Most galaxies belong to large structures called superclusters (bright filaments seen in this simulation), which are separated by enormous voids (dark areas above) that harbor few galaxies at all. A galaxy's gravity can magnify the light of objects beyond it, so logically voids should do the opposite, dimming galaxies behind them. Now, however, new calculations in Physical Review Letters demonstrate "the bright side of voids": Because voids lack the gravitational pull of matter to restrain the universe's expansion, they expand faster than the overall cosmos, producing a Doppler shift that overwhelms the dimming and causes objects on a void's far side to look a few percent brighter than they otherwise would. Voids occupy more than half of the universe's volume, the researchers note, and should make some supernova explosions seem more powerful than they actually are. In fact, astronomers may have already unknowingly detected this effect, because they've observed that the peak brightness of what should be uniformly luminous supernovae varies more from explosion to explosion in isolated galaxies, which are more likely to lie on the edge of a void, than in galaxies residing in clusters.
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