Dark matter is thought to be the ghosts that helped build the structured universe, ghosts that the universe needed to make galaxies happen. I say “ghosts” because dark matter doesn’t interact with the universe in ways beyond gravity; the electromagnetic force doesn’t touch dark matter so we can’t see it or interact with it.We can try to detect it indirectly by looking for very specific byproducts of its rare interactions with real matter, and do so here on Earth now with detectors deep underground — so that normal matter via cosmic rays is blocked out by the planet’s crust — and we see it in the universe by the gravitational effects it has on different things. It’s not a thing that can be touched or captured. Nonetheless, it is most matter in the universe, 80-percent of all matter even. That is, in a universe of ghosts, the world of stuff is a small minority. Naturally, understanding these ghosts is one of the most pressing and mysterious fields of theoretical physics.The Milky Way, our home, should be full of dark matter. It could/should be passing through you right now unseen and unfelt. We should be surrounded by a “halo” of dark matter, according to current models of how galaxies form and move. But new measurements have bad news for our attempts to detect it, however, indicating that our patch of space is entirely without dark matter. That is, our neighborhood is all real stuff. In a volume more than four times as large as ever before, researchers at Chile’s Universidad de Concepcion calculated the mass of matter within our Sun’s neighborhood, finding it matches up too perfectly with its visible, real matter content.“The amount of mass that we derive matches very well with what we see — stars, dust and gas — in the region around the Sun," said Christian Moni Bidin, the lead author of a forthcoming paper in The Astrophysical Journal, in a press release. "But this leaves no room for the extra material — dark matter — that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!” Note that this is the best calculation of our neighborhood’s mass ever done.It’s not quite this easy, however. Dark matter, whether it figures into astrophysicist’s mass measurements or not, is needed to explain how all of that mass moves. It’s not enough to say that we maybe we just live in a dark matter-less bubble.“Despite the new results, the Milky Way certainly rotates much faster than the visible matter alone can account for,” said Moni Bidin. "So, if dark matter is not present where we expected it, a new solution for the missing mass problem must be found. Our results contradict the currently accepted models. The mystery of dark matter has just become even more mysterious. Future surveys, such as the ESA Gaia mission, will be crucial to move beyond this point."It could just mean that our local dark matter halo is just in a particularly funny shape that misses the Milky Way, but still surrounds it doing the stuff it should do. In a way that would be the least interesting explanation. I’m game for something spookier.Reach this writer at michaelb@motherboard.tv.
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