Einstein’s theory of gravity may have to be rewritten, after a team of astronomers at the University of St Andrews discovered a 10-million-light-year-wide ring of small galaxies moving away from us much faster than predicted.

A present-day near-miss of two spiral galaxies NGC 5426 and NGC 5427, which may be comparable to the early flyby of the Andromeda galaxy past our own Milky Way Galaxy. Image credit: ESO.
The newly-discovered ring of galaxies is expanding rapidly like a mini Big Bang, according to St Andrews astronomers Indranil Banik and Dr. Hongsheng Zhao.
They believe our neighboring galaxy, Andromeda, once flew past our Milky Way Galaxy at close range, creating a sling-shot of several dwarf galaxies.
“If Einstein’s gravity were correct, our Galaxy would never come close enough to Andromeda to scatter anything that fast,” Dr. Zhao said.
If true, the discovery would force a new understanding of gravity and about our cosmos, as such a galactic flyby only makes sense if gravity weakens more slowly as galaxies drift apart than mainstream thinking suggests.
“The ring-like distribution is very peculiar. These small galaxies are like a string of raindrops flung out from a spinning umbrella,” Banik said.
“We found there is barely a 1 in 640 chance for randomly distributed galaxies to line up in the observed way, and we traced their origin to a dynamical event when the Universe was only half its present age.”
This tsunami-like wake in the sky was likely stirred up by a near-miss of the speeding Andromeda galaxy with the Milky Way.
The two galaxies always orbited each other in a plane and would have scattered tiny galaxies in their paths, perhaps explaining why the speeding dwarfs are in a plane also containing the Milky Way and Andromeda.
“In Einstein’s gravity paradigm, hypothetical dark matter is always invoked,” Banik said.
“Such a high speed requires 60 times the mass we see in the stars of the Milky Way and Andromeda.”
“However, the friction between their huge halos of dark matter would result in them merging rather than flying 2.5 million light-years apart, as they must have done.”
“Science progresses through challenges. Together with two other known planes of closer-in satellites, this gigantic ring forms a serious challenge to the standard paradigm,” said Dr. Marcel Pawlowski, an astronomer at the University of California, Irvine, who prompted Banik’s discovery.
The discovery will be reported in the Monthly Notices of the Royal Astronomical Society (paper #1 and paper #2).
(From: http://www.sci-news.com/astronomy/ring-small-galaxies-04707.html)