Zone of Avoidance

What is this region in space and why do stars and even entire galaxies appear to shun it?

The Zone of Avoidance (ZOA) is a narrow band in the night sky in which very few galaxies can be seen. To reflect this barren-looking region, astronomers nicknamed the band the “Zone of Avoidance’, as compared to other parts of the sky, celestial bodies seem to be actively avoiding this patch of space.

Interestingly, however, the ZOA is actually a misnomer of sorts, as while it is true that very few galaxies are visible within it, it’s not because they are not there or are intentionally ‘avoiding’ it, but rather that they are obscured by the interstellar matter of our own galaxy, the Milky Way.

This occurs as the interstellar dust, attenuation (loss of flux intensity) and stars in the plane of the Milky Way – referred to as the galactic plane – obstruct approximately 20 per cent of the extragalactic sky at visible wavelengths. As a result, this combination of factors makes it extremely difficult to discern cosmic phenomena accurately. For instance, it’s hard not to confuse foreground stars with background galaxies.

Recent developments in space astronomy have made good headway in exploring this obscured part of the night sky by employing surveys of it at longer wavelengths than visible light, such as in infrared.

At these wavelengths, attenuation is almost entirely eradicated, making probing the ZOA more viable. In light of this, many galaxies have now being discovered there – Maffei 1 and 2 and Dwingeloo 1 to name just three -and more are being found each year.