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Planets Without Stars or Mini-Solar Systems?
iamlucky13 writes "An article today on space.com discusses the discovery of 6 objects by the European Southern Observatory in Chile that are smaller than typical brown dwarfs, larger than Jupiter, and not orbiting any stars. The objects are surrounded by disks of gas and dust possibly similar to the early solar system. In addition to presenting astronomers with a new group of objects to study, the finding also deepens the debate over what makes a planet. The scientists responsible for the discovery sidestep the question by calling them 'Planetary Mass Objects,' or planemos."
This is an excellent question. The idea of objects like these comprising dark matter has been tested with the MACHO project ( http://wwwmacho.mcmaster.ca/ ) which attempts to detect objects like this through gravitational lensing events. Unfortunately, the data from this experiment seem to suggest that they don't comprise enough mass to explain Milky Way observations.
That's correct, though the MACHO experiment places its best limits on much more massive objects than Jupiters; for now it is conceivable that such objects could be a significant part of the dark matter. OTOH, there is no way (without huge modifications to what we know about the early universe) to make the majority of the dark matter anything (dust, rocks, planetesimals, planets, brown dwarfs, white dwarfs, neutron stars) that are made from atoms; we now know that the atomic component of the Universe must be only a few percent of the total. So though these could be part of the dark matter, they can't be all of it.
David W. Hogg -- assoc prof, NYU Physics
If these things made up the "dark matter" then it wouldn't be dark -- these objects (it might not be clear from the article) were found because they emit strongly in the infrared. In short, they can't make up the majority of the dark matter, either observationally or theoretically. Good idea, though.
David W. Hogg -- assoc prof, NYU Physics