Can a habitable planet orbit a black hole?

Hyperaxion Mar 10, 2020

Paul M. Sutter – astrophysicist at Stony Brook and the Flatiron Institute – published an article on, in which he affirms the possibility of life on planets that orbit supermassive black holes. According to him, the forces around a black hole are capable of heating a planet, however, for life to exist, the planet must orbit at the speed of light.

Sutter’s study started with life as we know it here on Earth, which needs liquid water and oxygen to survive. The researcher says that it is very difficult to find water in its liquid form, as well as a heat source that does not cause it to evaporate. However, despite these factors, balance is possible in the so-called “habitable zone of the stars” and also under the icy crusts of some moons of planets outside our system.

Credit: GettyImages).

The scientist said that although black holes look inhospitable to life at first, after all, they are made of pure gravity and, therefore, pull anything close to their horizons, it is still theoretically possible that there could be life on a planet orbiting one. This is because the universe is permeated by something called Cosmic Microwave Background Radiation (CMB), which is the remaining radiation from the beginning of the universe.

Read more: The most distant black hole ever observed

CMB is by far the largest source of radiation in the cosmos and floods all stars and galaxies by many orders of magnitude. Sutter explains that CMB is cold, has an average temperature of 3° above absolute zero, however, when its light falls into a black hole, it turns blue, being pumped to higher energies, changing to infrared and even ultraviolet proportions. Thus, in a black hole, the CMB goes from cold to very hot. This could act as a heat source for the planet orbiting the black hole.

How is life possible on planets that orbit black holes?

When the CMB falls into a rotating black hole, it can focus the light on a narrow beam, causing a single point to appear in the sky, similar to a star.

(Credit: GettyImages).

If a planet is able to approach a black hole, it will become very hot, and its ice can be converted into liquid oceans (a potential home for life). Sutter ponders that “for life to thrive, it also needs a heat sink, which can be easily supplied by the black hole itself. Close to it, gravitational distortions increase the appearance of the event horizon”. The researcher explains that in a radius of 1% above the event horizon, the hot CMB shrinks to fill only a small disk.

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The scientist concluded his article by stating that, although life on a planet orbiting a black hole is possible, the scenario would not be pretty, because the planet would have to orbit at the speed of light for life on it to continue to exist in these conditions. Every second on this planet would be equivalent to many hours here on Earth. Sutter also said, “Still, the work shows that we need to keep our minds open when it comes to potential homes for life, including some of the most terrible environments in the universe.”

Related topics:

black hole habitable planet


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