Scientific Computing, Galaxies & Your First-Year STEM Roadmap

Speaker’s Background & Daily Work

  • Professional identity
    • Self-described scientific computer coder who studies galaxies.
    • Prefers coding and data analysis over social interaction; finds joy in “just doing Python for years.”
  • Core research workflow
    • Collect digital telescope images and spectra (breaks starlight into a rainbow).
    • Runs custom scripts (with commented code) to infer galaxy composition, structure, evolution.
    • Teaches a course on scientific computing next semester, focused on coding for a scientific goal, not for software-engineering elegance.

Scientific Computing vs. Computer Science

  • Scientific Computing
    • Goal-oriented: code is a tool to answer a physical question, make a plot, test a hypothesis.
    • Code quality acceptable if it gets the science right.
  • Computer Science / Software Engineering
    • Focus on algorithms, computational efficiency, code style, scalability.
    • A computer scientist may dislike an astronomer’s “quick-and-dirty” scripts; astronomers may feel CS rigor is unnecessary overhead for exploratory work.
  • Takeaway: two distinct cultures; learn which standards matter in which context.

First-Year Coursework vs. Research Mind-set

  • Intro STEM classes
    • Physics, calculus, etc. present well-posed problems with known answers.
    • Students are evaluated on reaching that single correct solution.
  • Research reality
    • Often no known answer—and sometimes not even a known question.
    • Success requires formulating meaningful questions, tolerating ambiguity, self-direction.
  • Student types
    • “Classroom stars” may feel uneasy in open-ended research.
    • Strugglers in class sometimes thrive in research creativity.
  • Action item for students: Over next 1–21\text{–}2 years, discover whether you fit better in an engineering/problem-set environment or an open research environment.

Astrophysics vs. Astronomy (Terminology)

  • Historically
    • Astronomy: observations, telescope operation.
    • Astrophysics: theoretical modeling, simulations, coding.
  • Modern practice: roles blur; terms largely interchangeable.
  • Personal joke: speaker chooses term “depending on if I like you.”

Spectroscopy & Data Products

  • Spectrum = brightness vs. wavelength; reveals chemical composition, temperature, velocity.
  • Example shown: stellar spectrum image (details skipped in talk).
  • Workflow: capture spectrum ➔ digital file ➔ parse with Python ➔ derive metallicity, redshift, etc.

Telescope Optics & “Light Buckets”

  • Your eye ≈ 2 cm2\,\text{cm} diameter telescope (“light bucket”).
  • Larger mirror ⇒ gathers more photons per second ⇒ detects fainter objects.
  • Sharpness (angular resolution) depends on mirror diameter and design; faintness and sharpness often trade off.
  • Atmospheric seeing limits sharpness from ground; space telescopes remove atmosphere “wiggle,” yielding crisper images.

Rubin Observatory (LSST) Wavelength Coverage

  • Operates primarily in optical band (visible + a bit of near-IR) because Earth’s atmosphere is largely transparent there.
  • Infrared & ultraviolet mostly blocked; require special instruments or space telescopes.

Galaxy Formation Simulations & Dark Matter

  • Hierarchical model: small halos merge into larger galaxies.
  • Simulation endpoints often represent present-day universe.
  • Changing dark-matter properties (e.g., “warm” vs. “cold”) alters satellite-galaxy counts and large-scale structure.
  • Model with too few satellites is observationally ruled out (Milky Way hosts ≈70\approx 70 known satellites).
  • Research strategy: propose variants, run sims, confront every model with multiple observational constraints.

Dark Matter: Properties & Detection

  • Hypothesis: non-luminous particles interacting via gravity alone.
  • Local flux estimate: ∼105\sim 10^5 particles/s cross a human-sized area.
  • Direct-detection experiments
    • Huge underground vats (xenon or argon) shielded from cosmic rays.
    • Look for rare nuclear recoils that flash light.
    • Expected rate: ≈ 44 events/year in tonne-scale detector.
  • Must satisfy many empirical tests before replacing current paradigm; peer review and reproducibility essential.

Cosmic Expansion vs. Local Gravity

  • Universe expands, but gravitational binding dominates on small scales.
    • Inside Milky Way or Local Group (Milky Way + Andromeda) expansion is negligible.
    • Expansion matters on hundreds of Mpc scales (“halfway across the universe”).
  • Everyday paradox: galaxies merge locally even while universe globally stretches.

Satellite Galaxies & Mergers

  • Milky Way has ≥70\ge 70 satellites; Andromeda is a massive companion.
  • Milky Way–Andromeda merger in ∼4×109\sim 4\times10^9 years; affects night sky but unlikely to cause stellar collisions due to vast inter-stellar spacing.

