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It was a sheer accidental discovery

Dr Lawrence Rudnick leads the team of astronomers at the University of Minnesota who recently discovered the biggest hole in the universe. Satyen Mohapatra brings in excerpts from an exclusive interview.

india Updated: Aug 30, 2007 04:16 IST
Satyen Mohapatra

Dr Lawrence Rudnick leads the team of astronomers at the University of Minnesota who recently discovered the biggest hole in the universe. It is nearly a billion light years in length and contains nothing whatsoever — no gas, no stars, not even the so called 'unseen dark matter.'

Dr Rudnick and his team drew their conclusion by studying data from the US's National Radio Astronomy Observatory's (NRAO) VLA Sky Survey (NVSS), a project that imaged the entire sky visible to the Very Large Array (VLA) radio telescope.

Excerpts from Dr Rudnick's exclusive interview to the Hindustan Times:

Is this the biggest void ever found ?

Yes, there are very few voids larger than 150 million light years across. There is one void that is about 250 million light years across.

This new one, at a billion light years across has a volume 40 times larger than the largest previously known.

What is the scientific importance of this discovery?

One of the key questions in cosmology today is the development of structure in the universe. The universe started out very homogeneous, with fluctuations of the order of only several parts per hundred thousand.

Out of those tiny ripples, gravitational clumping (the areas where density was higher and gravity stronger tending to pull in surrounding material and making it clumpy) led to all the structure we see today — planets, stars, galaxies, clusters. Without this structure, we would not be here.

<b1>Our discovery raises questions about our understanding of how that structure developed. After the formation of clumps there are less dense regions left behind, the voids. Our void at 1000 million light years diameter, is so far beyond what had been seen or expected, that it is not yet clear whether it is consistent with our current understanding of how these structures developed. We may have to rethink these matters now.

Again, the effects we see depend on the existence of dark energy , which is the most abundant form of energy in the universe today, and whose nature is completely unknown. (Dark energy opposes the self attraction of matter and causes the expansion of the universe). Ours is the first demonstration of the action of dark energy at a specific location in space.

Our work also removes a thorny problem we faced while theorising about the early universe. How do we explain the cold spot found in the map of the Cosmic Microwave Background radiation made by the Wilkinson Microwave Anisotopy Probe (WMAP) satellite launched by NASA in 2001?

Previous ideas suggested there were some special conditions in the early universe, but these explanations were somewhat ad hoc.

Our work suggests that things were normal in the early universe in this regard, and it was during the passage of the cosmic background radiation (literally the remnant heat left over from the Big Bang) through the void, that it was made cold.

How did you make this discovery?

It was somewhat accidental. I had been studying the NVSS survey and was frustrated with my progress. One morning I decided to look in the direction of the WMAP cold spot.

I found an anomaly there — many fewer radio galaxies than there should have been seen in a random spot. I knew it was important, but not why.

My graduate student, Shea Brown, came in and I told him to look at what I found but could not understand. His immediate reaction was: 'that’s the integrated Sachs-Wolfe effect that we just studied in cosmology!' So then we knew we were dealing with a void, but had no idea how big or how deep. So the two of us marched down to Professor Liliya Williams office, and told her she had to help us out.

As an expert in cosmology and large scale structures, Professor Williams did all the calculations which resulted in our claim for a billion light year diameter void.

How far away is the void ?

Between 6 to 10 billion light years away. Since there is nothing to measure, we have to make our best estimate of which radio sources were missing. We hope to have more information in the future.