The tiny blobs spin in the water and attract their neighbors. They are aligned into six-sided, ordered, repeating patterns as they gather together.
The Patiria miniata are living, self- moving sea stars that are governed by forces of physics.
Spinning sea star embryos gathering themselves into a living crystal. (Tan et al., Nature, 2022)
The formation of a crystal with components that are actually living has never been connected to the formation of a crystal.
This was an amazing phenomenon that has never been reported before.
Fakhri, MIT physicist Tzer Han Tan and colleagues are studying active matter, systems where each component uses energy to move about, throwing the whole group out of balance.
These systems can have unexpected properties. The sea stars are no exception.
The embryo uses its hair-like cilia to spin. Spontaneous ripples start flowing through the structure they've formed when enough people gather at the surface of the water
Fakhri says they're as big as the crystal itself.
Model of the ripples with arrows and color coding to indicate each embryo's direction. (Tan et al., Nature, 2022)
Alexander Mietke is a theoretical biophysicist at MIT and study author.
You would expect these ripples to die out quickly because of the water's effect. The system has some strange behavior.
The researchers modeled the embryo's movements to see how they pull water towards themselves. Their neighbors are pulled towards them as well in a reciprocated attractive force.
Another horizontal force that isn't reciprocated within the system is created by the water flowing down. The whole crystal structure rotates as well.
The waves show the physics of odd elasticity. It's odd because according to classical laws of physics, a crystal floating in water shouldn't power it through the environment if it's just damaged.
The morphing in shape of an object could have some interesting mechanical properties.
That is the theory. It is an area of physics being explored.
In nature, there are some intriguing possibilities.
After 30 hours, the structure is gone. Tan et al. are in Nature.
Once the baby sea stars form the floating, living crystal structure it holds itself together for a few days before the embryo's development causes it to break.
Understanding these physical properties could help us.
Fakhri says that it would be possible to build a swarm of soft, spinning robots that could interact with each other.
They could be designed to move through the sea in order to do useful work. The interactions allow for a new range of physics to be explored.
It's currently a mystery as to why the baby sea star galaxies form.
Sea star embryos don't usually hang out at the water's surface so this living crystal phenomenon is unlikely to happen in the wild.
The research was published in a journal.
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