The galaxy SGAS 0033+02 is visible multiple times in this image due to gravitational lensing. It appears as a curved arc just to the upper right of the very bright star, and also as two small round dots above and to the right of the star, respectively. Credit: ESA/Hubble & NASA, E. Wuyts
This star- and galaxy-studded image was captured by Hubble’s Wide Field Camera 3 (WFC3), using data that were collected for scientific purposes. The object of interest was a galaxy that is visible in the bottom left corner of the image, named SGAS 0033+02. What makes this particular galaxy interesting is a little unusual — it appears not just once in this image, but three times. The thrice-visible galaxy is a little difficult to spot: it appears once as a curved arc just to the upper right of the very bright star, and twice more as small round dots above the star and to the right of the star respectively.
SGAS 0033+02’s multiple appearances in the same image are not the result of an error, but instead are due to a remarkable phenomenon known as gravitational lensing. Gravitational lensing occurs when the light from a very distant galaxy — such as SGAS 0033+02 — is curved (or ‘lensed’) by the gravity of a massive celestial object that lies in the foreground, between the distant galaxy and the Earth. SGAS 0033+02 was discovered by its namesake, the Sloan Giant Arcs Survey (SGAS), which aimed to identify highly magnified galaxies that were gravitationally lensed by foreground galaxy clusters. SGAS 0033+02 is of special interest because of its highly unusual proximity in the sky to a very bright star. The star is useful, because it can be used to calibrate and correct observations of the lensed SGAS 0033+02.
This is quite remarkable.