Posts by Ken Strain

Re: Cool.

The point about dark matter on the scale of the Universe as a whole is that, even if all the material that could ever be stars or ever has been stars is included along with the mass of the visible stars, the physics of how the elements formed just after the big bang tells us that most of the gravitational attraction is not due to normal matter (called "baryonic", as it is protons and neutrons mainly).

The accepted view of the origin of black holes like the "20,000" mentioned is that these are collapsed stars and hence were in fact accounted for in the baryonic matter budget. If instead they were made separately (in the big bang) without ever have being in the form of normal matter, then they could count for some of the cosmological dark matter, but that is viewed as rather unlikely.

So, while these black holes could (very slightly) affect the rotation curves of galaxies and be called dark matter in that sense, they are probably not part of the cosmological dark matter.

Ken

Re: Two solar masses (in energy) escaped

For large black holes "slowly" is no exaggeration - if my arithmetic is right, for the final black hole in this event, that's more than a hundred million, billion, billion, billion, billion, billion, billion times the current age of the Universe (roughly, or over 10^72 years).

Ken

Re: I have a question . . .

@John Mangan. I asked some astrophysicist colleagues about this. Essentially the collapse without forming a star can only happen if there is no pressure, which requires collapsing dust, rather than gas (so it won't happen as far as we know). If there is gas the collapse happens just as you say, heating up and forming a star on the way to a black hole, at least in every scenario we could think of.

ps. Rgds from JimH, HarryW, DaveR.

Re: How powerful is a gravitational wave close to the source?

Very rough order of magnitude calculation: to get "meters of magnitude" distortion on an Earth-size planet requres a strain (i.e. diameter change/diameter in this case) of more than about 1m/10^8m. So for the pulse of waves from the final merger to cause such an effect, the planet would need to be about 1/10000th of a lightyear away. The systems Advanced LIGO detected were around 1 billion LY away and produced a peak strain in the detectors of around 1 part in 10^21. The strain is inversely proportional to distance so we are looking for 10^13 times smaller distance. That is about 6 astronomical units, or a little more than the distance of Jupiter from the Sun.

It seems unlikely that there could be a planet in an orbit like that (it would have had to survive whatever formed the black holes, e.g. supernovae, then stayed in a stable orbit for probably billions of years for the eventual merger).

Ken

ps. If you are the same JM that was previously involved in all this - very best wishes!