11 June 2012

Brown dwarfs may support PDM

Some evidence from brown dwarfs may support PDM


I have been blogging about a theory I call Parallel Dark Matter (and here and here), which I may not be the first to propose, though I seem to be the first to flesh the idea out.

We see fewer brown dwarfs than we expected

In recent news, here and here, a visual survey of brown dwarfs (Wide-field Infrared Survey Explorer, or WISE) shows far fewer of them than astronomers expected.
Previous estimates had predicted as many brown dwarfs as typical stars, but the new initial tally from WISE shows just one brown dwarf for every six stars.
Note the ratio between observed occurence and predicted occurence: 1/6. That's not the last word, though. Davy Kirkpatrick of WISE says that:
the results are still preliminary: it is highly likely that WISE will discover additional Y dwarfs, but not in vast numbers, and probably not closer than the closest known star, Proxima Centauri. Those discoveries could bring the ratio of brown dwarfs to stars up a bit, to about 1:5 or 1:4, but not to the 1:1 level previously anticipated

But gravitational lensing appeared to show that they were common

But gravitational microlensing events suggested that brown dwarfs are common; if they weren't, it'd be unlikely that we'd see gravitational microlensing by them to that degree.
While I don't have the breadth of knowledge to properly survey the argument for brown dwarf commonness, it's my understanding that this was the main piece of evidence for it.

This is just what PDM would predict

PDM predicts that we would "see" gravity from all six branes, but only visually see the brown dwarfs from our own brane.
The ratio isn't exact but seems well within the error bars. They found 33, so leaving out other sources of uncertainty, you'd expect only a 68% chance that the "right" figure - ie, if it were exactly the same as the average over the universe - would be between 27 and 38.
Note that PDM predicts a 1/6 ratio between gravitational observations and visual observations. I emphasize that because in the quotes above, the ratios were between something different, visual observations of brown dwarfs vs visible stars.

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