Calculations show that our galactic home, the Milky Way, died at some point in its history. So, we are now in its second life.

Academics at Tohoku University believe the Milky Way experienced a dark age when the formation of new stars dramatically stopped.

Astronomer Masafumi Noguchi from the Tohoku University has made some calculations that reveal some previously unknown details. Researchers published the results in the July 26 edition of Nature.

Mr. Noguchi proposes that the stars in our galaxy were formed in two distinct epochs.

Analyzing The Gases

He analyzed so-called alpha process elements (α-elements) such as oxygen, magnesium, and silicon, thanks to a process called cold flow accretion. When the Universe was still in its early stages, some 10 billion years ago, a significant amount of these gases was abundant in the stars. Therefore, researchers can date cosmic objects by analyzing these gases.

During this period, the gas quickly began to accumulate α-elements released by explosions of short-lived type II supernovae. But after a while, 7 billion years ago, shock waves appeared, thus, heating the gas to high temperatures. Therefore, the gas stopped flowing into the galaxy and stars ceased to form.

During this sad epoch, the explosions of supernovae injected iron into the gas swirling in and around the Milky Way and changed its composition.

As the gas cooled down, it began flowing back into the galaxy some five billion years ago. Thus, the creation of the second generation of stars – including our own sun – began.

However, Benjamin Williams from the University of Washington, who wasn’t involved in this study, says our neighbor galaxy, Andromeda, also formed stars in two separate epochs. Noguchi’s model predicts that massive spiral galaxies like the Milky Way and Andromeda experienced a gap in star formation. Whereas smaller galaxies made stars continuously.

“Future observations of nearby galaxies may revolutionize our view about galaxy formation,” says Noguchi.

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Thumbnail image: Milky Way by NASA’s Spitzer Space Telescope. Credit: NASA/JPL-Caltech/S. Stolovy (SSC/Caltech)