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Just Passing Through? Rogue Star Grazed Our Solar System Very Recently

| 19 Feb 2015 16:31

Roughly 70,000 years ago, a binary star formation brushed against our solar system - and it might have been visible from Earth.

It's terrifying enough that Earth is basically a cosmic shooting gallery for passing asteroids. But in the grand scheme of things it's fairly normal - Earth survived such impacts in the past, after all. Besides, there are entire stars just drifting through space that could've completely ruined our day - and we actually came very close to meeting one recently. If you looked at the right spot in the sky 70,000 years ago - a time when modern humans were just establishing themselves - you might have spotted a small, flaring binary star system as it made its way through the Oort Cloud.

The Oort Cloud, for those not in the know, is a spherical cloud of ice-based comets at the very edge of our solar system, roughly 100,000 AU from the sun. This binary star system - dubbed Scholz's star - passed by at a distance of 52,000. In more conventional terms, that's only 0.8 of a light year away. For context, the closest star to Earth (Proxima Centauri) is 4.2 light years away from us.

Scholz's star, which is technically a star and brown dwarf companion, were spotted about 20 light years away. It still managed to generate significant attention from scientists because it had a very slow tangential motion - which is astronomer-speak for its path across the sky.

"Most stars this nearby show much larger tangential motion," Professor Eric Mamajek from the University of Rochester explained. "The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had 'recently' come close to the solar system and was moving away. Sure enough, the radial velocity measurements were consistent with it running away from the Sun's vicinity - and we realized it must have had a close flyby in the past."

At that distance, Scholz's star is 50 times fainter than what we usually see with the naked eye. That said, it's a magnetically active system, which means it periodically flares to become thousands of times brighter than normal. Our ancestors might very well have spotted it for minutes or even hours at a time when such a flaring event occurred. Whether they would have known the light was an entire freaking star system is another question entirely.

Prior to Scholz's star, astronomers predicted that the rogue star HIP 85605 would near our solar system in the next 240,000 to 470,000 years. Thanks to new calculations generated from this information however, it now seems HIP 85605 won't even enter the Oort Cloud at all. In the meantime, this data will be used to determine what other stars recently passed through our solar system - and which ones are still on the way.

Source: The Astrophysical Journal, via University of Rochester

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