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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Unexpectedly Heavy Stars from Long Ago Puzzle Astronomers (SPACE.com)

Ancient stars found in the outer reaches of our Milky Way are surprisingly chock full of some of the heaviest chemical elements, which could have formed in the galaxy's early history, a new study reveals.

When astronomers found abnormally large amounts of heavy elements like gold, platinum and uranium in some of the oldest stars in the Milky Way they were puzzled, because an abundance of very heavy metals is typically only seen in much later generations of stars.

To investigate this mystery, researchers observed these ancient stars over the course of several years using the European Southern Observatory's fleet of telescopes in Chile. They trained their telescopes on 17 "abnormal" stars in the Milky Way that were found to be rich in the heaviest chemical elements.

The results of the study are detailed in the Nov. 14 issue of the Astrophysical Journal Letters.

"In the outer parts of the Milky Way there are old 'stellar fossils' from our own galaxy's childhood," the study's lead author Terese Hansen, an astrophysicist at the Niels Bohr Institute at the University of Copenhagen, said in a statement. "These old stars lie in a halo above and below the galaxy's flat disc. In a small percentage — approximately 1-to-2 percent of these primitive stars — you find abnormal quantities of the heaviest elements relative to iron and other 'normal' heavy elements." [Top 10 Star Mysteries]

Hansen and her colleagues calculated the orbital motions of the stars, which led to an important clue about what kind of mechanisms must have created the heavy elements in the stars.

According to the researchers, there are two possible theories to explain these ancient stars, both centered around supernova explosions, when massive stars run out of fuel and collapse in energetic bursts.

Shortly after the universe was created, it was dominated by light elements like hydrogen and helium. As clouds of these gasses clumped together and collapsed in on themselves under their own gravity, the first stars were formed.

At the heart of these stars, hydrogen and helium merged together and formed the first heavy elements like carbon, nitrogen and oxygen.

When these massive stars died in supernova explosions, they spread the newly formed elements as gas clouds into space. These gas clouds eventually collapsed in on themselves again to form new stars containing the heavier elements. Throughout this process, the newer generations of stars become richer and richer in heavy elements.

After a few hundred million years, all of the known chemical elements existed. But the very early stars contained only a thousandth of the amount of heavy elements that are seen in the sun and other stars today. Hansen and her colleagues suggest that some early stars may have been in close binary systems. In such a twin star system, when one star went supernova, it would have coated its companion star with a thin layer of heavy elementslike gold and uranium.

"My observations of the motions of the stars showed that the majority of the 17 heavy-element-rich stars are in fact single," Hansen said. "Only three belong to binary star systems — this is completely normal, 20 percent of all stars belong to binary star systems. So the theory of the gold-plated neighboring star cannot be the general explanation."

Another theory is that early supernovas could shoot jets of these elements in different directions, dispersing them into the surrounding clouds of gas that eventually formed some of the stars we see today in the Milky Way.This scenario could help explain how many of the old stars became abnormally rich in heavy elements, the researchers said.

"In the supernova explosion the heavy elements like gold, platinum and uranium are formed and when the jets hit the surrounding gas clouds, they will be enriched with the elements and form stars that are incredibly rich in heavy elements," Hansen said.

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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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Asteroid Near Earth Discovered by Amateur Astronomers (SPACE.com)

A team of amateur astronomers has discovered a previously unknown asteroid in orbit that brings it near the Earth, highlighting the contributions regular folks can make to planetary defense, scientists announced Wednesday (Oct. 12).

The skywatchers spotted the asteroid, which is known as 2011 SF108, in September using a telescope in the Canary Islands. While 2011 SF108's orbit appears to bring it no closer to Earth than about 18 million miles (30 million kilometers), it still qualifies as a near-Earth object — the class of space rocks that could pose a danger to our planet.

The team took advantage of an observation slot sponsored by the European Space Agency's Space Situational Awareness (SSA) program to make the find, according to an ESA announcement.

"As volunteer work, it is very rewarding," said Detlef Koschny, head of near-Earth object activity for SSA, in a statement. "When you do spot something, you contribute to Europe's efforts in defending against asteroid hazards." [Photo of newfound asteroid 2011 SF108]

Amateurs make a find

Asteroid 2011 SF108 was discovered by the Teide Observatory Tenerife Asteroid Survey (TOTAS) team, a group of 20 skywatching volunteers. They used the 1-meter telescope at the European Space Agency's Optical Ground Station on Tenerife in the Canary Islands.

Specifics on the asteroid's estimated size were not detailed in the ESA announcement.

The telescope observed for four nights, running automated asteroid surveys using software developed by amateur astronomer and computer scientist Matthias Busch from the Starkenburg Amateur Observatory in Heppenheim, Germany.

Busch's software flags potential space rocks, but the finds must be confirmed by human eyes. The software scored a hit during the observing session of Sept. 28 and 29, researchers said.

"Images are distributed to the entire team for review, and any one of them could be the discoverer of a new asteroid," Koschny said. "This time, the luck of the draw fell to Rainer Kracht."

Kracht, a retired schoolteacher who lives in Elmshorn, Germany, is therefore 2011 SF108's official discoverer. He now has found 46 asteroids, researchers said.

To date, about 8,000 near-Earth objects have been discovered worldwide, but many thousands more are suspected to exist. Astronomers are keen to find as many of them as possible, so they can better assess the chance that a big, dangerous space rock will slam into Earth sometime soon.

Since starting their SSA-sponsored survey work in January 2010, the TOTAS amateur astronomers have identified nearly 400 candidate asteroids, 20 of which have been confirmed and named, researchers said.

Determing the orbit

After examing telescope images from three separate nights, the TOTAS team was able to determine 2011 SF108's orbit well enough to declare it a near-Earth object.

The team sent news of its find to the Minor Planet Center in Cambridge, Mass., the worldwide clearinghouse of information about comets and asteroids.

While 2011 SF108 appears not to pose much risk to Earth for the foreseeable future, further observations could help refine its orbit and our assessment of just how dangerous it might be, researchers said. But for now, the team can bask in the glow of discovery for a spell.

"It was really an exciting moment when I saw 'our' asteroid appearing on my computer screen," Koschny said. "It confirms the excellent quality of work done by the entire TOTAS team."

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