Re-Examined IceCube Data Firms Up Case For Extra-Galactic Neutrinos

In 2013, the IceCube neutrino telescope detected dozens of high-energy neutrinos. Now, reports Astronomy magazine, researchers "have sorted through the billions of subatomic particles that zip through its frozen cubic-kilometer-sized detector each year to gather powerful new evidence in support of [those] 2013 observations confirming the existence of cosmic neutrinos." According to the report, Albrecht Karle from UW-Madison notes that while the neutrino-induced tracks recorded by the IceCube detector have a good pointing resolution, within less than a degree, the IceCube team has not observed a significant number of neutrinos emanating from any single source. ... “The plane of the galaxy is where the stars are. It is where cosmic rays are accelerated, so you would expect to see more sources there. But the highest-energy neutrinos we’ve observed come from random directions,” said Karle. “It is sound confirmation that the discovery of cosmic neutrinos from beyond our galaxy is real.”

IceCube

[flopsquad]

“It is sound confirmation that the discovery of cosmic neutrinos from beyond our galaxy is real," said the IceCube team leader, adding, "Plus nobody I know got killed in South Central LA... today was a good day."

O'Shea Jackson

[turkeydance]

did a good job.

Confirming the obvious

[techno-vampire]

Yes, I understand that you need to back everything up with hard evidence, but did anybody seriously doubt that some of the neutrinos we were observing came from outside out galaxy?

Re:

[JoshuaZ]

Well, it wasn't obvious that they weren't coming from a combination of the sun and the galactic center. The sun might be producing a few much higher energy neutrinos than we expect which would indicate a deep misunderstanding in our models of the core but it was definitely a possibility. The galactic center is very poorly understood, and there's a lot of dust in the way, so some neutrino production method there would have been very plausible.

Re:

[techno-vampire]

If some of them are produced by our sun, they should be produced by all mainstream stars in and outside of our galaxy. And, if the core of our galaxy is emitting them, so should the cores of other galaxies. To me, at least, that implies that at least a few of those we detect should be of extra-galactic origin, but it's still nice to have it confirmed. (Actually, it would be much more interesting if we weren't detecting extra-galactic neutrinos because then astrophysicists would have to work out why.)

Re:

[JoshuaZ]

Well yes, but keep in mind that we detect a much larger fraction of the neutrinos from the sun. So if the sun was producing a lot more high energy neutrinos than we expect, some of it could show up here. (Although really that would be ruled out by other considerations- IceCube has directional data for where it detects the neutrinos and that would show up very soon, and in fact, for various reasons related to the shape of the detector, it can only detect a small set of solar neutrinos anyways.)

Re:

[techno-vampire]

Again, if you stop and think about it, you'll realize that we should expect most of the neutrinos detected to come from the Sun, because it's the nearest significant source. As I wrote above, all this experiment really does is confirm that what we expected is what's really happening, but that's not a bad thing.

Re:

[JoshuaZ]

High energy neutrinos like the ones under discussion should be being produced by the sun unless we are very wrong about how the stellar core acts. In that regard, ruling that out is important, just as ruling out these as being produced by high energy events in our galaxy.

Re:

[techno-vampire]

Of course, but unless our theories are very, very wrong, we should also be seeing at least a few, coming in from directions that make it unlikely that they came from anywhere in our galaxy, and it's nice to have that confirmed. However, I doubt that anybody really expected any other results and that's what my original post was talking about.

Re:

[wnfJv8eC]

You don't get it. with stars emitting, likely in all directions, we should still have higher concentration from the plane of the galaxy. Evenly spread over the means emissions are coming at us from all over the universe. One could almost see this as the universe as being 'closed'. Nothing from the big bang, even neutrino are getting out.

Re:

[techno-vampire]

No, you're the one who doesn't get it. Having them concentrated in the plane of the Milky Way would mean that almost all of them were coming from this galaxy and that few, if any, were being emitted by the rest of the universe, and that would be rather hard to explain. What we're actually seeing is exactly what we'd see if the simplest explanation (all stars and galaxies emit neutrinos at about the same rate, relative to their size) were correct.

The current status

[JoshuaZ]

As of right now, the only confirmed neutrino sources we have that aren't artificial are the sun and SN 1987A https://en.wikipedia.org/wiki/SN_1987A [wikipedia.org]. SN 1987A was a supernova in 1987 (the first one discovered that year, hence the A). The supernova was in the Large Magellanic Cloud, a very nearby galaxy (which is close enough and small enough that there's been some question whether we should really call it a separate galaxy). The supernova was one of the every few that was close enough that it was visible to earth by the naked eye. While every supernova is believed to create many neutrinos (and in fact this flood is an important part of the process) most supernovas are too far away for us to detect the neutrinos from the supernova because neutrinos are so hard to detect.

As of right now, we don't have any way of making any neutrino detector that is more sophisticated than putting a big bunch of mass in the way and hoping to notice when neutrinos happen to hit it by sheer chance (which is extremely rarely). IceCube is one of a next-generation detector where we have used pre-existing mass, in this case, ice as the South Pole for the bulk of the detector. It turns out that the ice very deep down under high pressure (from the ice above it) is nearly perfectly transparent at the light frequencies need, while the bulk of ice on top blocks out stray light and a lot of stray particles that would swamp the signal.

Detectors like IceCube can be used to actually detect the neutrinos from a supernova before the supernova's light reaches Earth. This isn't due to the erroneous claim from a few years ago that neutrinos travel faster than light, but rather because when a supernova occurs, the light from the core of the star takes multiple hours to get out of the core because of all the mass in the way, while the neutrinos aren't slowed down by this almost at all. This means that the neutrinos effectively get a few hours head start on the light- since they are traveling so close to the speed of light, they get to keep almost all this head start by the time they reach Earth. In the case of SN 1987A the neutrinos did as predicted arrive a few hours before the light. This means we can if we detect a neutrino burst and can get its directional data (which IceCube can approximately do) then we can point our telescopes at a supernova *before the light arrives at Earth* which means we'll get to see the very beginning of the supernova and hopefully get a much better understanding.

Right now, to assist in this there is a Supernova Early Warning System http://snews.bnl.gov/ [bnl.gov] which is tied in to the various big detectors so it can let astronomers know that a neutrino surge has been detected- this could of course be a supernova, but there's also the even more exciting possibility of an as yet unrecognized event that produces a lot of neutrinos. It will be very important in either case that a lot astronomers get a good early look at it, both professional and amateur, so the system is designed so that anyone can sign up for alerts from it. So if you are an amateur astronomer you should probably sign up- they send out about once test alert a year.

Don't Forget Atmospheric Neutrinos!

[Roger W Moore]

As of right now, the only confirmed neutrino sources we have that aren't artificial are the sun and SN 1987A

Don't forget atmospheric neutrinos. These are created in the showers produced when cosmic rays strike the upper atmosphere. Since they pass through the planet you detect them from all over the globe. The Earth itself is also a natural source of neutrinos from radioactive decay and there are some experiments, such as SNO+, that are looking for these 'geo-neutrinos'.

Re:

[JoshuaZ]

Good points. I was aware of them,but forgot about them when writing my comment.

Re:

[mister_playboy]

http://science.slashdot.org/st... [slashdot.org]

Today

[Anonymous Coward]

Was a good day.