The universe has a huge hole in it that dwarfs anything else of its kind. The discovery caught astronomers by surprise.

The hole is nearly a billion light-years across. It is not a black hole, which is a small sphere of densely packed matter. Rather, this one is mostly devoid of stars, gas and other normal matter, and it's also strangely empty of the mysterious "dark matter" that permeates the cosmos. Other space voids have been found before, but nothing on this scale.

Astronomers don't know why the hole is there.

"Not only has no one ever found a void this big, but we never even expected to find one this size," said researcher Lawrence Rudnick of the University of Minnesota.

Rudnick's colleague Liliya R. Williams also had not anticipated this finding.

"What we've found is not normal, based on either observational studies or on computer simulations of the large-scale evolution of the universe," said Williams, also of the University of Minnesota.

The finding will be detailed in the Astrophysical Journal.

The universe is populated with visible stars, gas and dust, but most of the matter in the universe is invisible. Scientists know something is there, because they can measure the gravitational effects of the so-called dark matter. Voids exist, but they are typically relatively small.

The gargantuan hole was found by examining observations made using the Very Large Array (VLA) radio telescope, funded by the National Science Foundation.

There is a "remarkable drop in the number of galaxies" in a region of sky in the constellation Eridanus, Rudnick said.

The region had been previously been dubbed the "WMAP Cold Spot," because it stood out in a map of the Cosmic Microwave Background (CMB) radiation made by NASA's Wilkinson Microwave Anisotopy Probe (WMAP) satellite. The CMB is an imprint of radiation left from the Big Bang, the theoretical beginning of the universe.

"Although our surprising results need independent confirmation, the slightly colder temperature of the CMB in this region appears to be caused by a huge hole devoid of nearly all matter roughly 6 to 10 billion light-years from Earth," Rudnick said.

Photons of the CMB gain a small amount of energy when they pass through normal regions of space with matter, the researchers explained. But when the CMB passes through a void, the photons lose energy, making the CMB from that part of the sky appear cooler.

CHICAGO: Four galaxies are slamming into one another in the largest galaxy merger ever observed – throwing billions of stars off into space in a remarkable fireworks display.

Eventually – in a process that may take up to 100 million years to play out – the galaxies will merge to form a galactic monster up to 10 times as massive as our own Milky Way.

Though the galaxies have remained intact, gravitational forces have contorted them, flinging billions of stars into space. These are visible in a plume emanating from the central, largest galaxy.

Formation clues

"This merger tells us an interesting story about how the biggest galaxies in the universe are made," said Kenneth Rines of the U.S.'s Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts. "The biggest galaxies in the universe are the ones found in the centres of groups and clusters, just like this quadruple merger."

Rines heads a team of astronomers who spotted the merger by chance while using Arizona's WIYN Observatory to image clusters of galaxies five billion light-years away. He said he noticed an odd plume in the centre of one of the clusters, which further analysis proved to be a massive galactic merger. The find was confirmed using data from the U.S. space agency NASA's Spitzer Space Telescope.

The team reports the cosmic collision in the current Astrophysical Journal Letters.

Galaxy mergers are relatively common – many of the universe's large galaxies were formed when smaller galaxies collided in the first few billion years following the Big Bang. In five billion years, the Milky Way itself will combine with our neighbour, the Andromeda Galaxy, producing a slew of new stars.

'Minor mergers' where a large galaxy and several small ones combine occur more frequently. One elaborate example has been observed around the distant Spiderweb galaxy, write the researchers. In this case, the galaxy's gravity is drawing in around a dozen dwarf galaxies. While experts have also observed many 'major mergers' of pairs of similarly sized galaxies, this new merger is the first ever seen between larger groups of galaxies of such massive proportions.

"Dry merger"

The quadruple merger is also unusual in that it is resulting in the formation of surprisingly few new stars. Typically during a galactic merger, gas clouds become so dense that they collapse into new stars and astronomers would expect to observe a "fossil record" of the merging process, said Rines. This would reveal a sequence of stars of different ages.

However, the giant merger adds to evidence that galaxies can collide without producing new stars. These so-called dry mergers, which are gas-poor, occur without leaving a trace of evidence in the form of new stars.

Risa Wechsler, a theoretical cosmologist and astrophysicist from Stanford University in California, commented that while dry mergers have been observed before, this paper supplies "clear evidence" for one of the largest ever seen. "The dynamical information from the stars in this kind of merging event can provide powerful information on the formation history of galaxies and clusters."

(Rapaport…February 16, 2004) The Harvard-Smithsonian Center for Astrophysics has announced the discovery of a mass of crystallized carbon formerly known as star BPM 37093, now known as the biggest diamond in the galaxy, fifty light years away from Earth in the constellation Centaurus. The diamond is estimated to be 2,500 miles across and weighs approximately 10 billion-trillion-trillion-carats – a one, followed by 34 zeros. Travis Metcalfe, an astronomer from the Harvard-Smithsonian Center for Astrophysics and leader of the team who discovered the gem, says “You would need a jeweler’s loupe the size of the sun to grade this diamond. Bill Gates and Donald Trump together couldn’t begin to afford it.”

When asked to estimate the value of the cosmic jewel, Ronald Winston, chief executive officer (CEO) of Harry Winston, Inc., indicated that such a large diamond probably would depress the value of the market, stating, “Who knows? It may be a self-deflating prophecy because there is so much of it.”

The diamond is actually the crystallized interior of a white dwarf – or the hot core of a star that is left over after the star uses up its nuclear fuel and dies. It is made mostly of carbon and is coated by a thin layer of hydrogen and helium gasses.

Five billion years from now, our sun will die and become a white dwarf. Approximately two billion years after that, its ember core will crystallize as well, leaving a giant diamond in the center of our solar system. A paper announcing this discovery has been submitted to The Astrophysical Journal Letters for publication. The Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. Scientists within the organization are classified into six research divisions where they study the origin, evolution and ultimate fate of the universe.