Supernovae and Neutrinos

Supernovae are the most common and powerful nuclear bombs of nature. And also it is one of the most useful phenomena for particle physics and astrophysics.



In supernovae, in which the nucleus collapses, a huge number of protons are converted into neutrons through the absorption of electrons, with the subsequent release of neutrinos. The implementation of this process is one of the most important roles of weak nuclear interaction in nature. Somehow - scientists are still working on this issue - the resulting shock waves (perhaps unknown force helps us so far?) Tear the star apart.



One of the most exciting events in the history of astronomy was the explosion of a giant blue star in the largest of our satellite galaxies, the Large Magellanic Cloud, which occurred in 1987. This bright spot is easy to see south of the equator. Astronomers, who looked at the sky with the naked eye in February 1987, saw a star in the Cloud, which should not have been there. This simple observation gave rise to the greatest wave of astronomical activity that swept through the southern half of the Earth, since every astronomer who had such opportunities hurried to take advantage of such an event that occurs once in a lifetime.



A supernova shines so brightly that its light can temporarily surpass the glow of the entire galaxy containing it. However, only a small part of its energy is emitted in the form of light, or in the form of other forms of energy, which eventually turn into light. Most of the supernova energy rushes out in the invisible form of the above-mentioned neutrinos.



Here are some amazing figures taken from the tutoring site of Stephen Myers, who works as an astronomer at the Socorro National Radio Astronomy Observatory (New Mexico).

Almost all supernova energy of 1987 was transformed into lightweight, weakly interacting neutrinos. As a result of the collapse of the nucleus, 10 ⁵⁸ neutrinos were created. On February 24, 1987, about 10 ¹³ neutrinos from this supernova passed through your body! The bodies of the order of a million people on Earth have interacted with these neutrinos, although, of course, without any consequences.

Yes, that's right - 10 trillion neutrinos passed through your body resulting from the explosion of a star located 160,000 light years - several times farther than the center of the Milky Way. What a wonderful universe we have.



Thousands of trillions of neutrinos passed through several neutrino detectors, and only a couple of dozen of them reacted with something. These collisions were recorded for 13 seconds. At that moment, no one looked at this event with particular attention, but after they noticed the supernova, the experimenters returned to the data and discovered this squall of neutrinos in the data. It happened about 20 hours before the first observation of an unexpected star in the Large Magellanic Cloud. This discovery was the birth of neutrino astronomy, which is now an active area of ​​research.



The study of old photographs led to the discovery of one of them, in which the light of a supernova is visible, recorded only 3 hours after the arrival of neutrinos on Earth. Since the supernova shockwave had to sneak inside the exploding star out before the debris could begin to shine, and the neutrinos generated by the explosion could instantly penetrate the star’s layers, the delay between the arrival of the neutrino and the arrival of the light was to be expected.



This story is wonderful and interesting, but why did I start talking about it? There are two reasons for this.



First, recently [the original article is dated 2011 - approx. transl.] we found a relatively close-located supernova, which was very interesting for astronomers. But the press showed a lack of understanding of the scale.

• Many headlines wrote about "The Brightest Supernova in 40 Years ," " The Youngest and Next Supernova in Decades ." I do not think that in order to calculate the time that has passed since the 1987 supernova, you need a degree in physics.
• This supernova is located 20 million light years - more than 100 times farther than the 1987 supernova.
• This supernova can be seen by amateurs, but only with a very good telescope or with very good binoculars on a dark night - the naked eye will not be enough. The supernova of 1987 was bright enough to see it with the naked eye.

Why such inconsistencies? Supernovae come in different types. In 1987, we saw a type II supernova, in which the star's core collapses, and protons, as described above, turn into neutrons, with neutrinos flying out. And the recent supernova is of type Ia , which explodes in a different, not completely understandable way yet. Supernovae Ia are extremely important for astronomy - they show a high regularity that can be used to measure the distance to them from the Earth. This fact played a central role in the discovery that the cosmological constant of the Universe, which is sometimes called "dark energy," is not zero. Therefore, astronomers are very pleased to explore the type Ia supernova in full detail and with the help of modern equipment - especially one that was discovered shortly after the explosion.



In general, the brightest and the closest and most useful for science supernova type Ia for several decades (we do not consider the 1986 supernova, which was difficult to see and study) - although it is not at all as bright or close as the 1987 supernova Ii.



Secondly, there were rumors about neutrinos moving faster than the speed of light in the blogosphere [later they were refuted by finding an experimental error - approx. trans.]. A beam of high-energy neutrinos from the CERN laboratory allegedly arrived at the Italian laboratory in Gran Sasso earlier than expected - this was observed in the OPERA experiment,



But such statements should be treated with a healthy skepticism. In particular, this follows from observations of the 1987 supernova.



As I have already said, all the neutrinos from the 1987 supernova arrived on Earth in an interval of 13 seconds, and then light from the supernova came after them almost three hours later. This delay was approximately equal to the expected. Such coincidences clearly testify in favor of the fact that neutrinos moved neither much slower nor faster than light — they moved at about the same speed. Think about it: these neutrinos flew for 168,000 years, about 5 trillion seconds, and arrived on Earth with a spread of not more than 13 seconds apart, and 3 hours (10,000 seconds) before light. If neutrinos moved one millionth faster than light, they would have come many months before the light. If one millionth part slower - they would have arrived a few months after the light. And if neutrino speeds differed from each other by one billionth, they would arrive with a spread not in 13 seconds, but in hours.



In short, these data indicate that neutrinos were moving at the speed of light with extremely high accuracy - up to several parts per billion.



To measure the effect of a difference of several parts per billion at the speed of neutrinos traveling from CERN to Gran Sasso - over a distance of 730 km that light can travel in 1/400 seconds, it would be necessary to measure the travel time of a neutrino with an accuracy of a fraction of a nanosecond (one billionth of a second). It is very difficult to measure time more precisely in nanoseconds; coordinating clocks 730 kilometers apart would be an achievement in itself. In physical experiments, picosecond measurement (one trillionth of a second) is very rare — a typical interval for LHC experiments is 100 picoseconds or more.