Star Blasted Through Solar System 70,000 Years Ago

Astronomers have discovered a star that carried out a stellar hit-and-run 70,000 years ago… and our solar system was the victim.

Highlighted by astronomers at the University of Rochester and the European Southern Observatory, the star — nicknamed “Scholz’s star” — has a very low tangential velocity in the sky, but it has been clocked traveling at a breakneck speed away from us.

In other words, from our perspective, Scholz’s star is fleeing the scene of a collision with us.

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“Most stars this nearby show much larger tangential motion,” said Eric Mamajek, of the University of Rochester. “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.”

Scholz’s star was named after its 2013 discoverer Ralf-Dieter Scholz of the Leibniz-Institut für Astrophysik Potsdam (AIP) in Germany, but its official designation is “WISE J072003.20-084651.2″ after being positioned in data collected by NASA’s Wide-field Infrared Survey Explorer (WISE) telescope between 2010 and 2011.

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Using data from the Southern African Large Telescope (SALT) and the Magellan telescope at Las Campanas Observatory in Chile, Mamajek and his collaborators were able to measure the star’s spectra and radial velocity. Through these observations they were able to deduce that Scholz’s star is a dim red dwarf approximately 20 light-years away. It is actually part of a binary system, with its partner being a small brown dwarf (or a ‘failed star’).

Taking these data, the researchers were able to model several different orbital possibilities and deduce that the star almost definitely (to a 98 percent certainty) came within 0.8 light years from the sun. Although this is still quite a margin, the star would have careened though the Oort Cloud — a hypothetical region filled with frozen cometary nuclei surrounding the solar system.

Like a car speeding through a cloud of mosquitoes, Scholz’s star would have likely splatted some comets and scattered many more during its close encounter, although the overall effect on the Oort Cloud would have likely been minimal, the researchers point out.

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The researchers also calculated that at its closest approach, Scholz’s star would have only been a 10th magnitude star, approximately 50 times dimmer than what we could normally see on a clear night without the aid of a telescope. However, as the star is known to be magnetically active, our ancestors may have looked up in wonder at flaring events on the star that would have lasted for minutes to hours at a time. To any observers paying attention at the time, these flaring events would have appeared out of nowhere in the night sky, boosting the brightness of the red dwarf by a thousand times.

Although rare over evolutionary timescales, as this most recent discovery shows, close encounters with stars do happen regularly over galactic timescales and astronomers are working to spot any more stars that may have buzzed our solar system in the recent past or may do in the future.

The recently-launched European Gaia mission, for example, is currently mapping and measuring the velocities of a billion stars in our galactic neighborhood, so the true frequency of solar system hit-and-runs may soon be revealed.