Hidden in the globular cluster Terzan 5 is the binary system IGR J17480-2446. One of its members is a neutron star that behaves strangely. It spins at just 11 hertz (11 revolutions per second) and cools suspiciously slowly after an outburst. Usually, such stars spin hundreds of times faster and cool briskly — here, it's the opposite.
The slowed cooling forces us to assume that the star's outer crust contains a layer with low thermal conductivity. It seems to consist of amorphous, "glassy" material — not crystalline but disordered, like hardened caramel. Such a layer arises naturally when matter falling from the companion star destroys the original crystalline lattice of the crust. This is not a defect but a natural stage of growth.
From the amount of accreted matter (about 2.4 millionths of a solar mass), we can tell that accretion has just begun. The star is a newborn by the standards of such systems. Its slow rotation and thermal state resemble the properties of "recycled" pulsars, but its origin is likely different. The authors suggest it was born in an electron-capture supernova — a special type of explosion that gives almost no "kick" and leaves the star spinning slowly.
Thus, the system IGR J17480-2446 becomes a window into the first moments of a neutron star's life. The glassy crust, slow cooling, and modest weight of accreted matter — all are strokes in the portrait of an infant we've caught in its cradle.
The glassy crust of a neutron star resembles not window glass but an amorphous metal — a substance without a crystalline lattice, like a frozen liquid. On Earth, such materials are made by ultra-fast cooling of a melt.
In Robert Forward's novel "Dragon's Egg," intelligent beings live on a neutron star, their biochemistry based on nuclear reactions. The glassy crust from the new paper could be their "soil."