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| The Big Bang (left), the wavy lines illustrate the distortion; the warped light received by the ACT (right); the new Dark Matter map (lower left). Credit: Lucy Reading-Ikkanda/Simons Foundation/ACT Collaboration |
For millennia, humans have been fascinated by the mysteries of the cosmos.
From ancient civilizations such as the Babylonians, Greeks, and Egyptians to
modern-day astronomers, the allure of the starry sky has inspired countless
quests to unravel the secrets of the universe.
Although models explaining the cosmos have been around for centuries, the
field of cosmology, in which scientists employ quantitative methods to gain
insights into the universe’s evolution and structure, is comparatively
nascent. Its foundation was established in the early 20th century with the
development of Albert Einstein’s theory of general relativity, which now
serves as the basis for the standard model of cosmology.
Now, a set of papers submitted to The Astrophysical Journal by researchers
from the Atacama Cosmology Telescope (ACT) collaboration has revealed a
groundbreaking new image that shows the most detailed map of matter
distributed across a quarter of the entire sky, reaching deep into the
cosmos. It confirms Einstein’s theory about how massive structures grow and
bend light, with a test that spans the entire age of the universe.
“We’ve made a new mass map using distortions of light left over from the Big
Bang,” says Mathew Madhavacheril, lead author of one of the papers and
assistant professor in the Department of Physics and Astronomy at the
University of Pennsylvania. “Remarkably, it provides measurements that show
that both the ‘lumpiness’ of the universe and the rate at which it is
growing after 14 billion years of evolution are just what you’d expect from
our standard model of cosmology based on Einstein’s theory of gravity.”
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| The light captured by the ACT was used to produce a cosmic microwave background lensing mass map, a visualization of the distribution of dark matter in our sky. (Image: The Atacama Cosmology Telescope collaboration) |
The authors note that the lumpiness quality is attributed to the uneven
distribution of dark matter throughout the universe and that its growth has
remained consistent with earlier predictions. And, despite making up 85% of
the universe and influencing its evolution, dark matter has been hard to
detect because it doesn’t interact with light or other forms of
electromagnetic radiation. As far as we know dark matter only interacts with
gravity.
Funded by the National Science Foundation, the ACT was built by Penn and
Princeton University and started observations to track down the elusive dark
matter in 2007. The more than 160 collaborators who have built and gathered
data from ACT, which is situated in the high Chilean Andes, observe light
emanating following the dawn of the universe’s formation, the Big Bang—when
the universe was only 380,000 years old. Cosmologists often refer to this
diffuse light that fills our entire universe as the “baby picture of the
universe,” but formally it is known as cosmic microwave background radiation
(CMB).
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| Image: Lucy Reading-Ikkanda/Simons Foundation |
The team tracks how the gravitational pull of large, heavy structures
including dark matter warps the CMB on its 14-billion-year journey to us,
like how a magnifying glass bends light as it passes through its lens.
“When we proposed this experiment in 2003, we had no idea the full extent of
information that could be extracted from our telescope,” says Mark Devlin,
the Reese Flower Professor of Astronomy at the Penn and the deputy director
of ACT.“We owe this to the cleverness of the theorists, the many people who
built new instruments to make our telescope more sensitive and the new
analysis techniques our team came up with.”
Penn researchers Gary Bernstein and Bhuvnesh Jain have led research mapping
dark matter by using visible light emitted from relatively nearby galaxies
as opposed to light from the CMB. “Interestingly, we found matter to be a
little less lumpy than the simplest theory predicts,” Jain says “However,
Mark and Mathew’s beautiful work on the CMB agrees perfectly with the
theory.”
“The stunning ACT dark matter maps severely narrow down the times and places
where the simplest theory could be going wrong,” Bernstein says. “One
speculation is that a new feature of gravity or dark energy is appearing
just in the last few billion years, after the era ACT is measuring.”
References:
Frank J. Qu et al, The Atacama Cosmology Telescope: A Measurement of the DR6
CMB Lensing Power Spectrum and its Implications for Structure Growth, arXiv
(2023).
DOI: 10.48550/arxiv.2304.05202
Niall MacCrann et al, The Atacama Cosmology Telescope: Mitigating the impact
of extragalactic foregrounds for the DR6 CMB lensing analysis, arXiv (2023).
DOI: 10.48550/arxiv.2304.05196
Mathew S. Madhavacheril et al, The Atacama Cosmology Telescope: DR6
Gravitational Lensing Map and Cosmological Parameters, arXiv (2023).
DOI: 10.48550/arxiv.2304.05203
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Space & Astrophysics