Stars memorize rebirth of our home galaxy

August 22, 2018, Tohoku University
Schematic diagram showing two stages of star formation in the Milky Way galaxy according to Noguchi. In upper illustration, blue (cold) and red (hot) indicate gas. The color map in bottom panel shows distribution of the elemental composition of stars calculated by Noguchi's model with the purple line indicating how the elemental composition of the gas changes over time (Credit: M. Noguchi, courtesy of Nature). Overlaid contours show the distribution of solar neighborhood stars observed by APOGEE, a spectroscopic device attached to the 2.5 m telescope of the Alfred P. Sloan Foundation at Apache Point Observatory in New Mexico (Credit: M. Haywood et al. A&A, 589, 66 (2016), reproduced with permission © ESO).

The Milky Way galaxy has died once before, and we are now in what is considered its second life. Calculations by Masafumi Noguchi (Tohoku University) have revealed previously unknown details about the Milky Way. These were published in the July 26 edition of Nature.

Stars in the Milky Way formed in two different epochs through different mechanisms. There was a long dormant period in between, when ceased. Our home galaxy has turned out to have a more dramatic history than was originally thought.

In calculating the evolution of the Milky Way over a 10 billion-year period, Noguchi included the concept of "cold flow accretion," a new idea proposed by Avishai Dekel (The Hebrew University) and colleagues. It describes how collect surrounding gas during their formation. Although the two-stage formation was suggested for much more massive galaxies by Yuval Birnboim (The Hebrew University) and colleagues, Noguchi has been able to confirm that the same picture applies to our own Milky Way.

The history of the Milky Way is inscribed in the of , because stars inherit the composition of the gas from which they are formed—in effect, stars "memorize" the element abundance in gas at the time they are formed.

There are two groups of stars in the solar neighborhood with different compositions. One group is rich in α-elements such as oxygen, magnesium and silicon. The other contains a lot of iron. Recent observations by Misha Haywood (Observatoire de Paris) and colleagues revealed that this phenomenon prevails over a vast region of the Milky Way. The origin of this dichotomy was unclear. Noguchi's model provides an answer to this long-standing riddle.

Model prediction for three different regions of the Milky Way (Credit: M. Noguchi, courtesy of Nature). Contours are from observations by APOGEE (Credit: M. Haywood et al. A&A, 589, 66 (2016), reproduced with permission © ESO).

Noguchi's depiction of the Milky Way's history begins at the point when cold gas streams flowed into the galaxy (cold flow accretion) and stars formed from this gas. During this period, the gas quickly began to accumulate α-elements released by explosions of short-lived type II supernovae. These first-generation stars are therefore rich in α-elements.

When shock waves appeared and heated the gas to high temperatures 7 billion years ago, the gas stopped flowing into the galaxy and stars ceased to form. During this period, retarded explosions of long-lived type Ia supernovae injected iron into the gas and changed its elemental composition. As the gas cooled by emitting radiation, it began flowing back into the galaxy 5 billion years ago (cooling flow) and made the second generation of stars rich in iron, including our sun.

According to Benjamin Williams (University of Washington) and colleagues, 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. Noguchi expects that "future observations of nearby galaxies may revolutionize our view about galaxy formation."

Explore further: The Milky Way's long-lost sibling finally found

More information: Masafumi Noguchi, The formation of solar-neighbourhood stars in two generations separated by 5 billion years, Nature (2018). DOI: 10.1038/s41586-018-0329-2

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5 / 5 (3) Aug 22, 2018
Neguchi's theory is sufficient enough a quantum leap of explanatory power that he might well be in the running for a Nobel Physics nomination.
3 / 5 (2) Aug 22, 2018
The most interesting conjecture I took from this article? Is the question of how different would be the composition of the Type I and Type II planetesimal disks?

Would the earlier generation of planets be metal-poor? Would there have resulted a smaller population of Rocky Worlds?

As a side-note to this. Whatever elemental scarcity that resulted would severely curtail the likelihood of Living Worlds.

Decreasing the possibility & the probability of Old Generation planets evolving intelligent life.

This provides evidence for my speculation that we, Humanity, have the misfortune to be "Sooners" in the time span of the Universe & our Galaxy.

That it seems more & more likely that it will be tens of billions maybe hundreds of billions more years before the widespread of Living Worlds & Space-faring civilizations, will be possible.

And no, I don't care what fantasy themed, comicbook culture you hallucinate about. I want to see multiple verified evidence.
4.2 / 5 (5) Aug 23, 2018
In calculating the evolution of the Milky Way over a 10 billion-year period, Noguchi included the...

Hang on! Noguchi has been continuously calculating this for 10 billion years? Forget about this astronomy; What is his secret for longevity?
blazh femur
5 / 5 (2) Aug 23, 2018
Is anything in the universe NOT alive? Even stars and chemistry evolve!
5 / 5 (1) Aug 24, 2018
bf, interesting conjecture, Using that logic would explain iron "evolving" into rust. Trees "evolving" into petrify. Seashells "evolving" into chalk. Republicans "evolving" into fossils. A logical progression!
5 / 5 (1) Aug 28, 2018
While rocky planets may have been scarce at the time of the first galactic formation, due to the low metallicity (anything higher than Helium, by Astronomer Speak) but there is still opportunity for the Gas Giants to have been formed and evolve, picking up heavier elements as they become more abundant, and then moons when more rocky material abounded.

Science Fiction has explored the idea of life on jovian and super-jovian planets and figure that they would be either a combination of swimmers in the deeps and balloon like 'jellyfish' or sponge filter feeders and photosynthesizers of some sort, direct use of ionization products?

But the possibility of life seems to be high in most cases, at least Earth, which is all we have truly explored so far, and not all of it yet, and we find life most everywhere we go. Even in places we, ourselves cannot survive in, they thrive.

Seems to me life is a basic force in reality, sort of like how crystals can be found everywhere, so with life.
not rated yet Aug 28, 2018
Yep, there's been a whole lot of imaginative speculation. And not a shred of proof. Wishing for alien life has achieved the same results as wishing for fairies and angels and cavemen riding dinosaurs.

And though the evidence plies up like the Rockies against the fabulous and the fantastical? Doesn't matter! The credulous will stubbornly, hysterically even, continue to deny reality.

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