Enormous hole in the universe may not be the only one

April 22, 2015 by Carole Mundell, The Conversation
Enormous hole in the universe may not be the only one
The cold spot in the cosmic microwave background radiation, which is a snapshot of the light from the big bang, that researchers have failed to explain for over a decade. Credit: ESA Planck Collaboration

Astronomers have found evidence of a giant void that could be the largest known structure in the universe. The "supervoid" solves a controversial cosmic puzzle: it explains the origin of a large and anomalously cold region of the sky. However, future observations are needed to confirm the discovery and determine whether the void is unique.

The so-called cold spot can be seen in maps of the Cosmic Microwave Background (CMB), which is the radiation left over from the birth of the universe. It was first discovered by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) in 2004 and confirmed by ESA's Planck Satellite. For more than a decade, astronomers have failed to explain its existence. But there has been no shortage of suggestions, with unproven and controversial theories being put forward including imprints of parallel universes, called the multiverse theory, and exotic physics in the .

Now an international team of astronomers led by Istvan Szapudi of the Institute for Astronomy at The University of Hawaii at Manoa have found evidence for one of the theories: a supervoid, in which the density of galaxies is much lower than usual in the known universe.

Swiss cheese universe

To understand the effect of a void, imagine the universe is like a Swiss cheese, with holes – voids – corresponding to empty spaces devoid of matter and gravitational pull. When a photon, a particle of light, from the CMB encounters a void it will lose energy but regain it as it exits.

However, since we believe that the universe is constantly expanding, the photon will exit into a medium that is less dense than before it entered the void. Lower density means weaker gravitational pull on the emerging photon. This means that the photon cannot make up all the energy it lost and ends up with a little less energy – and hence lower temperature – than light from regions on the sky that did not pass through the void.

This process explains why the spot is 70 μK colder than the surrounding chilly CMB radiation, which is 2.7 K in whichever direction one looks on the sky. Tiny fluctuations imprinted by processes in the early universe do exist in this remarkably even temperature distribution, but they typically only differ by 18μK.

But it isn't the first time researchers have claimed to find a supervoid that explains the cold spot. In 2007, radio astronomers announced they had found a low density region when they counted the number of radio sources towards the direction of the cold spot but competing studies at visible wavelengths appeared to dispute their findings.

Other studies searched for voids at particular distance – or redshifts – towards the direction of the cold spot but found no convincing evidence of any deficit in galaxy counts. To count the galaxies closer to home and check for the existence of a nearby void required a significant increase in the area of the sky astronomers could survey. This capability came with new catalogues of objects identified in wide-field all-sky surveys.

Future observations

Istvan and his team used two sets of data by matching objects discovered at infrared wavelengths by Nasa's Wide Field Survey Explorer (WISE) with colours in visible light measured by the robotic telescope Pan-STARRS1 to make a tomographic map of the distribution of galaxies in the cold spot.

A dip in the numbers of galaxies in the centre of the cold spot signaled the presence of the largest known structure in the universe – a supervoid stretching 1.8 billion light years across the sky when universe was 11.1 billion years old – which is relatively recent on cosmic timescales.

This is an exciting result – but the study is complex, with a number of errors that can creep in due to various assumptions. Understanding the density of the universe on near and far sides of the void is more challenging than one might expect and the simple assumption of a single, giant void is – as the authors point out – likely to be naive. More detailed maps of the supervoid will help determine whether it has substructure within it.

But future observations mapping different regions of the sky will also check how rare the void is. The chance of an accidental alignment between the cold spot and the supervoid seems small, but not impossible. The race is therefore on to find other voids in order to confirm the supervoid's relationship with the cold spot. The team already have plans to use the Dark Energy Camera -– which recently shed new light on dark matter – to investigate another candidate void near the constellation Draco. Ultimately, understanding the nature of voids and cold spots might require modifications to our favourite cosmological models or perhaps even models of gravity itself.

