Astronomers discovered a free planet, some 100 light years away. It's a sizeable beast, several times the size of Jupiter and way out in free space, no star anywhere close. Free planets are very hard to see since they lack a sun to light them up. This one was detected by its infra red emissions.
Are free planets the "Massive Halo Objects" (Macho's) of the missing mass discussion? We are pretty such that the universe needs more mass, a lot more mass, than we can see glowing in the night sky. This bit of knowledge comes from watching galaxies rotate. Speed of rotation depends upon mass of the galaxy. Heavier galaxies have to rotation faster to create enough centrifugal force to prevent the stars from getting sucked down into the galaxy center. This bit of physics comes to us from Isaac Newton and is taught in freshman college physics. That is where I learned it.
The mass of the galaxies was estimated by counting all the stars in the galaxy and assuming that the stars were of average mass. Doing this came up short of mass, a lot short, say one or two times the observed (luminous) mass. Two solutions were suggested. There might be a new sub atomic particle with mass like a proton but as hard to detect as a neutrino. This was dubbing Weakly Interacting Massive Particle (wimp for short). This came up shortly after the Higgs boson was discovered, leaving a lot of particle accelerators and accelerator physicists looking for something to do. The other idea was a "Massive Halo Object" (Macho for short).
This newly discovered free planet is a Massive Halo Object. There might be more, they are hard to detect so there might be a lot more. Question: How many free planets would there have to be to furnish the missing mass? Is it a reasonable number? Or is the required number so high that we would have noticed free planets zipping by the earth already?
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