Searching For The Culprit Behind The Universe’s Great Cold Spot
By Judith E Braffman-Miller
The Cosmic Microwave Background (CMB) radiation is the most ancient light that can be observed. This primordial, wandering light began its long, treacherous, mysterious journey nearly 14 billion years ago–and it is an almost-uniform background of radio waves that flow throughout the entire Universe. The CMB was liberated very long ago, when the newborn Cosmos had at last cooled down sufficiently to become transparent to light and other forms of electromagnetic radiation, approximately 380,000 years after the Universe was born in the wild exponential inflation of the Big Bang. The Cosmos keeps its secrets well. One of its best-kept secrets involves a bizarre region of the sky observed in these primordial microwaves that astronomers have found to be mysteriously large and cold compared to what they usually expect to observe. This enormous Cold Spot has defied explanation–and, as such, it well may have an exotic origin, such as being the tattle-tale result of a primeval collision between our Universe and another universe inhabiting an incomprehensibly vast Multiverse. In 2016, a team of astronomers offered a new explanation for the mysterious origin of this enormous Cold Spot.
Many astronomers have proposed that this strange feature is a supervoid. A supervoid is a vast region of Space that contains very few galaxies. In the distant reaches of the space between galaxies, there are strange and lonely corners that are almost entirely bereft of everything except atoms. In these immense regions, only atoms–haunting a haze of hydrogen gas left over from the Big Bang–occupy these almost barren regions, which are the voids. On the largest scale, this diffuse material is arranged in a network of filamentary structures called the “cosmic web”. This immense structure resembles the web woven by a gigantic spider, and it is spun from invisible material known as the dark matter. The dark matter is composed of exotic, non-atomic, and as yet unidentified particles. The gigantic, massive filaments of the invisible cosmic web are outlined by a multitude of starlit galaxies, while the voids are almost entirely empty. The entire immense structure, that resembles a natural sponge or, perhaps, a familiar honeycomb, appears to be composed of heavy dark matter filaments and almost barren voids that are wrapped around one another. Some astronomers have suggested that the entire cosmic web is really composed of only one enormous filament and one gigantic void, tangled up together into a complex structure.
The Bootes void or the Great Void is one example of a supervoid. It is an immense, approximately spherically shaped region of space that hosts very few galactic constituents. It is situated in the vicinity of the constellation Bootes, from which it derives its name. The Bootes void is approximately 330 million light-years in diameter, and is one of the largest known voids in the Universe. Its discovery was reported by Dr. Robert Kirshner et al. back in 1981. Dr. Kirshner is of the Clowes Professor of Science Emeritus at Harvard University in Cambridge, Massachusetts.
However, a supervoid is unlikely to explain the origin and nature of the Cold Spot in the CMB, according to the results of the new survey. If it is determined that the Cold Spot is not a supervoid, then it is time for scientists to consider more exotic explanations. The researchers, led by postgraduate student Ruart Mackenzie and Dr. Tom Shanks in Durham University’s Centre for Extragalactic Astronomy, publish their results in the October 2016 issue of the Monthly Notices of the Royal Astronomical Society (MNRAS). Durham University is in Durham, UK.
The Most Ancient Light
The CMB is a relic of the Big Bang birth of the Cosmos itself, and it covers the entire sky. At a frigid temperature of 2.73 degrees above absolute zero (or -270.43 degrees Celsius), the CMB displays certain anomalies–including the mysterious Cold Spot. This strange hole in the Cosmos is approximately 0.00015 degrees colder than its environment..
The CMB radiation whispers tantalizing hints that there are some wonderful secrets that the Universe is still keeping from us–and it will not disclose them without a struggle. This ancient light can tell the secret story about an extremely ancient and vanished era when all that existed was a turbulent sea of furious, brilliant radiation and a flood of countless elementary particles. The primordial Universe was not a peaceful expanse. At the time the CMB was first released, the Universe was overflowing with searing-hot ionized gas. This extremely hot gas was almost completely uniform, but it did have some extremely tiny deviations–small spots that were very, very slightly (only 1 part in 100,000) more or less dense. These very tiny alterations in intensity left behind, as something of a gift to astronomers, a map of the primordial Universe, unveiling an ancient era that existed long before there was an Earth, and people on our planet who could stare up at the sky and wonder about its myriad mysteries.
The Universe today ultimately emerged from this primeval sea of elementary particles as the Cosmos greatly expanded and grew colder, and colder, and colder. The CMB radiation is the beaming, tattle-tale afterglow of our Universe’s babyhood, and it contains the fossil imprints that have been left as a legacy by those primordial particles. This very ancient wandering light carries the pattern of extremely tiny intensity variabions from which scientific cosmologists can try to determine the characteristics of the Universe.
When the CMB first began its long journey billions of years ago, it was beautifully brilliant–like the surface of a star, such as our own Sun–and it was also searing hot. However, the continual expansion of the Universe has stretched it a thousand times over since then. This expansion caused the wavelength of the ancient light that lingers to be stretched, as well. Today, the CMB is an almost unimaginably frigid 2.73 degrees above absolute zero.
