More than meets the eye

Meet NGC 5728, a spiral galaxy around 130 million light-years from Earth. This image was captured using Hubble’s Wide Field Camera 3 (WFC3), which is extremely sensitive to visible and infrared light. Therefore, this image beautifully captures the regions of NGC 5728 that are emitting visible and infrared light. However, there are many other types of light that galaxies such as NGC 5728 can emit, which WFC3 cannot see.

In this image, NCG 5728 appears to be an elegant, luminous, barred spiral galaxy. What this image does not show, however, is that NGC 5728 is also a monumentally energetic type of galaxy, known as a Seyfert galaxy. This extremely energetic class of galaxies are powered by their active cores, which are known as active galactic nuclei (AGNs). There are many different types of AGNs, and only some of them power Seyfert galaxies. NGC 5728, like all Seyfert galaxies, is distinguished from other galaxies with AGNs because the galaxy itself can be seen clearly. Other types of AGNs, such as quasars, emit so much radiation that it is almost impossible to observe the galaxy that houses them. As this image shows, NGC 5728 is clearly observable, and at optical and infrared wavelengths it looks quite normal. It is fascinating to know that the galaxy’s centre is emitting vast amounts of light in parts of the electromagnetic spectrum that WFC3 just isn’t sensitive to! Just to complicate things, the AGN at NGC 5728’s core might actually be emitting some visible and infrared light — but it may be blocked by the dust surrounding the galaxy’s core.