The "Peekaboo Galaxy"
Until recently this distant dwarf galaxy was impossible for us to see, not because we didn't have telescopes that could have seen it but because the bright star appearing next to it was concealing it.
As you'll be aware, our Sun is moving around the Galaxy every 230 million years or so, as do most other stars in our nights sky, but not every star follows the same path, and can appear to be moving much faster from our perspective. The star next to the galaxy was one of these high proper-motion stars, and over the last 50-100 years has slowly moved away revealing behind it a galaxy, and hence the name "Peekaboo".
The dwarf galaxy appears to be 20 million light years from Earth in the constellation of Hydra, and has got scientists excited due to it's chemical make up, having a very metal poor environment similar to what is expected at the start of the universe. In astronomy Metals are any element above Helium, so when we say Metal Poor, we mean it's Hydrogen and Helium almost exclusively.
The puzzle here is, this galaxy doesn't appear to have any old population stars, with the oldest around 2 billion years old (our own Star is almost 5 billion) and you'd really expect to see more metals in such stars.
Source:
https://www.universetoday.com/159045/a-star-was-blocking-a-galaxy-but-now-its-moved-enough-that-astronomers-can-finally-examine-what-it-was-hiding/
