Scientists have a pretty good idea of how things die. stars. However, capturing his explosive demise at the right time is not easy. In fact, it has never been possible to follow in real time with a giant star like the red supergiant. At least not until now. And it is that, for the first time, it has been possible to make a precise follow-up, both of its last moments and of the explosion that gave rise to the formation of a supernova.
The scientists responsible for such a find are astronomers from the Berkeley University and its results can be seen in a study published in The Astrophysical Journal.
Although the result has just been released, in reality this follow-up began in September 2020, when the WM Keck Observatory, located on the volcano Mauna Kea of Hawaiii, obtained the first records of the birth of the supernova. Immediately, the data obtained by space and ground telescopes from around the world was analyzed. Measurements at different wavelengths were achieved and, with them, it was possible to reconstruct the chronicle of an announced death. That of a great red giant located 120 million light years from Earth.
An explosive fuel leak
Broadly speaking, a star forms when a large mass of relatively cool gas contracts, raising its temperature greatly. Once this occurs, a series of nuclear reactions in which the nuclei of hydrogen atoms found in the star combine with those of an isotope of hydrogen, called deuterium. Thus, helium begins to form and energy is released.
Therefore, hydrogen and deuterium are the first fuel of the stars. But, like the gasoline in a car, there comes a time when they are used up. And the stars cannot refuel. Deuterium is used up first, so the hydrogen begins to react with lithium and other light metals. Until they also run out. At that point, hydrogen has no choice but to start something known as catalytic reaction of nitrogen and oxygen. Thus, helium can continue to form from hydrogen. But hydrogen also ends up being used up. And there is no more to do. There are only all those helium atoms that have been formed and that will now merge with each other, while the star swells, cools its surface and acquires a reddish tone. We have reached the stage of red giant.
Later, if there is no other way to obtain energy, it can contract to form a white dwarf or directly collapse, resulting in a neutron star, supernova, or black hole. Depending on its size.
That is what happened to this red supergiant whose death they have captured in direct. It collapsed to directly give rise to a supernova. In fact, it was the supernova that caught the attention of scientists, but all of the above could be identified, achieving a unique milestone in history.
From the death of a red supergiant to the birth of a supernova
The supernova that was identified in Hawaii was type II, because it is richer in hydrogen than type I. When analyzing the data from various telescopes, it was found that it corresponded to a red giant star, which had been observed a few months earlier thanks to the Pan-STARRS, a telescope used by the Institute of Astronomy at the University of Hawaii.
The only thing left to do was to reconstruct history. During those months this giant star had had a great increase in its brightness. This, as explained in a release The authors of the study, could indicate that, before collapsing, some stars of this type (and perhaps most) “undergo significant changes in their internal structure that result in the tumultuous gas ejection”. Thus, it had to swell to a size comparable to that of the Jupiter’s orbit.
All this is really novel, because until now it was believed that the red supergiant progenitors of the type II supernovae they remained quiet, with no evidence of violent eruptions or light emission before exploding. This finding, therefore, changes everything that was thought based on theoretical data. “This is a breakthrough in our understanding of what massive stars do just before they die,” he said. Wynn Jacobson-Galán, lead author of the research. “Direct detection of pre-supernova activity in a red supergiant star has never been observed before in an ordinary type II supernova. For the first time, we saw a red supergiant star explode.”
How did the explosion of this giant star originate?
The mere fact of capturing in real time the explosion of this giant star and the consequent formation of a supernova is a great find. But, in addition, these scientists need to know why everything has been much more abrupt than previously thought.
And they already have some theories. For example, they believe that, after exhausting all the fuel in the form of hydrogen and helium, nuclear combustion reactions could occur that would explain this large release of gaseous material.
In fact, the models that have been carried out in this regard suggest that the fusion as a last resort of elements such as neon and oxygen could generate gravitational waves that would send off some of the outer regions of the star. In addition, just before collapse the same can occur with a very short stage in which it is used silicon As fuel.
In short, this has been a unique milestone, which can also give us very interesting information about the end of some stars. In the words of one of the study’s authors, Raffaella MarguttiIt has been like witnessing the explosion of “a time bomb.” And the best part is that this pump still has a lot to teach.