We now have even more strong evidence that our galaxy sits inside a gigantic void, and it could help resolve a disagreement over the speed at which the Universe is intensifying.
The new study denies a basic assumption about how unusual our place is in the cosmos, and submits that we are sitting in what could be the largest known void in the Universe.
Not that science targets to be a giant buzzkill, but cosmologists tend to turn on the straightforward idea that there’s nothing special about our time and place in nature until we have some reason to contemplate otherwise.
This assumption, founded on the cosmological principle – the spreading of matter across space is quite even when seen from a huge enough distance – means that when we search, our viewpoint on the Universe shouldn’t be measured particularly unique. On scales greater than about 250 million light-years, this naturally holds true, but at certain point, the Universe surprises to look a little like, well, Swiss cheese.
Holes (or voids) in the scattering of matter can occur on numerous scales, from gaps in where we’d assume stars in the middle of a galaxy to complete collections of voids that give the presence of a 1.8 billion light year wide-ranging“cold spot” in the Universe’s background radiation. With the idea of dark matter, the photograph of the Universe is now one of collections of galaxies connected by long, unseen filaments, with bubbles holding less stuff in between.
The hint that the Milky Way Galaxy sits in a backwater rather than a interstellar urban center was suggested in 2012 by astronomers Amy Barger ,Ryan Keenan and Lennox Cowie, who published their study on what is now mentioned to as the KBC void. Their calculations predicted that the void could be a giant one, too. At about 1 billion light-years across, it would be 7 times larger than the average void, placing it in the running for the leading known void in the Universe. One ofAmy Barger’s students, Ben Hoscheit from the University of Wisconsin-Madison (UWM), has now evaluated her previous work; presenting variations in the arrangement of the early Universe still matches with their observations.
“What Ben has revealed is that the density shape that Keenan measured is steady with cosmological observables,” said Amy Barger from the University of Hawaii’s Department of Physics and Astronomy (DPA).
This steadiness is important – the fact we possibly sit in a void isn’t just a piece of exciting trivia, it disturbs how we define an important cosmological factor. The Hubble Constant (HC) is a number that defines how the Universe is expanding, evaluated by measuring the manner light from distant objects stretches as they travel, and then working out how far they are. While we’ve identified for almost a century that the Universe is expanding, but in recent years, many calculations on the constant have put forward that the rate of expansion was much slower in the early Universe.
“No matter what method you use, you should get the identical value for the expansion speed of the Universe today,” says Hoscheit.
These numbers are according to the cosmological principle, so if there is something a slight different about our place in the Universe, we might need to take that difference into account. For instance, one constant as restrained by the Hubble Space Telescope depends on supernovae that shatter in galaxies nearby (and thus nearby in time) with a expected amount of energy.
Measurements using information taken by the Planck observatory instead use the CMB (Cosmic Microwave Background).
One understanding for the difference is the Universe was growing slower when the radiation from the Cosmic Microwave Background (CMB) was produced back when the Universe was beginning, and is now expanding faster. Tiny differences in the CMB are supposed to turn out as large-scale arrangements in the Universe, as well as the clusters of galaxies nearby relatively empty voids. It’s those tiny baby bubbles that Ben Hoscheit looked at.
Hoscheit says, “Photons from the Cosmic Microwave Background encode a baby photo of the very early Universe. But, actually those tiny temperature differences are precisely what let us to conclude the Hubble Constant through this cosmic method.”
Hoscheit offered his findings at a recent conference of the American Astronomical Society, so they are yet to go through the peer-review procedure. Keeping all of that in mind, the KBC void and its part in the Hubble Constant is still far from proven. It also doesn’t rule out a speeding up Universe, even if it does present questions on how we should be calculating it. In any case, Hoscheit’s work demonstrates there are not any observations we can at this time make to indicate the void theory is empty.
“One always wants to discover consistency, or else there is a difficult problem somewhere that needs to be fixed,” says Barger.
The study has been presented at the 2017 American Astronomical Society conference.
