Astrophysics 101

An Interactive Introduction

Welcome, Future Astrophysicist!

This interactive tutorial is designed to introduce you to some of the fundamental concepts in astrophysics. We'll explore the vastness of space, the mechanics of celestial bodies, the lives of stars, the grandeur of galaxies, and the very fabric of our expanding universe. Each section includes a brief explanation and a simple 3D simulation to help you visualize these amazing phenomena. Let's begin our journey through the cosmos!

1. Celestial Mechanics: The Dance of Planets

Gravity is the invisible force that governs the motion of everything in the universe, from apples falling to Earth to planets orbiting stars. Johannes Kepler, building on earlier work, formulated laws describing planetary motion. In essence, planets move in elliptical orbits around their star, with the star at one focus of the ellipse. Planets also sweep out equal areas in equal times, meaning they move faster when closer to their star and slower when farther away.

Simulation: A planet (blue) orbiting a central star (yellow). Use your mouse to rotate the view.

2. Stellar Evolution: The Lives of Stars

Stars are not eternal; they are born, live for millions or billions of years, and eventually die. They form from vast clouds of gas and dust called nebulae. Gravity pulls this material together, heating it until nuclear fusion ignites in the core, marking the birth of a star. The star then enters its main sequence phase, fusing hydrogen into helium. What happens next depends on the star's mass. Lower-mass stars like our Sun will eventually swell into red giants, shed their outer layers to form planetary nebulae, and leave behind a dense core called a white dwarf. Massive stars live shorter, more dramatic lives, ending in spectacular supernova explosions that can leave behind neutron stars or black holes.

Simulation: A highly simplified visual representation of a star's life stages. Observe changes in size and color.

3. Galaxies: Cosmic Islands

Galaxies are colossal systems containing billions or even trillions of stars, along with gas, dust, and dark matter, all bound together by gravity. They come in various shapes and sizes, including spiral galaxies (like our Milky Way), elliptical galaxies, and irregular galaxies. Spiral galaxies are characterized by a central bulge, spiral arms where new stars are often formed, and a surrounding halo. Understanding galaxies helps us comprehend the large-scale structure of the universe.

Simulation: A particle system forming a rotating spiral galaxy. Use your mouse to rotate the view.

4. Cosmology: The Expanding Universe

Cosmology is the study of the origin, evolution, and ultimate fate of the universe. One of the most profound discoveries in cosmology is that the universe is expanding. In the 1920s, Edwin Hubble observed that distant galaxies are moving away from us, and the farther away they are, the faster they are receding. This is known as Hubble's Law. This expansion implies that the universe was much smaller and denser in the past, leading to the Big Bang theory.

Simulation: Particles moving away from a central point. Notice how particles farther away appear to move faster.