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A wave of exploding stars may have provided the conditions for building the solar system.
New research probing a nearby star-forming region is examining conditions that may have been similar to those found in the early solar system in an attempt to unravel the unique mystery of how radioactive elements essential to the formation of planets are arrived in the environment around the Sun. The new discovery concludes that such particles are common in star-forming regions, suggesting that the processes that shaped the solar system are readily available throughout the galaxy.
Scientists used tiny clues from some of the earliest solid material that condensed from the cloud of dust surrounding the newborn sun, material that then built the planets. A key ingredient here is aluminum-26, an element built inside stars and which has a relatively short lifespan of around 100,000 years. Because the first planets probably took around a billion years to form, the presence of this element suggests a nearby source.
Related: Supernova photos: stunning images of star explosions
By observing the conditions found in the nearby star formation region Ophiuchus, scientists have determined that the most likely source of aluminum-26 for our solar system is a series of nearby supernovas, rather than a single lucky event.
“Much of the work on understanding the source of aluminum-26 and other short-lived radionuclides in the solar system has, of necessity, been quite idealized,” John Forbes, astronomer at the Flatiron Institute in New York and lead author of the new research, Space.com told via email. “Ophiuchus offers us a real-life example of how this can play out, which is extremely helpful when it comes to such a complex process.”
the research was published today (August 16) in the journal Nature.
Death to life
Researchers chased aluminum-26 by focusing on inclusions rich in calcium-aluminum (CAI), which are submillimeter-sized grains found in meteorites. Planets are formed when the residual matter from a star’s birth condenses into smaller clusters. CAIs provide an important source of heat during planetary formation, dry up the worlds and reduce the amount of water that survives. But where do these tiny fragments come from?
Aluminum-26 is one of the many metals produced in the fiery hearts of massive stars. When the star goes away supernova and explodes, it spills its entrails across the neighboring galaxy. Theoretically, a single supernova could be the source of all the aluminum in the solar system. However, according to Forbes, current estimates of the aluminum yield of supernovas are just not high enough most of the time to explain our solar system.
“For some star masses that become supernovae, enough aluminum-26 is produced, but due to the rapid decay of aluminum-26, this supernova should have occurred extremely recently and be in the correct range of mass, ”Forbes said. “It is possible, but not likely.”
Ophiuchus is a typical star-forming region located near the solar system; right next to it is a cluster of massive stars. Giant stars have a short lifespan compared to the extended lifespan of the sun: a star 8 times more massive than ours will only live 40 million years, compared to 10 billion years for the sun. This mortality makes them bad neighbors, as they can heat gas in neighboring regions of planet formation, thereby destroying planetary cores and disks. But giant stars balance out this planetary interference by sharing a supply of aluminum-26 when they explode, a material that can aid in the formation of planets.
Related: Secrets of the birth of the planet revealed in amazing images from the ALMA radio telescope
By studying Ophiuchus and its neighboring massive stars in multiple wavelengths, Forbes and his colleagues determined that the disks that would eventually form newborn stars in Ophiuchus would most likely be inundated with aluminum-26 from their dying neighbors. Because Ophiuchus is a typical region of star formation, with nothing to significantly distinguish it from most, this suggests that most stars, our sun included, receive an aluminum-26 flood from their front neighbors. their birth.
The team also researched The stars of Wolf-Rayet, which are more than 20 times more massive than the sun and have also been seen as potential donors of aluminum-26. Wolf-Rayet stars produce extremely strong winds, especially as they approach the end of their life. These winds strip the stars of their surface material, which includes aluminum-26, and blow it into the vicinity. According to Forbes, it’s possible that a single Wolf-Rayet star would produce enough aluminum to represent the material found in the early solar system.
However, when they studied the star-forming region of Ophiuchus, the team found no Wolf-Rayet stars to seed aluminum to their neighbors. “A person could have died in the last million years, but compared to a handful of supernovas that have occurred around this time, that’s just less likely,” Forbes said.
The new research has important implications for understanding the first solar system.
“The discovery that aluminum-26 will be readily available to some forming planetary systems is very exciting,” Fred Ciesla, a planetary scientist at the University of Chicago, told Space.com via email. Ciesla, who was not part of the new research, is studying the early formation of the solar system and the contribution of CAIs.
“Considering the many roles that Aluminum-26 played in shaping our solar system, this means that these same processes may have worked in other planetary systems,” Ciesla said.
Heating up the disc
The explanation for the arrival of aluminum-26 from several stellar deaths is not without challenges. In order to match the observations of meteorites, scientists must not only address the amount of aluminum, but also explain a so-called “global reset” of the aluminum in the star disk to synchronize their radiogenic clocks to give them the same. apparent formation. period. Such a reset would require a global warming event that would vaporize all the solids in the solar system.
Such a reset could have been caused by an explosion from the forming sun or an extremely nearby supernova, but Forbes admits that both of these assumptions have drawbacks. Although explosions have been observed during the formation of protostars, such explosions would only be able to heat the disk around the orbit of March, while the planetary formation continues further. Meanwhile, explaining it with a nearby supernova would require extreme precision – it would have to be close enough to heat the disk enough but far enough away to avoid destroying it completely, which Forbes calls “a pretty unusual situation.”
The researchers favor a variant of the first option, in which the angular momentum of the planetary disk is turbulent enough to finally bring all the material within range of the young star during its eruption.
But Ciesla is wary of this explanation. It shows grains of dust in meteorites that show signs of forming around other stars. These grains would be destroyed during global warming. Water would also be a problem. Scientists believe that part of the Earth’s water, asteroids and comets originated from the primitive solar environment based on the heavy water concentration of these objects. In the global warming event requested by the authors, this water would react with other hydrogen molecules and the heavy water enrichment would be lost.
“It didn’t happen, because we are seeing this heavy water, so global warming must not have happened,” Ciesla said.
He pointed out what he calls the generally accepted paradigm within the meteorite community. CAIs most likely formed near the sun, possibly by the same eruptions that the authors considered unlikely, and then were redistributed across the disc of matter by the mixing process.
According to Ciesla, the short period of CAI formation may be due to a combination of the small amount of time that encompasses when the sun was both hot enough to form CAIs, including aluminum-26, and to spread the CAI in the disc throughout its evolution. Such a process has been explored by several researchers, including Ciesla.
“It is certainly possible that you could explain the level of aluminum-26 in the solar system with some production from the sun via cosmic rays, but I’m not sure it works for other short-lived radionuclides whose daughter products are seen in meteorites, “Forbes said.
He also pointed out that the aluminum-26 observed by his team is centered on the neighboring massive star cluster of Ophiuchus.
“The fact that there is abundant aluminum-26 right next to this star-forming region really suggests that the enrichment occurs by mixing the aluminum-26 produced by neighboring massive stars,” he said. said Forbes.
Ciesla remains encouraged by the idea that aluminum-26 would be available for other worlds in the galaxy.
“While we know that planetary formation is robust, the question is how unique the conditions and evolutionary path followed by our solar system were,” Ciesla said.
“This article tells us that having aluminum-26 is not a very unique aspect of the history of our solar system.”
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