Neutrino fun facts!

“We should do astronomy because it is beautiful and because it is fun. We should do it because people want to know. We want to know our place in the universe and how things happen.” –John Bahcall

Of course you’re all going to watch the exciting Live interview with me on KGW tonight (streaming here; video should be posted after-the-fact here), but shouldn’t we give you some extra fun facts about neutrinos?

Here we go…

Both photons and neutrinos are created in the core of stars. But while photons take tens of thousands of years to reach the edge of the Sun, neutrinos make the trip in just over two seconds.

Image credit: X-ray: NASA/CXC/PSU/S.Park & D.Burrows.; Optical: NASA/STScI/CfA/P.Challis.

In 1987, the closest supernova in over 100 years went off in the Large Magellanic Cloud, 168,000 light years away. We detected 23 neutrinos from it; thus far, these are the only neutrinos ever detected from a supernova.

Illustration: NASA/CXC/M.Weiss; X-ray: NASA/CXC/UC Berkeley/N.Smith et al.; IR: Lick/UC Berkeley/J.Bloom & C.Hansen.

A typical supernova emits somewhere around 1057 neutrinos at once, about 1018 times the rate that our Sun emits them.

Image credit: NASA, ESA, R. Sankret and W. Blair.

The last supernova observed within our own galaxy went off in 1604, at a distance of about 20,000 light years away. One of the best candidates for the next supernova in our galaxy to go off is Betelgeuse, which is only 640 light years from us.

Image credit: A. Dupree, NASA.

Betelgeuse could go off any time in the next million years. The largest neutrino detector in operation today is Super Kamiokande-III in Japan, which houses 50,000 tonnes of water to interact with neutrinos.

Image credit: Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo.

If Betelgeuse went supernova today, Super Kamiokande-III would detect an estimated 13 million neutrinos.

A good neutrino detector, like OPERA (above, credit INFN), consists of more than 1,000 tonnes of mass for neutrinos to interact with.

Image credit: OPERA collaboration.

OPERA detected 16,000 neutrinos that were launched at it over the last three years. Out of more than 100,000,000,000,000,000,000.

If OPERA were extended to be a light-year in length and were made out of solid lead, it would still interact with fewer than half of the neutrinos that passed through it.

The three types of neutrinos in the standard model are the lightest particles with a non-zero mass ever discovered. The upper limit on the mass of the heaviest neutrino is still more than 4 million times lighter than the electron, the next lightest particle.

Image credit: Lawrence Berkeley National Lab.

Oxygen molecules at room temperature move at a mean speed of about 440 meters per second. Because they are so light, neutrinos at room temperature would move at speeds more than 80% the speed of light.

Image credit: WMAP and SDSS.

The coldest depths of intergalactic space are at temperatures of just 2.73 Kelvin, heated primarily by the leftover radiation from the Big Bang.

A neutrino at this temperature would still be moving at 7% the speed of light.

Image credit: Aaron Leanhardt (right) and Tom Pasquini (left) of MIT.

The coldest temperature ever achieved in a laboratory is about half of one nanoKelvin above absolute zero. Neutrinos at that speed would still move at nearly 300 m/s, or more than 20 times as fast as Usain Bolt at top speed.

Pretty interesting stuff about neutrinos, isn’t it? Well, what are you waiting for, come watch me live! (Or if it’s too late, taped.)

34 thoughts on “Neutrino fun facts!

  1. Speaking of confirming OPERA’s findings, I find this September 21, 2004 paper entitled;

    “Proposal to Measure the Speed of Mu-type Neutrinos to Two Parts in 10^6”

    Lay person question is two parts in ten to the sixth close to six sigma?
    Anyhoo. Cost estimate under $320k capital and $30k per year operating costs.
    Sounds like a deal.

  2. what is the difference between neutrinos and antineutrinos? i read that they have oppoiste spin, but i thought identical particles could have opposite spin too.
    i just don’t know what makes a particle “matter” or “antimatter”

  3. If you missed the broadcast, you can always watch it here:

    Don @1, with the TeVatron shutting down today, the big experiment that Fermilab will now take part in is sending neutrinos to a mine shaft in Minnesota, where they’re expected to measure the neutrino travel time to a 2 nanosecond accuracy!

    Steve @2, if that’s truly how big Icecube is, that would be larger than the latest Super Kamiokande!

    David @3, neutrinos are different than say, electrons and positrons. While electrons and positrons can each be spin +1/2 or -1/2, neutrinos can only have “left-handed helicity” (which makes more sense to talk about than spin, since they’re so ultra-relativistic), while antineutrinos can only have “right-handed helicity”.

