I’m a second-year PhD student in computer science at UC Berkeley advised by Ben Recht.
Previously, I received my Bachelor’s in electrical engineering and computer science from MIT and my Master’s in human rights studies from Columbia University.
I work on on interdisciplinary applications of computer science, from
astrophysics to history to politics.
My research has been featured in over 100 media outlets and has been
liked and shared tens of thousands of times on social of media.
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03 COSMIC EVOLUTION2019-21
A stylized version of a stellar evolutionary tree from our most recent publication. Picture design by Carolina Jofré.
BACKGROUND:
Essentially, every single star that exists in the universe today (as long as it is not actively exploding) is a blueprint of the chemistry of the specific part of the galaxy where that star was born, at the time of its birth. When a star dies, it donates its processed chemical material back to into galaxies to be recycled into the next waves of star formation. Over the span of Gigayears, many stars explode and produce more and new elements. This began during the Big Bang -- where the first elements hydrogen and helium were produced. As a result, each star is like a fossil of the exact chemical makeup and range of elements available at the time of its birth.
Astronomers have studied the chemical evolution of stars for some time now in an attempt to discover the relationships between stars. Unfortunately, most data in astronomy has incredibly high uncertainties, so astronomers must reconcile how to maximize the potential knowledge that can be gained from this uncertain data. So far, attempts to model and simulate chemical evolution have attempted to do this by creating synthetic stellar populations and approximating Galatic evolution events. However, these models face quite the challenge – approximating quite literally the most complex entropy-increasing system in the universe – and, as a result, often produce inaccurate predictions
This drove us to find an alternative, or possibly auxiliary, approach to modeling Galactic chemical evolution, drawing techniques from a well-developed field of biology that solves a parallel problem.
APPROACH:
After the publication of Darwin’s the Origin of Species in 1859, it took almost a century for DNA to be recognized as the
mechanism for biological inheritance. It is a molecule that allows the
traits of an organism to be passed from one generation to the next. Yet
without any knowledge of DNA, Darwin understood that heritability
underpinned descent with modification,
which in turn underpinned evolution. He depicted the patterns of
descent among organisms as an evolutionary tree. If there is some
heritability in a system, then a tree of descent is an extremely apt
model. Today, in all branches of biology, trees – now more generally
known as phylogenies – are a major tool for analysing evolutionary
histories.
At first sight, it might seem that
the underlying principle of heritability necessary for a phylogenetic
analysis does not occur in galaxy evolution. After all, they have no DNA
or genes. However, heritability does play a role in the chemical
evolution of galaxies. The stars forming and dying in galaxies are both
carriers of chemical information and responsible for the modification
and evolution of galactic chemical composition. Indeed, stars are the
main producers of chemical elements heavier than helium in the Universe.
In each star formation episode, stars of a wide range of masses are
born. The massive stars die quickly and eject new heavy elements into
the existing interstellar medium (ISM), hence modifying the galactic
chemical composition. This new material collapses to form gas clouds,
which form new generations of stars. These stars inherit the chemical
composition of the dead stars.
The field of phylogenetics has been studied and developed by biologists for almost two centuries and has grown into a highly complex field, where researchers work with millions of DNA data points on thousands of samples driven by complex statistical models. However, the first evolutionary biologists formed trees from small samples of taxa, and characterized their traits by continuous, decimal measurements (not unlike chemical abundances). No one knew what DNA was yet. There were no prior assumptions about evolutionary rate. There was no way to track significant evolutionary disruptions or massive bursts of diversification (like the Cambrian Explosion). The adaptability of these original mathematical models incrementally revealed these interesting features of evolution.
This is consequently, what makes phylogenetics so well-suited for modeling stellar evolution. Every star is related, just how every species is related, even if you have to trace their origins all the way back to the Big Bang.
From 2019 to 2021, I developed pipelines to generate phylogenetic trees and map the chemical evolution of stars in the galaxy based on their elemental makeup. I collaborated with
Dr. Paula Jofré
of the University of Diego Portales in Santiago, Chile.
In 2017, Dr. Jofré was the first to link concepts in biological evolution like DNA and parental genealogy to cosmic evolution.
We developed a
robust methodology for creating a phylogenetic tree, a biological tool
used for centuries to study heritability. Combining our phylogenetic methods with
information on stellar ages, we reconstructed the
shared history of 78 stars in the solar neighbourhood.
We performed a robust stability analysis, to confirm our tree has real phylogenetic signal, as typical in studies of evolutionary biology. Additionally, we performed an analysis of the stellar kinematics and chemistry, to confirm these patterns match those shown in the phylogeny, as typical in studies of stellar chemical evolution. Finally, we compared our evolutionary tree to real astronomical theories; our tree which, given no prior assumptions about the internal and external events in Galactic chemical evolution, reveals evidence for existing astrophysical theories.
We demonstrate the immense
potential of a phylogenetics to study cosmic evolution, where with borrowed techniques from biology we can study
key processes that have contributed to the evolution of the Milky Way.
PUBLICATIONS:
Using heritability of stellar chemistry to reveal the history of the Milky Way
Holly Jackson, Paula Jofré, Keaghan Yaxley, Payel Das, Danielle de Brito Silva, Robert Foley
Monthly Notices of the Royal Astronomical Society, 2021
Paper
arXiv
Traits for chemical evolution in solar twins: Trends of neutron-capture elements with stellar age
Paula Jofré, Holly Jackson, Marcelo Tucci Maia
Astronomy & Astrophysics, 2020
Paper
arXiv
SELECTED PRESS:
Interview with MIT News