Since we were not around with cameras at the time, that picture, obviously, cannot be the one above (NGC 602 star-forming region within the Small Magellanic Cloud, a minor staellite of the Milky Way.) But our sun would also be in such a scene – even an older one – before its birth, say astronomers.
Relying on radiometric measurements on unstable isotopes (types of an element with same number of protons but differing number of neutrons) in meteorite inclusions, in effect comparing their theoretical halflives with decay history in the samples, astronomers have calculated the age of the Sun as 4,567.3 billion years with a margin of error of only 160.000 years. But life starts before birth. So with information provided by ages of evidence dug out from some heavy radioisotopes, a team of astronomers have reconstructed the prenatal development of the solar system, which they liken to the embrionic and fetal stages of human lives.
According to this picture, the final 1 percent of such heavy metals like gold, silver or platinum was added to the giant molecular cloud, in which the Sun would evolve, by a massive star which ended its brief existence with a tremendous supernova explosion 100 million years before the solar nebula cradling the nascent sun and would-be planets condensed out of the medium.
Then, about 30 million years before the birth of the Solar System, an evolved Sun-like star which had swollen to hundreds of its normal size in its red-giant stage, puffed some heavy elements it had manufactured in its outer layers – including rare-earth elements like those used in your smart phones – into interstellar space with its envelope, enriching the medium from which new suns would arise. Its dead core, squeezed into Earth dimensions, should be glowing somewhere around as a “white dwarf”.
Starting off from the known decay rates of the unstable radioactive isotopes, researchers conclude that the final one percent of such elements synthesised by what is called the “s- process” neutron capture (“s” for slow) were added to the molecular cloud through such an event. After an incubation period of some thirty years, a denser part of the nursey collapsed on itself to form the Sun and its siblings which subsequently dispersed.
Stars are formed, often as clusters, when sections of the giant molecular gas and dust clouds which make up the bulk of galaxies collapse due to a number of causes. While Sun-like stars live for billions of years and smaller ones have much longer lifespans, Stellar behemoths far more massive than Sun spend their fuel within a few tens of millions of years at most, and punctuate their lives with titanic supernova explosions. Heavy elements (those heavier than iron, the ultimate product of fusion reactions in the core) formed in outer layers shortly before the end or in the supernova explosions, are thus flung into space to mix in the clouds to “enrich” (in astronomer-speak) the material from which new generations of stars will form. Hence, planets and all living things on them, including ourselves, are made of materials baked inside the now-defunct stars.
Hydrogen fuel is converted into heavier elements up to carbon and oxygen in the cores of sun-like stars, and up to iron in giant stars. How, then, there are a host of elements far heavier than iron? A part of the elements synthesised in the cores of stars are transported into outer layers with convection. There they are metamorphosed into heavier elements (up to bismuth) by capturing neutrons, some of which turn into protons through a process called minus beta decay.
This “slow process” takes place in lengthy periods at the outer layers of stars where neutrons are relatively sparse. As the star begins leaving the long, stable period of its life called “main sequence” during which pressure from the reactions in the core balance the inward push of the star’s mass, heavy elements diffuse into the space. In the “rapid process”, on the other hand, heavy elements synthesised in the core and fusing layers surrounding it like onion skins, capture neutrons in large numbers when they smash into them by the powerful shock wave. They undergo similar beta decays to convert into still heavier elements and their isotopes.
The team of astronomers and astrophysicists led by Dr. Maria Lugaro and Prof. Alexander Heger of Monash University (Australia) deduced the times of latest seeding of the cloud before the birth of the Solar System, by comparing the remaining abundances of radioactive heavy isotopes in meteorites dating to the formation of the Sun, with what the theories predict.
Researchers focused on 182Hf (hafnium) with a halflife of nine million years and I 129I (iodine) with a longer, 16-million-year halflife, comparing their current masses with those they had started out with, to calculate their ages.Their conclusion: 129I, was synthesised about 100 million years ago together with such precious metals.
as gold and silver, through “r-process” (“r” for rapid) neutron capture in a supernova explosion when the tremendously powerful shock wave smashed into the previously formed, less-heavy elements formed in the downfalling envelope, causing them to absorb neutrons in the heavy flux environment. Then they beta decayed into heavier ones in the blink of an eye before being catapulted into space. 182Hf, on the other hand, was puffed into space 30 million years before the Sun’s birth, after it was synthesised in the relatively neutron-poor, bloated envelope of a star of similar mass in its death throes.
After these products of either slow or rapid neutron capture processes incubated for 30 million years alongside other elements, a denser region of the molecular cloud collapsed to form the Solar System.
- 1. “Probing the solar system’s prenatal history”, Science, 8 August 2014
- 2. “Step closer to birth of the sun”, Monash Üniversity, 7 August 2014
- 3. http://en.wikipedia.org/wiki/Supernova_nucleosynthesis