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posted by Fnord666 on Thursday June 08 2017, @09:09PM   Printer-friendly
from the I’m-mr.-lonely dept.

Observations made in 2013 by University of Wisconsin–Madison astronomer Amy Barger and her students showed that our galaxy, and much of the Laniakea Supercluster as well, resides in a great cosmic void. Building upon this work of his adviser, Ben Hoscheit made observations of 120,000 galaxies to measure how the density of galaxies changes with distance from the Milky Way. The findings, presented at the June 6 meeting of the American Astronomical Society, show that the Milky Way indeed resides in a vast cosmic abyss some two billion light years across, with the Milky Way being within a few hundred million light years of its centre, where galaxies are much fewer and farther between than in most of the rest of the universe. This could explain the discrepancies between measurements of the Hubble Constant which use relatively nearby supernovae and Cepheid variables to measure it (71.9 ± 2.7 km/s/Mpc) and those which use more distant observations like the cosmic microwave background (67.74 ± 0.46 km/s/Mpc). The nearby supernovae and Cepheids would be accelerating more quickly and yielding that bigger value for the Hubble constant because they are feeling an extra gravitational pull from the matter at the edges of the void we are in. This obviously does not affect the CMB or anything much further away. From the UW–Madison press release:

Cosmologically speaking, the Milky Way and its immediate neighborhood are in the boondocks.

In a 2013 observational study, University of Wisconsin–Madison astronomer Amy Barger and her then-student Ryan Keenan showed that our galaxy, in the context of the large-scale structure of the universe, resides in an enormous void — a region of space containing far fewer galaxies, stars and planets than expected.

Now, a new study by a UW–Madison undergraduate, also a student of Barger’s, not only firms up the idea that we exist in one of the holes of the Swiss cheese structure of the cosmos, but helps ease the apparent disagreement or tension between different measurements of the Hubble Constant, the unit cosmologists use to describe the rate at which the universe is expanding today.

[…] The tension arises from the realization that different techniques astrophysicists employ to measure how fast the universe is expanding give different results. “No matter what technique you use, you should get the same value for the expansion rate of the universe today,” explains Ben Hoscheit, the Wisconsin student presenting his analysis of the apparently much larger than average void that our galaxy resides in. “Fortunately, living in a void helps resolve this tension.”

The reason for that is that a void — with far more matter outside the void exerting a slightly larger gravitational pull — will affect the Hubble Constant value one measures from a technique that uses relatively nearby supernovae, while it will have no effect on the value derived from a technique that uses the cosmic microwave background (CMB), the leftover light from the Big Bang.

[…] The void that contains the Milky Way, known as the KBC void for Keenan, Barger and the University of Hawaii’s Lennox Cowie, is at least seven times as large as the average, with a radius measuring roughly 1 billion light years. To date, it is the largest void known to science. Hoscheit’s new analysis, according to Barger, shows that Keenan’s first estimations of the KBC void, which is shaped like a sphere with a shell of increasing thickness made up of galaxies, stars and other matter, are not ruled out by other observational constraints.

“It is often really hard to find consistent solutions between many different observations,” says Barger, an observational cosmologist who also holds an affiliate graduate appointment at the University of Hawaii’s Department of Physics and Astronomy. “What Ben has shown is that the density profile that Keenan measured is consistent with cosmological observables. One always wants to find consistency, or else there is a problem somewhere that needs to be resolved.”

Other coverage at ScienceNews, Starts With A Bang, and Wired.


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  • (Score: 2) by edIII on Friday June 09 2017, @12:46AM (2 children)

    by edIII (791) on Friday June 09 2017, @12:46AM (#522875)

    Yo Momma's snatch so big, you could spin the Milky Way around in it and never touch the sides.....

    (I tried)

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  • (Score: 2) by Snotnose on Friday June 09 2017, @02:41AM (1 child)

    by Snotnose (1623) on Friday June 09 2017, @02:41AM (#522900)

    Yeah, the "yo mama snatch so big" hit me in the first millisecond and was rejected in the second millisecond as too obvious. Let's change the question. "There are a lot of bad yo mama jokes here, but damned if I can think of a good one".

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    • (Score: 0) by Anonymous Coward on Friday June 09 2017, @08:24PM

      by Anonymous Coward on Friday June 09 2017, @08:24PM (#523243)

      it would have worked if you sub in "loose" for "big"