Atom bomb-sized blast in Russia may have been caused by a black hole

A giant explosion that shook part of Russia more than a century ago has never been categorically explained.

And yet, some scientists believe that it could have been the result of a very close encounter with a mysterious form of black hole .

The extraordinary blast occurred just after 7am on 30 June, 1908, above the Podkamennaya Tunguska river in what is now modern-day Siberia.

Its force was estimated to have been equivalent to as much as 15 megatons of TNT, making it 1,000 times more powerful than the atomic bomb dropped on Hiroshima and Nagasaki in 1945, as the Encyclopaedia Britannica notes.

The phenomenon flattened around 800 square miles (2,000 square kilometres) of the surrounding land – an area larger than London – with the impact heard up to 1,000 kilometres away.

In 1927, Semyon Semyonov, a local farmer who lived 70 km south-southeast of the blast’s epicentre, recalled his experience , saying: ‘‘I sat on the steps of my house facing north. Suddenly the sky in the north split apart, and there appeared a fire that spread over the whole northern part of the firmament.

“At this moment I felt intense heat, as if my shirt had caught fire. I wished to tear my shirt off and throw it away, but at this moment a powerful blast threw me down from the steps.

“I fainted, but my wife ran from the house and helped me up. After that we heard a very loud knocking, as if stones were falling from the sky.’’

Other witnesses described seeing a “second sun” up above, as thunderous roars and dazzling flashes filled the sky, and burning trees crashed down around them.

Others, in the village of Nizhne-Karelinskoye, some 450 km from the epicentre, recounted seeing a “blindingly bright body of bluish-white colour that was flying above for about 10 minutes” and “looked like a tube”.

“There was an enormous mass of black smoke and a loud knocking, but not of thunder,” the local newspaper Sibir reported just days after the disaster.

“The buildings were trembling and a fire of indefinite shape gushed out from [a] small dark cloud.

“All the village inhabitants ran from their houses in terror. Women were crying and everyone thought Armageddon had arrived.’’

The most puzzling aspect of the whole occurrence was that, despite experts largely concluding that the event must have been the result of an asteroid impact, no crater was left behind.

Indeed, the lack of a gaping hole remains a source of great debate, despite some scientists claiming that it formed a nearby lake .

Inevitably, the mystery has prompted a whole range of theoretical explanations, including the somewhat outlandish hypothesis that the blast was caused by a primordial black hole passing directly through the Earth .

There are three main types of black hole, of which primordial ones are the smallest.

The most common kind (the medium-sized ones) are known as “stellar” black holes, and these form when the centre of a massive star collapses upon itself.

The largest kind, are called “supermassive,” which were likely formed by the collapse of supermassive stars in the early universe, and which can continue to grow by feeding on smaller objects or merging with other supermassive black holes.

And the runts of the group, the primordials, are, in fact, purely hypothetical: scientists are yet to find definitive proof that these do now, or ever have existed.

According to NASA : “Scientists theorise that primordial black holes formed in the first second after the birth of the universe.

“In that moment, pockets of hot material may have been dense enough to form black holes, potentially with masses ranging from 100,000 times less than a paperclip to 100,000 times more than the Sun’s.

“Then as the universe quickly expanded and cooled, the conditions for forming black holes this way ended.”

And whilst it’s highly possible that all primordial black holes evaporated as the cosmos aged, it’s also possible that some could still linger across the universe.

In fact, some experts have even suggested that mini primordial black holes, smaller than an atom, could be passing harmlessly through Earth on a daily basis.

Then, in a 1973 paper , published in the journal Nature , a team of physicists based at the University of Texas, suggested that the Tunguska explosion could have been caused by a larger primordial black hole crashing through the planet.

The researchers posited that a black hole with the mass of a large asteroid would explain the lack of impact crater, as well as the ethereal blue “tube” mentioned by witnesses.

"Most of the radiation from the shock front would be in the vacuum ultraviolet and would be absorbed and reradiated at longer wavelengths," the study’s authors wrote.

"There would be little hard X radiation and the accompanying plasma column would appear deep blue."

The experts then suggested that, despite not leaving a crater, the black hole could have left an exit wound on the other side of the world.

"[The black hole] would enter the Earth, and the rigidity of rock would allow no underground shock wave," they explained.

"Because of its high velocity and because it loses only a small fraction of its energy in passing through the Earth, the black hole should very nearly follow a straight line through the Earth, entering at 30° to the horizon and leaving through the North Atlantic in the region 40°-50° N 30°-40° W.

“This exit provides a check for the whole hypothesis."

The authors then recommended that investigations be carried out to search for shockwaves and disturbances of the ocean in and around that potential “exit” location.

Suffice it to say, no such evidence has since been found, and the existence of primordial black holes remains an enigma.

Meanwhile, if you’d like a more widely credited – though, admittedly, more prosaic explanation for the Tunguska disaster – you should turn back to asteroids.

The broadly accepted explanation is that an asteroid, or meteoroid, measuring around 50 to 80 metres (between 160 and 262 feet) across, exploded in an airburst 10 to 14 kilometres (six to nine miles) above ground, as IFL Science notes.

Estimates suggest the celestial missile weighed around 220 million pounds (99 million kilogrammes) and entered the Earth’s atmosphere at around 54,000 kilometres (around 33,555 miles) per hour before breaking up into multiple balls of fire.

The sudden release of energy from the explosion generated a powerful shockwave that radiated outwards, razing the surrounding area.

But because the blast occurred up in the air, no impact crater was created.

Still, the remoteness of the region where the disaster took place and the limited instrumentation available at the time means we don’t have definitive proof of what caused the extraordinary event.

The good news is, according to the Royal Museums Greenwich , a Tunguska-type event is only expected to occur, on average, once every century.

But wait, doesn’t that mean we’re overdue one now…?

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