TZ Star

Kind: A Thorne–Żytkow object — a stellar body with a neutron star core. In-universe the class is infrastructure as much as astrophysics: hollowships use them for slingshot acceleration, and unexplained artifacts keep exiting them at relativistic speed. Discovered/invented: Natural object; the type is real (Thorne–Żytkow objects are a theoretical class named for the two astrophysicists who proposed them). The empire’s operational use of them for Hollowship slingshot is the invented part. Based on: A neutron star embedded inside a normal stellar envelope.

Summary

The surgeon explains TZ stars for the Empiral Archive as a class “known across the empire for its miraculous flashes and fits, given its neutron star core.” Hollowships routinely enter TZ-star systems to accelerate off the motherstar, a manoeuvre that saves them “hundreds of years in journey duration.”

The chapter’s reveal is that TZ stars are also the exit points of an unknown phenomenon. Three recorded instances across several centuries of empire observation:

1. A “science voidship” detects an object exiting an unnamed TZ star at ~70% c, in composition unlike any known empire material. The voidship cannot catch it.
2. About sixty years later, an astronomy satellite at Orb Flain catches a second exit event. The object is perfectly spherical, changes course by ~90° without pausing (“possibly with a little Higgs trick, we don’t know”), and is compositionally identical to the first.
3. The Vasily Incident at Orb Ertia — a third sphere, same composition, same 70% c — hits the hollowship Vasily and is the first one the empire is able to examine (via the cauterising nanoparticle residue on Ivan Tellinger).

Because all three events come out of TZ stars, the Galactic Human Empire has been stationing hollowships in TZ-star systems on purpose, using ordinary slingshot traffic as cover for what is effectively an empire-funded observation campaign. The Vasily’s 120,000 longsleepers died for the data.

Effects / capabilities

• Slingshot acceleration for hollowships — the operational reason the empire routes long-haul traffic through TZ systems.
• Exit points for unknown spheres — a repeating anomaly the empire treats as actionable intelligence.

Limitations / dangers

• TZ stars are dangerous neighbours under any ordinary model (neutron-star cores, flashes, fits).
• The sphere events make TZ systems physically deadly to any ship passing through at the wrong moment.

Appearances

• Ch. 05 — A Dictionary: Orb Ertia’s motherstar; also referenced as the site of the earlier-unnamed-TZ and Orb Flain events.

Related

• Hollowship, Vasily, Vasily Incident
• The Dictionary — what has been exiting them.
• Orb Ertia, Orb Flain

Open questions

• Why TZ stars specifically? No in-story answer. Candidate explanations: neutron-star cores enable some kind of emission physics humans don’t understand; TZ stars are waypoints the senders chose for accessibility; the entry side is from a causally disconnected region and TZ stars are its natural exit.
• How many total exit events has the empire catalogued? Three are named; the pattern of deliberate hollowship placement suggests the empire expects more.
• Is there an entry event — something going into a TZ star before each exit — that the empire might one day detect?