Galaxy UGC 477 is so faint you can see further galaxies through its spiral arms. HST/NASA/ESA

Not all galaxies are shiny and bright; some of them are actually quite dim, which makes them a lot more difficult for us to spot in the night sky.

One of these objects is UGC 477, recently observed by the Hubble Space Telescope. The galaxy is located 110 million light-years away in the constellation of Pisces. UGC 477 is a low surface brightness (LSB) galaxy, and although it is the same size as the Milky Way, it is significantly fainter.

UGC 477 has a higher gas-to-star ratio than your average spiral galaxy, meaning that this galaxy has not produced many stars over cosmic time. Astronomers think that this is due to where UGC 477 is in the universe. Galaxy mergers are the principal mechanism to induce large episodes of star formation, but this galaxy could be in or near a void. Being all alone and lacking companions, this galaxy didn’t have many collisions in its past.

LSB galaxies were first proposed in 1976 by British astrophysicist Mike Disney, and the first one, Malin 1, was only discovered in 1986. Due to their modest brightness, LSB galaxies are obviously very difficult to detect; some of them are 250 times fainter than the night sky that surrounds them.

This fact has created an imbalance in galactic surveys: LSB galaxies end up being underrepresented, even though they play a role as important as any other galaxy in our understanding of how the universe has changed over the past 13.8 billion years.

Some have argued that by studying LSB objects, we could learn more about dark matter than from other galaxies. Dark matter is the mysterious substance that outweighs normal matter – which makes up everything we can see – six to one.

Dark matter influences how galaxies rotate and interact, and astronomers believe that by looking at galaxies like UGC 477, whose evolution relies on how dark matter behaves, we can better understand the mysterious substance.

Hopefully, the James Webb Space Telescope – the successor to Hubble – will be able to discover even more LSB galaxies and help us crack one of the big mysteries of the universe. 


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