70,000 years ago, a rogue star crossed our solar system


Too close for comfort – a team of astronomers from the United States, Europe, Chile and South Africa concluded that a dark star had passed through the Oort Cloud, the distant cloud of comets our solar system. The star missed Earth by less than a light year and passed five times closer than the current nearest star, Proxima Centauri.

Artist’s impression of Scholz’s star and its brown dwarf companion (foreground) during its flight over the solar system 70,000 years ago. The Sun (left, background) would have appeared as a bright star. The pair are now about 20 light years away.
Credit: Michael Osadciw / University of Rochester.

In an article published in Letters from the astrophysical journal, lead author Eric Mamajek of the University of Rochester and his team studied the speed and trajectory of a low-mass star system – WISE 0720-0846 (nicknamed “Scholz’s Star”). Due to its low light, the star was discovered only a year ago by astronomer Ralf Dieter-Scholz in Potsdam, Germany, through the use of NASA’s Wide Field Infrared Survey Explorer (WISE). , who mapped the entire sky in infrared during the years 2010 and 2011.

Since its discovery, it exhibited interesting characteristics. although it was quite close (“only” 20 light years away) it showed very slow tangential motion, ie motion across the sky. By studying its trajectory and speed, astronomers have discovered that the star is approaching or moving away from our solar system. They reconstructed its past movement and quickly realized that it was moving away from our solar system, meaning it had passed through (or very close to) in the past.

“Most nearby stars show much greater tangential motion,” says Mamajek, associate professor of physics and astronomy at the University of Rochester. The small tangential movement and proximity initially indicated that the star was most likely heading towards a future close encounter with the solar system, or that it had ‘recently’ approached the solar system and was moving away. Radial velocity measurements were consistent with it moving away from the vicinity of the Sun – and we realized it must have had a close flyby in the past. ”

Scholz’s star moved much faster than expected and missed Earth by “a mustache”, that is, in astronomical terms. It went about 0.8 light years from Earth, 8,000 billion kilometers; this happened 70,000 years ago. It might sound like a lot, but it’s really too close for comfort. This corresponds to an earlier theory, which proposed that such close-up overflights occur every 100,000 years or so. These encounters could strike the Oort Cloud and trigger “comet showers” in the solar system.

“Sure enough, the radial velocity measurements were consistent with it moving away from the vicinity of the sun – and we realized it must have had a close flyby in the past,” Mamajek said in a report. Press release.

The star is a rogue star – a star that has escaped the gravitational pull of its home galaxy and is independently moving into or toward the intergalactic vacuum; the movement of rogue stars is often difficult to predict. A 2012 study claimed that rogue planets riddle the Milky Way, and although rarer, there are also rogue stars in our galaxy.

Currently, Scholz’s Star is a small, inconspicuous red dwarf in the constellation Monoceros, about 20 light years away. The star is part of a binary star system, composed of a low mass red dwarf star (with a mass of about 8% that of the Sun) and a “brown dwarf” companion (with a mass of ‘about 6% of that of the Sun). Red dwarfs are by far the most common type of star in the Milky Way, at least in the vicinity of the Sun, but due to their low light, they are difficult to observe and study. Brown stars are “failed stars” – substellar objects not massive enough to sustain hydrogen-1 fusion reactions in their nuclei, unlike … well, stars.

Journal reference:

  1. Eric E. Mamajek, Scott A. Barenfeld, Valentin D. Ivanov, Alexei Y. Kniazev, Petri Väisänen, Yuri Beletsky, Henri MJ Boffin. THE CLOSEST KNOWN OVERVIEW OF A STAR IN THE SOLAR SYSTEM. The Journal of Astrophysics, 2015 ; 800 (1): L17 DOI: 10.1088 / 2041-8205 / 800/1 / L17


Arline J. Mercier