What is a Nebula?
A nebula is a giant cloud of dust and gas in space. Some nebulae (more than one nebula) come from the gas and dust thrown out by the explosion of a dying star, such as a supernova. Other nebulae are regions where new stars are beginning to form. For this reason, some nebulae are called “star nurseries”.
How does dark nebula form?
Dark nebulae are interstellar clouds that contain a very high concentration of galaxy dust, gas and plasma. This allows them to scatter and absorb all incident optical light from background stars or a reflection nebula creating irregular shapes that have no defined boundaries.As a result, a dark nebula or an absorption nebula formed which completely opaque at visible wavelengths. They are most obvious when located in front of a bright emission nebula or in a region that is very rich in stars.
What is the temperature inside the dark nebulae?
The average temperature inside a dark nebula ranges from about 10 to 100 Kelvin, allowing hydrogen molecules to form and star formation to take place. Large dark nebulae that can contain over a million solar masses of material and extend over 200 parsecs are known as giant molecular clouds.
Dark nebulae captured at Telok Kemang Observatory.
There are different kinds of dark nebula, the Horsehead Nebula is the most famous which is also known as NGC2023. It was found in the constellation of Orion. Despite its popularity, the Horsehead Nebula is not easy to spot. Large dark nebula can be seen by the naked eye, often appearing as dark patches scattered in the sky.
The Dark Horse Nebula
The Dark Horse Nebula is a huge dark nebula that obscures part of the brightest regions of our Milkyway galaxy. It is also known as “Great Dark Horse” because it is one of the largest groups of dark nebulae in the sky. It is sometimes called The Prancing Horse and only can be seen from the darkest places that lie in the equatorial constellation Ophiuchus. Any amount of light pollution or moonlight will obscure this large region of dust.The rear of The Great Dark Horse consists of the Pipe Nebula (B59) and the Snake Nebula (B72).
The Pipe Nebula (B59)
The Pipe Nebula which is part of the Dark Horse Nebula appears silhouetted against the rich star clouds close to the center of the Milkyway in the constellation of Ophiuchus. B59 located at a distance of about 600-700 light-years away from the Earth. Dense cores of dust within the Pipe Nebula are collapsing to form new stars. The Pipe Nebula has two main parts, which are the pipe stem and the bowl of the pipe.
The Snake Nebula (B72)
Another part of Dark Horse Nebula is the Snake Nebula, also listed as Barnard 72 (B72) that located in the constellation Ophiuchus at the center of our Milkyway Galaxy. B72 was a few light-years across and about 650 light-years away from the Earth. The width of a Snake Nebula spans the angular width of a full moon.
Next, a strong resemblance to a jumping dolphin was B252 named Dolphin Nebula. This type of dark nebula was located in the constellation of Scorpius. This interstellar cloud is sufficiently dense to completely block the light from thousands of background stars in the direction towards the center of our galaxy.
On the other hand, the Black Hole Nebula is the largest dark nebula. It is very dense and opaque, located in the constellation of Sagittarius. A 12th magnitude star can be seen in it, as the location of the star is in the foreground of B92.B92 is located at a distance of 10 000 light-years from Earth. Many dark nebulae carry a starting designation with the letter B-referring to Edwin Barnard, an early astrophotographer who cataloged them.
Written by : Hamidatul Aina Binti Elham
Internship Student UM, 2019