A nearby star-forming region may explain the mystery of tiny grains from beyond the solar system.
A wave of exploding sprouting stars may have provided the conditions required to build the solar system.
New research probing a nearby star-forming region examines conditions that may have been similar to those found in the early solar system to try to solve the outstanding mystery of how radioactive elements essential to planet formation arrived in the environment around the sun. The new finding concludes that such particles are common in star-forming regions, suggesting that the processes that formed the solar system are readily available throughout the galaxy.
Scientists used the tiny clues of some of the first solid material that condensed from the cloud of dust surrounding the newborn sun, material that later built the planets. A key ingredient here is aluminum-26, an element built inside of stars and one that has a relatively short lifetime of roughly 100,000 years. Because the first planets likely took a billion years or so to form, this element's presence suggests a nearby source.
By observing the conditions found in the nearby star-forming 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 fortunate event.
"Most of the work on understanding the source of aluminum-26 and other short-lived radionuclides in the solar system has, by necessity, been quite idealized," John Forbes, an astronomer at the Flatiron Institute in New York City and lead author of the new research, told Space.com by email. "Ophiuchus offers us a real example for how this may play out, which is extremely useful when dealing with such a complex process."
The research was published today (Aug. 16) in the journal Nature.
Death to life
Coalescence of life
[ed.: " Coalescence of life" - much better IMHO]
The researchers hunted aluminum-26 by focusing on calcium-aluminum rich inclusions (CAIs), which are submillimeter-sized grains found in meteorites. Planets form when material left over from the birth of a star condenses into smaller clumps. CAIs provide a substantial source of heat during planetary formation, drying out worlds and reducing the amount of water that survives. But where did these tiny fragments come from?
Aluminum-26 is one of many metals produced in the fiery heart of massive stars. When the star goes supernova and explodes, it spreads its innards across the nearby galaxy. Theoretically, a single supernova could be the source of all of the aluminum in the solar system. However, according to Forbes, current estimates for the aluminum yield of supernovas just aren't high enough most of the time to explain our solar system.
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The new research has important implications for understanding the early solar system.
"The finding that aluminum-26 is going to be readily available to some forming planetary systems is very exciting," Fred Ciesla, a planetary scientist at the University of Chicago, told Space.com by email. Ciesla, who was not part of the new research, studies early solar system formation and how CAIs contributed.
"Given the many roles that aluminum-26 played in the formation of our solar system, this means those same processes may have operated in other planetary systems," Ciesla said.
Reheating the disk
The explanation of aluminum-26's arrival from multiple stellar deaths doesn't come without its challenges. In order to match observations from meteorites, scientists need to not only address the quantity of aluminum, but also to explain a so-called "global reset" of the aluminum in the stellar disk to synchronize their radiogenic clocks to give them the same apparent formation period. Such a reset would require a global heating event that would vaporize all of the solids in the solar system.
Such a reset could have been caused by an outburst from the forming sun or from an extremely nearby supernova, but Forbes admits both these hypotheses have drawbacks. Although outbursts have been seen in forming protostars, such explosions would only be capable of heating the disk out to roughly the orbit of Mars, while planetary formation continues farther out. Meanwhile, explaining it with a nearby supernova would require extreme precision — it would have to be close enough to sufficiently heat the disk but far enough away to avoid destroying it completely, which Forbes calls "quite an unusual situation."
The researchers favor a variant of the first option, one in which the angular momentum of the planetary disk is turbulent enough to eventually bring all of the material within reach of the young star as it flares.
But Ciesla is wary of that explanation. He points to dust grains in meteorites that show signs of formation around other stars. These grains would be destroyed in a global heating event. Water would also be a problem. Scientists think that some of the water in the Earth, asteroids and comets came from the early solar environment based on these objects' concentration of heavy water. In the global heating event called for by the authors, that water would react with other hydrogen molecules and the heavy water enrichment would be lost.
"This has not happened, as we see that heavy water, so the global heating must not have happened," Ciesla said.
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"The fact that there's abundant aluminum-26 available right next door to this star-forming region is really suggestive that the enrichment happens by mixing in aluminum-26 produced by nearby massive stars," Forbes said.
Ciesla remains heartened by the idea that aluminum-26 would be available to other worlds in the galaxy.
"While we know that planetary formation is robust, the question is how unique were the conditions and evolutionary pathway that our solar system followed," Ciesla said.
"This paper tells us that having aluminum-26 is not a very unique aspect of our solar system's story."
Entire article available here.
