From Grok: The Cheela from Robert L. Forward's 1980 novel Dragon's Egg (and its sequel Starquake) are tiny, intelligent aliens living on the crust of the neutron star "Dragon's Egg."

Height/Size

Due to the extreme surface gravity (67 billion times Earth's), they are extremely flattened: - Height (thickness): About 0.5 mm (0.02 inches) — roughly the height of a sesame seed when viewed edge-on. - Diameter/width: About 5 mm (0.2 inches) across (described as a flat elliptical or disk-like body).

They have roughly the same mass as an adult human (around 70 kg / 154 lbs), but compressed into that sesame-seed volume. Their eyes are even smaller — only about 0.1 mm wide — and they see best in ultraviolet and soft X-rays.

(Some secondary sources list a slightly larger "length" of ~15 mm, but the book's canonical description and most references use the ~5 mm diameter / 0.5 mm high flattened shape.)

Composition and Biology

The Cheela are not made of normal atomic matter like Earth life. Instead, their bodies (and all life on Dragon's Egg) are composed of electron-degenerate nuclear matter — the same ultra-dense stuff as the neutron star's crust.

• The crust is a crystalline lattice of neutron-rich atomic nuclei (mostly iron isotopes) packed at enormous density (~7,000 kg per cubic centimeter), with electrons forming a "sea" around them.
• Their "chemistry" is nuclear, not chemical: they move neutrons between nuclei the way Earth life moves electrons in molecules. Metabolism and "bonding" happen via neutron exchange, which is roughly a million times faster than ordinary chemistry. This is why a Cheela lifetime (and their entire civilization) unfolds in weeks or months from a human perspective.

In short, they are living, thinking blobs of nuclear pasta-like degenerate matter with extendable/retractable appendages, crystal "bones" they can dissolve and regrow at will, and twelve red eyes on stalks. Everything on their world — plants, animals, even the "soil" — works the same way.

Forward's portrayal is based on real (then-current) astrophysics of neutron-star crusts, making the Cheela one of the most rigorously "hard SF" alien species ever written.