The protagonist of this article is a neutron star, but not just any; it is, neither more nor less, than a magnetar, which is a very special kind of neutron star. ASIM, one of the scientific instruments installed on the International Space Station, has identified an extremely violent magnetic eruption emitted by a magnetar located approximately thirteen million light years from Earth.
Yes, it is a huge distance, but the intensity of the flash that this object unleashed was brutal: in just a tenth of a second it emitted as much energy as our Sun in 100,000 years. This event was identified by scientists on April 15, 2020, and since then a group of technicians led by CSIC astrophysicists has been studying it to better understand the strange properties that magnetars have.
The article containing its conclusions has been published in Nature a few hours ago, and it is a very valuable tool that allows us to enter the interior of one of the most exciting objects that we can find in the cosmos. Magnetars are rare and rare; in fact, so far cosmologists they have barely managed to identify thirty, and when they erupt they unleash one of the most violent cosmological events ever witnessed by humans.
Neutron stars are born when supernovae mark the end of the stellar beat
Before we delve into magnetars to find out what they are and why they have such strange properties, it is worth reviewing. what is a neutron star. After all, as we have seen, a magnetar is a kind of neutron star. When a massive star exhausts its source of energy, an imbalance occurs between gravitational contraction, which pulls the star’s matter inwards, towards its interior, and the pressure of radiation and gases, which tries to make the star expand. .
During the stage in which the star maintains the fuel reserves necessary for the nuclear fusion reactions to take place within it, both forces counteract each other, keeping the star in balance. But when the energy source is exhausted, the radiation and gas pressure stops, and the gravitational contraction, which can no longer be counteracted, causes the star to collapse. At that moment its iron core contracts abruptly, and the upper layers of material fall on it, bouncing and being thrown with a gigantic outward energy. A supernova has just occurred.
If you want to delve much more deeply into the different phases through which the life of a star passes, I suggest you take a look at the article that I link right here. In it we explain these processes in more detail. Let’s move on. The iron core of the star does not emerge unscathed from this event. The enormous pressure to which it is subjected causes very important changes in its structure, which is why it is no longer made up of ordinary matter, with its protons, neutrons and electrons, and is now made up of what astrophysicists call degenerate matter.
Gravitational contraction causes very severe changes in the structure of the iron core, which is now made up of degenerated matter.
If the object that remains after the star has ejected its outer layers into the mid-stellar in the form of a supernova has more than 1.44 solar masses, a value known as chandrasekhar boundary In honor of the Indian astrophysicist who calculated it, the stellar remnant will once again collapse to form a neutron star. A few moments before the supernova occurs, the iron core of our massive star is subjected to the enormous pressure of the upper layers of material, and also to the incessant action of gravitational contraction.
These processes trigger a mechanism of a quantum nature that entails very important changes in the structure of matter, causing the iron in the stellar nucleus, which is subjected to a very high temperature, se fotodesintegre under the action of high-energy photons, which constitute a form of energy transfer known as gamma radiation.
These high-energy photons manage to disintegrate the iron and helium accumulated in the core of the star, giving rise to the production of alpha particles, which are helium nuclei that lack their electron envelope, and therefore have a charge. positive electrical, and neutrons. In addition, a mechanism known as beta capture in which we are not going to inquire so as not to overly complicate the article. The important thing is that we know that it causes the electrons of the iron atoms to interact with the protons of the nucleus, neutralizing their positive charge and leading to the production of more neutrons.
A cubic centimeter fragment of a neutron star weighs approximately 1 billion tons.
During this process the initial matter, which was made up of protons, neutrons and electrons, becomes solely by neutrons because, as we have just seen, electrons and protons have interacted by electron capture to give rise to more neutrons. From that moment on, the star is no longer made up of ordinary matter; It has been transformed into a kind of huge crystal made up only of neutrons.
And this brings us to what is undoubtedly the most surprising characteristic of neutron stars: their density. The mean radius of one of these objects is approximately ten kilometers, but its mass is enormous. Compared, for example, with stars that are in the main sequence, or even white dwarfs, neutron stars are very small, and accumulating so much mass in such a small space causes that a fragment of a cubic centimeter of a neutron star weighs approximately, no more, no less, billion tons.
What is a magnetar and what makes it so special
We already know with some precision what a neutron star is, so we can investigate magnetars with less effort and greater guarantees of success. These magnetars are nothing more than a peculiar class of neutron stars capable of expelling a gigantic amount of energy for a brief moment of time. in the form of gamma rays and X-rays. As we saw at the beginning of this article, the magnetar identified by the ASIM instrument on the Space Station emitted as much energy in a tenth of a second as our Sun in 100,000 years.
What the researchers from the Institute of Astrophysics of Andalusia, which belongs to the CSIC, have achieved during the meticulous analysis of the data collected by ASIM is to measure the oscillations in the brightness of the magnetar during the instants of greatest energy projection. In this way they have managed to understand a little better what causes these colossal energy eruptions. Much remains to be done to fully understand this mechanism, but these astrophysicists believe that its origin lies in the instabilities of its magnetosphere, which are something like small earthquakes that take place in the crust of the star.
The Alfvén waves bounce off the crust of the neutron star and interact with each other, causing the emission of large amounts of energy
This layer is about a kilometer thick, and oscillations known as Alfvén waves which are also present in the Sun. These waves bounce off the star’s crust and interact with each other, causing the emission of large amounts of energy. The new information from this study about the magnetic stresses in the interior and periphery of neutron stars has been made possible by the high quality of the data collected by the ASIM instrument.
However, Javier Pascual, one of the researchers from the Andalusian Institute of Astrophysics who participated in the study, explains how complicated the data analysis has been: «The detection of oscillations It has been a challenge from the point of view of signal analysis. The difficulty lies in its brevity, whose amplitude decays rapidly and becomes embedded in background noise. It is difficult to distinguish the signal from the noise. We owe this achievement to sophisticated data analysis techniques that have been applied independently by different team members. “
Thanks to the efforts of these Spanish astrophysicists, and also that of many other researchers scattered all over the planet, today we know neutron stars a little better than yesterday. And yes, as we have verified throughout this article, they are one of the most amazing objects that we can observe in the universe of which we are part. There is still a lot of work to be done to better understand both this and other phenomena about which we hardly know a handful of things, but we can be sure that the effort is worth it.
Images | NASA Goddard Space Flight Center