Black holes have always been those mystical celestial bodies that always seem to gobble up everything around them. They have a dark aura associated with them and this has nothing to do with them being dark! But you surely don’t know that a black hole sun can actually be friendly. Now you must be thinking… Black hole as sun?

Well to remind you according to the second law of thermodynamics, life requires a temperature difference to provide a source of useable energy. Life on Earth exploits the difference between the sun and the cold vacuum of space, but what if you flip the temperatures around, with a cold sun and a hot sky? That’s exactly the condition of a planet orbiting a black hole according to Tomáš Opatrnýof Palacký University in Olomouc, Czech Republic.

Black hole: just the name is black!

Though these huge celestial bodies are named black holes, they are anything but black. Most black holes are actually among the brightest objects in the universe because gas and other matter falling in are superheated and glow as it accretes. But when it is the case of a satiated black hole, the temperature is zero that is according to Opatrný, it can act as the cold sun very well.

According to Opatrný, a very old black hole that has already cleared its surroundings and which is not further fed is the ideal cold sun. His team calculated that an Earth-sized planet orbiting a black hole that appeared a similar size to our sun in the sky could extract around 900 watts of useful power from this temperature difference which will be enough for life to potentially exist, but hardly enough to run a civilization.

Supporting life

The Cosmic Microwave Background (CMB) which proposes that presently the rest of the universe is at a temperature of about -270 ˚C was hotter according to Avi Loeb of Harvard University 15 million years after the Big Bang. In all probability it was around 27˚C. That means at that time, it must have been warm enough to host liquid water.

At this temperature, a planet around a sufficiently cool black hole would receive 130 gigawatts of power, around a millionth of what the sun provides Earth. That’s enough to support complex life, though extremely short into the universe’s existence.

Loeb also adds that though the idea of a cold sun and a hot sky to support life is interesting, but in practice it is unlikely to occur in the universe. “There is always matter falling at some level into a black hole,” he says, meaning the black hole sun wouldn’t stay cold enough for long.

Black holes: our future home?

What will happen once all the stars die out and perish? Obviously, life will migrate to other planets. But that will take at least 100 trillion years. Even then, it’s more likely that any future beings will absorb light from accreting matter rather than dwell under a cold sun, as by then the CMB will have faded into nothing.

This is how humans are…. worrying about the world after 100 trillion years when life isn’t guaranteed even for the next second! Irony of the human mind!

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Author: Technology Blog