Galactic science weird portal-like thing underground

[MIC6890]

I am currently playing galactic science and I pressed f3+A to reload the chunks. Then i saw a weird portal-like thing underground. I wanted to ask if anyone knows what this is why it it exists.

 

[MIC6890]

I've been told there's an easter egg down there.
That might be it.

ok, thanks, i never heard of it.