Our brilliant, blazing, roiling Sun is a lonely star; a solitary fiery sphere suspended in Earth’s daytime sky. Although our Sun is bereft of stellar companionship, it sometimes has visitors. In February 2015, a group of international astronomers from the United States, Europe, Chile and South Africa announced that they have recently determined that 70,000 years ago a dim alien star probably paid our Solar System a visit–a very close visit! Indeed, this faint stellar invader is likely to have marched through our Solar System’s very remote shell of cometary nuclei, termed the Oort Cloud. No other star is known to have ever brushed past our Solar System at such a close distance–five times closer than the current nearest neighboring star, Proxima Centauri.
In a research paper published in the February 10, 2015 issue of the Astrophysical Journal Letters, lead author Dr. Eric Mamajek, associate professor of physics and astronomy at the University of Rochester in New York, and his collaborators studied the trajectory and velocity of a low-mass, dim little stellar sparkler named Scholz’s star. Actually, Scholtz’s star is a low-mass red dwarf star that is part of a binary system–with a mass of merely 8% that of our Sun. The other member of this duo is a brown dwarf, that sports a puny mass of 6% that of our Star. Red dwarf stars are the most abundant, longest-lived, and coolest true stars in our Galaxy. Brown dwarfs, on the other hand, are interesting little substellar spheres that are often referred to as failed stars. Although brown dwarfs probably are born the same way as true stars–from the collapse of a particularly dense blob embedded in a cold, dark, molecular cloud–they fail to attain sufficient mass to light their nuclear-fusing fires like true stars do. However, brown dwarfs, puny as they are when compared to their more successful stellar kin, are still much more massive than gas giant planets like our own Solar System’s Jupiter.
The formal designation of Scholz’s star is WISE J072003.20-084651.2. It derived its more casual nickname to honor its discoverer–the astronomer Dr. Ralf-Dieter Scholz of the Leibniz-Institut fur Astrophysik Potsdam (AIP) in Germany. Dr. Scholz is the first to have reported the discovery of the faint nearby star late in 2013. The WISE part of the little star’s designation refers to NASA’s Wide-field Infrared Survey Explorer (WISE) mission, which mapped the entire sky in infrared light in 2010 and 2011, and the J number part of the designation refers to the stellar sparkler’s celestial coordinates. 바카라사이트
Scholz’s star is a dim little denizen of the constellation Monoceros, which is 20 light-years away–at least, at present. However, when the little red dwarf made its closest brush past our Solar System thousands of years ago, it would have been a 10th magnitude star–approximately 50 times dimmer than can normally be observed with the unaided human eye at night. It is magnetically active, however, and this can cause stars to “flare”–and for one brief shining moment in cosmic time become thousands of times brighter. Therefore, it is possible that Scholz’s star may have been visible to our ancient ancestors 70,000 years ago for minutes or hours at a time during its rare episodes of flaring.
The little star’s trajectory indicates that 70,000 years ago it passed approximately 52,000 astronomical Units (AU) away–or about 0.8 light-years, which is equivalent to 5 trillion miles. One AU is equal to the mean separation between Earth and Sun, which is 93,000,000 miles. Indeed, the astronomers explain in their paper that they are 98% certain that the little star made a close brush through what is known as the outer Oort Cloud–a remote and mysterious region at the very edge of our Solar System that is inhabited by trillions of sparkling, icy cometary nuclei a mile or more across. Oort Cloud objects are generally thought to be the source of long period comets orbiting our Sun after their orbits have been gravitationally perturbed.
The Oort Cloud is named for its two discoverers, the Dutch astronomer Jan Oort and the Estonian astronomer Ernst Opik. Therefore, this spherical cloud composed primarily of icy planetesimals is more precisely designated the Opik-Oort Cloud. The Oort Cloud is believed to be a shell that surrounds our Sun at a distance of up to 100,000 AU, which places it at 50% of the way to Proxima Centauri. The Kuiper Belt and the scattered disk–which are the other two domains of comet-like objects–are less than one thousandth as far from our Sun as the Oort Cloud. The outer limit of the Oort Cloud marks the cosmological boundary of our Sun’s sphere of influence–the boundary of our Star’s gravitational dominance.