Vivimos en un Cementerio de Supernovas

When 15 supernovas explode together, both in time and in proximity, a large-scale explosion occurs. I should not be surprised that such a violent event radically transformed the region of the surrounding space. The interstellar dust was dragged by the forces of these simultaneous explosions, creating a monumental vacuum of low-density matter and a shock wave that continues to rush through the galaxy to this day at a speed of 6 km per second. In its stele, it plasmas, reaching a temperature of 1 million degrees Celsius. This simultaneous heating of the interstellar medium, similar to Swiss cheese, is what is now called a hot bubble, and represents both the end of the stars and its beginning. But this is not a distant structure that dates back to a remote corner of the universe. Our solar system does not even go directly towards it. We are inside it, heading headlong towards its origin. Welcome to our local hot bubble. What scientists now understand is the local environment that exists around our solar system. It is an environment that we are still exploring, but its nature is becoming increasingly clear. So, what do we know about the local hot bubble? I am Rafael González, and you are watching Astrum. Join me today as we walk through the stellar explosions and talk about how scientists came to determine that we were in the heart of a cataclysm. The local hot bubble was not always known. First identified in the 1970s, from observations of X-ray emissions of low energy detected throughout the sky, the hypothesis was raised that the local hot bubble was a large cavity in the interstellar medium, called a superbubble, full of mild gas of millions of degrees and low density. In the 1990s, scientists discovered that X-ray emissions could occur anywhere where neutral atoms interact with the solar wind, which questioned the idea that the emissions should point to a large hot bubble. But soon, the evidence would reveal that the hypothesis of previous decades was correct. In 2014, NASA confirmed the existence of the local hot bubble, or LHB, by its acronym in English, through the X-ray diffuse emission of the local galaxy mission. While mild background radiation may come from other sources, such as comets, the mission discovered that only 40% of the low-energy X-ray fog came from the interior of our solar system. This confirmed that the dominant source was the X-ray diffuse emissions emanating from the interstellar plasma region of millions of degrees known as LHB. While this confirmed the existence of the bubble, the questions about what could create such a massive vacuum and what could explain the thousands of young stars around it. The predominant answer turned out to be both violent and fascinating. Recent research suggests that the local hot bubble was the result of about 15 supernova explosions that occurred sequentially in a span of a few million years, with eruptions relatively close to each other. Scientists estimated that the first of these massive stellar explosions occurred approximately 14 million years ago, each one ejecting huge amounts of energy, ejecting the interstellar material surrounding it and heating the remaining gas to extreme temperatures. Evidence of these ancient explosions has been preserved in the geological record of our Earth, in deposits of deep-water sediments, in the form of a special isotope called Iron 60. This radioactive isotope may come from various sources, but it is believed that the most common source of Iron 60 are supernova explosions. We know that the origin of this isotope is extraterrestrial, because the Earth cannot produce Iron 60 on its own, and similar deposits have also been found on the Moon. The reason why this radioactive isotope is special is because we know its average life and we know that another radioactive isotope is disintegrated in Cobalt 60, before finally disintegrating a stable element in Nickel 60. Iron 60 has an average life of 2.6 million years, while Cobalt 60 has a relatively short average life of only 5.3 years. Therefore, when finding a deposit that contains these elements, scientists can compare the quantities of Iron 60, Cobalt 60 and Nickel 60, as if it were an elementary clock, to determine when that material was deposited on our planet. And fortunately, international research teams have discovered several deposits of this type in the last two decades. In 2016, deposits of Iron 60 were found in deep-sea crust samples, taken from the Pacific, Indian and Atlantic Oceans. This indicates two distinctive peaks in the radioactive residues that pointed to several supernovas in a not very distant past, and not very far from our solar system, just 326 light-years away. The samples showed an Iron 60 peak between 3.2 and 1.7 million years ago, and another peak between 6.5 and 8.7 million years ago. Nuclear physicist Anton Wallner, who directed one of these research teams that studies deposits, stated that the fact that the most recent residues spread over a million and a half years suggests that there were a series of supernovas that occurred one after another in close succession. Astrophysicist Dieter Breitscheuert, who directed a second team of scientists, identified a probable source of these supernova explosions, which would have occurred between 196 and 423 light-years from the Sun. These supernovas that created our local hot bubble could have been part of an aged stellar cluster whose surviving members are now associated with the stellar group Scorpio Centauri. Using the deposits of Iron 60, the team was able to track the signals of two supernovas, one that occurred 1.5 million years ago and the other 2.3 million years ago, as a result of the death of stars with 8.8 and 9.2 times the mass of our Sun, respectively. In fact, our local hot bubble, or BCL, continues to grow today, although at a much slower rate than when the supernovas exploded millions of years ago. Expansion speed has stabilized at about 6 km per second, according to astrophysicist Katherine Zacker. In 2022, Zacker published a pioneering article that reconstructed the evolution of our galactic neighborhood, tracking the chain of events that created our local hot bubble, and led to the formation of all the young stars that we see today in the vicinity. From there, they made an incredible discovery. Using data from the Gaia telescope of the European Space Agency, Zacker and his team managed to build a three-dimensional space map that shows that, less than 500 light-years from our planet, all the young stars and regions of stellar formation reside on the surface of our local hot bubble. With these positions and three-dimensional movements of the stellar clusters, they traced 20 million years of stellar formation history near our local hot bubble. The implications were clear. All the regions of stellar formation known, near our solar system, had formed along the outer edge of the local bubble, by absorbing gas during