The Abyss of Barnard 68, a Great Dark Spot in the Firmament

On the vast canvas of the cosmos, where starlight typically reigns supreme, there are regions in which darkness not only persists, but dominates. One of them is Barnard 68, a dark nebula that, despite its apparent invisibility, holds one of the most fascinating secrets of the universe: the birth of a star.

Located in the southern constellation of Ophiuchus, about 407 light-years from Earth, Barnard 68 is one of the closest interstellar clouds to our solar system. To the naked eye—or even through conventional optical telescopes—it appears as a black blotch that hides the glow of thousands of stars lying behind it.

It is so dense that it hardly allows any visible light to pass through. In astronomical terms, it is known as an absorption nebula, also called a Bok globule: a small, dense, and cold concentration of gas and dust floating in the spiral arms of our galaxy, the Milky Way.

dark nebula barnard 68 — Another view of Barnard 68, to the right of the image. Credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev / Wikimedia Commons

Its discoverer, American astronomer Edward Emerson Barnard, cataloged it in 1919 as part of his pioneering work on dark nebulae. The complete catalog was published in 1927 and included around 350 of these regions. Since then, Barnard 68 has become a key observational target for understanding the earliest stages of star formation.

With a mass approximately twice that of the Sun and stretching across half a light-year, Barnard 68 is a remarkably well-defined structure. Its sharp edges and spherical shape suggest that it is in a delicate balance: the thermal pressure of the gas within it counteracts the gravitational pull attempting to collapse the cloud into a more compact point. This state resembles a soap bubble suspended in the air, gently oscillating as it resists both expansion and collapse.

This type of stability, though temporary, is a rare and precious phenomenon. Observations suggest that this cloud is in an oscillatory phase, like a water-filled balloon trembling at the slightest stimulus. But gravity, as always in the universe, is patient. Astronomers predict that Barnard 68 will collapse within about 200,000 years, initiating the process that will give rise to a new star. That will be the moment when gravity overcomes internal pressure, concentrating the material until the necessary conditions for nuclear fusion are met.

Despite its opacity at visible wavelengths, advances in astronomical technology have allowed scientists to peer inside. Thanks to the Very Large Telescope (VLT), located at Cerro Paranal in Chile, about 3,700 background stars have been detected whose light is filtered through the cloud. Around a thousand of these stars can only be seen in the infrared spectrum, which more easily penetrates the dense curtain of dust.

These studies have enabled scientists to precisely map the internal distribution of dust in Barnard 68. The variation in the amount of light that manages to pass through offers clues about the cloud’s density and shape. More recently, the Herschel Space Observatory provided crucial data for understanding its internal temperature and the arrangement of dust particles: an extremely cold atmosphere, at just 16 Kelvin (−257 °C), making it one of the coldest known places in the universe.

The proximity of Barnard 68 makes it a true natural laboratory for astronomers. Unlike more distant and chaotic molecular clouds, its relative closeness and isolation allow for a detailed analysis of the physical processes that govern its stability and evolution.

A 2006 study suggests that the cloud vibrates as if it had been disturbed recently, perhaps by another nearby cloud or a stellar shock wave. These vibrations could be the prelude to its final collapse, the first step toward the birth of a new star.

Curiously, Barnard 68 has been mistaken on more than one occasion for the Boötes Void, a vast region of the universe apparently empty of galaxies. Although both share a dark and enigmatic aesthetic, they are unrelated: one is a dense and nearby cloud, and the other a massive low-density area on a cosmological scale.

Images of Barnard 68, taken with advanced instruments, are hauntingly beautiful. The contrast between its total blackness and the starry background makes it an icon of the deep sky. It is a visual paradox: a hole in the universe that is not empty, but brimming with matter and potential. An absence that actually represents a beginning.

This article was first published on our Spanish Edition on April 24, 2025: El abismo de Barnard 68, una gran mancha oscura en el firmamento