Astronomers identify binary system believed to have invaded our solar system 70,000 years ago

Artist's impression of Schulz's Star (Image: Michael Osadciw/University of Rochester)

An international team of astronomers from the US, Europe, Chile, and South Africa have identified a star system that most likely passed through the outer edge of our solar system at a distance of 0.8 light years some 70,000 years ago. The rogue system, nicknamed Scholz's star, is comprised of a red dwarf with a mass of roughly eight percent of our parent star, while its partner, a brown dwarf, was found to be only six percent as massive as the Sun.

The discovery makes the star system the closest to have ever approached our own Sun, but the team believes it unlikely that it penetrated deep enough into the Oort cloud (a region of space outside the heliosphere thought to contain more than a trillion small icy bodies) to trigger a comet shower. However, it is possible that the system was visible at times from Earth.

Whilst the red dwarf would have been around 50 times too faint to observe with the naked eye at its closest approach to Earth, the unusual magnetic qualities of the binary system may have caused the star to flare to thousands of times its ordinary brightness. This flare may have been observed by our ancient ancestors, lasting for minutes or possibly even hours at a time.

To work out the rogue star system's trajectory, and calculate whether it had encroached on our solar system, the astronomers needed to work out the tangential velocity and the radial velocity of the red dwarf. The tangential velocity was ascertained by applying the Doppler shift method whilst observing light thrown out by the star, whilst radial velocity was discerned with the use of spectograph equipment fitted to the South African Large Telescope and the Magellen telescope at the Los Campanas Observatory, Chile.

Once these two values where ascertained, Eric Mamajek, associate professor of physics and astronomy at the University of Rochester, New York, worked with Scott Barenfeld, a graduate student at Caltech, California, to run 10,000 computer simulations on the possible orbits of the system. These were performed in order to calculate whether the wandering giants passed through our solar system. It was found in 98 percent of the simulations that the star system did indeed pass through the outer Oort cloud, in what in astronomical terms could be described as a near miss.

The recent launch of ESA's Gaia satellite, designed to create a three-dimensional map of our galaxy, will make the process of discerning which of our immediate celestial neighbors passed close – and possibly even interacted with our solar system in the distant past – a lot easier.

The team's findings were recently published in Astrophysical Journal Letters.

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