There are no known stars or galaxies that start with the letter "Y". This is because the naming conventions for these celestial objects don't typically use the letter "Y".

Here's why:

* Stars: Most stars are named based on their constellation and their position within it (e.g., Alpha Centauri, Proxima Centauri). Some stars have specific names that have historical origins (e.g., Sirius, Polaris).

* Galaxies: Galaxies are often named based on their location in the sky, their shape, or their discoverer (e.g., Andromeda Galaxy, Whirlpool Galaxy, Messier 101).

While there might be some exceptions or unconventional names, it's extremely unlikely to find a star or galaxy that starts with the letter "Y".