Two monster stars raced past our Sun, creating a protective shield around Earth

When the Hubble telescope observed interstellar clouds surrounding our solar system in the 1990s, it picked up something odd that had no explanation. It spotted ionisation in the clouds, a process in this case where atoms had lost electrons. While the reason for this remained a mystery for years, scientists have now found what happened in the clouds. According to a study published in The Astrophysical Journal, two massive stars raced past our sun millions of years ago, leading to a scary encounter. Researchers from the University of Colorado Boulder revealed that this flyby happened 4.4 million years ago, and the stars were approximately 30 light-years away from the Sun, and 13 times more massive than our star. When the duo paid this visit, it led to the stars emitting powerful radiation, leading to ionisation in the local clouds around the solar system.

This event not only solves a decades-old mystery, but according to the researchers, can also throw light on why Earth is a habitable planet. To understand what happened to these clouds, the researchers simulated what the solar system and surrounding region would have looked like millions of years ago. Michael Shull, an astrophysicist and lead author of the study, said in a statement that this was like a "jigsaw puzzle", since the Sun and the solar system are moving at a speed of 93,000 kilometres per hour. Every object, as we know now, would have been all over the place at the time.

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The two stars life 400 light-years away today

They also know which two stars zoomed past the Sun. Epsilon Canis Majoris, also known as Adhara, and Beta Canis Majoris, or Mirzam, which live in the Canis Major constellation, are likely the culprits in this case. They are both hot and heavy, burning at temperatures of 38,000 and 45,000 degrees Fahrenheit. In comparison, our Sun's maximum temperature is only about 10,000 degrees Fahrenheit.

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Epsilon and Beta Canis Majoris came around 30-35 light-years from the Sun, or 281 trillion kilometres, which means both of them would have been clearly visible from Earth. “If you think back 4.4 million years, these two stars would have been anywhere from four to six times brighter than Sirius is today, far and away the brightest stars in the sky,” Shull said. Another thing to note is that these clouds could be the reason why Earth is able to harbour life. The event led to the ionisation of hydrogen and helium in the clouds, which now shield the solar system from ionising radiation.