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Asked by anon-214572 to Helen, Farah, Dave, Cheryl, Bastian, Alun on 11 Jun 2019.
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Dave Underhill answered on 11 Jun 2019:
toughie! neutrinos are one of the fundamental particles (which means they are not composed of any other particles) along with electrons and muons and quarks etc. the difference with neutrinos is that they are NEUTRal, they do not have any electric charge (unlike ELECTRons), thus they are not affected by electromagnetic forces but only by gravity and so are able to pass through matter without any interaction!! They are created in the core of stars (well any nuclear reaction really) but given that they do not interact with materials only gravity (which is its own can of worms), and their absolutely minuscule mass they are extremely difficult to study and many questions remain unanswered concerning them, such exactly what mass do they have!??
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Comments
Harrison commented on :
Let me add a bit to Dave’s nice answer. As he noted, neutrinos are created at the center of the sun (its core). But, because neutrinos can go through a huge amount of stuff without being stopped (that is, they interact extremely weakly with matter), neutrinos can travel from the sun’s core to Earth with ease. The neutrinos reach the sun’s photosphere (its “surface”) in a couple of seconds and, like light, require another 8 minutes and 20 seconds to reach your skin. So, right now, roughly 100 billion neutrinos per second cross every square centimeter of your skin and, amazingly, these neutrinos were created a mere 500 seconds ago in the sun’s core. This is one reason why a huge effort has been made over the past half-century to try to measure these neutrinos: they allow us to probe the sun’s core directly. On the other hand the light that we receive from the sun, which like neutrinos is created in the sun’s core via nuclear reactions, struggles to reach the sun’s photosphere. That’s because, ironically, the sun is opaque to light! In fact, even though light travels at the speed of light (186,000 miles per second, or 300,000 km/s, or 7 times around the world per second) it takes the light about a million years to travel from the sun’s core to its photosphere! So, the light that is lighting up today was created a million years ago! This means that we can’t use light to probe the sun’s core now. But, we can use neutrinos.
Dave commented on :
Again, Harrison to the rescue! great answer – I didn’t realise it took a million years for light to pass from the core to the photosphere!! fascinating stuff