Astronomers discover a part of the planet's nucleus around a dead star

Regardless of their size, the researchers say that the planetesimal is very dense. After all, the body must be relatively sturdy if it is able to withstand the severe gravitational forces near a white dwarf. According to Manser, although the object could potentially have a density up to 39 g / cm3 (several times more than the Earth's inner core), they expect it to be closer to 7.7 g / cm3, which is more comparable to pure iron or the cores of rocky planets.

"We can say with certainty that it will not be the core of a gas giant, because these should have a different composition," said Manser, "and the material we see that was added by the white dwarf does not match that of the white dwarf – material you would expect to see from the outer layers or core of a gas giant. "

Instead, the planetesimal probably originated from a torn rocky planet as its host star passed from a normal star to an inflated red giant, to a white dwarf.

"In our own solar system, when the Sun becomes a red giant, it will engulf Mercury, Venus and most certainly the Earth," says Manser. But the planetesimal revealed in this research is probably "farther and farther in the system, like an analog of the asteroid belt or a planet in farther orbit, which is then scattered to the white dwarf".

Based on the iron-charged composition of the planetsimal, Manser says that he was either pushed to the white dwarf as a result of interactions with giant planets or a super-Earth and partially destroyed, either "broken during a planet-planet collision, producing an asteroid-like 16 Psyche in our own solar system", before migrating inward.

The planetesimal rotates about every 40 minutes and rotates around the white dwarf about every two hours. With such a short orbital period, researchers expect the planetesimal to be very close to its host star. In fact, according to the study, if the object gravitated around the Sun (about 100 times the diameter of the white dwarf), it would literally be inside our star.

In addition, the shape of the planetsimal orbit seems to be more elongated (or eccentric) than that of your average planet, although Manser points out that additional data is needed to confirm this eccentricity. Often, when an object has a very eccentric orbit, this indicates a powerful past interaction that has driven it out of the round orbit it received when first forming the object in a circular protoplanetary disk. Thus, if the eccentric orbit is confirmed, it could serve as further proof of the planetary's violent past.

Gassy white dwarf

The white dwarf, named SDSS J122859.93 + 104032.9 (SDSS1228 abbreviated), currently represents about 70% of the mass of the Sun and is about 410 light-years away from the constellation Virgo. SDSS1228 is particularly noteworthy as it is part of an extremely rare class of white dwarfs that harbor planetary discs composed of gas and dust. Although Manser reports that there are approximately 40 to 45 white dwarves that contain only dust-only discs, only seven (or 0.07% of all white dwarfs) have discs that also contain gas.