The Small Magellanic Cloud and NGC 602

The Small Magellanic Cloud (SMC) is one of the Milky Way’s closest galactic neighbors, some 200 thousand light-years distant. It has a diameter of about 7,000 light-years and contains several hundred million stars, about a total mass of approximately 7 billion times the mass of the Sun. Even though it is a dwarf galaxy, the SMC is so bright that it is visible to the unaided eye from the Southern Hemisphere, near the equator.

New Chandra data have detected X-ray emission from young stars, with masses similar to our Sun, at the region known as the Wing of the SMC. In this composite image of the Wing, the Chandra data are shown in purple, optical data from the Hubble Space Telescope are shown in blue, and infrared data from the Spitzer Space Telescope are shown in red. Astronomers call all elements heavier than hydrogen and helium — that is, with more than two protons in the atom’s nucleus — “metals.” The Wing is a region known to have fewer metals compared to most areas within the Milky Way, and also relatively lower amounts of gas, dust. Taken together, these properties make the Wing an excellent location to study the life cycle of stars and the gas lying in between them. Not only are these conditions typical for dwarf irregular galaxies like the SMC, they also mimic ones that would have existed in the early universe.

Most star formation near the tip of the Wing is occurring in a small region known as NGC 602, which contains a collection of at least three star clusters. One of them, NGC 602a, is similar in age, mass, and size to the famous Orion Nebula Cluster. Using Chandra, astronomers saw extended X-ray emission, from the two most densely populated regions in NGC 602a. The extended X-ray cloud likely comes from the population of young, low-mass stars in the cluster, which have previously been picked out by infrared and optical surveys using Spitzer and Hubble, respectively. This emission is not likely to be hot gas blown away by massive stars, because the low metal content of stars in NGC 602a implies that these stars should have weak winds. X-ray emission traces the magnetic activity of young stars and is related to how efficiently their magnetic dynamo operates. Magnetic dynamos generate magnetic fields in stars through a process involving the star’s rotation speed and convection, the rising and falling of hot gas in the star’s interior. The combined X-ray, optical, and infrared data also revealed, for the first time outside our galaxy, objects representative of an even younger stage of evolution of a star. These so-called “young stellar objects” have ages of a few thousand years and are still embedded in the pillar of dust and gas from which stars form, as in the famous “Pillars of Creation” of the Eagle Nebula.

Credits: NASA, Wikipedia.