its expansion. The stellar clusters are a field in which we are learning more and more, especially as our telescopes obtain new images. Here you have a spectacular image of the dark cloud Camaleón 1, one of our closest stellar storerooms, taken by a dark energy camera of the Víctor M. Blanco telescope, 4 meters high, at Cerro Tololo Inter-American Observatory. By studying the propagation of stellar light from within, scientists can unravel details about how stars are formed, which can help us better understand the impact of the local hot bubble on our current galaxy. From the birth of the local hot bubble, 14 million years ago, Saker and his colleagues identified four eras of stellar formation in the bubble's envelope. About 16 million years ago, the birth of the stellar cluster Centaurus Superior Lupus, or UCL, followed by the stellar cluster Centaurus Inferior Crux, or LCC. These were formed about 49 light-years away, and about 14 million years ago, these stellar populations were the source of the stars that became supernovas and created our local bubble. About 10 million years ago, the first of the four eras of stellar formation is observed after the formation of the LHB. The Scorpio Superior Association and the oldest stellar populations of Ophiuchus are born in this first era. 6 million years ago, the second era of stellar formation formed the Corona Australis and the oldest stars of Taurus. Then, about 2 million years ago, the stars of Lupus and Chameleon, as well as the youngest stellar populations of Taurus and Ophiuchus, were formed in the third era. And finally, our current time is within the fourth era of stellar formation. We can observe the dense star-forming molecular gas that surrounds the LHB, which will eventually lead to the birth of more stellar clusters along the outer edge of the bubble. With all this stellar creation, you may be surprised to know that we are intruders. Our Sun was not formed within the local bubble. In fact, the Sun was about 978 light-years away when the first supernova exploded in UCL and LCC, and only joined the LHB about 5 million years ago, when its trajectory through the galaxy led it inside the bubble. With the trajectory shown in yellow dots, you can see the location of our Sun just before entering the local bubble. And now, by pure coincidence, our Sun is close to the center of the LHB. By entering the heart of what once was a boiling oven, scientists were interested in mapping the current temperature within the local bubble. You may wonder why we are so calm, if the plasma temperatures here can reach a million degrees. The key is in the density of that plasma. Look at this 3D map from the Zacker 2022 publication. It shows our local hot bubble in dark blue. The density within our bubble is extraordinarily low, as it contains approximately 100 times less hydrogen than the typical interstellar medium. Therefore, although the temperature of this gas is shot at around a million degrees Kelvin, giving rise to the diffuse X-rays emissions that we have observed throughout the sky, we do not have much to worry about. The monitoring of the temperatures within the local bubble has provided more evidence of their existence. The extensive exploration of X-rays by the distribution of image telescopes, better known as the X-ray telescope ERROSITA, has managed to collect the study of soft X-rays from all over the sky in more detail to date. This data has been used to map the LHB and our solar neighborhood in more detail than ever before. Launched in 2019 aboard the German joint Russian mission SPECTRUM ROENTGEN GAMMA, or SPECTER-RG, the data from the X-ray telescope ERROSITA have allowed a team of scientists, led by the Max Planck Institute of Extraterrestrial Physics, to create a 3D map of the LHB and identify a temperature gradient where the galactic south was slightly warmer than the galactic north. This dichotomy of temperatures could be explained by the supernova explosions of the last millions of years. And by creating this bubble map, the team also discovered that the LHB extends towards the poles of the galactic hemisphere. This is because the hot gas of the bubble expands in the direction with less resistance, which turns out to be the one that moves away from the galactic disk of the Milky Way. In addition to identifying the temperature variations and the shape of the bubble, the team collected this and other data to create an even more detailed map of our galactic neighborhood. On the new 3D map, our local hot bubble looks like a three-dimensional, blue, white, yellow and red spot, surrounded by other galactic structures and even superimposed. These other structures represent remnants of supernovae known as the rubber nebula, which is shown here in red, and dense molecular clouds, which are shown here in orange. With the new data and 3D maps, it seems likely that these superbubbles are common in our galaxy, creating a Milky Way similar to a Swiss cheese. The cavities of our galaxy, similar to a Swiss cheese, are perforated by gigantic supernova explosions, and new stars are formed along the edges of the holes created by the dying stars. And as in the case of Swiss cheese, it seems that some of these superbubbles could have tunnels that connect them with other bubbles or other structures, suggesting that our local hot bubble could be part of an intricate network of similar characteristics throughout our galaxy. For example, we have the Canis Majoris tunnel, which is located in the galactic disk of the Milky Way, and is believed to connect our local hot bubble with the rubber nebula or another larger nearby superbubble. But the new 3D map also revealed another previously unknown interstellar tunnel that extends towards the Centauri constellation and possibly connects our local bubble with the nearby superbubble Loop 1. While these interstellar tunnels are fascinating, our current understanding of them is limited. However, these hot gas tunnels and stellar-shaped bubbles, shaped by the death of the oldest gigantic stars, am amazed by how powerful and interconnected the evolution of our local galactic neighborhood is. This suggests that stars are not only born and die in isolation, but that their energy production continues to shape the environment for millions of years after their disappearance. And as our observation tools become more sophisticated, we begin to discover the magnitude of these hidden structures. The next time you look at the night sky, you may remember that we are surrounded by unusual patterns, like our local bubble in the Milky Way, excavated by ancient cataclysms, and that some of those stars you see are actually stuck to the walls of a cavity devastated by a supernova that connects with other parts of the galaxy through interstellar tunnels. A big hug to the patrons who support me in my mission to spread science. Subscribe and leave a like to support the channel. Thank you for your visit and see you in the future.