Comment by jolt42
3 hours ago
> neutrinos coming from outside the solar system How do we know this and why do we care where they came from?
3 hours ago
> neutrinos coming from outside the solar system How do we know this and why do we care where they came from?
Since neutrinos don’t interact with much of anything, its path doesn’t deviate from its origin. Different origins emit neutrinos with different levels of energy. When a neutrino hits a nucleus, the blue light emitting particle in ice follows closely the same direction. Measuring the direction and the magnitude (lighting energy) of the vector we can classify its origin. Collecting a bunch of the same signature we know there's an object at that direction emitting at that energy level. From the vector and energy we kind of know whether it’s from the solar system or not.
Identifying the origin let us see objects behind dust clouds or other obstacles.
> When a neutrino hits a nucleus, the blue light emitting particle in ice follows the same direction.
How does this not violate conservation of momentum? Are you saying every single collision is head-on?
Most paths of the high energy observable collisions follow a very close alignment to the original neutrino's path. The forward momentum of a high energy neutrino completely dominates the collision. Imagine an one-ton ball hitting a billiard ball. Doesn't matter what direction the billiard ball was going; the resulting path is the one-ton ball's path.
In other cases, the particle being collided is scattered and won't show up in the detector. Low energy neutrino collisions also have very faint light and difficult to detect. Solar system produced neutrinos are in this category.
We know this because
- In the beginning, for the first couple of events, only because they have way higher energies than anything in the solar system could produce - By now, with enough data collected, their origin correlates very well with the milky way - we are close to identifying several far away galaxies as well
This is the significance. Contrary to some statements published today, IceCube was not primarily built to study Neutrinos, it was built to study the universe using Neutrinos.
That's why we care where they are coming from, we want to learn about the astrophysical objects that produce them.