Art credit: B. Saxton (NRAO)     Photo: Patrick O'Leary (U MN)

Frequently Asked Questions

Professional article, scheduled for publication in Astrophysical Journal, 12/07

Conference presentation by Shea Brown

Authors' home pages: LR     SB     LLRW

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  Cartoon credit:  David Endelman  (Sign Garden)

Frequently asked Questions

Have you found the center of the Universe?

    No. Our current understanding of the structure of the universe is that it has no center. If the new void were the center, then we would detect galaxies rushing towards us from the void* - but we don't. Instead, the motions of galaxies are away from us, as if we were the center. However, this does not mean we're in a special place; because the overall space is expanding, an obsever from any galaxy would also see everything moving away.     * (after reference frame corrections, for the sticklers)

Is the void really empty?
    Probably not. It is "mostly" empty of both normal and dark matter. It is filled with radiation and dark energy. If it had small amounts of matter, we would not be able to tell. We simply calculated the size of void needed to creat the WMAP "cold spot" if the void were empty of all matter. If you start putting matter back in, we would have to increase the size of the void.

How was the void discovered?
    Partially by accident. Out of frustration one morning with another research project, LR decided to look at NVSS survey of radio galaxies and found that there were significantly fewer radio galaxies in the direction of the WMAP* "cold spot". He was rescued from confusion over this finding by graduate student SB, who identified it as due to the integrated Sachs-Wolfe effect and thus due to a void. LLRW then put in the necessary physics/cosmology and calculated the extent of the void. In reviewing the literature in preparation for publication, they found that this region had already appeared in a table of significantly correlated NVSS/WMAP regions (scheduled for publication, MNRAS), but not recognized as representing a giant void.
    See the explanatory diagram for some details.
* (named in memory of LR's Ph.D. thesis advisor, David T. Wilkinson)

Are there more voids like this?
    Probably. Our current surveys of the universe have not yet been of large enough volumes to find voids of this size. First though, it is important that we and other astronomers confirm that the new void is not simply a statistical fluke, and that there are no attractive alternatives to explain the data.

Can I see the void?
    Unfortunately not. Even our most powerful optical telescopes would have trouble picking it out. However, you can look in its direction and imagine it. It is southwest of the constellation of Orion, in the river constellation Eridanus. If you could see it, it would cover an area of at least 40 full moons. See the picture below.

Does the void have a name?
    Not yet. And just to keep things confusing, there is already an "Eridanus Void" in the same direction, which is very close to us, about 100 Million light years away, compared to the 6 to 10 billion light years distance of the new giant void.

Is the void a giant black hole?
    No, a black hole is matter, and the void is largely free of matter. The unusual thing about a black hole is that it traps light, but still has mass and gravity. To produce the WMAP cold spot, our void has to be quite empty of matter, even in the form of black holes.