Demonska hvezda

A Demon in the Sky

Arab astronomers called it Ra's al-Ghul — the demon's head. Greeks placed it in Perseus's hand as the eye of Medusa's severed head. In Hebrew: Rosh ha Satan. Chinese: Tsi She — a pile of corpses. Every civilization that looked at it saw something evil.

No wonder. Algol blinks. Every 2 days, 20 hours and 49 minutes it dims from magnitude 2.1 to 3.4 — a full step — and returns in ten hours. More reliable than any clock. People saw it for millennia before they understood why.

The Eighteen-Year-Old Deaf-Mute Who Solved It

In 1783, seventeen-year-old John Goodricke — deaf-mute from birth after a bout of scarlet fever encephalitis — published an elegant explanation: Algol blinks because another star orbits it, regularly blocking its light. It was the first correct model of an eclipsing binary in the history of astronomy.

Goodricke didn't have a telescope powerful enough to see the companion. But his logic was flawless: the period is precise, the depth constant, the profile symmetric. The only explanation is geometric.

The Royal Society awarded him the Copley Medal — the highest scientific honor of the era. Two years later, at twenty, he died of pneumonia from nights spent observing in the cold.

Three Stars in One

Algol isn't a double star — it's a triple system. The main pair A-B orbits every 2.867 days: A (B8V, 3.17 solar masses, 13,000 K) is a hot blue star, B (K0IV, 0.70 solar masses) is a cool orange subgiant — but inflated to 3.48 solar radii. The third member C (A7m, 1.76 solar masses) orbits the pair in a wider orbit with a 1.86-year period.

The Algol paradox: the smaller star B is more evolved than the larger A. This makes no sense — larger stars age faster. Solution: B was originally the more massive star but lost mass through transfer to A. It literally 'fattened up' its companion, leaving behind a cool remnant.

Anatomy of a Blink

The primary eclipse lasts 10 hours. The cool subgiant B (4,500 K, larger diameter) passes in front of the hot A (13,000 K), blocking 70% of its light. The 1.27-magnitude drop is visible to the naked eye — to anyone who knows when to look.

The secondary eclipse is shallow (0.05 mag) — hot A passes in front of cool B, but B is so faint that covering it changes almost nothing.

The third star C adds another modulation: its gravity causes precession of the A-B orbit with a ~32-year period. The inclination slowly changes, and with it the eclipse depth. By 2050, the drop will be ~0.1 mag shallower than today.

What TESS Sees

TESS observed Algol across three sectors (18, 58, 85) over 1,845 days. A total of 124,882 measurements. Brightness variation is 50% — a drop from 1.06 to 0.56 normalized flux. This is directly visible to the naked eye.

The dominant period in the periodogram is 1.434 days — exactly half the orbital period of 2.867 days. Why half? Because TESS sees TWO eclipses per orbit: the deep primary (B in front of A) and shallow secondary (A in front of B). Both contribute to the signal at frequency 1/P and 2/P.

Additional harmonics (0.718d = 1/4 P) show that the eclipsing profile is not a sinusoid — it's a sharp V-curve. This means a large diameter of the eclipsing star B and a moderate orbital inclination (81.4°).

A Clockwork on the Entropy Scale

Algol's spectral entropy is eta = 0.434. This places it in the ordered zone — but higher than Epsilon Aurigae (0.124) or Przybylski's Star (0.476, though a different kind of order).

Why not lower? Because Algol's eclipsing curve is not a clean sinusoidal tone — it's a sharp V-shaped curve with harmonics. Each harmonic adds spectral energy to additional frequencies, raising entropy. Paradoxically: the more precise the geometric clockwork, the more harmonics it generates, the higher the entropy.

Algol is a clockwork with a sharp ticking hand — not a smooth pendulum.

Three Thousand Years of Fear

Algol is the only star every civilization named 'evil'. Egyptians recorded it in the Cairo Calendar around 1244 BCE — the first known record of a variable star. Arab astronomers systematically observed it from the 9th century. In European astrology it was 'the most unfortunate star in the sky'.

Why did everyone see a demon? The answer lies in the visual impression: a star that regularly dims and returns, like an eye that closes and opens. In an era when stars were fixed and eternal, this was terrifying. The only star in the sky that blinked.

Where Algol Sits on the Scale

Spectral entropy eta = 0.434 places Algol in the middle of the ordered zone — a geometrically precise eclipsing signal with harmonics from the sharp eclipse profile.

The Eye That Won't Close

Algol has blinked for billions of years. It will blink for billions more — until star B fully dissolves or the system breaks apart. During that time, species that no longer exist saw it, and species that don't yet exist will see it.

John Goodricke understood it after five months of observation. He died two years later, at twenty. But his explanation — geometric eclipsing — stands to this day. The first eclipsing binary, the first detection of mass transfer, the first triple system model. Everything started with the 'demon star'.

Where We Meet Standard Physics

Algol is the prototype of semi-detached eclipsing binaries. The Algol paradox -- the less massive star is more evolved -- is resolved by mass transfer (Crawford 1955). The 2.867-day period is stable over centuries. But TESS data show entropy of 0.434 -- precisely at the order-chaos boundary. Algol does not balance by accident.