Ever wondered what makes up most of the universe? You might be surprised to learn that a staggering 95% is invisible, composed of mysterious dark matter and dark energy! Astrophysicists are on a quest to map this hidden realm, and they're using a fascinating technique: warped galaxies. This is how they do it.
Dark matter and dark energy are the universe's unseen architects. While we can't directly see them, their influence is undeniable. Dark matter acts as cosmic scaffolding, shaping galaxies and clusters, while dark energy drives the universe's accelerating expansion. But how do scientists study something they can't see? They observe how these invisible components affect the visible universe.
A team of astrophysicists at the University of Chicago did precisely this, focusing on a new area of the sky to unravel the secrets of the hidden cosmos. They utilized data from the Dark Energy Survey (DES), which collected observations between 2013 and 2019 using the Dark Energy Camera (DECam) on the Blanco Telescope in Chile. Over those years, DES meticulously measured the shapes of over 150 million galaxies across a vast area of the sky, approximately an eighth of the total sky. These measurements help scientists refine their understanding of how mass is distributed throughout the universe and how dark energy behaves.
But here's where it gets controversial... DES has also played a role in a major puzzle concerning the Lambda-CDM (LCDM) model, the standard model used to describe the universe. Some studies of the nearby universe using galaxy surveys like DES have seemed to disagree with predictions based on the early universe, as inferred from the cosmic microwave background (CMB) – the leftover radiation from the Big Bang.
Enter the Dark Energy Camera All Data Everywhere (DECADE) project. This project took advantage of images collected by DECam, expanding the data set to nearly double the number of galaxies with measured shapes by including data from thousands of square degrees beyond the DES region. Because these images weren't originally intended for weak lensing, this expanded data set offers an independent way to re-examine the earlier LCDM inconsistencies.
So, how do warped galaxies help? The answer lies in gravitational lensing. When massive objects bend the light from distant galaxies, it's called gravitational lensing. This phenomenon is a powerful tool for mapping the distribution of mass in the universe, including both ordinary matter and the elusive dark matter. It can also shed light on the role of dark energy.
In weak gravitational lensing, the galaxies don't appear dramatically stretched. Instead, their shapes are subtly distorted (sheared) as their light passes through and around matter on its way to Earth. The signal is incredibly faint, so researchers use statistical methods to detect it.
