The Milky Way 'Died' Once And The Solar System Is Living Through Its Revival

Outside of Earth's immediate family in the solar system, the planet is part of a much bigger cosmic neighborhood: the Milky Way galaxy.

It turns out the galaxy is hiding a tumultuous past, as new stellar data reveals that the Milky Way has died once and is currently in its second life.

Two Types Of Stars In The Galaxy Spark Interest

A new study published in the journal Nature used the chemical compositions of stars to uncover details on the galaxy's history. After all, the stars' composition should reflect the abundant elements in the galaxy at the time that they were formed.

Two distinct groups of stars based on chemical composition were discovered: one set rich in α-elements such as oxygen, magnesium, and silicon, and another one more rich in iron.

While the reason behind the stark difference between the two groups used to be unclear, Masafumi Noguchi, an astronomer from Tohoku University and lead author of the new study, believes that his new model offers a plausible explanation.

The Milky Way's First, Second Lives

According to Tohoku University, Noguchi analyzed the galaxy's history over a 10 billion-year period, starting from the time cold gas streams entered the galaxy and stars began to form from the gas. This period included many short-lived Type II supernovae, which ejected plenty of α-elements into space. These elements quickly became part of the gas streams and eventually formed the first-generation stars.

Then 3 billion years later, shock waves appeared and heated the gas, which spurred the gas to stop flowing into the galaxy. As a consequence, the formation of stars ceased as well, and the Milky Way "died."

Things remained relatively quiet for 2 billion years until another round of explosions — this time from long-lived Type Ia supernovae — spewed out iron. The gas, at this point cooled down by emitting radiation, began streaming back into the Milky Way, sparking it back to life.

Just like what happened in the earlier days of the galaxy, stars began to form, this time rich in iron. One of these stars is the sun.

What It Could Mean For Galaxy Evolution

According to Science Alert, Noguchi's model could potentially spark a change in evolution models of galaxies.

After all, a previous study published in The Astrophysical Journal in 2017 has revealed that another galaxy, the Andromeda nebula, also had two separate epochs of star formation.

This could mean that smaller galaxies enjoy continuous star formation, but larger ones such as the Milky Way and Andromeda nebula experience a gap of "dead time" in between churning out stars.

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