It is not so often that astronomers are losing words when they make a space-related discovery, but the picture above from NASAHubble’s telescope managed to do just that. Of all the tools we have available to explore outer space, Hubble has repeatedly proven to be one of the best. The 31-year-old telescope has made countless discoveries over the years, whether it’s answering questions about our own solar system or exploring galaxies millions of light-years away.
In 2021 alone, Hubble has been on a lot. It captured a large ‘eye’ in the middle of a constellation, learned new information about Jupiter’s large red spot, and even identified a ‘ghost’ galaxy that was completely devoid of dark matter. All of this has happened despite a scare earlier this year – one that caused Hubble to be offline for a month due to an ugly computer error.
NASA has just shared one of Hubble’s latest discoveries, and it may be one of the most head-scratching of the entire year. Looking at the picture above, everything seems pretty normal at first. The image shows a large cluster of galaxies deep in space, with Hubble focusing on two of them. The first, labeled ‘single image’, is a galaxy with a bright center and many stars around it. Where things get interesting, the galaxy is labeled ‘mirror image’. Not only does it look like a galaxy mirroring itself, but it is also a replica of the galaxy ‘single image’ above it. In other words, there are three observations of the same galaxy for no apparent reason. After first seeing the ‘double’ galaxy in 2013, astronomer Timothy Hamilton admitted that he and his team “was really blunt.”
The real reason behind this mysterious galaxy
If it sounds impossible that there are three instances of the exact same galaxy, it’s because it is. What really happens here is something called a ‘gravitational lens’ – a visual trick that occurs when a large amount of matter distorts light from other galaxies. Gravitational lenses are quite a familiar thing today, but in 2013 when Hamilton discovered these confusing galaxies, that was not the case.
In this particular situation, NASA explains the lens as follows: “A precise alignment between a background galaxy and a foreground galaxy cluster produces two enlarged copies of the same image of the distant galaxy. This rare phenomenon occurs because the background galaxy extends across a space ripple.” Another way of thinking about it is like wavy reflections in a swimming pool. When the afternoon sun shines brightly on an outdoor pool, the light from the sun appears at the bottom of it with swirling, wavy reflections. As Richard Griffiths of the University of Hawaii explains, “Ripples on the surface act as partial lenses and focus sunlight in bright squirming patterns on the bottom.”
This is essentially what happens in the picture at the top of this article, albeit on a much larger scale. A ripple in space takes light from the individual image galaxy, enlarges and distorts it, and this is what is seen with the mirrored image galaxy. It’s a big oversimplification of all the science and research that went into getting to this answer, but that’s ultimately how the picture is explained. If it’s anything, it’s a good reminder of how much we still need to learn about space. In just 8 years, astronomers went from not understanding this photo to having a logical explanation for it. In the next 8, 16 or 32 years, who knows what other mysteries we also have answers to.
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