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Comment by beedeebeedee | Hacker News Reader

Is this going to annihilate us? I didn't see them mention any safety risks, but it sounds similar to a quasar to me (a non-astronomer), and I think if one of those is pointing at us, we're toast. If they just detected the light, and the matter is going 99.9% of the speed of light, does that mean we're toast tomorrow? Next week? Next year?

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Well it seems like we've detected 3 other jets pointed straight at us as the black hole devoured a star so it seems like a very common event on a geological time scale. The fact that we managed to evolve and are still here is a decent sign.

>The team says the black hole's jet may be pointing directly toward Earth, making the signal appear brighter than if the jet were pointing in any other direction. The effect is "Doppler boosting" and is similar to the amped-up sound of a passing siren.

>AT 2022cmc is the fourth Doppler-boosted TDE ever detected and the first such event that has been observed since 2011.

Also, I believe that as the universe's volume expands, the probability and intensity of being in the direct path of any particular such jet goes down. Then again, the frequency of these events may (or may not) be increasing at a rate that more than counteracts that. (I'm just speculating here, I'm not a cosmologist!)

Most of the threat from relativistic jets is from within ones own galaxy (and at worst, its local group). So, yes as the universe expands the risk from the latter should decrease, the risk from the former wouldn't really change due to expansion. The risk probably does still come down, but more due to age as larger clouds of gas get used up and spread around by supernovae, preventing enough mass from gathering for the things that produce relativistic jets.

One possible answer to the Fermi paradox is that we're early because the universe may have only recently gotten calm enough for life to survive long enough to develop intelligence.

As far as I understand it, gravitational lensing would affect the trajectory of particles travelling different speeds differently. So it would seem entirely possible that the matter wouldn't even be pointed at us. That assumes that either is being significantly affected by gravity of course.

Also bear in mind that though the light of 1000 trillion suns has been pointed at us, it's not like we have a second sun in the sky right now. It's really, really far away.

It's 8 billion light years away. We'll be fine.

If the matter is trailing at 99.99% the speed of light as reported, it gives us 800k years.

The matter was traveling at 99.99% the speed of light in the jet. While we generally consider space to be a friction-less vacuum for something like a spaceship, that isn't true for things like a stream of particles traveling across the universe. Even if the Earth stood still in this exact position for another 800,000 years (which it won't, since our galaxy is not stationary, nor is the solar system, and there is of course the expansion of space as well), very little of the physical matter from this jet would hit us.

Wouldn’t it give us way more than that? If it were traveling at 100% the speed of light it would take 8 billion years right?

The light has already taken 8 billion years to get here. The particles have also been traveling for that time and are only 800,000 years away now.

“Hey Siri, set a reminder for…”

For now!

I'd believe the small percent of a percent of the sky we're in for it to be pointing at us is still a large swath of trillons of miles.

And 850k years from now - our galaxy would have moved from it's location anyways. Some other galaxy will probably waltz into it.

Very interesting. Does this imply (assuming these jets have been occurring for a very very long time) that we'd be able to see the consequences of other jets in other galaxies/planets? Said another way, have we ever observed something that could actually have been "... some other galaxy waltzing into it"?

One of Earth's past mass extinction events is hypothesized to have maybe been caused by a gamma ray burst[0]. I don't know enough to speculate whether it could have been caused by one of these jets instead.

[0] https://en.wikipedia.org/wiki/Late_Ordovician_mass_extinctio...

If it is going to, would you even want to know?

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