Stars form inside vast collections of molecular hydrogen called molecular clouds, sometimes called stellar nurseries or star forming regions. Instabilities in the clouds cause gas to collapse in on itself, and when enough material gathers and the density reaches a critical stage, a star begins its life of fusion.
But molecular clouds aren’t always alone. They often exist in association with other clouds, and astronomers call these formations Cloud Complexes. The Chamaeleon Cloud Complex (CCC) is one of the closest active star forming regions to Earth. It’s further divided into three substructures called dark clouds, or dark nebula. They are Chamaeleon 1 (Cha1), Chamaeleon 2, and Chamaeleon 3.
NASA created a new composite image of Chamaeleon 1 based on Hubble images, and the vivid panorama brings Chamaeleon I to life.
The CCC is a massive star-forming region (SFR) that occupies most of the Chamaeleon constellation. The complex is about 65 light-years wide is about 160 parsecs (522 light-years) away.
There’s a lot going on in this image: dark dusty molecular clouds shelter young stars as they form, other bright blue young stars light up striking reflection nebula, and jets of ionized gas slamming into nearby dust clouds at hundreds of kilometres per second create bright clumps of nebulosity called Herbig-Haro (HH) objects.
When young stars are still forming and accreting material from their surrounding disks, they can emit powerful jets of ionized gas. The jets are also called MHOs—Molecular Hydrogen emission-line Objects. The star emits the jets from its poles and they create MHOs aligned with the star’s rotational axis. Sometimes there are several MHOs near a single star.
In this Hubble image, a protostar sits in the white-orange cloud near the bottom. The narrow jets of ionized gas in this part of Cha 1 create the Herbig-Haro object HH 909A. HHs don’t last long and astronomers can watch as they change over the years.
These Hubble images aren’t just for visual enjoyment. Everything about young stars is interesting to astronomers, and Hubble’s succeeded at imaging the environments around young stars, including Herbig-Haro objects. This video shows how the Herbig-Haro HH 46, which isn’t in Cha1, changed in 14 years.
HH 909A will undergo changes similar to the ones in the video. In fact, lots will change inside Cha1, and young stars will drive most of that change. When stars emerge from their dark nebula as fully-formed balls of fusion, their powerful stellar winds will shape the gas that surrounds them. The bright blue nebula is an example of the interaction between the young stars and the gas.
In the nebula in the leading image, the star isn’t energetic enough to ionize the gas. If it were, the gas would then emit its own light as an emission nebula. Instead it’s a reflection nebula, where the light from the star is scattered, making the dust in the cloud visible. Reflection nebulae are often blue for the same reason our sky appears blue: blue light is scattered more efficiently. The scattering is called Rayleigh Scattering after the discoverer, British physicist Lord Rayleigh.
Our Sun was born the same way the stars in the Hubble image were: inside a molecular cloud. Stars form in groups inside these clouds, and our Sun may have had thousands of siblings. In its earlier epochs, the Sun was part of a star cluster, the same types of clusters we see in the sky today.
The Sun’s siblings drifted away from one another, and the Sun dispersed the gas and dust in its immediate surroundings long ago. Its stellar wind spread the gas and dust back into the ISM, to eventually be taken up in another molecular cloud and begin the star formation cycle all over again.
But at one time in its early days, our Sun may have had its own reflection nebula. That would’ve been a remarkable sight.
We’ll never know exactly where our Sun formed and whether it had a nebula, or what that nebula might have looked like. But we can gaze at this Hubble image and wonder about it. Each time we look at young stars forming in a cloud complex like Cha 1, with its Herbig-Haro objects, its nebula, and its jets of ionized gas, it’s a glimpse back in time to our own beginnings.
Because, somewhere in the disk of gas and dust swirling around the young Sun, surrounded by thousands of stellar siblings, embedded in all that raucous mayhem, a rocky planet began to take shape.