May 10, 2020 – KM3Net…No, Not a new Radio Station

In a continuing effort to figure out this universe scientists have gone beyond the electromagnetic spectrum to gather information.  The electromagnetic spectrum, with all its information, only presents us with 5% of the universe. Albert Einstein predicted things like gravitational.  It took over a hundred years before technology would catch up and allow scientists to detect them.  We don’t quite know how to use gravitational waves yet, but we will.

Neutrinos are a different story.  Postulated by Wolfgang Pauli in 1930 and first detected experimentally by Cowan, Reines, Harrison, and McGuire in 1956, the neutrino has lately become essential in understanding how our universe works.

Neutrinos are elementary particles, like the electron, but they have way less mass, no charge, come in three flavors, and vary their mass among three possibilities as they travel.  They generally do not interact with other matter. Because neutrinos interact with other matter rarely, they are exceedingly difficult to detect.  Neutrino detectors are huge (cubic kilometers), use exotic detection schemes, and are in exotic locations such as under the Antarctic Ice.  They are expensive.  So, what’s the big deal about neutrinos?

Neutrinos are byproducts of radioactive activity and not affected by magnetic fields or other forms of matter, so they represent a way to “see” exactly where an event, such as neutron stars merging, took place.  The light or cosmic rays from the event gets deflected by magnetic fields during their voyage so they don’t identify the exact location.  Other events include stellar collisions, novae and supernovae, and when cosmic rays interact with Earth’s atmosphere.

Enter KM3Net (Cubic Kilometer Neutrino Telescope).  It is the latest iteration of neutrino detectors.  Currently there are two sites in development, both at the bottom of the Mediterranean Sea. One is near France, named ORCA, and one near Italy, named ARCA.

The deep Mediterranean waters protect these scopes from spurious signals such as normal cosmic rays.  However, as neutrinos interact with water molecules, they produce Cherenkov radiation.  This will be useful for determining the neutrino’s energy and direction.  Each site will be set up in a cubic kilometer formation looking somewhat like an underwater mine field.  The detectors are glass spheres a little smaller than a basketball, with 31 sensors inside.  The plan is to deploy more than 6000 detectors split between the two sites.  ORCA will look at neutrinos generated by cosmic ray interaction with Earth’s atmosphere.  ARCA will look at those produced by cataclysmic events far away, possibly including colliding dark matter.

Both scopes look downward, detecting neutrinos passing through Earth (most zip right through).  ORCA, with its expected denser population of neutrinos might also produce an x-ray like picture of Earth’s insides.  That’s cool!

What’s in the Sky?

May 11-15; before sunrise; south-southeast:  Watch the waning gibbous Moon move eastward daily past Jupiter, Saturn, then Mars.  On May12 the Moon makes a nice triad with Jupiter and Saturn.