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Astronomers put quasars in their place

04.10.2002


A team of UK astronomers, led by postgraduate student Ed Hawkins, has made a decisive step toward resolving an argument that has rumbled on in the astronomical community for decades. The scientists from the University of Nottingham have been investigating the properties of quasars and nearby galaxies. As part of this study, they have overturned previous analyses which suggested that these two classes of object are physically associated, thus confirming the alternative, more widely-held view that quasars are some of the most distant objects in the Universe.



Quasars are star-like in appearance, but seem to be flying away from Earth at velocities comparable to the speed of light. The majority of astronomers believe that this high speed is a result of the expansion of the Universe, and that the quasars are traveling so fast because they are at enormous distances. However, a vociferous minority, including such notable figures as the great astronomer Fred Hoyle, has argued forcefully that quasars are much closer by. In particular, they have pointed to apparent associations between quasars and nearby galaxies, suggesting that the quasars have somehow been ejected from these galaxies in the recent past.

One of the pieces of evidence to support this idea was the tentative discovery that quasars only seem to move away from galaxies at particular speeds: for example, a surprisingly large number of quasars seem to be moving relative to neighbouring galaxies at speeds of 59% of the speed of light. If the quasars were actually on the far side of the Universe, how would they know to move at exactly 59% of the speed of light relative to a completely unrelated foreground galaxy?


Very little progress has been made toward resolving this controversy, essentially because there just hasn`t been enough data to tell whether the apparent associations between galaxies and quasars are real or just coincidences. However, this has all changed with two newly-completed huge surveys undertaken with the Anglo-Australian Telescope, one measuring the positions and velocities of 200,000 galaxies, and the other measuring the same quantities for 25,000 quasars. "These enormous new data sets offered a great opportunity to take another look at this question," said Hawkins. "To do as fair a test as possible, we discussed with the supporters of both theories what they would expect to see before we analyzed the data."

By carefully sifting through these datasets, Hawkins and collaborators found 1647 examples of quasars that appear close to galaxies, and hence might be associated. Sadly for the nearby-quasar supporters, there was no excess of quasars moving at 59% of the speed of light, or any of the other "magic speeds" that had previously been tentatively identified. Without this evidence to support an association between quasars and galaxies, the case for quasars being flung out of nearby galaxies is much weakened.

Hawkins concluded "it`s a shame, as it would have been great to find that the conventional view of quasars is all wrong. However, it`s also something of a relief to know that most astronomers have not been barking up completely the wrong tree for the last thirty years."

Prof. Michael Merrifield | alfa

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