Dwarf star Wolf 359 endures after fictional Borg battle

Wolf 359 photographed several years apart so you can see its movement across the sky. The star travels 0.4 arc seconds per year – the moon’s diameter in 4,500 years – against the distant starry background. Credit: ESO, Digitized Sky Survey, U.K. Schmidt Telescope, PPARC and the Association of Universities for Research in Astronomy, Inc. (AURA).

The Borg were probably the most frightening and evil of all the alien races in Star Trek: The Next Generation. Outside of their collective group, nothing mattered. It was just kill, kill, kill and assimilate. If you were captured, the Borg hooked you into the network, sucked every thought from your brain and used the knowledge to destroy the next heroic attempt to snuff them out.

A famous fictional battle took place between the good guys and the Borg happened in the year 2367 near the star Wolf 359. Why Wolf 359 was chosen I don’t know, but it is a real star and a special one at that. Perhaps the writers wanted a star near Earth to bring home the impending threat to our own solar system.

Wolf 359 is a very faint star located in the southern half of Leo the Lion. This map shows the sky facing east in late Jan. – early Feb. around 9 p.m. local time. Created with Stellarium

Wolf 359 was the 359th star of more than a thousand found discovered by German astrophysicist Max Wolf to have a large motion across the sky, what astronomers refer to as proper motion. All stars are moving around the center of the Milky Way galaxy. Nearby stars generally appear to move more quickly across the sky than distant ones because they’re closer to us. Kind of like driving along the freeway where a service station quickly recedes into the distance while the distant mountain ahead appears nearly still for many miles.

Astronomers are able to measure distances to stars with large proper motions, and once you know distance, you know how big and bright a star really is. What we learn from them can then be applied to more distant stars, the movements of which are nearly impossible to detect. That’s why Wolf cataloged as many of these stellar midges as he could.

The size of our sun and Wolf 359 compared. Illustration: Bob King

Outside of the sun, Wolf 359 is the third closest star to Earth after the Alpha Centauri system and Barnard’s Star. Just 7.7 light years away, it’s one light year closer than the sky’s brightest star, Sirius. You’d think something so close would outshine Sirius or at least be visible with the naked eye. I wish. Wolf 359 shines at a paltry 13.5 magnitude, requiring at least an 8-inch telescope to see.

Unlike Sirius, which is both hotter and nearly twice as large as the sun, Wolf 359 is a red dwarf only about 16% the size of the sun or approximately 140,000 miles across. That’s hardly twice the size of Jupiter. If Wolf 359 were at the center of our solar system, you’d need binoculars to see it as a disk. Not only that, but with an energy output of 1/10th of 1% of the sun, it would only be as bright as ten full moons squished into a tiny dot.

Astronomer Max Wolf

Red dwarfs are red because their surfaces are cool, and like an ember, emit more red light than green or blue. They’re also small. Wolf 359 is about as small as star can be and still fuse hydrogen atoms together in its core to create energy the way the sun does. Its surface cooks at at a tepid 4,000-4,700 degrees F, cool enough to allow molecules like water and carbon monoxide to form. You won’t find that happening on old Sol.

Despite its diminutive persona, Wolf 359 will outlast the sun and nearly every star we see in the night sky. Being cool, red dwarfs burn their hydrogen fuel frugally compared to larger stars that devour theirs at prodigious rates. Not only that, but hydrogen is continually recycled throughout the interior of red dwarfs and available for burning. In sun-sized and larger stars, hydrogen is converted into helium ash, which settles in the core. The sun will continue to burn hydrogen in its old age, but only in a thin shell around the core.

When the sun runs out of fuel in another 5 billion years and evolves into a white dwarf star, Wolf 359 will keep the home fires burning for up to 10 trillion years. No matter what happens in science fiction, Wolf 359 will endure.