A wandering black hole caught feeding on the run

wwglb about 22 hours ago 54 commentsRead Article on phys.org

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Discussion (54 Comments)Read Original on HackerNews

dotancohen•about 17 hours ago

While the conclusions of the observation are interesting, what really stood out to me was the observations themselves. That black hole is 20 million light years away, in another galaxy! And we have multiple high enough resolution observations to conclude how the gas orbits the black hole and gets dragged along behind it. That's nuts.

Towaway69•about 17 hours ago

What blows my mind is that 20 million light years also means that what we're observing something that happened 20 million years ago. We're looking into the very distant past, at something that might well no longer exist.

Turn that around and there well could be other lifeforms observing the Earth with dinosaurs roaming around on it. Perhaps observing the impact of a giant meteor onto the earth.

The light of that meteor impact on Earth is still roaming the universe. If only we could travel faster than that light.

himata4113•about 16 hours ago

What is even more crazy is that we can actually look as far as the beginning of the universe just because of how long it takes for particles from the other side of the universe to reach us.

ilt•about 15 hours ago

I’m not a science person but I think I understand the crux of what you’re saying here - have a question though: are those particles finite? And those are light particles, right? Is the number of those particles increasing the longer they travel?

Sorry if questions don’t make sense…

dotancohen•about 15 hours ago

  > What blows my mind is that 20 million light years also means that what we're observing something that happened 20 million years ago.

Well... Not really. It took the entirety of the book A Brief History Of Time to even grasp a cusp of this, so I know I won't convince you in a short HN comment, but "now" is the collection of events that currently affect us. Due to causality, events outside our light cone have not occurred yet. They have no more influence than does an egg falling off the counter that has yet to hit the floor. The egg breaks only when it hits the floor - events only occur in our reference frame when they could affect outcomes in our reference frame. C is the propagation of causality, the fact that light travels at that speed in a vacuum doesn't affect that.

ckcheng•about 11 hours ago

> but "now" is the collection of events that currently affect us.

Just to see if I understand what you’re saying…

So a hypothetical photon from the big bang (era?) gets observed now means the big bang is happening now?

A dinosaur decays to bones and now gets observed means the dinosaur died just now - not that it died millions of years ago?

(Dinosaur = photon from a star or something. Decay = red shift. Or a real dinosaur— guess it’s the same now.)

anonzzzies•about 13 hours ago

But that 20m year old light is in our past light cone; we can say it is in our past. If it is not in our light cone, we cannot communicate any temporal info so we cannot say if it’s now, past or future in reference to us as observer.

andrewflnr•about 10 hours ago

I think you misunderstood Hawking. "Now" in the relativistic sense is not the same as our past light cone. Reference frames for simultaneity are defined by relative motion. Galaxies without too big a redshift are close enough to moving at the same speed we are, and thus being in our same reference frame, that simultaneity (and times relative to the present) are reasonable to talk about.

steve_adams_86•about 11 hours ago

From a practical perspective this makes perfect sense to me. But we do know the photons travelled over a period of time, right? Where those photons came from, ‘now’ is something else. Though it doesn’t matter practically, those events did occur in the past, before they were a part of our now. Or am I missing something?

ShinyLeftPad•about 12 hours ago

It's crazy only if you use a specific geocentric version of "now".

phyzix5761•about 9 hours ago

Actually we don't know the speed of light in one direction[0]. So we could actually be seeing things as they are in this moment or at any other moment in time for all we know.

[0] https://www.youtube.com/watch?v=pTn6Ewhb27k

GoblinSlayer•about 8 hours ago

If you send light around the universe, is it in one direction?

Towaway69•about 17 hours ago

LegacySurvey deep link[1].

Zooming out from there and one gets an appreciation for how (in)significant we really are.

[1] https://www.legacysurvey.org/viewer?ra=195.8160&dec=-17.4268...

wglb•about 22 hours ago

Paper in Arxiv https://arxiv.org/abs/2608.10719

yegle•about 9 hours ago

Wow, the Westlake University was funded in 2018 as a private research university.

kwoff•about 10 hours ago

Reminds me of https://science.nasa.gov/asset/hubble/runaway-black-hole-nea... A supermassive blackhole drawing in dust on such a scale that it's creating new stars in its wake as it zips by. (The picture is my desktop background. I think it nicely illustrates three fundamental shapes of the universe: 1) spheres (gravity dominates), 2) disks (angular momentum winning over gravity), 3) straight lines (no gravity))

caffeinejunk1e•about 18 hours ago

Project Hail Mary