Riddled With Holes
If you picture what the universe looks like, you can imagine it as Swiss cheese. The sizes of holes, or voids, in the matter of the universe vary greatly. One example would be the cold spot that was found in the Universe's radiation. Galaxies are connected by filaments of dark matter that cannot be seen.
This means that the Milky Way exists in one of these voids, specifically the KBC void, which a 2013 study showed to be not as densely packed with matter as other voids. It's like our galaxy rests in a cosmological backwater — the Outer Rim, so to speak. A new study from the University of Wisconsin-Madison which was presented at the 2017 American Astronomical Society meeting confirms that the Milky Way does indeed reside in an enormous void.
However, the researchers claim that being in this huge KBC void also helps resolve the differences in measuring the rate the universe expands — the Hubble Constant, the number used to describe this cosmic expansion.
The Universe is Expanding?
There are two ways to measure the expansion of the universe. One is a local determination using the Hubble Space Telescope, which relies on observations of supernovae that exploded in galaxies nearby. The other is a cosmic determination that relies on Cosmic Microwave Background (CMB) data — the Big Bang's residual noise — taken by the Planck observatory.
One possible explanation for the differences in the Hubble Constant measurement is due to differences in time. Hubble's observations rely on cosmic objects nearer in terms of time, while the CMB was emitted back when the universe was young. Simply put, being in a void with considerably lesser matter affects the measurement taken by observing supernovae explosions. On the other hand, the CMB technique doesn't distort the measurement at all.
"No matter what technique you use, you should get the same value for the expansion rate of the Universe today," lead researcher Ben Hoscheit said in a press release. “Fortunately, living in a void helps resolve this tension."