B How Old is the Milky Way Galaxy?

[Simon Peach]

It seem incredulous to me that the Milky Way was formed just 13.775 million years after the start of the universe. If this is correct was it in the form that it is today?

 

[Bandersnatch]

All galaxies are thought to have formed from the primordial gas collapsing gravitationally. This process is in some sense ongoing, but it has long since consisted predominantly of smaller clumps merging into larger ones - that is to say, of smaller galaxies colliding to form larger ones.
The exact process - meaning sizes and number of proto-galaxies - by which our galaxy has formed may never be known, because the collisions scramble information about pre-collision state. But the model in general is not that complicated.
The video below shows a simulation of a galaxy similar to the Milky Way being formed. It starts with the primordial gas being roughly homogeneously distributed, before collapsing upon itself. Helpful annotations explain the process:

 

[stefan r]

It seem incredulous to me that the Milky Way was formed just 13.775 million years after the start of the universe. If this is correct was it in the form that it is today?

Wikipedia says 150 million years to form the first stars. Before that it was just gas.

The disc of the milky way forms 8 to 10 billion years ago. So structurally things were very different. It is possible that the dividing lines between galaxy groups was already clear at 13 million years. You could mark off a clump of gas and say this part is heading for the local group and will merge into the milky way. Gas on the other side of the plane will drift toward Maffei group. That would not have any of the features we associate with galaxies. No stars, bars, or spirals.

 

[alantheastronomer]

It seem incredulous to me that the Milky Way was formed just 13.775 million years after the start of the universe. If this is correct was it in the form that it is today?

You're confusing 13.775 billion years which is the present day age of the Universe since the start of the Big Bang, with the age of the Milky Way galaxy, which is 13.2 billion years. That's basically the age of the globular clusters, which formed first. Then it took a few billion years for the disk to settle down and start forming stars.

 

[TEFLing]

You're confusing 13.775 billion years which is the present day age of the Universe since the start of the Big Bang, with the age of the Milky Way galaxy, which is 13.2 billion years. That's basically the age of the globular clusters, which formed first. Then it took a few billion years for the disk to settle down and start forming stars.

I understand there's evidence of a major disruption from 10-8 Gya during which few new stars formed, perhaps due to a collision and merger of some sort

 

[alantheastronomer]

I understand there's evidence of a major disruption from 10-8 Gya during which few new stars formed, perhaps due to a collision and merger of some sort

That's interesting! Do you have a link to a source? My knowledge of recent advances is woefully inadequate...

 

[phinds]

It seem incredulous to me that the Milky Way was formed just 13.775 million years after the start of the universe. If this is correct was it in the form that it is today?

Interesting. I had never before heard of a galaxy being incredulous.

 

[TEFLing]

That's interesting! Do you have a link to a source? My knowledge of recent advances is woefully inadequate...

http://www.stsci.edu/~tremblay/Research1.html
https://www.researchgate.net/figure/Stellar-ages-in-the-GES-Milky-Way-field-sample-in-the-thin-disc-in-blue-and-in-the-open_fig1_317100616
https://www.newscientist.com/articl...nce-has-the-milky-way-formed-stars-in-bursts/

Figure 2. Our derived stellar formation history for the Galactic disk in 1 Gyr total age bins (black histogr

 

[TEFLing]

https://www.scmp.com/news/world/eur...on-course-nearby-galaxy-set-hit-milky-way-say

this article appears to imply a major merger. Interaction event with the large magellanic cloud. About a billion years ago. Perhaps that could account for the burst of star formation over the past billion years as reported by the new scientist magazine:

"Nonetheless it is intriguing that if the Milky Way did have two bursts of star formation, they match similar bursts in the Magellanic Clouds, the two largest satellite galaxies of the Milky Way (see ‘The Galactic empire’, New Scientist, 1 December 1990). The Magellanic Clouds have formed lots of stars in the past 100 million years; they also did so between 3 and 5 billion years ago.

Some astronomers think that the Magellanic Clouds get stirred up when they pass close to the Milky Way. This turbulence then induces star formation in the Clouds. If the bursts in the Milky Way are real – a big if – then the Magellanic Clouds may also do the same to the Milky Way."

 

[TEFLing]

https://www.space.com/42901-milky-way-galaxy-large-magellanic-cloud-crash.html

"Even though the LMC is currently heading away from the MW, dynamical friction acting on such a heavy galaxy will cause its orbit rapidly to lose energy and, approximately a billion years from now, to turn around and head towards the center, where it is destined to merge in another 1.5 billion years or so," the researchers wrote in the new paper, which was published online Friday (Jan. 4) in the journal Monthly Notices of the Royal Astronomical Society."

 

[alantheastronomer]

I read the Monthly Notices article, and the model they used to estimate the amount of dark matter in the LMC is based on an extrapolation of dark matter estimated to be found in other external galaxies, while the estimate that was found to be much less, based on actual observations of the LMC was minimized. This leads me to be somewhat skeptical of their prediction of a merger in a billion and a half years...

 

[TEFLing]

https://phys.org/news/2019-01-milky-neighbors-pace.html

 

[alantheastronomer]

https://phys.org/news/2019-01-milky-neighbors-pace.html

This is just a press release reiterating the conclusions of the MNRAS journal article...