A long time ago, the Milky Way died and then it came back to life, explains a Japanese scientist after analyzing the data on the chemical composition of the stars inside the galaxy.
Based on their chemical composition, stars in the Milky way can be divided into two categories: a group is more abundant in α elements, which are: oxygen, magnesium, silicon, sulfur, calcium, and titanium. The second group of stars contains less α elements but more iron.
The difference between these stars means that something happened while they were formed, explains the study which was recently published in the journal Nature.
According to Astronomer Masafumi Noguchi of Tohoku University, the difference between the two groups is given by the difference of time when they were formed, with a period of no star formation between the formation of the groups.
Noguchi based his model of the evolution of Milky Way over a period of 10 billion years on the 2006 theory of cold flow galactic accretion.
The theory was initially proposed to be used on very large galaxies which already suggested that they had stars that formed in two stages. Noguchi believes that this theory applies to our galaxy – considering that there are two different groups of stars with a different chemical composition.
The chemical composition of stars was dependent on the gases that formed it. Taking into account that the early Universe didn’t have heavy metals present – they were created in stars and propagated into space after those stars became supernovae.
Stars Ceased to Form – the Dead Period
Noguchi’s model shows that the first stage of the creation of stars was when the galaxy got cold gas from outside, being the primary component of the first stars. Some of these stars died after almost 10 million years and became Type II supernovae – releasing α elements in the galaxy, helping to form other new stars.
But after almost 3 billion years, things took a different turn, explains Tohoku University in a release:
“When shock waves appeared and heated the gas to high temperatures 7 billion years ago, the gas stopped flowing into the galaxy and stars ceased to form.”
After 2 billion years, other supernovae took place and spewed iron into space. The gas cooled and stars started forming again – which happened almost 5 billion years ago.
The second generation of stars are the ones with a higher composition of iron, including our Sun which is almost 4.6 4.6 billion years old.
That second generation includes our Sun, which is about 4.6 billion years old.
The model argues that galaxies might have had a different evolution, in which there was a dead period.
Andre Blair s is the lead editor for Advocator.ca. He holds a B.A. in Psychology from the University of Toronto, and a Master of Science in Public Health (M.S.P.H.) from the School of Public Health, Department of Health Administration, at the University of North Carolina at Chapel Hill. Andre specializes in environmental health, but writes on a variety of issues.