Stars memorize rebirth of our home galaxy

Date:

Share post:

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 journal Nature.

Stars memorize rebirth of our home galaxy
The Milky Way galaxy [Credit: Tohoku University]

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




Noguchi has calculated the evolution of the Milky Way over a 10 billion year period, including “cold flow accretion”, a new idea proposed by Avishai Dekel (The Hebrew University) and colleagues for how galaxies 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.

Stars memorize rebirth of our home galaxy
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, Nature 2018]. 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 history of the Milky Way is inscribed in the elemental composition of stars because stars inherit the composition of the gas from which they are formed. Namely, 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 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.

Stars memorize rebirth of our home galaxy
Model prediction for three different regions of the Milky Way [Credit: M. Noguchi, Nature 2018]
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 contain 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 the elemental composition of the gas. 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 nebula, also formed stars in two separate epochs. Noguchi’s model predicts that massive spiral galaxies like the Milky Way and Andromeda nebula 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”.

Source: Tohoku University [August 21, 2018]

ADVERTISEMENT

spot_img

Related articles

Astrophysicists find when galaxies rotate, size matters

A team of astrophysicists analysed 1418 galaxies and found that small ones are likely to spin on a...

Something's amiss with aliens and arsenic

The stage was set by a coy news release from NASA that hinted at a discovery tied to...

New research looks at how ‘cosmic web’ of filaments alters star formation in galaxies

Astronomer Gregory Rudnick sees the universe crisscrossed by something like an interstellar superhighway system. Filaments — the strands...

Cold, dry planets could have a lot of hurricanes

Nearly every atmospheric science textbook ever written will say that hurricanes are an inherently wet phenomenon -- they...

Iron volcanoes may have erupted on metal asteroids

Metallic asteroids are thought to have started out as blobs of molten iron floating in space. As if...

What ingredients went into the galactic blender to create the Milky Way?

In its early days, the Milky Way was like a giant smoothie, as if galaxies consisting of billions...

Comet’s trip past Earth offers first in a trio of opportunities

Comet hunters still have a chance to see comet 45P/Honda-Mrkos-Pajdusakova in the next few days using binoculars or...

The last survivors on Earth

The world's most indestructible species, the tardigrade, an eight-legged micro-animal, also known as the water bear, will survive...