Spiral galaxies are a stunning sight. As Don Lincoln explains in one of this week’s TED-Ed lessons, these galaxies were thought to rotate in highly predictable dances, with stars close to the center moving slowly and stars further away rotating quickly because they are pulled by the mass of the stars between them and the center. The stars located very far from the galaxy center were thought to rotate extremely slowly because of the reduced pull of gravity.
Only, that’s not how the stars on the edges of galaxies move at all. As Lincoln explains in this lesson, a crisis in astronomy occurred when it was discovered that these stars actually rotate much more quickly than expected. Scientists had to take another look at the Newton’s theories of gravity and mass to figure out why their predictions were so wrong.
Today, scientists have a hypothesis that explains the unexpected movement — galaxies are surrounded by dark matter. Lincoln shares that dark matter can be thought of as “the cloud which surrounds most galaxies.” While dark matter is affected by gravity and adds to the total mass of the galaxy, it is not able to emit or absorb light.
Want a more detailed explanation than what’s covered in this 3-minute talk? After the jump, a TED Talk which explains much more.
Patricia Burchat: Shedding light on dark matter
In this talk from TED2008, physicist Patricia Burchat explains that 96% of our universe is composed of dark matter and dark energy. While dark matter can be thought of as the spherical clouds around galaxies, dark energy is something completely different — it’s the force that is making the universe expand and galaxies move further apart. However, both dark matter and dark energy are still largely mysteries. In this talk, Burchat outlines what can be done to find evidence of these phenomena that can’t be seen.