“Supervoid.” It’s not just a cool band name anymore. Scientists have long understood voids as part of the topography of the universe, but a team of astronomers led by István Szapudi at the University of Hawaii at Manoa has discovered evidence of a so-called “supervoid” – perhaps the largest known structure in the universe.
Voids are the vast, unusually empty areas in the deep reaches of space between the next largest known structures in space – what scientists call “filaments” of galaxies bound together by gravity. As the name suggests, voids are unique among cosmic structures in that they are characterized by an unusually low density of celestial objects, rather than a grouping of massive objects. But to better understand the scientific value of what amounts to a vast emptiness, we need to go back to the prevailing explanation of the birth of our universe.
A cold hole in the sky
In 2004, astronomers studying the leftover light from the Big Bang – known as the “cosmic microwave background” (CMB) – discovered an unusually large, unusually cold spot in the sky. Although the standard cosmological model of the universe allows for a certain degree of fluctuation in temperature throughout the early universe, nothing in the standard model explained an area quite so large and cold. Scientists would either have to find a reasonable explanation for the spot or revisit their paradigmatic understanding of the beginnings of the universe.
While scientists have proposed a few different explanations for the spot, the recent discovery by Szapudi’s team makes the strongest argument that a cosmic void of unprecedented size is at least partly responsible. The team went in assuming the presence of a void and studied a region of deep space much closer to earth, something no previous attempt to explain the Cold Spot had done. When the team found a region containing about 10,000 fewer galaxies than it should have contained, they knew they’d hit on something.
How scientists discovered the largest known structure in the universe
The team used data from Hawaii’s Pan-STARRS1 (PS1) telescope and NASA’s Wide Field Survey Explorer (WISE) satellite to argue for the existence of a “supervoid,” an unusually empty region of space about three billion light years away from earth and about 1.8 billion light years across. To put that in perspective, the diameter of the observable universe has been estimated to be as large as 156 billion light years across. Szapudi himself suggested that the supervoid was “the largest individual structure ever identified by humanity.”
Because of the sheer vastness of the void and the constantly expanding nature of the universe, the wavelength of leftover electromagnetic radiation from the Big Bang gradually elongates as it makes the unimaginably long journey through it, accounting for the lower temperatures observed on earth. But as with many new discoveries about our universe, every answer seems to lead inevitably to more questions.
Professor Carlos Frenk, a cosmologist at the University of Durham, told The Guardian that the supervoid only accounts for about 10% of the low temperatures in the Cold Spot, meaning that a paradigm-bending explanation could still be in the works. If anything, he said, the supervoid is good evidence for the existence of dark energy, a mysterious energy that permeates space and which scientists believe is responsible for the continuously accelerating expansion of the universe.
In the meantime, Szapudi’s team is scheduled to continue its work by incorporating data from the Dark Energy Survey to study both the recently discovered supervoid and another void near the constellation Draco.
(Featured Image: The mysterious “Cold Spot” in the cosmic microwave background, circled in the bottom right. Credit: ESA)