A new Pulsar Planet has been discovered, and it is a beaut.
The first exoplanets discovered, were found around a pulsar: PSR B1257+12.
This is because planets are ubiquitous and pulsars allow precision measurements enabling planet detection.
That was almost 20 years ago, since then one other pulsar planet system has been discovered, PSR B1620-26, which was quite different from 1257+12.
Pulsar observations are a long term game, you do better, generally, by having long time series, and more systems are being continuously discovered and monitored – as opposed to main sequence stars, a lot of those are already known.
Now, finally, yet another exoplanet system around a pulsar, millisecond pulsar, has been discovered, and this one is even more different.
The paper: “Transformation of a Star into a Planet in a Millisecond Pulsar Binary.” by Bailes et al. appears in the 26th of August issue of Science, and describes observations of PSR J1719-1438, recently discovered by the Australian Parkes radio observatory
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!
Probably a yellow diamond, likely has some trace nitrogen inclusions, probably glowing red on one side, as the pulsar radiation blasting out at about 1/3 solar luminosity, is heating the tidally locked near side to a few thousand K (Teff < 4,500 K).
So, how did we get this?
Basically, the pulsar had a low mass companion whose orbit was close enough to come into contact with the pulsar after it formed, and the star transferred mass onto the pulsar as it evolved, spinning the pulsar up to the current millisecond period in the process.
The orbit of the star moved closer as it evolved, and the interaction became stronger, and some of the stellar mass was blown away, and then as the pulsar lit up, possibly spinning faster than it is now, the pulsar radiation ablated some of the last bit of the star, similar to the Black Widow Pulsar
Then, just before the star was ablated away completely, the compact core of the star, which is essentially pure carbon at that point, fell back into a denser remnant, which could no longer be ablated significantly, as the pulsar luminosity faded, leaving a cold, carbon crystal, the mass of Jupiter.
A different way to make a different planet.
Depending on the exact temperature of the planet, with a bit of luck, it ought to be observable with Hubble, and the nearside and farside temperature differences ought to be quite visible as the planet orbits around the pulsar.