Lightning Inside A Volcanic Ash Cloud In Patagonia.

Blanet: A new class of planet that could form around black holes

The dust clouds around supermassive black holes are the perfect breeding ground for an exotic new type of planet.

Blanets are fundamentally similar to planets; they have enough mass to be rounded by their own gravity, but are not massive enough to start thermonuclear fusion, just like planets that orbit stars. In 2019, a team of astronomers and exoplanetologists showed that there is a safe zone around a supermassive black hole that could harbor thousands of blanets in orbit around it.

The generally agreed theory of planet formation is that it occurs in the protoplanetary disk of gas and dust around young stars. When dust particles collide, they stick together to form larger clumps that sweep up more dust as they orbit the star. Eventually, these clumps grow large enough to become planets.

A similar process should occur around supermassive black holes. These are surrounded by huge clouds of dust and gas that bear some similarities to the protoplanetary disks around young stars. As the cloud orbits the black hole, dust particles should collide and stick together forming larger clumps that eventually become blanets.

The scale of this process is vast compared to conventional planet formation. Supermassive black holes are huge, at least a hundred thousand times the mass of our Sun. But ice particles can only form where it is cool enough for volatile compounds to condense.

This turns out to be around 100 trillion kilometers from the black hole itself, in an orbit that takes about a million years to complete. Birthdays on blanets would be few and far between!

An important limitation is the relative velocity of the dust particles in the cloud. Slow moving particles can collide and stick together, but fast-moving ones would constantly break apart in high-speed collisions. Wada and co calculated that this critical velocity must be less than about 80 meters per second.

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What is this dark spot in the center of the image?

This NASA/ESA Hubble Space Telescope image features the star cluster Trumpler 14. One of the largest gatherings of hot, massive and bright stars in the Milky Way, this cluster houses some of the most luminous stars in our entire galaxy.

The prominent dark patch, close to the centre of the cluster is a so called Bok globule: this is an isolated and relatively small dark nebula, containing dense dust and gas. These objects are still subjects of intense research as their structure and density remains somewhat a mystery.

Credit: NASA & ESA, Jesús Maíz Apellániz (Centro de Astrobiología, CSIC-INTA, Spain)

Le Tempestaire (Jean Epstein, 1947)

Astronauts talking about viewing the earth from the moon, from The Overview Effect: Awe and Self-Transcendent Experience in Space Flight

Fallstreak Holes

Occasionally clouds appear to have a hole in them; these are known as fallstreak holes or hole-punch clouds. (Image credit: J. Stevens/NASA; via NASA Earth Observatory) Read the full article

Stars again