The discovery is exciting not just for cosmologists, but also for technologists. In the future, new facilities – such as the Large Synoptic Survey Telescope – will survey the whole sky every few nights for a decade. Mining the torrent of data that will allow astronomers to search for large-scale structures such as voids and clusters and to make discoveries of new explosive or time-variable objects such as supernovae and gamma ray bursts. Combining these approaches in a new era of data-driven discovery may open new, exciting windows on our .

Explore further: Cold cosmic mystery solved: Largest known structure in the universe leaves its imprint on CMB radiation

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douglaskostyk
5 / 5 (1) Apr 22, 2015
"However, since we believe that the universe is constantly expanding, the photon will exit into a medium that is less dense than before it entered the void. Lower density means weaker gravitational pull on the emerging photon. This means that the photon cannot make up all the energy it lost and ends up with a little less energy – and hence lower temperature – than light from regions on the sky that did not pass through the void."

How is this energy loss any different than that of a photon that has not crossed the void, which has experienced a similar loss due to the expanding universe?

Stevepidge
1.7 / 5 (6) Apr 22, 2015
Too many epicycles.
big_hairy_jimbo
5 / 5 (1) Apr 22, 2015
"voids – corresponding to empty spaces devoid of matter and gravitational pull. When a photon, a particle of light, from the CMB encounters a void it will lose energy but regain it as it exits."

WHY???? Why lose energy and then regain it?? Why change at all??? IF SpaceTime is expanding, is the VOID also expanding??
viko_mx
1 / 5 (5) Apr 23, 2015
Now because such cosmic phenomena supporters of the big bang will have to revise again the story of the universe and its age. But this should not surprise us because their main job is it to adapt the observed reality to the promoted by promoted by entertainment for the convenience for some people theories in society.
IMP-9
3 / 5 (6) Apr 23, 2015
WHY???? Why lose energy and then regain it??


Gravitational redshift. It's climbing from a lower potential into a higher one, it is redshifted just like a photon climbing up out of the earth's gravitational field.
big_hairy_jimbo
5 / 5 (1) Apr 23, 2015
@IMP-9 but what is in the void to create this potential?? IS it a void made of Dark Matter?
nevermark
2.3 / 5 (3) Apr 25, 2015
@big_hairy_jimbo, When a photon moves away from a gravitational body it doesn't lose momentum, as a particle with mass would, it loses frequency.

If a photon is moving between galaxies evenly distributed on all sides, the effects of gravity mostly cancel out. But if a photon moves away from galaxies into a region where there are none it loses frequency to the strong gravity it is moving in opposition too.

Conversely, when a photon "falls" from an empty void toward galaxies, it picks up frequency again.
big_hairy_jimbo
2 / 5 (2) Apr 25, 2015
Ahhh, thanks all. I now understand!!! ?Yes I am familiar with E=hf and can now see it is the gravitational tug from the Matter behind it, as it moves into the void that redshifts, then blue shifts on exit as it approaches matter on the other side of the void. Oh and that should be balanced if the universe has an even density, which would rely on a static universe. Hence why a difference in photon energy reveals expansion!!! I get it now!!!! So if energy is lost, then surely that energy has gone into the expansion of the Universe?? So is it the VOIDS that are causing expansion?? Where does that missing energy go? Where did the missing energy from the CMB go, since it was obviously very energetic photons when it started near the Big Bang Event.
Mike_Massen
3 / 5 (2) Apr 28, 2015
viko_mx claims
Now because such cosmic phenomena supporters of the big bang will have to revise again the story of the universe and its age
From what perspective, that your god as claimed by Moses knew better ?

How does your god communicate, anything better than humans, ie actually god like - proof ?

viko_mx claims
But this should not surprise us because their main job is it to adapt the observed reality to the promoted by promoted by entertainment for the convenience for some people theories in society.
What does this even mean, that a search for truth is an entertainment and the observed reality can be adapted - er no, its observed, its the interpretation that demands physics & maths and that means asking questions - that way the ingress of dogma at the highest levels of Science can be challenged much like the dogma at the lowest levels of religion - which has NO discipline unlike Science.

Tell us viko_mx, what are the attributes of your claimed god ?
docile
Apr 28, 2015
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