It makes long, long time, l a galaxy that represents the origin of mankind, ‘he died’ at some point in their history before experiencing a ‘renaissance’ dramatic, according expose scientists from Tohoku University (Japan) in a study published in the journal Nature.
Thus, the Milky Way experienced a dark age when the formation of new stars abruptly stopped. But this bleak era may have triggered the process that led to the ‘second life’ or second chance for the galaxy and take the shape that allowed intelligent life to emerge in one of its spiral arms.
Stars formed at two different times through different mechanisms
The expert Masafumi Noguchi has calculated the evolution of the Milky Way over a period of 10 billion years, including the “ cold flow accumulation or accretion “, a new idea proposed by Avishai Dekel (of the Hebrew University) and his colleagues, on how galaxies collect surrounding gas during their formation. Although these suggested two-stage formation for much more massive galaxies, Noguchi has been able to confirm that the same picture applies to our own galaxy.
There was a long latent period in which star formation in the Milky Way ceased. And our home galaxy has turned out to have a more dramatic history than we originally thought and that is written in the elemental composition of the stars. This means that the stars ‘memorized’ events in the past because they show what gas was present during their birth.
Noguchi’s description then begins 10 billion years ago when cold gases rushed into the Milky Way to form the first stars. Then about 3 billion years later, it all went wrong. “Shock waves appeared and heated the gas to high temperatures 7 billion years ago,” the study says. “The gas stopped flowing into the galaxy and the stars stopped forming.”
During this very unflattering time, supernova explosions injected iron into the gas circling the Milky Way and changed its composition. As the gas cooled, it began to flow back into the galaxy about 5 billion years ago and began the creation of the second generation of stars, including our own Sun.
And the rest is history. Or rather, our history.
Where does this mystery come from?
There are two groups of stars in the solar neighborhood with different compositions. One is rich in α elements like oxygen, magnesium, and silicon. The other contains a large amount of iron. Recent observations by Misha Haywood (Observatoire de Paris) and her colleagues revealed that this phenomenon is prevalent over a vast region of the Milky Way. The origin of this dichotomy was not clear. Noguchi’s model provides, as we see, an answer to this puzzle.
According to Benjamin Williams of the University of Washington and his colleagues, our neighboring galaxy, Andromeda, also formed stars at two different times. Noguchi’s model predicts that massive spiral galaxies like the Milky Way and the Andromeda Nebula experienced a star formation gap, while smaller galaxies continuously formed stars. Noguchi hopes that “future observations of nearby galaxies may revolutionize our view of galaxy formation.”
The future
We already know that in about 4 billion years, the Milky Way will collide with the Andromeda Galaxy in a collapse of cosmic proportions. And while this event will be very dramatic, the differences between the stars are believed to be so great that the actual number of collisions is likely to be small. Our own solar system will likely survive this process – if it still exists – although it seems unlikely that humanity will be present to witness this incredible event.
Reference: Masafumi Noguchi, The formation of solar-neighborhood stars in two generations separated by 5 billion years, Nature (2018). DOI: 10.1038 / s41586-018-0329-2
