I am genuinely curious about this. I *kind of* understand that gravity, like light, moves at the speed of light (right?). So then would our solar system, and millions of other star systems, just continue orbiting what USED to be the super massive black hole in the center of our galaxy, if said black hole just suddenly (hypothetically) collapsed/vanished? How does that not violate the laws of physics?
Furthermore – let’s say a star… a hundred light years away went supernova. We’re still receiving it’s light for a hundred years right? It would just look totally normal to us in the sky, for the next hundred years. Well let’s say that supernova was so awesomely powerful as to truly push our planet out of orbit from our sun. What happens first? Does that star’s supernova explosion light up in the sky, or does that impact from this supernova hit us and cause catastrophic damage? What’s faster – the impact or the supernova?
I really want to understand distance/time better as it relates to astrophysics, I just can’t comprehend the insane distance and the deltas between distance + time = what we experience on earth. It’s truly humbling.
In: Physics
First, to clear up a couple of misconceptions, our sun and everything else in the solar system does NOT orbit a supermassive black hole at the center of the galaxy. Everything in the galaxy orbits the center of mass of the galaxy. A supermassive blackhole is completely insignificant in terms of the total mass of the galaxy. Just for comparison, the supermassive black hole at the center of our galaxy is estimated to be roughly 4.3 million solar masses, whereas the total mass of the Milky Way is estimated to be no less than 1.5 *trillion* solar masses, of which 90% is dark matter. That means that black hole is about 0.00028% of the mass of our galaxy. Second, the galactic center is not an object, but an area of space, and there’s no method by which it can just “collapsed on itself”.
That being said, you’ve answered your own question simply by knowing that changes in gravity propagate at the speed of light. Earth is roughly 8 light minutes from the sun. If the sun were to magically disappear, we would not notice for 8 minutes. We would receive sunlight for 8 more minutes, and the Earth would continue to orbit the spot where the sun was for 8 minutes. That doesn’t violate the laws of physics because it literally *is* a law of physics.
The same applies to your supernova scenario. The star goes supernova, but we don’t see it for 100 years. The rest of your scenario is impossible though. There’s no such event that can cause gravitational disturbances strong enough to toss planets from orbit 100 light years away, and supernovae don’t create debris that can fly through space and smash into other planets. There’s nothing to impact or cause damage. What you get is radiation, gas, dust, and charged particles. The radiation travels at the speed of light, but everything else goes slower. The charged particles can travel very close to the speed of light, but the gas and dust might only be expanding outward at a few km/s. That’s roughly the same speed as spacecraft in Earth orbit. It would take millions of years for that dust to reach earth.
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