    Anon @4, but of course! Shouldn’t every theoretical astrophysicist have a huge, stylin’ beard and moustache, a shaved head, and a kilt?

  4. You seemed incredibly nervous as they prepped you for the broadcast, but once u got on you were like Sly Stallone in Over The Top after he spins the hat around.

    Perhaps you could try to get the network to give you a once a week science update on stuff like the jwst, double slit experiment, dark matter/energy, gravity, black holes, ect…

  5. I agree with crd2 (6): In Germany the TV-broadcaster WDR had for about 10 years each week 15 minutes “Alpha Centauri” with Professor Dr. Harald Lesch. Perhaps you could perform it similar, but, please with some more diagrams and computer graphics… Lesch nearly everything explained just with his hands, and a piece of chalk, but not at his board…

  6. OK, some thinking and then my question.

    But of course as you said, ” Supernova 1987A, which took place in the Large Magellanic Cloud 168,000 light-years away.” and the “This supernova was discovered, optically, on February 24, 1987. About three hours earlier, 23 neutrinos were detected over a timespan of less than 13 seconds.”

    So after 168,000 years in cold space at 2.7K or so the neutrinos were still going at nearly the speed of light. So even though neutrinos have rest masses that make them “the lightest particles with a non-zero mass ever discovered”; there measured masses must be extremely high. From our point of view those 10^20 neutrinos emitted from the Opera detector must have an enormous mass.

    Now with so many neutrinos emitted just from an accelerator, and so many more daily from the sun and there being 10^11 stars in the milky way. There must be a lot of neutrinos emitted by the Milky Way galaxy every day for billions of years.

    Now neutrinos must eventually get captured in orbits around some galaxy (even if they originally escape from the galaxy that produced them). And since neutrinos maintain a great velocity relative to any galaxy; it stands to reason that they would mostly orbit outside the galaxy at just below relativistic speeds. And there moving mass would make them the biggest particles in the universe since they would be travelling at relativistic speed.

    So why question is this: why aren’t neutrinos a candidate particle to be dark matter? It would seem that they would orbit in a halo around galaxies and they would have enormous mass. What are the objections to neutrinos as dark matter? And I assume the answer is not that there are not enough of them; because that problem would only require that we miscalculated the number of neutrinos in the universe.

    So why aren’t neutrinos a serious dark matter candidate to explain the missing mass of the universe. Now I assume that such fast neutrinos would be considered hot dark matter (not cold); but I don’t understand how that makes a difference.

    OK anyone, please educate me; i’d just like to know. Why can’t things like galaxy rotation discrepancies and gravitational lensing be due to neutrinos? Thanks.

  7. As you say, neutrinos would be “hot” dark matter. This is ruled out by the large-scale structure of the universe.

    As Ethan has pointed out repeatedly in past posts on dark matter, it’s not enough for a proposal to explain just galactic rotation or lensing effects, a theory of dark matter has to be consistent with all of the observational evidence.

    Your basic assumptions are wrong too. There is no reason why neutrinos would get captured by any galaxy. At all but the most minute energies they will exceed the escape velocity of whatever galaxy created them, and from then on they will cruise the intergalactic spaces until they bump into a black hole or chance to interact with some matter. The kind of sequence of gravitational interactions needed to slow a relativistic neutrino down to galactic orbital speeds is simply not going to happen.

    The laws of basic orbital mechanics don’t get repealed for neutrinos just because they’re small; if something is in an orbit around some mass, then its speed must be lower than the escape velocity at each point in the orbit. Galactic escape velocities are not very large – for example, at our solar system’s location within our galaxy, the escape velocity is only around 550 km/sec (around 0.2% of the speed of light, and therefore a neutrino at cosmic background temperature would escape).

  8. Here’s another question; since neutrinos rarely interact with normal matter, why would their speed be dependent on the temperature? I thought temp is a function of kinetic energy at the atomic scale. How would a neutrino absorb energy or lose it? Wouldn’t neutrinos normally carry the temperature of a stellar core? If they slow down at low temp, why did the neutrino pulse from the 1987 supernova arrive 3 hrs before the visible light? Even if it got a head start, wouldn’t it have slowed going through millions of light years of deep space?

  9. I’m being a very pedantic chemist, but

    It’s not 2.73 Kelvin

    It should be 2.73 kelvins

    According to the U.S. Census Bureau’s year 2000 census, it seems the average Texas Kelvin household had 2.74 Kelvins.

