50 ASTRONOMY • SEPTEMBER 2015
Cannibal star
Astronomers dreamt up the
idea of Thorne-Żytkow
objects — dead stars inside
dying stars — in the 1970s.
Only recently have they
tracked one down.
by Yvette Cendes
In an infinite universe,
even the most bizarre thought
experiments by astronomers — per-
haps conceived late at night, perhaps
proposed simply to see how weird
stars can get — can come to pass.
Imagine a massive star, near the end
of its life and puffed up to the red
supergiant phase, with a tiny neutron
star, the skeletal remnant of an even
more massive star, at its core. No one
knows quite how this Frankenstar
might form or how long it would
live, and the fusion process would be
anything but normal, yet the phys-
ics checks out. This mysterious star,
called a Thorne-Żytkow object (TZO),
could exist. But does it? Amazingly, 40
years after its conception, astronomers
think they might have found one of these
stars, and it has the potential to upend our
understanding of stellar evolution.
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A neutron star — the tiny (not to scale here), mostly dead
remnant of a massive star — hidden inside a dying red supergiant
becomes an entirely new stellar oddity called a Thorne-Żytkow object.
DON DIXON FOR ASTRONOMY