This effect looks extremely realistic thanks to the correct equations behind it.
Tech Art Director of Research and Development at Gearbox and Founder of Overdraw.XYZ Ryan James Smith has unveiled a stunning black hole effect made in Unreal Engine and Niagara, UE's next-generation VFX system. According to the artist, it took a year and a half to finish this simulation and make it look as realistic as possible. Using mathematical equations, the artist has managed to implement physically correct gravitational lensing and make the black hole curve the light in a natural-looking way.
What's more, the artist released a small breakdown that explains how gravitational lensing was set up, how the accretion disk was created, how Niagara was used, and more. You can check out the breakdown down below or by visiting Ryan's Twitter page.