You know the story. Clouds of dust and gas collapse to form stars like our Sun, around which the swirling maelstrom of debris slowly coalesces into a system of planets.
Sure, it’s a little simplistic, but this basic account explains not only our own cosmic past, but that of every one of the 5,000-odd exoplanets discovered to date.
A recent analysis by a team of researchers from Poland and the US points to a surprising new method for world-building, one that could generate some of the largest populations of planets in the Universe.
What’s more, many of the planets formed this way are like nothing else in the Universe.
In a study that is yet to be peer-reviewed, Polish Academy of Sciences astrophysicist Bhupendra Mishra and his team calculated the physics required for planet building not around a star, but the king of all cosmic beasts, an active supermassive black hole.
Don’t let the name black hole fool you. While the horizon marking a black hole’s boundary is by definition darker than my mood after a night of no sleep and before I’ve had my first coffee, anything circling close to its edge is bound to spill out plenty of high-energy radiation.
In the center of galaxies, these behemoths can create active galactic nuclei (AGN) – dense concentrations of gravity surrounded by a blazing swirl of obliterated stars, gas clouds, and spaghettified aliens (we assume).
Such active black holes are often host to a thick disc of material stretching for hundreds of trillions of miles.
The push-and-pull of radiation, friction, and gravity determines not just how quickly a black hole swallows this material, but how matter might accrete into growing balls of rock and gas.
Physicists use the term streaming instability to describe the hypothetical bump-and-grind responsible for generating baby “planetismals” in the cooler outer fringe of orbiting material.
To determine whether the forces at work at the edges of a black hole’s accretion disc might produce streaming instabilities, Mishra and his team ran the numbers for a particular kind of AGN, one presumed to have regions stabilized by a strong magnetic field.
The results were shocking.
“We estimate that of order tens of millions of planetary mass objects can form in outer regions of AGN accretion disks,” the team writes in their report.
That would make supermassive black holes some of the Universe’s most productive nurseries for planet formation.
Since most of the dust clumping together consists of heavier elements, these planetesimals would most likely be rocky bodies like Earth. Only bigger. A lot bigger. Like stellar-mass bigger.
While some might gather enough hydrogen and helium to trigger fusion, the majority of these gargantuan balls of rock won’t ever become stars.
“The geophysical structure and evolution of these objects is unknown, and probing it is beyond the scope of the current work,” the team writes, acknowledging their cores would probably squeeze hard enough to overcome the push of electrons, squeezing atomic nuclei closer together into an exotic material.
Where stars do form, most would live fast and die young as supernovae.
Empirical evidence is needed to validate the existence of these bizarre planetary systems. But based on the modelling alone, it’s possible that some of the most destructive objects in a galaxy could also be some of the most fertile.
This research is available on the pre-publish server arXiv.
Source Phys.org
Fact-checked by Bronwyn Thompson
