China's PandaX Project Looks For Dark Matter In the Heart of a Marble Mountain 62
the_newsbeagle writes "Chinese engineers love their superlatives: Biggest dam, fastest train, etc etc. Now they've constructed the deepest underground dark matter detector beneath a mountain in Sichuan province. Such dark matter seekers have to be buried deep to shield them from cosmic rays, because that radiation would be picked up by the detector and could be confused for radiation generated by dark matter. Other dark matter detectors are similarly subterranean: LUX, in the United States, is at the bottom of an abandoned mine in South Dakota, and a European effort called XENON lies below the Gran Sasso mountain. The Chinese researchers hope their PandaX detector will finally reveal the much-hypothesized, never-seen dark matter particles known as WIMPs."
XENON is US-led (Score:5, Informative)
Re:Dark Matter is only a filler (Score:5, Informative)
We're talking about that one decimal place before the decimal point: current observations indicate more than five times as much dark matter as known matter. It's not just a little bit of round-off error in how much dust there is between stars, but apparently most of the stuff in the universe (at least, before you get to "dark energy," which is "twice as big" again, but far more poorly understood).
Re:Dark Matter is only a filler (Score:4, Informative)
Sounds like what you're talking about are compact halo objects [wikipedia.org], e.g. brown dwarfs, black holes, etc. The broad consensus is that there is nowhere near enough of this material to explain the high velocity of stars in the outer parts of the galactic disk/s. Also we have observations such as the bullet cluster [wikipedia.org] which are very difficult to explain without proposing invisible gravitating material.
Having said that, you might be right, maybe we'll find out.
WIMPs (Score:5, Informative)
Re:Dark Matter is only a filler (Score:4, Informative)
We can make estimates of the amount of dust out there based on the light we see from distant stars. Where there is dust, it will scatter light passing through it (and modify the spectrum). There are lots of open questions about how much and what kind of dust is out there --- this isn't a "solved" problem --- however, best estimates plus known uncertainties don't put this within range of explaining dark matter. So, we still need dark matter to "make the math work out."
Re:A Marble mountain? A mountain made of marble? (Score:4, Informative)
Just about every kind of rock has background radiation of its own, which must be dealt with (some more than others). However, radiation from rocks is typically easier to deal with than cosmic rays from space --- it's lower energy stuff that can be blocked by a few extra layers of extra lead/copper shielding (carefully screened for even lower radioactivity), instead of energetic particles that go through hundreds of meters of material unhindered. You have to worry about things like radon (radioactive gas) seeping out of the rocks and getting into the equipment; but, these are known effects to watch out for deal with by proper ventilation/sealing.