PLAIN/TEXT

TRANSMISSION: DAILY ●

ISSUE 28/30 · PHYSICS

~4 MIN

NOW / HUBBLE + WEBB · WEEK 05 — FROM RULES TO EMERGENCE

The radius of no return

START HERE

Concentrating mass into a smaller region lets you get closer to it, where its gravitational effects become stronger.

A black hole is a region where gravity traps every outward path. Its event horizon is the boundary beyond which even light can no longer return to the outside universe.

The horizon is not a solid shell, but its size gives us a concrete way to picture the scale of a black hole.

/ WHY NOW

In July 2026, NASA reported a black hole in the Omega Centauri star cluster with a mass about 4.46 times the Sun’s. A mass written in ‘Suns’ is still hard to picture.

For an ideal non-spinning black hole, a rule from gravity translates that mass into an event-horizon radius: about three kilometres for each solar mass.

/ THE IDEA

The event horizon is the boundary past which even light cannot return to the outside universe. It is not a solid surface sitting in ordinary space.

For an ideal non-rotating, uncharged black hole, the Schwarzschild solution says radius grows directly with mass. Double the mass and the horizon radius doubles.

THE FORMAL IDEA

rₛ = 2GM ÷ c² ≈ 3 km × (M ÷ Sun’s mass)

rₛ = Schwarzschild event-horizon radius

G = gravitational constant; M = black-hole mass

c = speed of light

RUN THE TINY EXAMPLE

Picture the Omega Centauri black hole

Mass M = 4.46 solar masses

Radius ≈ 3 km × 4.46 ≈ 13.4 km

Double the mass to 8.92 Suns → radius doubles to about 26.8 km

The calculation turns an abstract mass estimate into a horizon with roughly city-scale radius. It also makes the linear prediction visible: twice the mass gives twice the radius in this ideal model.

/ SO WHAT?

This linear rule converts black-hole catalogues into physical scale. The newly found object is several times heavier than the Sun, yet its idealised horizon radius is only about thirteen kilometres.

ONE CAVEAT

Astrophysical black holes generally spin, changing horizon geometry and the detailed relationship. The three-kilometre rule is for the ideal Schwarzschild case and describes a radius, not a material edge.

KEEP THIS

For a simple black hole, each solar mass adds roughly three kilometres to the radius of no return.

SOURCE TRAIL

[1] NASA — Hubble and Webb find Omega Centauri black hole (13 July 2026)

NEXT: A function that delegates to itself

HARD IDEAS. PLAIN TEXT.

You are receiving this because you asked for one clear computer-science or physics idea each day.

UNSUBSCRIBE · VIEW IN BROWSER
Plain/Text / Brickston Consulting · 30 N Gould St Ste N, Sheridan, WY 82801 US · knowledge@plaintext.click