by Ancient cosmic light that has uniformly filled the universe since about 400,000 years after the Big Bang could act as a treasure map that leads scientists to the secrets of dark matter.
The Cosmic Microwave Background (CMB) refers to the first light to travel freely throughout the universe. His journey began after space expanded and cooled enough to allow electrons and protons to form the first atoms, meaning electrons were no longer scattering photons, and the universe immediately went from opaque to transparent.
A new upgraded camera called the SPT-3G picked up the CMB, or “surface of final scattering” as it is sometimes called. SPT-3G is located on the South Pole Telescope, and has been able to capture the phenomena after five years of operations and these initial data point to exciting future developments.
“The CMB is a treasure map for cosmologists,” Zhaodi Pan, lead research author and scientist at Argonne National Laboratory, said in a statement. “Its subtle variations in temperature and polarization provide a unique window into the infancy of the universe.”
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However, as any pirate will tell you, every good treasure map needs a key to read. In the case of this cosmic treasure map, the distribution of dark matter is revealed only in light of Albert Einstein’s 1915 theory of gravity: General relativity.
Read Einstein’s cosmic map
Astronomers believe that all galaxies are enveloped in vast halls of dark matter; in fact, this mysterious form of matter is so ubiquitous that it makes up 68% of all matter in the universe.
However, because dark matter is not made of atoms made up of electrons, protons, and neutrons – collectively known as baryons – it does not interact with light. However, dark matter has mass, which means it interacts with gravity.
This is where general relativity comes in. Einstein’s theory of gravity states that all objects with mass cause curvature in space-time, the unified 4-dimensional entity consisting of three dimensions of space and one dimension of time.
When light from a background source passes over this curve in space due to mass, its path is redirected. For massive objects, such as galaxies, background light can be bent so much that the galaxies or stars from which it originates appear to have moved in the sky. In extreme cases, light passing through this intermediate object can take paths around the object that are curved to varying degrees, meaning that a single source can sometimes even appear at multiple points in the same image.
This effect is called gravitational lensing, and it is used very effectively by instruments such as the James Webb Space Telescope to see faint galaxies in the early universe. A more subtle version of this effect, gravitational microlensing, can be used to gain more information about the lensed object – in this case, dark matter.
To get a picture of a universe-wide web of dark matter, however, scientists need an equally cosmically widespread source of light. So the CMB is the best light for epic dark matter lensing investigation.
The SPT-3G was particularly able to take advantage of the lack of interference present in the dry, stable atmosphere and remote location of the South Pole Telescope. In the process, the investigation added further supporting evidence to Einstein’s general relativity, ie
“The more we learn about the distribution of dark matter, the closer we get to understanding its nature and role in the formation of the universe we live in today,” Pan said.
Although the new analysis is the result of a few months of operation in 2018, CMB lens measurements are already competitive in this field.
“One of the really exciting parts of this study is that the result comes from what is essentially commissioning data from when we were just starting observations with the SPT-3G – and the result is already amazing,” Amy Bender, a research author and physicist at Argonne, said in the statement: “We have another five years of data that we’re working on analyzing now, so this hints at what’s to come.”
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Even with a dedicated group of computers at Argonne Laboratory’s Computing Resource Center, analyzing months of data from the SPT-3G camera is painstaking work that takes years.
Future results from the camera could help scientists tackle another long-standing cosmic mystery: the nature of dark energy, the unknown force driving the universe’s accelerating expansion.
“Every time we add more data, we see more things we don’t understand,” Bender said. “As you peel back layers of this onion, you learn more and more about your instrument and also about your scientific measurement of the sky.”
The first results from the SPT-3G camera were published last year in the journal Physical Review D.
