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Barnard 33, more popularly known as the Horsehead Nebula, and NGC 2023 are both part of the Orion Molecular Cloud, a star-forming region covering large swathes of the Orion constellation.
Though they are in close proximity to one another, the two nebulae are vastly different, making them quite the odd couple.
Horsehead Nebula
The Horsehead Nebula is one of the most photographed objects in the sky. Its odd shape is the result of intense radiation from a nearby star. This solar wind blows across the dark cloud, shaping the horse’s prominent head and jaw. Astronomers estimate that this radiation will also likely be the nebula’s demise — it could disintegrate the Horsehead in about five to 10 million years.
This image is a compilation of images taken by the Euclid telescope, the Hubble Space Telescope, and the James Webb Space Telescope. It give us a glimpse of the Horsehead Nebula in remarkable detail.
The iridescent waves adorning the area below the horse’s neck are called Herbig-Haro objects. These peculiar features occur when infant stars eject gas at hundreds of miles per second and it crashes into surrounding material, causing shockwaves that make the gas glow. This scarlet hue is the result of the hydrogen gas behind the nebula. It’s being ionized by a young, multiple-star system just out of view called Sigma Orionis.
At the nebula’s base, the bright light from young stars still taking shape pierces through the otherwise dark and moody image. And we're not being hyperbolic here. The Horsehead Nebula is categorized as a dark nebula.
But what exactly makes it so black? An abundance of thick dust is the culprit. Essentially, the cloud of debris blocks the bright light behind the nebula and causes the Horsehead to appear dark in color.
In fact, the dark molecular cloud is only visible because the silhouette of the horse is standing against a bright red glow.
NGC 2023
Beneath the shadow of the Horsehead Nebula (and often overshadowed by it) sits an unlikely companion: a bright, colorful emission and reflection nebula called NGC 2023. It's the really big white circle.
NGC 2023 is a vast structure. In fact, it's one of the largest we’ve seen, at 10x10 arcminutes (for comparison, our Sun’s diameter is about 30 arcminutes).
The nebula is illuminated by a massive young B-type star called HD 37903, seen at its center. Categorized as a blue star, it’s one of the hottest star types, measuring between 10,000 - 25,000 Kelvin (17k - 35k Fahrenheit) at the surface. That's at least twice the temperature of our Sun.
Ultimately, the star reflects onto the clouds of interstellar dust that make up the NGC 2023 nebula, resulting in the glow. And all these clouds of gas and dust makes NGC 2023 the perfect birthplace for stars. Over time, “clumps” of hydrogen and helium within the nebula merge with one another. When they accumulate enough mass, a thermonuclear reaction takes place — and a star is born.
And there you have it. Yet another example of how opposites attract, even way out in the cosmos.
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