What Is a Galaxy? (Evolving Definition)

  • Classical definition: gravitationally bound collection of stars + dark matter that formed together.
  • Recent ultra-faint discoveries blur line between galaxy and star cluster.
    • Record faint system: total luminosity ∼16L⊙\sim 16 L_{\odot} yet dynamically a galaxy.
  • Active research topic; sometimes centerpiece of conferences and PhD theses.

Fundamental Physics Reminder

  • Newtonian gravity: F∝1r2F \propto \dfrac{1}{r^{2}}.
  • Modifying exponent (e.g. F∝1r1.8F \propto \dfrac{1}{r^{1.8}}) breaks many well-verified observations.
    • Simulations with altered law fail to reproduce planetary or galactic systems.

Black Holes at Galactic Centers

  • Virtually every large galaxy hosts a super-massive black hole (SMBH).
  • Evidence
    • Stellar orbits measured around invisible massive object (e.g., 4×106 M⊙4\times10^6\,M_{\odot} SMBH at Milky Way center).
    • 2020 Nobel Prize recognized this work (Genzel & Ghez).
  • Categorized as “normal” matter end-product of stellar evolution, not exotic dark matter.

Human Spaceflight: Fuel & Radiation Constraints

  • Rocket-science without math insight
    • Rocket equation shows exponential fuel demand; spacecraft become “all tank.”
    • Star Wars ships implicitly possess “infinite gas”—not plausible with current physics.
  • Mars habitability challenges
    • No global magnetic field ➔ high cosmic-ray dose.
    • Study suggests lethal exposure after ≈4\approx 4 years without heavy shielding.
    • Distance scale analogy: if Earth–Moon fits on your hand, Earth–Mars ≈ walk across campus.
    • Robotic missions are far easier; sustained human habitation “not even remotely close yet.”

Undergrad Research Opportunities & Advice

  • First year: focus on passing Physics I/II\text{Physics I/II} & calculus; use tutoring resources.
  • Yale (and many universities) provide paid summer research positions.
    • Seek mentors, knock on doors, email faculty, contact Director of Undergraduate Studies (DUS).
    • Typical timeline: start summer after first year; semesters often too busy.
  • Build relationships early (first-year seminars, office hours) to secure future recommendation letters.

Personal Anecdotes on Academic Trajectory

  • Earned C+ in intro physics yet succeeded by placing herself among higher-level peers—thrives when surrounded by excellence.
  • Graduate-school path
    • Initially enrolled at New Mexico State (not a top program for her needs).
    • Dropped out, networked serendipitously with Space Telescope Science Institute director, reapplied.
    • Joined UC Santa Cruz—one of the premier astronomy PhD programs; retook GRE, “crushed it.”
  • Moral: seek environments that challenge you; being the best in a weak cohort may hinder growth.

Miscellaneous Q&A Nuggets

  • Why “Milky Way”? Uncertain etymology—encouraged students to “go wiki it.”
  • Star Wars tech realism: hyper-fuel & unlimited refueling are fictional conveniences.
  • Definitions recap: visible light ≈ optical band; cold vs. warm dark matter affects small-scale structure.
  • Ratio analogy: Earth–Moon vs. Earth–Mars travel distances.
  • “Can of humans” joke on sending people to Mars; complexity far exceeds robotic probes.
Key Numbers & Equations Reference
  • Eye aperture: ∼2 cm\sim 2\,\text{cm}.
  • Milky Way satellites: ≈70\approx 70.
  • SMBH mass (Milky Way): ∼4×106 M⊙\sim 4\times10^{6}\,M_{\odot}.
  • Dark-matter flux: ∼105\sim 10^{5} particles per room per second.
  • Xenon detector expectation: ∼4\sim 4 dark-matter events per year.
  • Milky Way–Andromeda merger timeline: ∼4×109 yr\sim 4\times10^{9}\,\text{yr}.
  • Rocket-equation concept: exponential fuel requirement m<em>fuel∝eΔv/I</em>spm<em>\text{fuel}\propto e^{\Delta v/I</em>{sp}} (mentioned qualitatively).

Action Items for Students

  • Decide where you fall on the problem-solving ↔ question-finding spectrum.
  • Complete foundational physics & math early; use tutoring.
  • Engage faculty in seminars and office hours; cultivate mentors.
  • Apply for summer research funding; start emails in spring.
  • Place yourself in challenging peer groups to spur growth.