Our galaxy died many billions of years ago
New calculations by a team of scientists have revealed previously unknown details about our galaxy. We live in a 'zombie galaxy'.
Long, long ago, the galaxy that represents the origin of humanity, 'died' at some point in its history before experiencing a dramatic 'renaissance', according to scientists from the University of Tohoku (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 grim era could have triggered the process that led to the 'second life' or second chance for the galaxy and take the form that allowed intelligent life to emerge in one of its spiral arms.
Stars formed in two different epochs through different mechanisms
The expert Masafumi Noguchi has calculated the evolution of the Milky Way over a period of 10 billion years, including the "accumulation or accretion of cold flow," a new idea proposed by Avishai Dekel (of the Hebrew University) and his colleagues, about how galaxies collect the surrounding gas during their formation. Although these suggested the formation in two stages for much more massive galaxies, Noguchi has been able to confirm that the same image applies to our own galaxy.
There was a long latent period in which the star formation in the Milky Way ceased. And our natal galaxy has turned out to have a more dramatic story than we originally thought and 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.
The description of Noguchi begins then 10,000 million years ago when the cold gases rushed towards the Milky Way to form the first stars. Then, some 3,000 million years later, everything went wrong. "Shockwaves appeared and heated the gas at high temperatures 7,000 million years ago," the study says. "The gas stopped flowing into the galaxy and the stars stopped forming."
During this unpleasant time, the supernova explosions injected iron into the gas that revolved around 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 the creation of the second generation of stars began, 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 such as oxygen, magnesium and silicon. The other contains a large amount of iron. Recent observations by Misha Haywood (Observatoire de Paris) and his colleagues revealed that this phenomenon prevails over a vast region of the Milky Way. The origin of this dichotomy was not clear. The Noguchi model provides, as we see, an answer to this riddle.
According to Benjamin Williams of the University of Washington and his colleagues, our neighboring galaxy, Andromeda, also formed stars in two different eras. Noguchi's model predicts that massive spiral galaxies such as the Milky Way and the Andromeda Nebula experienced a gap in star formation, while smaller galaxies formed stars continuously. Noguchi hopes that "future observations of nearby galaxies can revolutionize our vision of galaxy formation."
The future
We already know that in about 4,000 million years, the Milky Way will collide with the Andromeda Galaxy in a collapse of cosmic proportions. And, although this event will be very dramatic, it is believed that the differences between the stars are so great that it is likely that the actual number of collisions will be small. Our own solar system probably survives this process-if it still exists-although it seems unlikely that humanity will be present to witness this incredible event.
