Our galaxy has already died once and the stars remember it
The Milky Way had already died once, but it managed to “come back from the dead” and we are now in its “second life” – claims Japanese scientist Masafumi Noguchi. His research has revealed previously unknown details about our galaxy.
Calling a galaxy dead or alive depends on whether stars are formed there. Young galaxies are very bright and a lot of stars are forming there and at a fast rate. The old ones, on the other hand, are devoid of young stars. No new stars form there, which is why they are considered dead. Sometimes galaxies can "come back from the dead", If they acquire enough material and resume stellar processes in theirorcze. It appears that the Milky Way is one such galaxy.
Masafumi Noguchi of Tohoku University based his claims on a study of the chemical composition of stars in our galaxy. A publication on the subject appeared in the pages of the „Nature”.
In much of the Milky Way, stars can be divided into two distinct populations based on their chemical composition. The first group is rich in so-called elements α – oxygen, magnesium, silicon, sulfur, calcium and titanium. The second is less abundant in elements α, But it has much more iron.
According to Noguchi’s calculations’ego, the populations are separated by five billionoin the years. The implication is that the Milky Way has undergone a long period of dormancy, in which theostar formation processes have ceased. Two roThe different populations represent two roThe different periods of star formation, along with the rest period between them.
Based on the cold flow accretion theory, whichora describes howob galaxies collect the surrounding gas, proposed in 2006 by Avishai Dekel of Hebrew University, Noguchi modeled the evolution of the Milky Way over a period of 10 billionoin years. Originally, the Dekel model was proposed for much larger galaxies, suggesting that massive galaxies form stars in dwoch stages. But because of the dichotomy of the chemical composition of its stars, Noguchi believes that this applies to roof the Milky Way.
The chemical composition of stars depends on the gasow, with ktorich are forming. The early Universe lacked certain elementsow – if only heavy metals. That’s because they originated in stars and spread through the Universe when those stars went supernova.
In the first stage, Noguchi suggests, the galaxy accumulated cold gas from outside the. This gas merged to form the first generation of stars. After about 10 million years, which is relatively krotkim period in the cosmos, someore of these stars died in a type II supernova. This event scattered the elements α throughout the galaxy, whichore entered poLater in the composition of new stars.
When shock waves appeared and heated the gas to high temperatures around 7 billionow years ago, the gas stopped flowing into the galaxy and stars stopped forming. During a gap of about 2 billionoin years there was a second round of supernovae. However, these were already other supernovae, type Ia, ktore usually occur when a star reaches an age of more than a billion years.
The second wave of supernovae enriched the galaxy with iron. When the gas has cooled sufficiently to begin forming stars again – about 5 billionow years ago – stars already consisted of a much higher proc. Iron than earlier generations of. This second generation also includes our Sun, ktore is about 4.6 billion years old.
The model presented by the compositeoł Noguchi’s finding appears to be consistent with recent research on our closest galactic neighbor, Andromeda, whichora is considered to be of a similar class and size as the Milky Way. Last year, a paper was published indicating that in Andromeda the stellar processes of theoThe experiments were held in dwoch stages, with a relatively quiet period between them.