What IF a Black Hole the Size of a Coin suddenly appeared on Earth

 Coin sized black Hole appeared on Earth

Super massive black holes, millions of times the mass of our Sun, eat stars for breakfast. But how dangerous would a small black hole be? Could it swallow up the entire planet? Or would it just rip apart anyone close to it? 

Black holes are extremely dense. They aren't really holes, but instead, huge amount of mass. If it was possible for you to create one, you'd have to slam a lot of particles together in a tiny, tiny space. In practice if you were able to collapse all the particle of mount Everest and create a black hole, that black hole would be just a few atoms across. Even then, you wouldn't want to stand close to it. For 10 meters around it, the gravitational pull of that tiny hole would be as strong as gravitational pull at Earth's surface. 

So, what trouble could a coin-sized black hole cause?

The answer depends on how you define size. Would our hypothetical black hole be as wide as a coin? Or would it have a coin's mass? 

Scenario 1: The Balck hole with a diameter of a coin. 

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Looks pretty small, right? Well, because black holes are so dense, this one would be about the same mass as Earth. It would also have the gravitational pull one billion billion times greater than our planet does. But the Earth wouldn't just fall into black hole. Rather it would orbit it while having chunks of the planets eaten with every pass. Earth's rotation would slow down this banquet, preventing the black hole from swallowing all of it. Whatever mass of Earth was left, would collapse into a disk of hard rock and start rotating around the black hole. By that time, the black hole would have doubled in mass. Suprisingly, it would leave the Moon unharmed, only causing it's orbit to become more elliptical. You wouldn't be so lucky. The black hole would consume you before you even realized what was happening. 

Scenario 2: The black hole with a mass of a coin.

If a 5 gram coin suddenly collapsed into a black hole, that black hole would be terribly tiny. Compared to an atom, it would be as small as an atom compared to the Sun. And still, it would be terrifying. You see, the smaller a black hole is, the more Hawking radiation it releases. Simply put, black holes evaporate, spewing particles back into space. In our case, the black hole would evaporate way to fast - in just a fraction of second. Its insignificant mass of five grams would be converted into a significant 450 terajoules of energy, and cause a massive explosion. That would be like detonating 100,000 tonnes of TNT. The explosion wouldn't tear the whole Earth apart, but it would affect anything that happened to be near it. 

So it would be best if this black hole - causing coin wasn't in your pocket. Despite all the technology we've invented, humans aren't able to compress matter into a black hole even that small. Maybe one day, when space travel is more widely available, we'll be able to capture a black hole from amongst the stars, and learn from it.

Detecting colliding supermassive black holes: The search continues

In a new study, researchers have developed an innovative method to detect colliding supermassive black holes. The study has just been published in the Astrophysical Journal and was led by postdoctoral researcher Xingjiang Zhu from the ARC Center of Excellence for Gravitational Wave Discovery (OzGrav) at Monash University.

At the center of every galaxy in the universe, there is a supermassive black hole millions to billions times the mass of the sun. Big galaxies are assembled from smaller galaxies merging together, so collisions of supermassive black holes are expected to be common in the cosmos. But merging supermassive black holes remain elusive: No conclusive evidence of their existence has been found so far.

One way to look for these mergers is through their emission of gravitational waves—ripples in the fabric of space and time. A distant merging pair of supermassive black holes emit gravitational waves as they spiral in around each other. Since the black holes are so large, each wave takes many years to pass by Earth. Astronomers have used a technique known as pulsar timing array to observe gravitational waves from supermassive binary black holes—so far to no avail.

In parallel, astronomers have been looking for the collision of supermassive black holes with light. A number of candidate sources have been identified by looking for regular fluctuations in the brightness of distant galaxies called quasars. Quasars are extremely bright, believed to be powered by the accumulation of gas clouds onto supermassive black holes.

If the center of a quasar contains two black holes orbiting around each other (instead of a single black hole), the orbital motion might change the gas cloud accumulation and lead to periodic variation in its brightness. Hundreds of candidates have been identified through such searches, but astronomers are yet to find the smoking-gun signal.

"If we can find a pair of merging supermassive black holes, it will not only tell us how galaxies evolved, but also reveal the expected gravitational-wave signal strength for pulsar watchers," says Zhu.

The OzGrav study seeks to settle the debate, determining if any of the identified quasars are likely to be powered by colliding black holes. The verdict? Probably not.

"We've developed a new method allowing us to search for a periodic signal and measure quasar noise properties at the same time," says Zhu. "Therefore, it should produce a reliable estimate of the detected signal's statistical significance."

Applying this method to one of the most prominent candidate sources, called PG1302-102, the researchers found strong evidence for periodic variability; however, they argued that the signal is likely to be more complicated than current models.

"The commonly assumed model for quasar noise is wrong," adds Zhu. "The data reveal additional features in the random fluctuations of gas accumulation onto supermassive black holes."

"Our results are showing that quasars are complicated," says collaborator and OzGrav Chief Investigator Eric Thrane. "We'll need to improve our models if we are going to use them to identify supermassive binary black holes."