  10. @Artor: The way normal matter (in this context, excluding neutrinos) gets the temperature of its surrounding is by electromagnetic interaction with its neighbouring atoms or molecules. Since neutrinos don’t do this, the only factor of their KE/temperature is the energy of the subatomic process that produced them (and, to a minor degree, the velocity of the particle(s) that produced it).

    And, SN 1987a was only about 168,000 light-years away, not millions. So, if you assume the neutrinos had a three hour head start to begin with, they would have to go about 2×10^-9 c (0.6 m/s) slower than light to get here at the same time as the light. Of course, there are other possibilities of combinations of lead time and arrival time difference. I don’t know how well the lead time has been constrained, but for all I know, those neutrinos might have had a 24 hour head start, and lost 21 hours by the time they got here.

  11. Afterthought: I think ‘baryonic matter’ is the phrase I should have used. I know normally ‘normal matter’ would include neutrinos, but figured the parenthetical would clear things up enough until I could remember the right term.

  12. @11 Andrew G
    thanks, that’s enough pointers for me to search and better understand. I knew there was an answer; I’d just couldn’t find it. Thanks.

    I’m over my head, so I stop here.

  13. @17 Andrew G

    As I said, I’m way over my head.

    But I still have to think. I uncovered this bit of theory.
    Neutrino energy quantization in rotating medium
    Alexander Grigoriev & Alexander Studenikin 2008 conclude:
    “From this (eq 16) it follows, for instance, that low energy (but still relativistic) antineutrinos can have bound orbits inside a rotating star. This can lead to the mechanism of low-energy neutrinos trapping inside rotating neutron stars.”

    I have no idea whether this paper is credible or not. But if neutrinos can have bound orbits in neutron stars; then maybe in rotating galaxies also. Just a thought.

    p.s. I’m not disputing what you’ve said; just trying to put another interesting idea (speculation) in perspective.

  14. Yes, but escape velocity for a neutron star is on the order of 200,000 km/s*, compared to (assuming Andrew G. is right) 550 km/s for a galaxy. So it’s much, much easier for a neutron star to capture orbiting neutrinos than for a galaxy.

    * I just used Newtonian gravity for this, not GR, so it may be somewhat off, but it gives the idea that it blows away galactic escape velocity.

  15. Oh, and that escape velocity is for the surface of the neutron star. It would be even higher inside, of course.

  16. And, to follow-up my followup, I found a formula for relativistic escape velocity, and it only changed the outcome by about 5%. Insignificant to the overall point.

  17. I’m being a very pedantic chemist, but

    It’s not 2.73 Kelvin

    It should be 2.73 kelvins

    Both are wrong. It’s “kelvin”. Or “K”. And never “degrees” kelvin.

  18. @20, 21, 22 Randy Owens
    You make good sense. Right, slap my forehead, I just didn’t think of it. Thanks.

  19. This is very interesting, but I have heard that neutrinos can travel at either the speed of light, or at least very close. You said that the speed is variable, but the highest speed you mentioned neutrinos could move at was 80% of the speed of light. Was that just under certain conditions, or is this because it hasn’t yet been proven that they can go as fast as I said?

  20. Neutrinos at room temperature move at 80% the speed of light, per the OP.

    Presumably neutrinos produced in a supernova, or by other violent sources, can get to be much hotter than that, and hence go much faster.

  21. Question – What constitutes an interaction of a neutrino with other matter? Is it every time a neutrino hits an atomic nucleus or can a neutrino pass straight through an atomic nucleus?

  22. This is very interesting. When I took a trip to Fermilab in Illinois, I heard that they were doing some tests with neutrinos, where they sent them across 400 miles to see if they could control the neutrinos direction. It worked! I had also heard that neutrinos don’t interact with other particles. If this is true, how are they detected?

  23. The thing that cools down neutrinos is the expanding universe, i.e. redshift. We have two classes of neutrinos flying around, (1) those left over from the bigbang fireball, these have presumably cooled off quite a bit. Anyone know what temperature these “primordial” neutrinos should be at. If they are cools enough, they could contribute to dark matter, although I don’t think they are supposed to ne numerous enough. Then we have nuetrinos which were created by nuclear reactions in stars supernovas, and neutron stars, these shouldn’t be red shifted so much, so this pop should be very hot. I think the cross section of neutrino versus nucleus is strongly energy dependent, the primordial ones probably don’t interact at all?

    Anyone have any numbers for the table below.
    (1) Estimated mass in the universe in primordial and modern neutrinos. How does it compare to talap dark matter mass?

    (2) How much energy is flying by in these neutrinos? How does it compare to the energy in starlight and cosmic rays?

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