Barnard 68, mistakenly thought to be a black hole, is actually a mass...

Author: Huang Xianghong Duan Yuechu

There are many fascinating celestial bodies hidden in the vast Milky Way, and Barnard 68 is undoubtedly one of the most mysterious. It is often mistaken for a black hole in space, but in fact, it is a cloud of dust that temporarily appears dense and opaque. This unique celestial body has attracted the attention of countless astronomers and astronomy enthusiasts. Let us explore its mysteries together.

Barnard 68 is about 500 light-years away from Earth, located in the direction of Ophiuchus. It is only about half a light-year wide, but spans a vast space of about 5 trillion kilometers. When we observe it, we will find that it is like a compact, opaque and clearly defined mysterious object, as if a piece of it has been "dug out" from the starry background, presenting a unique "negative space" effect, which completely blocks the light of the stars behind it, as if this is a dark abyss in the universe.

Barnard 68 is made up mostly of hydrogen, like most objects in the Milky Way. However, it is also rich in carbon, some of which is in the form of small molecules such as carbon monoxide, while the rest is made up of complex long-chain molecules, which astronomers call "dust." These dust particles are the key to why Barnard 68 is so dark. They have extremely strong light-blocking capabilities and can effectively block the propagation of visible light. In fact, the light emitted by any star on the other side of Barnard 68 will be weakened by as much as 15 trillion times.

To understand this light-blocking effect more intuitively, we can imagine that if the sun is placed on the other side of Barnard 68, the sun observed from the earth will become extremely dim, even reduced to a fourth-magnitude star that is difficult to detect in the sky with light light pollution. Such a strong light-blocking ability makes Barnard 68 very easy to be misidentified. For example, it is often mistaken for a huge cosmic void. But in fact, a cosmic void is a vast space with a diameter of millions of light years and almost no galaxies, which is completely different from Barnard 68.

Although Barnard 68 is extremely dark overall, astronomers can still detect information about it through some clever methods. Because the dust cloud is relatively thin at the edge, the light of some background stars can be observed through the edge. The closer to the center, the more light is absorbed, and the dimmer the star becomes. At the same time, the dust has a stronger ability to absorb blue light, while red light is relatively easier to penetrate, which causes the stars observed through the dust cloud to not only become dimmer, but also appear noticeably red. In addition, infrared light can pass through Barnard 68 more easily, so when observing with an infrared telescope, more stars hidden behind the dust cloud can be seen. Through precise measurement and analysis of these phenomena, astronomers are able to calculate the dust content inside the dust cloud.

In addition to the dust content, the temperature of Barnard 68 is also an important research indicator. As a member of the Bok globules, Barnard 68 is extremely cold, with an edge temperature of about minus 256 degrees Celsius and a center temperature of minus 265 degrees Celsius, just a little above absolute zero. However, it is this weak "trace of warmth" that allows Barnard 68 to resist the collapse of its own gravity. Although its mass is only three to four times that of the sun, this is usually enough to trigger gravitational collapse. The internal heat is like an invisible supporting force, allowing Barnard 68 to remain relatively stable like a cold, near-vacuum balloon.

However, this delicate balance will not last forever. Through careful observations, astronomers have discovered that there seem to be two high-density "cores" inside Barnard 68, one close to the center and the other at the short "tail" on the southeast edge. Radio wave observations show that this "tail" may have once been an independent smaller cloud that is now merging with Barnard 68. This process broke the original gravitational balance inside the cloud, causing Barnard 68 to begin to collapse. And this collapse process may indicate that it will usher in a "bright future" - forming stars.

During the collapse, matter continues to gather toward the center, and the density and temperature of the center will continue to rise. After hundreds of thousands of years of evolution, one (or even multiple) stars are expected to be born in the core of the cloud. Once stars are formed, the strong light they emit will blow away almost all the remaining matter in the cloud. Only a very small amount of matter captured by the star's gravity may condense and form a disk-like structure, laying the groundwork for the birth of planets.

Imagine that, billions of years from now, if life or even intelligent civilizations have emerged on these potential planets, alien astronomers might be curious about what they see when they look out into the universe, never able to peer through the young, star-swallowing mist of Barnard 68 to see what the universe once looked like. Perhaps by then, Earth and the sun will no longer exist, and the Milky Way will have gone through a lot of changes. Even so, we can still find some solace in such cosmic cycles, knowing that our sun was once born in a huge, dust-shrouded nebula, which eventually gave birth to countless stars and formed a stellar cradle that has long since dissipated.

As we can see, everything in the universe is constantly changing, and many things follow a cyclical law. We are fortunate to be able to observe mysterious and elusive objects such as Barnard 68, which gives us a deeper understanding and insight into the mysteries of the universe. On the road of exploring the universe, every new discovery is like a beacon, illuminating the direction we are going, and making us more in awe of this vast and magical universe.

References:

What's Inside Our Galaxy's Darkest Place? | Scientific American