Fantasist & Futurist
- Nov 23, 2002
"If you imagine a snail on the recently-discovered Earth-like planet orbiting Proxima Centauri - 4.243 light years away - moving at 1 cm a second, that's the angular motion we're resolving here,"
I'm glad they are far away. I wouln't like to fall in and wake up 1 000 years later in the future.
I've often wondered about that...If a black hole were to suddenly appear near out system, we wouldn't detect it.
I've often wondered about that...
If a black hole were relatively close to us but in an area of space where there are few background stars so that it's presence isn't revealed by its lensing effect (say well out of our galactic elliptical plane) and far enough away for its gravitational effect to be negligible then would it effectively be undetectable?
Thanks @Venusian Broon; I was figuring on three or four light years away but yes I figured we'd still see the gravitational lensing on galaxies. But what I was thinking about was if we didn't know it was there and it was against a relatively "boring" background, would we even notice it? Also if it isn't actually "eating" anything, ie any "stuff" around it is in stable orbits. Given that, just how noticeable would it be? Always thought it would make a nice catastrophe story; suppose it's travelling towards the solar system at high speed and will pass within say one light year - close enough to disturb planetary and asteroid/Kuiper belt orbits - but we don't notice it until it's say two hundred years from having an effect. Giving us that long to prepare for maybe a new period of meteor bombardment...How far away would a black hole need to be so that it's gravitational effect was 'negligible'? A naturally made Black hole would - unless there are such things like micro-blackholes - be at minimum about 3-4 times the mass of the Sun. I'd guess it could be pretty far out and still distort quite a lot of the planets orbits significantly - at least should be noticeable.
Not sure about what sort of distance is required for gravitational lensing, but I do believe the Sun should exhibit gravitational lensing (best placed at about 542 AU out apparently). That's pretty close in cosmic terms, so a black hole out at say 2 light years from Earth looks like it could be observed in this manner. I also think you won't be looking at nearby stars to lens but at very distant galaxies - of which they are everywhere.
I'd guess the best way to detect such an object, would be as an anomalous X-ray source, because any material falling into it would be ripped apart relativistically and generate these high energy photons.
"At roughly 750 million light years from Earth..." That's close in terms of the observable Universe. (13.8 Billion light years across). Not close enough to cause any concern of course. Also: "... says these supermassive black holes have a combined mass of 15 billion times that of our sun, or 15 billion solar masses."
Well, the folks in that galaxy were in for the ride of their lives, but since in spacetime that's also a "look-back time" of 750 million years, they've most likely already rode that one. It makes me wonder what that sort of thing would do to a galaxy like ours, and how long it would take to play out.
Astronomers have estimated the one at our galactic center to be 4.1 million solar masses. That's itty-bitty compared to the binary pair in the article.
We seem to be dancing on the edge of a gravitational maelstrom abyss.
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