Hubble is the oldest space telescope that is currently active, having spent twenty eight years in orbit. But this doesn’t stop it from surprising us over and over. The proof is in a recent photograph, containing a few rather unexpected elements.
Recently, during a study on Abell 370 – a mass of galaxies situated around four billion light years away, in the Whale constellation – Hubble spotted something in the foreground. While observing these several hundred galaxies, it isolated 22 asteroids, whose tails were creating streaks that looked like background astronomical phenomena.
The study was part of the Frontier Fields programme, which aims to photograph a few of the earliest galaxies of the Universe (or “relic galaxies”) in order to determine how they evolved over time. The position of the asteroid field is near the the ecliptic (the plane of our Solar System) where the majority of asteroids reside, which explains why astronomers saw so many crossings. The image was assembled using several exposures taken in visible and infrared light:
The asteroid tails appear here as white trails that look like curved streaks, an effect caused by parallax. In astronomy, parallax is an observation effect in which the apparent position of an object appears different depending on the viewpoint. For example, when Hubble is turning around the Earth and takes several images of the Galaxy, the asteroids appear to move in relation to the background stars and other galaxies.
While the white streaks have been identified as asteroid tails, the blue streaks are deformed images of distant galaxies from behind the cluster. This effect is known as gravitational lensing, in which the light coming from distant objects is deformed and amplified by the presence of an object situated between the observer and the target object. Although the blue streaks were expected, the white streaks caused by the asteroids came as a complete surprise to the scientists!