Astronomie - Astronomen durch 'größte bekannte' Supervoid verblüfft


Astronomers have detected the universe’s largest known cosmological supervoid in the Southern constellation of Eridanus.  Spanning some 1.8 billion light years, the team remains mainly baffled as to why such an extensive void — in which the “density of galaxies is much lower than in the known universe” — could have actually arisen.
“This supervoid is certainly rare,” Greg Aldering, a cosmologist at Lawrence Berkeley National Lab in California, told Forbes.  “Underdense by about 30 percent, it’s not completely empty.  But what’s rare is the [spatial] extent of this void itself.”
In a paper appearing in the journal Monthly Notices of The Royal Astronomical Society, István Szapudi, an astronomer at the University of Hawaii at Manoa, and colleagues describe how they used large scale three-dimensional sky maps to find and then study this newfound supervoid, located only some 3 billion light-years from our own Sun.
The team used maps created from data provided by Hawaii’s Pan-Starrs1 telescope and NASA ’s WISE satellite to search for voids in the direction of the Cosmic Microwave Background’s Cold Spot, which the University of Hawaii describes as “a larger-than-expected unusually cold area of the sky.”  Although the team notes that there are hints that there may be a causal connection between the foreground void and the universe’s earliest observable background radiation, their paper notes that further studies and observations will be needed to firmly establish this fact.
The Fornax Galaxy Cluster is one of the closest such groupings beyond our own Local Group of galaxies. Credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin
However, Aldering, who was not a part of the study, thinks that the void’s observed alignment with the background’s Cold Spot is more than just coincidence.  Even so, exactly what this would portend for known astrophysics remains a subject of debate.
Yet cosmologists have long known that the universe is organized into groups of observable structure — usually in clusters and even superclusters of galaxies.  But voids remain less understood although they are prevalent throughout the cosmos.  The so-called ‘Local Void’ remains the nearest-known void to our Milky Way galaxy.
Our own galaxy lies in a filament that borders a wall around our Local Void and, in fact, is making a large sideways motion away from our own Local Void’s center.
Voids outnumber clusters in large part because as the cosmos expands clusters tend to collapse and recollapse onto themselves, while voids expand and grow.  However, eventually, the voids bump into galactic superclusters, as well as each other, and thereby reach a spatial limit.
“Voids easily make up 50 percent of the universe and while clusters of galaxies collapse, voids grow,” said Aldering.  “If you have an underdensity, it’s going to grow.”
What would life be like inside such a huge void?
Because voids grow at a faster rate than higher-density regions of the universe, astronomers inside such a supervoid would likely have figured out that the universe is undergoing a Hubble-type expansion sooner than their Earth-based counterparts.
Although they would have fewer nearby galaxies to observe, says Aldering, the expansion rate of the galaxies they could track would produce a much bigger expansion effect than what astronomers are accustomed to observing from Earth.
Other than that, to a naked eye observer the night sky in a solar system inside a galaxy inside a supervoid wouldn’t appear noticeably different than it does from Earth, says Aldering.
And given the prevalence of such voids in general?
“If someone put you in some random location in the universe, you’d very likely end up in a void,” said Aldering.
Quelle: Forbes