goredsox wrote:CDM Density and CDM Homogeneity
It seems to me that if we accept the prevailing CDM model, that a lot can be inferred about it's local distribution by the behavior of our solar system, milky way, and local group. In other words, firm upper and lower limits on density can be inferred. I am curious as to how far this analysis has gone.
There are, very likely, thousands of papers on this topic, and dozens of books.
The distribution and density of CDM is now well constrained, in many galaxies, both ordinary and dwarf, including our own.
It's also well constrained in many galaxy groups and clusters.
For the solar system, the best constraints are upper bounds, such as reported in papers like the Iorio paper I referenced earlier and the pulsar observations which constrain the solar system barycentre acceleration.
It also appears that certain assumptions can be made about the lack of local clumpiness, (or in other words, the upper and lower bounds of expected homogeneity) since we do not believe that catastrophic changes in planetary orbits have occured for hundreds of millions of years. Or do we? I am still not sure how we know that. Any insight on how we know that the planets were orbiting 500 million years ago as they are today would be interesting to debate, as well as calculations of upper and lower bounds on homogeneity.
I'm less familiar with the literature on this, but the stability of the solar system (orbits, etc) has been studied for several centuries now; simulations of its history have been done for decades.
One fairly strong indication that nothing major has happened in the solar system - whether due to a passing star, a giant molecular cloud, a rogue 'Jupiter', or a CDM clump - is the lack of significant bombardment once the Late Heavy Bombardment era ended (approx 3.8 billion years ago), at least in the inner solar system (there are, as yet, few constraints on the absolute dates of cratering history in the outer solar system).
You did respond already to this latter concern by stating that footprints would be seen in orbits today. However, I am not sure how we would recognize a footprint of a brief, but severe, gravitational disruption, to be distinguished from, say, an eccentric orbit, which we do observe all the time; or, from say, a missing planet, that we never knew existed.
Largely through cratering history - at least the main belt asteroids are old and numerous; any severe disruption would have caused a spike in bombardment.
The same for the Kuiper belt, though the absolute age of those objects is not as well constrained as that of the main belt ones.
Ditto for the Oort cloud objects, and ditto re considerably lower certainty.
Nereid, I do appreciate your diligence in responding to the thread topic. I am also interested in hearing from any lurkers out there who want to seriously probe the implications of the CDM model.
As I said earlier, I think you'll get more discussion, from both keen amateurs and professionals, in other fora than this one.
Now, if you ask about galaxies ...