Now, those who love to see the wonders of the sky are having more fun than ever. Every day, at least one of the countless observatories currently operating on the ground or in space delivers stunning new snapshots, each depicting an alien world, exploding stars, colliding galaxies, or other astrophysical phenomena. provides a new perspective. Most of these images are odes to the power and unimaginable scale of the universe, carving stunning beauty out of epic violence.
But not everything in our galaxy (or beyond) is the result of such ostentatious chaos. Some of the most visually appealing celestial bodies are quiet, stable, and even calm. And it’s so dark that not only does it emit no visible light, it actually absorb It creates a deep blackness that looks like it has been cut out of space.
These shadowy expanses have many nicknames, including dark nebulae, dust clouds, and knots, but I prefer to call them bok globules. This name was given in honor of Bart Bok, the Dutch-American astronomer who studied them.
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Bok globules are small, dense clumps of cosmic dust. Millions of them are scattered around our galaxy. They are cold and impermeable to visible light, so until recently the only way to see them was in silhouette against a brighter background material. Although not as flashy as its star factory cousins such as the Orion Nebula, the Bok Globule can still make stars, albeit in a more artisanal manner. They create one or several stars at a time, which are mostly hidden from our prying eyes. Abyss of dust.
Of all the dark globules that can be seen with a telescope, my favorite is definitely Barnard 68 (colloquially referred to as B68). Located about 500 light-years from Earth, it is a fuzzy, comma-shaped, coal-black cloud that is only 0.5 light-years wide and about 5 trillion kilometers long. It is easily visible to us because it is located in the constellation Ophiuchus, with the star-filled center of the Milky Way galaxy in the background. B68 appears to us as negative space. absence number of stars.
Why is it so dark? Although B68 is made mostly of hydrogen gas (like almost everything else in our galaxy), it is also rich in carbon. Some of this element is trapped in small molecules such as carbon monoxide, but much of the rest exists instead in long, complex molecules that make up what astronomers commonly refer to as dust. . characteristic (or erase) A characteristic of dust is its ability to block visible light.
And dust clouds can actually be dark. In the case of B68, the star opposite us will have its light reduced by a factor of 1. 15 trillion. To put this into perspective, dimming the Sun in our sky this much would reduce it to a 4th magnitude star that would be difficult to spot even in slightly polluted skies. If you were on one side of B68 and the sun was on the other side, the sun’s light would be greatly attenuated over that half light year. It will become invisible to the naked eye.
Such extreme darkness exposes B68, and the Bok sphere more generally, to continuous misperceptions. A few years ago, astronomers discovered the existence of vast expanses of space with almost no galaxies. These are called cosmic voids and can be millions of light years in diameter. Sadly, I’ve seen quite a few breathtaking videos and articles depicting images of the B68. As an astronomer it’s infuriating to see this mistake because these are completely different objects, but the actual cavity being discussed is millions of times larger than our friendly Bok sphere. It’s also pretty funny because it’s big.
B68’s incredible light-absorbing ability relies on surprisingly small amounts of dust. Even in its densest core, B68 contains fewer than 1 million particles of matter per cubic centimeter. That may sound like a lot, but here on Earth, it’s the equivalent of a laboratory-grade vacuum. At sea level, Earth’s atmosphere is equivalent to about 10 vacuums.19 There are more molecules per cubic centimeter, which changes the air you breathe somewhat. 10 trillion times More dense than the best B68.
Despite the all-encompassing darkness, the density of B68 can be discerned. This is because, like other clouds, B68 becomes less dense towards its surroundings. This creates an interesting situation. From our vantage point, we can see some background stars through the relatively thin material at the edges, but the closer we get to the center, the more of that light is absorbed. Stars appear bright at the periphery of the cloud, but gradually dim as they approach the center. Such stars don’t just fade, because dust tends to absorb blue light better than red light, which passes through more easily. they too turned red. and infrared Light can pass through B68 more easily, so telescopes tuned to these wavelengths can see more stars. Astronomers can use its redness and dimness to measure how much dust is in the cloud.
Other techniques can also be used to measure the temperature of B68. Bok globules are extremely cold, and B68 is no exception, registering a bone-chilling -256 degrees Celsius at its ends, but dropping to just -265 degrees Celsius in its centre. This is just above absolute zero.
But that whisper of warmth is enough to support the globule against its gravity. Although B68 is not very large, containing only about 3 to 4 times the mass of the Sun, it is still usually more than enough to cause a gravitational collapse. However, the small amount of internal heat keeps the B68 inflated like a hot air balloon (or more accurately, like a frigid, near-vacuum balloon).
But this fragile impasse will not last forever. A close look at B68 shows what appears to be two distinct “cores” of denser material. One near its center and the other in its stubby “tail” near its southeastern end (bottom left of the photo above this article). Radio observations show that this tail was once a small independent cloud, but it has now merged with B68, disrupting the delicate balance of gravity inside the cloud. As a result, B68 may now be collapsing. This means that this dark cloud could literally have a bright future ahead of it. In other words, stars will form.
As the material collapses, the density in the core increases and the temperature associated with it increases. This condition would last for hundreds of thousands of years until a star is born in the center of the cloud (perhaps 100,000 years, given that B68 has enough material to form two Sun-like stars). more than one star is born). If that were to happen, almost all of the material remaining in the cloud would be blown away by the light of the newborn star – that is, except perhaps for a small portion under the control of the star’s gravity. , they can condense and collapse. It spins to create a disk of material that forms a planet.
And who knows? In another few billion years, perhaps some of these worlds will have life and, eventually, intelligence. As a result, in the distant future, alien astronomers will peer in and marvel at the universe they see, a sight they have probably never been able to glimpse. B68’s youthful Kasumi who devours starlight. Perhaps by then both the Earth and the Sun will have disappeared, and the galaxy will have turned into a completely different place. But even so, there is comfort in knowing that once upon a time we all began much the same way. Our sun was born in a huge dust-covered nebula and eventually shined with thousands of other stars, a stellar nursery that, like the children of the universe, was long ago scattered. is.
Everything in the universe is temporary, and much of it is cyclical. We are privileged to be able to observe what we can now observe, even if what we see is very difficult to see at all.
