An anarchic region of star formation captured

The Danish 1.54-meter telescope located at the European Southern Observatory (ESO) La Silla Observatory in Chile has captured a striking image of NGC 6559, an object that showcases the anarchy that reigns when stars form inside an interstellar cloud.

NGC 6559 is a cloud of gas and dust located at a distance of about 5,000 light-years from Earth in the constellation Sagittarius the Archer. The glowing region is a relatively small object, just a few light-years across, in contrast to the 100 light-years and more spanned by its famous neighbor, the Lagoon Nebula (M8). Although it is usually overlooked in favor of its distinguished companion, NGC 6559 has the leading role in this new picture.

The gas in the clouds of NGC 6559, mainly hydrogen, is the raw material for star formation. When a region inside this nebula gathers enough matter, it starts to collapse under its own gravity. The center of the cloud grows ever denser and hotter until thermonuclear fusion begins and a star is born. The hydrogen atoms combine to form helium atoms, releasing energy that makes the star shine.

These brilliant hot young stars born out of the cloud energize the hydrogen gas still present around them in the nebula. The gas then re-emits this energy, producing the glowing threadlike red cloud seen near the center of the image. This object is known as an emission nebula.

But NGC 6559 is not just made of hydrogen gas. It also contains solid particles of dust made of heavier elements such as carbon, iron, or silicon. The bluish patch next to the red emission nebula shows the light from the recently formed stars being scattered — reflected in many different directions — by the microscopic particles in the nebula. Known to astronomers as a reflection nebula, this type of object usually appears blue because the scattering is more efficient for these shorter wavelengths of light.

In regions where it is very dense, the dust completely blocks the light behind it, as is the case for the dark isolated patches and sinuous lanes to the bottom left-hand side and right-hand side of the image. To look through the clouds at what lies behind, astronomers would need to observe the nebula using longer wavelengths that would not be absorbed.

The Milky Way fills the background of the image with countless yellowish older stars. Some of them appear fainter and redder because of the dust in NGC 6559.