Astronomers discover largest known structure in the universe

(Reuters) - Astronomers have discovered the largest known structure in the universe - a group of quasars so large it would take 4 billion years to cross it while traveling at speed of light.

The immense scale also challenges Albert Einstein's Cosmological Principle, the assumption that the universe looks the same from every point of view, researchers said.

The findings by academics from Britain's University of Central Lancashire were published in the journal Monthly Notices of the Royal Astronomical Society and reported on the society's website on Friday.

Quasars are believed to be the brightest objects in the universe, with light emanating from the nuclei of galaxies from the early days of the universe and visible billions of light-years away.

"Since 1982 it has been known that quasars tend to group together in clumps or 'structures' of surprisingly large sizes, forming large quasar groups or LQGs," the society said.

This newly discovered large quasar group has a dimension of 500 megaparsecs, each megaparsec measuring 3.3 million light-years.

Because the LQG is elongated, its longest dimension is 1,200 megaparsecs, or 4 billion light-years, the society said.

That size is 1,600 times larger than the distance from Earth's Milky Way to the nearest galaxy, the Andromeda.

"While it is difficult to fathom the scale of this LQG, we can say quite definitely it is the largest structure ever seen in the entire universe," Roger Clowes, leader of the research team, said in a statement. "This is hugely exciting - not least because it runs counter to our current understanding of the scale of the universe."

Clowes said the team would continue to investigate the phenomenon with particular interest in the challenge to the Cosmological Principle, which has been widely accepted since Einstein, whose work still forms the basis for much of modern cosmology.

(Reporting by Daniel Trotta; Editing by Gary Hill)

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Astronomers Discover 18 Huge New Alien Planets (SPACE.com)

Astronomers have found 18 new alien planets, all of them Jupiter-size gas giants that circle stars bigger than our sun, a new study reports.

The discoveries increase the number of known planets orbiting massive stars by 50 percent. The exoplanet bounty should also help astronomers better understand how giant planets form and grow in nascent alien solar systems, researchers said.

The haul comes just a few months after a different team of researchers announced the discovery of 50 newfound alien worlds, including one rocky planet that could be a good candidate for life. The list of known alien planets is now well over 700 and climbing fast.

Staring at 'retired' stars

The researchers surveyed about 300 stars using the Keck Observatory in Hawaii and instruments in Texas and Arizona. They focused on so-called "retired" type A stars that are at least 1.5 times more massive than our own sun.

These stars are just beyond the main stage of life — hence the name "retired" — and are now ballooning out to become what's known as subgiant stars.

The team scrutinized these stars, looking for slight wobbles caused by the gravitational tug of orbiting planets. This process revealed 18 new alien worlds, all of them with masses similar to Jupiter's. All 18 planets also orbit relatively far from their stars, at a distance of at least 0.7 times the span from Earth to the sun (about 93 million miles, or 150 million kilometers). [Gallery: The Strangest Alien Planets]

Planet-formation theories

In addition to boosting the ever-growing alien planet tally, the new finds lend support to one of two theories that attempt to explain the formation and evolution of planets, researchers said.

This theory, called core accretion, posits that planets grow as gas and dust glom onto seed particles in a protoplanetary disk. Core accretion predicts that the characteristics of a planetary system — the number and size of planets, for example — depend strongly on the mass of the star.

The main competing theory, called gravitational collapse, holds that planets form when big clouds of gas and dust in the disk spontaneously collapse into clumps that become planets. According to this idea, stellar mass should have little impact on planet size, number and other characteristics.

As the exoplanet finds pile up, it seems that stellar mass does in fact play an important role. The 18 huge newfound alien worlds, which all orbit massive stars, add more evidence in support of core accretion, researchers said.

"It's nice to see all these converging lines of evidence pointing toward one class of formation mechanisms," study lead author John Johnson, of Caltech in Pasadena, said in a statement.

Johnson and his colleagues reported their results in the December issue of the Astrophysical Journal Supplement Series.

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