it. We are not close to Sagittarius A*, nor are we anywhere near the path of any theoretical jets. So, what will happen when the Fermi Bubbles reach the Solar system? Not much. Yes, while the remnant itself is indeed still beaming with gamma and x-ray, it is not even a mere fraction as powerful as the initial blast would have been. So if we survived that, we're going to be just fine when this reaches us.

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