Moiya McTier

An Autobiography of Our Galaxy

The Milky Way

Astrophysicist and folklorist Dr. Moiya McTier channels The Milky Way in this approachable and utterly fascinating autobiography of the titular galaxy, detailing what humans have discovered about everything from its formation to its eventual death, and what more there is to learn about this galaxy we call home. After a few billion years of bearing witness to life on Earth, of watching one hundred billion humans go about their day-to-day lives, of feeling unbelievably lonely, and of hearing its own story told by others, The Milky Way would like a chance to speak for itself. All one hundred billion stars and fifty undecillion tons of gas of it. It all began some thirteen billion years ago, when clouds of gas scattered through the universe's primordial plasma just could not keep their metaphorical hands off each other. They succumbed to their gravitational attraction, and the galaxy we know as the Milky Way was born. Since then, the galaxy has watched as dark energy pushed away its first friends, as humans mythologized its name and purpose, and as galactic archaeologists have worked to determine its true age (rude). The Milky Way has absorbed supermassive (an actual technical term) black holes, made enemies of a few galactic neighbors, and mourned the deaths of countless stars. Our home galaxy has even fallen in love. After all this time, the Milky Way finally feels that it's amassed enough experience for the juicy tell-all we've all been waiting for. Its fascinating autobiography recounts the history and future of the universe in accessible but scientific detail, presenting a summary of human astronomical knowledge thus far that is unquestionably out of this world.

In Chapter 3, we zoom out from planets to get a better understanding of the dynamical and chemical evolution of the Milky Way, which are both crucial for constraining the Galaxy's GHZ. We use the Extreme Deconvolution Gaussian Mixture Model to identify overdensities of stars in both velocity and action space, called moving groups and orbit groups, respectively. Velocities and actions are calculated using data from the early third data release of the Gaia mission. When we analyze the chemical abundance distributions of these moving and orbit groups with GALAH DR3 data, we find that using velocities alone to define moving groups, or even using velocities and actions together, yields an incomplete view of the underlying density distributions and their origins. Our chemical analysis also confirms expected chemical evolution trends in the Solar neighborhood. Next, we explore the effects of stellar motion and galactic dynamics on the habitability of planets in different regions of the Galaxy.

Moiya McTier

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