The European Southern Observatory’s Very Large Telescope brings us new face-on portraits of six spiral galaxies. But what is the science behind these delightful images?
Everyone loves stunning pictures of spiral galaxies, I have said this before and will no doubt say it again. The folks at the European Southern Observatory (ESO) know this too, and their latest public image release is a bumper set of serenely spinning spirals. The images were made with the observatory’s Very Large Telescope (VLT). This magnificent instrument is located on a mountain top in Chile and consists of an array of six 8.2m telescopes each equipped with adaptive optics to compensate for atmospheric image distortion. Each telescope in the array can be operated independently or combined, essentially forming a single very large telescope. In this mode, the VLT obtains images in the IR band superior to those made with the Hubble Space Telescope.
Apart from its “stop you in your tracks beauty”, why is is this set of images important? Let us look at the images in turn. All are taken in infrared light (IR) and this means we are not seeing them as the human eye would see them. Great lanes of interstellar dust run through all galaxies to a greater or lesser extent, blocking the light of stars. In the Milky Way such dust largely obscures the billions of stars of the galactic core which would otherwise dominate our night sky. However, IR passes easily through this murk, so the dust in these galaxies cannot be seen in the new ESO images, making them appear smoother and less textured than they do in visible light. Viewing galaxies with their streaks of dust stripped away is a perfect way to investigate the vast numbers of stars that make up the spiral arms.
NGC 5247 is a “grand design” barred spiral galaxy, lying 60–72 million light years (18.5-22 Mpc) away. This image presents an excellent view of its pinwheel structure and two major arms.
One of the largest galaxies in the Virgo Cluster, M100 is of about the same mass and size as our own Milky Way but it is dissimilar in other ways. Unlike our galaxy, M100 (also known as NGC 4321) is not barred and features extensive star-forming regions with many massive young stars around its centre. It is about 55 million light years (117 Mpc) from us.
A perfect barred spiral, NGC1300 is around 61 million light years (19 Mpc) from our galaxy (which is just a little smaller than NGC1300). The bar is about 3000 light years long. Oddly no supermassive black hole has yet been found to lurk at the centre of NGC1300. Such black holes are expected to be found in all spiral galaxies.
Another member of the Virgo Cluster, NGC4030 is a classic, tightly-wound spiral galaxy. We see many galaxies in Virgo and the surrounding constellations because when we look towards them we are looking out of the plane of the Milky Way into intergalactic space.
NGC2997 is not face-on to us being tilted at 45 degrees to us, so it appears rather elliptical. About 25-30 million light years from us, it is to be found in the southern hemisphere constellation of Antlia (the air pump).
Part of the same cluster as NGC1300, NGC1232 is also in Eridanus (lying on the Celestial Equator) and is about 60 million light years (18 Mpc) away. It is slightly distorted in shape and the gravitational tug of the smaller nearby galaxy NGC1232A (not visible in the image) is blamed for this.
These six images of galaxies are more than just pretty pictures but are part of a study of spiral galaxy structure led by Preben Grosbøl at ESO. His team hopes to improve our understanding of how billions of stars become arranged into such perfect spiral patterns thus giving us a deeper insight to how the Universe we see today came into being.