The song lyrics of Bruce Springsteen said, "everything dies baby, that's a fact. But maybe everything that dies someday comes back." Scientists now think that may not be that far from the truth when it comes to galaxies. Their new calculations show that the Milky Way galaxy may actually be in its second life after dying over a period of 10 billion years.
The new data comes from the Masafumi Noguchi of Tohoku University in Sendai, Japan and was published in Nature. Noguchi's theory says that stars were likely formed in two different epochs under two different sets of circumstances. It has been suggested for some time that two-stage galaxies are much larger than ours, Noguchi has been able to confirm that a process which is known as "cold flow accretion" played a crucial part in the formation of the Milky Way.
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Cold flow accretion describes how galaxies collect the gases surrounding them as they form. Since stars are naturally composed of the gases which formed them, these gases act as a history record similar to a tree's inner rings contain information about its environment. Noguchi's theory proposes the Milky Way got its beginnings around 10 billion years ago when cold gas streams containing what are called "alpha process elements".
"Alpha process elements" are α-elements like oxygen, magnesium and silicon which flows into the galaxy. Stars were formed from these gas of these a-elements and once they reached the end of their lives they exploded in the form of short-lived type II supernovae which are rich in the a-elements.
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Three billion years later, these alpha process supernovae's shock waves started to heat the gases to hotter and hotter temperatures. When the new temperatures rose, cold gas accretion ground to a halt. During this interregnum period, type la supernovae, which are longer lasting than type IIs, started injecting iron into these gases changing the elemental composition and therefore the stars.
When the gases began emitting radiation and cooled down around 5 billion years later, the cooling flow made its way into the galaxy and began creating a second generation iron-rich stars. Among these new stars was Earth's very own sun.
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