It is not very often that astronomers are speechless when making a space-related discovery, but the image above from POTThe Hubble telescope managed to do just that. Of all the tools at our disposal 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 investigating galaxies millions of light-years away.
In 2021 alone, Hubble has been doing a lot. It has captured a large ‘eye’ in the middle of a constellation, learned new information about Jupiter’s Great Red Spot, and even identified a ‘ghost’ galaxy completely devoid of dark matter. All of this has happened despite a scare earlier this year, one that caused Hubble to go offline for a month due to a nasty computer glitch.
POT just shared one of Hubble’s latest discoveries, and perhaps one of the most head-scratching of the entire year. Looking at the photo above, everything seems pretty normal at first. The picture shows a large cluster of galaxies in the depths of space, with Hubble focusing on two of them. The first, labeled ‘single image’, is an ordinary galaxy with a bright center and numerous stars around it. Where things get interesting is with the galaxy labeled ‘mirror image’. Not only does it look like a galaxy reflecting itself, but it is also a copy of the ‘single image’ galaxy above it. In other words, there are three sightings of the same galaxy for no apparent reason. After first detecting the ‘double’ galaxy in 2013, astronomer Timothy Hamilton admitted that he and his team “They were really stumped.”
If it seems impossible that there are three instances of the exact same galaxy, it is because it is. What is really happening here is something called ‘gravitational lensing’, a visual trick that occurs when a large amount of matter distorts the light from other galaxies. Gravitational lensing is a well-known thing today, but in 2013, when Hamilton discovered these puzzling galaxies, that was not the case.
In this particular situation, NASA explains the lenses as follows: “A precise alignment between a background galaxy and a foreground galaxy cluster produces enlarged twin copies of the same image of the remote galaxy. This rare phenomenon occurs because the background galaxy extends on either side of a ripple in the structure. from space”. Another way to think of it is like the wavy reflections present in a swimming pool. When the afternoon sun shines brightly on an outdoor pool, sunlight appears in the background with undulating, swirling reflections. As Richard Griffiths of the University of Hawaii explains, “The ripples on the surface act as partial lenses and focus sunlight in bright wavy patterns at the bottom.”
This is essentially what is happening in the image at the beginning of this article, albeit on a much larger scale. A wave in space is taking light of the single image galaxy, enlarging and distorting it, and that is what you see with the mirror image galaxy. That’s a huge simplification of all Sciences and the research that was carried out to come up with this answer, but ultimately this is how the photo is explained. If anything, it’s a great reminder of how much we still have to learn about space. In just 8 years, astronomers went from not understanding this photo to having a logical explanation. In the next 8, 16 or 32 years, who knows for what other mysteries we will also have answers.
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