Scientists peg ‘Scholz’s star’ as top contender in closest known flyby race

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A group of astronomers from US, Europe, Chile and South Africa has identified the closest known flyby of a star to our solar system – about 70,000 years ago through the Oort Cloud.

Based on the analysis of this low-mass star system nicknamed “Scholz’s star”, astronomers identified that the star passed through our solar system roughly 52,000 astronomical units away (or about 0.8 light years, which equals 8 trillion kilometers, or 5 trillion miles). This is astronomically close and our closest neighbor star Proxima Centauri is 4.2 light years distant.

In fact, the astronomers explain in the paper published in Astrophysical Journal Letters, that they are 98 per cent certain that it went through what is known as the “outer Oort Cloud,” a region at the edge of the solar system filled with trillions of comets a mile or more across that are thought to give rise to long-term comets orbiting the Sun after their orbits are perturbed.

Lead author Eric Mamajek from the University of Rochester said that most stars this nearby show much larger tangential motion and 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.

Mamajek added that the star’s radial velocity measurements were consistent with it running away from the Sun’s vicinity and not approaching and further analysis indicated that it must have had a close flyby in the past.

To determine the star’s trajectory the researchers looked at both its tangential velocity and radial velocity using spectrographs on large telescopes in both South Africa and Chile. When traced backwards, the measurements revealed the star’s position 70,000 years ago. The star is now about 20 light-years away in the constellation of Monoceros. It is part of a binary star system containing a brown dwarf companion.

Prior to this research, the top candidate for the closest flyby of a star to the solar system was the “rogue star” HIP 85605, which is predicted to come close to our solar system in 240,000 to 470,000 years from now.

However the latest research from Mamajek and his collaborators have also demonstrated that the original distance to HIP 85605 was likely underestimated by a factor of ten. At its more likely distance – about 200 light years – HIP 85605’s newly calculated trajectory would not bring it within the Oort Cloud.