As the Universe continued to expand and stretch, its matter and energy stretched along with it, and very quickly cooled off. The radiation hurled out by the glaring Cosmic fireball that filled the newborn Cosmos, traveled through the entire electromagnetic spectrum–from gamma-rays to X-rays to ultraviolet light–and then through the lovely multicolored rainbow of the visible light spectrum, which is the light that human beings can see. The ancient light was then stretched even further into the infrared and radio regions of electromagnetic spectrum. The afterglow of that ancient fireball, the CMB, fills literally every region of the sky, and it can be detected by radio telescopes. In the ancient Universe, Space glared with brilliant a fire, but as time went by, the fabric of Space continued to expand, and the radiation cooled off. For the very first time, Space grew dark in visible light–just as we observe it today.
George Gamow, Ralph Alpher, and Robert Herman were the first scientists to predict the existence of the CMB back in 1948. Alpher and Herman predicted that the temperature of the CMB would be approximately what scientists now measure it to be.
The CMB was serendipitously discovered in the 1960s by Dr. Arlo Penzias and Dr. Robert W. Wilson at the Murray Hill facility of Bell Telephone Laboratories in New Jersey–with an extremely important contribution made by Dr. Robert Dicke of nearby Princeton University, and his colleagues. Penzias and Wilson received the 1978 Nobel Prize in Physics for their serendipitous discovery.
In August 2007, a team of astronomers announced that they had discovered a bizarre and enormous hole in the Universe that was almost a billion light-years across, and apparently empty–or almost empty–of matter. Astronomers have known for a long time that, on the largest scales, the Universe possesses empty–or almost empty–voids, but these voids are much smaller than the enormous hole that is the Great Cold Spot.
As light makes its way up and down the gravitational hills and valleys of the Cosmos, the expansion of Space causes photons (particles of light) to both lose and gain energy–in a way that is unequal. This mechanism is termed the Integrated Sachs-Wolfe Effect. In the case of the CMB this is seen as cold imprints. It was previously proposed that a very large foreground void could, in part, imprint the CMB Cold Spot.–which has been the source of considerable confusion in models of standard scientific cosmology.
Earlier, most of the hunts for a culprit supervoid connected with the Great Cold Spot have estimated distances to galaxies using their colors. With the expansion of the Universe more remote galaxies have their light shifted to longer waveengths, in an effect known as a cosmological redshift. The more distant a galaxy is, the higher its observable redshift. In astronomy long ago is the same as far away, and so the more remote an object is in space, the more ancient it is in time. By measuring the colors of galaxies, their redshifts, and therefore their distances, can be calculated. These measurements, however, have a high degree of uncertainty.
So, what is the true culprit behind this gigantic hole in the Universe?
The Strange Secret Of The Universe’s Great Cold Spot
In their new study, the University of Durham astronomers presented the results of a comprehensive survey of the redshifts of 7,000 galaxies, and harvested 300 at a time using a spectrograph deployed on the Anglo-Australian Telescope at Siding Spring Observatory, Australia. From this greatly improved dataset, Dr. Mackenzie and Dr. Shanks could see no evidence of a supervoid that could be accused of being the culprit behind the mysterious CMB Cold Spot, in accordance with the standard theory.
The scientists found something else instead. What the astronomers found was that the Cold Spot region, previously thought to be underpopulated with galactic constituents, is actually divided into smaller voids that are surrounded by sparkling starlit clusters of galaxies. This so-called “soap bubble” structure looks like the rest of the Universe.
Mackenzie explained in an April 27, 2017 Royal Astronomical Society (RAS) Press Release that “The voids we have detected cannot explain the Cold Spot under standard cosmology. There is the possibility that some non-standard model could be proposed to link the two in the future but our data place powerful constraints on any attempt to do that.” The RAS is in London, England.
So, if there really is no supervoid that is the hidden culprit behind the CMB Cold Spot, simulations of the Standard Model of the Universe provides odds of a mere 1 in 50 that the Cold Spot formed by chance.
“This means we can’t entirely rule out that the Spot is caused by an unlikely fluctuation explained by the Standard Model. But if that isn’t the answer, then there are more exotic explanations,” Dr. Shanks commented in the April 27, 2017 RAS Press Release.
Dr. Shanks added that “Perhaps the most exciting of these is that the Cold Spot was caused by a collision between our Universe and another bubble universe. If further, more detailed, analysis of CMB data proves this to be the case then the Cold Spot might be taken as the first evidence for a Multiverse–and billions of other universes may exist like our own.”
However, at this time, all that can really be said is that the lack of a supervoid culprit explaining the Cold Spot has tilted the balance towards more exotic explanations. Ideas will have to be tested further by scientists using more detailed observations of the CMB–the most ancient light in the Universe.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.