Too Big to Fit on a Finger

The Galaxy's largest diamond?

The pulsar is a millisecond pulsar, with a 5.7 ms spin period, it is a little over a kpc away (call it about 4,000 light years). The system is old, most likely several billion years old.

The object orbiting it is Jupiter mass, with some uncertainty in the exact mass due to as yet unmeasured inclination, has an orbital period of 2.2 housrs! That implies an orbital radius less than a solar radius! The orbit is, near as we can tell, perfectly circular.

Further, the object is not overflowing its Roche lobe, implying a minimum mean density of 23! Possibly considerably larger.

From both observational constraints, and from theoretical grounds based on models of the origin of the object, it is most likely a pure cold crystalline carbon core of a low mass star, with the rest of the star accreted, blown away and ablated by the millisecond pulsar formation process.

Yes, it is a 10³¹ carat diamond.

That is 10,000,000 trillion trillion carats of hot sparkly rock!

I doubt that actual diamond as we know it (the crystalline form used for wedding rings and an industrial abrasive, and not much else), is actually the stable form of carbon at a density of 23.  On earth, diamonds have a density near 3.5.  But it's a fun story even if probably not true. The universe is a strange place.