A wandering black hole caught feeding on the run

(phys.org)

36 points by wglb9 hours ago

4 comments

dotancohen4 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.
- Towaway694 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.
 - ShinyLeftPad4 minutes ago
 It's crazy only if you use a specific geocentric version of "now".
 - dotancohen2 hours ago
 <pre><code> > What blows my mind is that 20 million light years also means that what we're observing something that happened 20 million years ago. </code></pre> 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.
 - anonzzzies53 minutes 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.
 - himata41133 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.
 - ilt2 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…
 - dotancohen1 hour ago
 Light is not a particle, nor is it a wave. However, under some circumstances it does behave like a particle - we even have a name for that (photon). However for purposes of this type of discussion - how it travels long distances - we need to look at the wave properties of light. The particle properties are more interaction-based.Light moves at the speed of causality - C - so it does not experience time. Therefore light never changes. However, for distant extra-galactic objects, the space that the light is traveling through is expanding! Thus the wave property of light is stretched out as well. So what was once visible light is now so stretched out (in our reference frame) that our eyes can't detect it (that's why the night sky is black).So yes, the light is finite. It itself experiences no change. The number of particles heading in our direction only changes when they encounter some types of mass, such as interstellar or intergalactic gad clouds.If you want to know why light is not a particle (and also not a wave) check out the dual-slit experiments. Fascinating stuff.
 ButlerianJihad1 hour ago
 > Light moves at the speed of casualty - CC is coulombsAnd casualty is a dead person
 dotancohen1 hour ago
 Typo corrected, thank you!
 - tappaseater2 hours ago
 The commenter is referring to the Cosmic Microwave Background (CMB). Whilst most of the universe is a dark void, if you tune a radio to a certain frequency, there's a faint, static buzz in the microwave part of the spectrum. It is heard no matter which direction you point the dish. This is a left-over from the Big Bang and started out as light but due to the expansion of space, the wavelength has increased, and that's why it's now received in the microwave part of the spectrum. There are lots of great explainers on the CMB and the history of its discovery is entertaining too. One of the easier concepts in cosmology, and one of the most important.
Towaway694 hours ago
LegacySurvey deep link[1].Zooming out from there and one gets an appreciation for how (in)significant we really are.[1] <a href="https://www.legacysurvey.org/viewer?ra=195.8160&dec=-17.4268&layer=ls-dr11&zoom=16" rel="nofollow">https://www.legacysurvey.org/viewer?ra=195.8160&dec=-17.4268...</a>
wglb9 hours ago
Paper in Arxiv <a href="https://arxiv.org/abs/2608.10719" rel="nofollow">https://arxiv.org/abs/2608.10719</a>
caffeinejunk1e5 hours ago
Project Hail Mary