Jumping into a black hole (ScienceCLic)

A Black Hole’s Event Horizon and an Hour-Long Descent A black hole is a spherical spacetime region whose event horizon separates an exterior from an interior where even light cannot escape. Near Sagittarius A* at the Milky Way’s center, a free fall begins while a ship remains on orbit to watch. The descent will last about an hour and end fatally, revealing how extreme gravity shapes what is seen.

A Blazing Accretion Disk: Radiation, Blue Glow, and Lensing A supermassive black hole captures stars and gas into a dense plasma disk rotating near light speed, heated by turbulence and friction to emit intense visible, ultraviolet, X‑ray, and gamma radiation. Protective assumptions add a heat‑ and radiation‑proof suit with a visor filter so details and background stars remain visible. The disk appears blue in visible light because shorter wavelengths dominate its emission, and one side looks brighter while the opposite is dimmer due to relativistic Doppler shifts from rotation. Strong gravity bends light, so the far side of the disk is lensed into a bright ring around the horizon, and background starlight is slightly blueshifted because our time runs slower than that of distant stars.

Relativistic Aberration and the Fading Disk near the Innermost Stable Orbit During the first ten minutes, motion‑induced aberration makes the black hole appear to shrink even as distance decreases, swinging incoming light toward the forward direction. After that, speed reaches about 4% of light and the black hole swells in view; light ahead brightens while light behind dims, another Doppler effect. Looking back, the ship’s clock appears to tick slower because signals it emits take longer to reach us. Minutes later we traverse the disk; by about 57 minutes the glow fades at the radius where matter can no longer orbit stably and begins spiraling inward rapidly. From there, everything accelerates.

Photon Sphere and the Never‑Seen Crossing Within two more minutes we are half the previous distance to the horizon; beyond the photon sphere any incoming light is fated to fall inward, and exactly on its boundary light can orbit the black hole. To observers on the ship, our image dims and slows, asymptotically freezing at the event horizon because our light takes ever longer to climb out. We, however, cross the horizon about 24 seconds after passing the photon sphere and can never return.

Inside the Horizon: Normal Local Physics and a Compressed Sky Nothing striking marks the instant of crossing; light from distant stars that fell with us still reaches us, and the orbiting ship remains visible though its clock seems slowed. Local spacetime remains nearly flat, so familiar behavior persists, and even light emitted below our eyes can move upward relative to our body to reach our gaze. The black hole’s dark silhouette occupies only about 15% of our field of view, while relativistic aberration compresses the sky ahead and expands it behind. The ship behind us even appears to grow in angular size as motion swings light into our view, yet any signal we send outward can no longer escape.

Spaghettification, Unknown Cores, and Correcting Myths About 30 seconds later, just before the center, tidal gravity surges, stretching and tearing the body into a spaghettified stream as if falling toward a flat, completely black surface while the circle of light intensifies. A tenth of a second after that, the shredded remnants reach the center, where current physics fails: singularities imply infinite curvature, yet many suspect they are artifacts of incomplete theory. Understanding this regime requires unifying gravity with quantum physics, and rotating black holes may introduce multiple horizons and instabilities whose consequences remain unclear. Two common misconceptions are corrected: in visible light the accretion disk is blue (orange images use false color for brightness), and we do not watch the entire history of the universe unfold because Doppler shifts and aberration dominate the view. Many mysteries persist at a black hole’s heart.