Reconstructing the Galactic history with a new tree

Reconstructing the Galactic history with a new tree

After intensive thinking, we have managed to put together a new tree to keep advancing towards merging Galactic evolution with phylogenetics

Our 2017 tree paper started paying off, my recognition as one of the Scientist-to-Watch by Science News in 2018 made the general public excited about Darwin’s theories applied to Space. I had to make the next step into a paper.  I was getting impatient, the public kept asking me about next steps.  Since 2017 with Payel Das and Robert Foley, all authors of the 2017 paper,  read and discussed, and read, and discussed, but we hadn’t managed to sit down and do actual work on a next step.

Until Holly Jackson came to visit the Astronomy Nucleus from June to August in 2019, as part of the MISTI exchange programme for undergraduate MIT students. Restless, Holly developed one algorithm after the next one, using different packages, different programming languages, different criteria, until the next stellar tree that could help us progress in our understanding of the evolution of the Milky Way was done. 

The tree could be used to reconstruct a very cool story, but we had to be confident about our results, and an undergraduate in computer science with astronomers are no experts in tree building systematics. We needed the input from experts. In October 2019, Keaghan Yaxley, Rob's PhD student in biology from Cambridge University, came over to Chile. We made further tests on Holly’s tree, and had endless discussions about how trees are built and what they tell us. Douglas Boubert, from Oxford University, and expert on Galactic dynamics, also had come to visit - that was a perfect coincidence for mentally training our natural understanding about the evolution of the Galaxy. 

The last day of their visit (Friday 18 of October 2019) we were in trance concluding our exciting new learning, and the Social boom leading to fire in streets and subway of Santiago were of secondary importance. Once we were too interrupted by the noises of alarms and police and helicopters outside, phone calls and messages telling “leave work immediately”, we decided to head back to hotels and home, so we walked for about 4-5 hours in the middle of the protests, a bit shocked to be back in reality.  

The protests quickly lead to curfews and suffering of Chilean people, so shortly they became my priority. Also shortly, in November 2019, that very 2017 tree paper put me as one of the 100 TIME Next, a list that highlights 100 raising leaders in their fields by TIME magazine, reminding me that we really had to conclude on that new tree we were working on. 

So we had to focus, and Holly came to Chile in January 2020 again. We systematically went through all the steps and started the draft paper which now, we proudly have concluded. 

Our new tree contains 4 times more stars, and 4 times more chemical abundance ratios which are used as our DNA proxy than the 2017 tree. Holly did an amazing job improving the procedure to the current one. Our new tree tell us a story which agrees remarkably well with the literature, though our story can be told from one diagram only: the phylogeny.  

The figure shows our final tree which has been manipulated by my sister Carolina who is a great artist. The Sun is highlighted as a special star.  With the stars coloured by their age (blue being old, pink being young) we can reconstruct the following history for the solar neighbourhood: the first stars formed long time ago in the Galactic disk, and quickly an event disturbed the evolution by changing the timescales significantly producing large number of stars simultaneously across the disk, represented by some chaos in the circular part. Such an event could be the merger with another galaxy, or simply the appearance of another class of stellar explosions. The disk managed after the event to reach an equilibrium and evolve relatively quietly until today. 

To constrain more the properties of the event altering the evolution of the disk, we must continue working and making better trees. But that are next steps. 

For more information, preprint here