Science News

On May 28th, 2024, Dr. Philip Mansfield, from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford, gave a talk to RCDS students titled “Why Dark Matter Is Real and Why It Matters,” hosted by the RCDS Physics and Astronomy Clubs.

In his engaging presentation, Dr. Mansfield tackled the big question of why scientists believe in dark matter, even though it’s invisible and undetectable by normal methods. He started by pointing out the differences between the predicted and actual rotation speeds of stars in galaxies. Using gravity theory and star mass estimates, scientists predicted how fast galaxies should rotate, but real observations showed significant differences.

To explain this mismatch, Dr. Mansfield offered three possible solutions: adjusting star masses, changing gravity theory, or introducing dark matter. He discussed various theories, from heavy stars and modified gravity to both ordinary and exotic dark matter, likely made up of new, undetected particles.

He then widened his focus to galaxy clusters, which, mostly made up of gas, also show mass discrepancies like individual galaxies. This suggests a more fundamental issue, making dark matter a strong candidate for explanation.

Dr. Mansfield used several methods to back the dark matter idea:

1. The “balloon analogy” explained pressure differences in galaxy clusters.
2. Analyzing the Cosmic Microwave Background (CMB) provided evidence from early universe fluctuations.
3. Gravitational lensing in colliding galaxy clusters, like the Bullet Cluster, mapped mass distributions, favoring dark matter over modified gravity.

He concluded that multiple lines of evidence—galaxy rotation curves, galaxy clusters, CMB data, and gravitational lensing—all strongly support the existence of dark matter. This invisible, collisionless substance, likely a new particle, is crucial for understanding our universe.

Dr. Mansfield stressed that scientific consensus comes from combining different pieces of evidence and expertise. His talk highlighted how important dark matter is in astrophysics and its role in shaping our understanding of the cosmos. He left the audience with an inspiring thought: the search for dark matter is not just about uncovering the unknown; it’s about pushing the boundaries of our knowledge and challenging our understanding of the universe. It is this pursuit that drives scientific discovery and keeps us reaching for answers beyond our current grasp.