With all the recent discoveries of supermassive black holes being at the center of nearly every galaxy, and the proposed "at least one planet" around (probably) every star.

Does this affect the estimated total mass of our universe?

Is Dark Matter necessary when planets and black holes are included in the calculation?

  • $\begingroup$ One should not be so severe on a new user. The question as edited is fine. $\endgroup$ – anna v Jan 17 '12 at 13:47

There is no need to recalculate, because the mass of the big black hole is already included when you measure the mass of a galaxy. A black hole is the same gravitational field as stars of the same mass, but its gravity is concentrated in a very small region by comparison.

The mass distributions in galaxies are partly found using rotation curves, which tell you how fast objects are spinning around the center. These curves tell you how the mass is distributed, and whether the center is a bunch of stars very close together, or a big black hole of the same total mass, the answer is pretty much the same. But because many galaxies looked like they had a very massive center which was not plausibly star material, it has long been suspected that most galaxies harbor supermassive black holes.

The discovery that the Milky Way's black hole is very important astronomically, because we can't directly see it, and it is in a very difficult to observe the direction toward the center of the galaxy, because it is obscured by galactic dust. But it is a confirmation of results long expected. It would have been more surprising for astronomers to not find a black hole at the center of the galaxy.

The difference is the black hole has no luminosity, but the dark matter is apparent in the rotation curves, it comes from a diffuse cloud of stuff around the galaxy. Further, the same diffuse cloud of dark stuff clustering under gravity is necessary to explain how galaxy clusters could be stable, and the formation of gigantic filaments like the great wall of galaxies.


As a star’s fusion fuel runs out the force of gravity takes over causing the star to collapse on itself. The star is rotating prior to the collapse and as it collapses this rotation at the core increases expediently. As the speed of the matter increases and gets closer to the speed of light, it's mass increases as well further fueling the collapse and in turn increasing its spin speed at the center. This is why time slows down as you get closer and closer to the center. The event horizon is the boundary where matter is converted to light by relative speed. So in a nut shell a black hole is matter converted to light that is self-contained by the original mass increased by velocity.

Glenn Minor


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