Illustration of a quasar (Image: ESO / M. Kornmesser)
Reading The universe contains countless galaxies, galaxy clusters and clusters, but - considering a sufficiently large section - is still relatively homogeneous. At any rate, that is the cosmological principle. According to this basic assumption, there should be no structures in the cosmos that are larger than about 370 Megaparsec - which corresponds to 1.2 billion light years. But now astronomers have discovered a quasar group that is well above that limit. The elongated cluster of active galaxy nuclei is 1, 200 megaparsec long - 1, 600 times the distance from the Milky Way to our neighboring galaxy Andromeda. The quasar group is thus the largest known structure in the universe, as the international research team reports. "It's hard to grasp the gigantic size of this formation: even light takes four billion years to get from one end to the other, " says lead author Roger Clowes of the University of Central Lancashire at Preston. "This is extremely exciting - not least because it contradicts our previous understanding of the size relationships in the cosmos."

Giant lumps of active galactic nuclei

Quasars are among the brightest objects in the universe. These nuclei of distant galaxies from the early cosmos radiate a huge amount of energy and can therefore be detected over long distances. Similar to many objects in the universe, these cosmic beacons often appear "lumpy" - they form so-called Large Quasar Groups (LQG). These groups are about ten times the size of typical galaxy clusters: instead of just two to three megaparseconds, they reach 200 or more. Typically, they comprise between five and 40 quasars, as Clowes and his colleagues explain.

Much larger but, so it was believed so far, even these giants of the early universe can not be. For if they were larger than about 370 megaparsec, they would contradict the cosmological principle - they would produce clumps of matter that, even looking at a large section of the universe, would no longer merge with the rest to form a homogeneous "carpet." display

Sky survey provided crucial data

"The discovery of such a huge structure now suggests that the universe is not homogenous on these scales, " Clowes and his colleagues note. After all, the quasar group baptized by them giant LQG takes an average of 500 megaparsec of space and is much longer. And in terms of the galaxy nuclei contained in it - 73 - it far surpasses all previously known groups, as the researchers report.

The astronomers discovered the quasar group in the evaluation of data from a large sky survey, the Sloane Digital Sky Survey (SDSS). For this, a 2.5 meter telescope with electronic detectors systematically scans an area on the northern pole of the Milky Way. Equipped with sensors for different magnitudes and five wavelengths, it can detect distant galaxies and quasars, as well as near brown dwarfs or asteroids. Clowes and his team now want to continue searching the SDSS data, hoping to find even more such extremely large objects. "We will definitely continue to investigate these fascinating phenomena, " says Clowes.

Roger Clowes (University of Central Lancashire, Preston) et al .: Monthly Notices of the Royal Astronomical Society, arXiv: 1211.6256 © science.de - === Nadja Podbregar

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