- #71
PeterDonis
Mentor
- 47,499
- 23,771
ClamShell said:So the Earth would grow as it collects dust. And the Sun would shrink as it collects dust. And a BH would grow as it collects dust.
Assuming that "grow" means "increase in radius", then yes. (I use radius instead of volume because a BH doesn't have a well-defined "volume". But you can define its horizon radius--more precisely, you can define the surface area of the horizon, and then define the radius ##R## of the horizon such that the horizon's surface area is ##4 \pi R^2##.) In terms of mass, all three will of course "grow" (increase in mass) as they collect dust. (And of course this is all assuming that no other processes are involved, which at least for the Sun is not a good assumption, as I discussed in a previous post. [Edit--also see my next post, the Sun isn't even close to being "cold, dead matter" so the analysis I was talking about doesn't apply to the Sun anyway.)
kochanskij said:And the radius of the 4 million solar mass SMBH at the center of the Milky Way galaxy would be about 11 million kilometers?
Yes.