Dharmachakra
All forms resolve to sunyata, essentially a photon without (sometimes with) charge or mass but clear luminosity.
As there is no shape or form but sometime can be a sphere or circle yet these shapes resolves to a rectangle when one uses written communications. I have yet to see a round book.
Dharmachakra is sometimes called the wheel of Truth or Dharma but as the truth or Dharma depends upon your (everyone) continuous meditations perception and experiences the wheel changes but does not change so here the Dharmachakra is represented by a dynamic period (.) that changes when you click on the link.
A period is a very good representation for the Dharmachakra as is the Vajra.
In a sense Dharmachakra is a dynamic teaching mandala, changing to meet your needs whether you want the change or not.
Mahamudra and Dharmachakra are connect as Heavenly beings in a very large space can be contained in a relatively very small space where people in this universe cannot do this. This is due to gravity, the mass times the square of the distance from the centers (everything is connected) while dualistic fixation of motion has time. This is the meaning of the square root of minus one(i = √−1), the complex relationships of phenomena. These relationships are not easy to describe with words but can be described with mathematics or directly understood with a lot of meditation.
A period in this world, though relatively small can contain a lot of Heaven. I am very skeptical that a black hole is a singularity. Singularity only work as a mathematical construct representing realities and is an approximation. The overuses of this approximations can distort the view of reality as earth is much more complex than a point.
Four dimensional time space simulations are very important for mankind to exists and live well in this universe so we can have the leisure to practice spirituality.
The flag of India below has a more tradition Dharmachakra symbol. More --> .