4 ms·

to go from a supernova to a black hole, it takes a couple of days. For a galaxy to be rearranged by a black hole, it take a couple of millennia. (my informatio

to go from a supernova to a black hole, it takes a couple of days. For a galaxy to be rearranged by a black hole, it take a couple of millennia. (my information is not precise nor the latest, so it could have been revised recently.)

dylan604 2y ago
> (my information is not precise you're in good company. most cosmological "dates" are not precise. for example, the age of the universe is suspected to be about 13.7 billion years +/- 20 million years. That's a really big +/- in years, but just 0.2% tolerance. the size of milky way is estimated at 26.8 ± 1.1 kiloparsecs. again, that's a lot of miles/kilometers of a range. it's not like they can run out and "pull tape" to take that measurement. it's one of my favorite quirks of astronomy. of course even the tolerances/variances are going to be astronomically large.
- lukan 2y ago
  I apologize in advance, but I still point to the relevant comic: https://xkcd.com/2205/ https://xkcd.com/2205/
- mr_mitm 2y ago
  I don't get it. Isn't precision always relative? Who cares how large the numbers sound in certain units?
  - oh2aa 2y ago
    No, precision or error can measured in absolute or relative terms. In either case, the unit is irrelevant, you could say +/- "0.000001 big bang timespan." The point is that in the realm of human experience, that tracking error is quite big.
AnimalMuppet 2y ago
Could you define what you mean by a galaxy being "rearranged" by a black hole?
- nashashmi 2y ago
  The theory behind spiral galaxies is that a black hole of considerable magnitude and time lies right in the center. Gravitational waves spirals out for millennia. They start moving towards the center but also move towards each other. Closest stars move towards the center and other stars begin following the close stars and so on. This should ordinarily end up like an octopus with multiple arms extending from the center outwards. But then the Universe must also be rotating like a disc. And so the galaxy spirals out with curved arms instead.
  - AnimalMuppet 2y ago
    So, yes, we think there is a massive black hole at the center of all (or just spiral?) galaxies. And gravitational waves move at the speed of light, so if something changes the mass of the central black hole, and the galaxy has a radius of 25,000 light years, it will take 25,000 years for that wave to propagate out to the rim of the galaxy, rearranging things along the way. But: 1. The massive, central black hole did not come from a supernova. There are no stars anything like that big. 2. Even if there were a huge central mass and it collapsed, that doesn't actually change the mass distribution as far as the rest of the galaxy is concerned. There is very little change to propagate. The existence of the huge central mass would have already "arranged" the galaxy. 3. Galaxies spiral with curved arms due to their own rotation, not due to the universe's rotation. If the universe were rotating like a disk (and that was causing the spiral of galaxies), then you would expect the spin of galaxies to all be aligned. And they aren't; not at all.

dylan604 2y ago

> (my information is not precise you're in good company. most cosmological "dates" are not precise. for example, the age of the universe is suspected to be about 13.7 billion years +/- 20 million years. That's a really big +/- in years, but just 0.2% tolerance. the size of milky way is estimated at 26.8 ± 1.1 kiloparsecs. again, that's a lot of miles/kilometers of a range. it's not like they can run out and "pull tape" to take that measurement. it's one of my favorite quirks of astronomy. of course even the tolerances/variances are going to be astronomically large.

lukan 2y ago
I apologize in advance, but I still point to the relevant comic: https://xkcd.com/2205/ https://xkcd.com/2205/
mr_mitm 2y ago
I don't get it. Isn't precision always relative? Who cares how large the numbers sound in certain units?
- oh2aa 2y ago
  No, precision or error can measured in absolute or relative terms. In either case, the unit is irrelevant, you could say +/- "0.000001 big bang timespan." The point is that in the realm of human experience, that tracking error is quite big.

AnimalMuppet 2y ago

Could you define what you mean by a galaxy being "rearranged" by a black hole?

nashashmi 2y ago
The theory behind spiral galaxies is that a black hole of considerable magnitude and time lies right in the center. Gravitational waves spirals out for millennia. They start moving towards the center but also move towards each other. Closest stars move towards the center and other stars begin following the close stars and so on. This should ordinarily end up like an octopus with multiple arms extending from the center outwards. But then the Universe must also be rotating like a disc. And so the galaxy spirals out with curved arms instead.
- AnimalMuppet 2y ago
  So, yes, we think there is a massive black hole at the center of all (or just spiral?) galaxies. And gravitational waves move at the speed of light, so if something changes the mass of the central black hole, and the galaxy has a radius of 25,000 light years, it will take 25,000 years for that wave to propagate out to the rim of the galaxy, rearranging things along the way. But: 1. The massive, central black hole did not come from a supernova. There are no stars anything like that big. 2. Even if there were a huge central mass and it collapsed, that doesn't actually change the mass distribution as far as the rest of the galaxy is concerned. There is very little change to propagate. The existence of the huge central mass would have already "arranged" the galaxy. 3. Galaxies spiral with curved arms due to their own rotation, not due to the universe's rotation. If the universe were rotating like a disk (and that was causing the spiral of galaxies), then you would expect the spin of galaxies to all be aligned. And they aren't; not at all.