The distribution of pairs of galaxies that orbit one another has verified key elements of the standard model of cosmology - suggesting the presence of dark energy. NASA/ESA The claim that mysterious dark energy is accelerating the Universe's expansion has been placed on firmer ground, with the successful application of a quirky geometric test proposed more than 30 years ago. The accelerating expansion was first detected in 1998. Astronomers studying Type 1a supernovae, stellar explosions called "standard candles" because of their predictable luminosity, made the incredible discovery that the most distant of these supernovae appear dimmer than would be expected if the Universe were expanding at a constant rate. 1 This suggested that some unknown force - subsequently dubbed dark energy - must be working against gravity to blow the universe apart. Since that time, studies comparing variations in the cosmic microwave background radiation - an echo from the Big Bang - with the distribution of galaxies today have allowed cosmologists to trace how the Universe has expanded, supporting the idea of dark energy. They have also suggested that the Universe is 'flat' - that is, it contains just enough matter to keep it delicately poised between collapsing in on itself and expanding forever 2 . "It's a very clever idea, it's unexpected, and it's going to take a while to determine whether it's accepted or not." Charles Alcock Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts These two assumptions have become a fundamental part of cosmologists' understanding of the Universe. Now Christian Marinoni and Adeline Buzzi of the Centre for Theoretical Physics at the University of Provence in Marseilles, France, have independently checked these ideas by analysing the geometry of orbiting pairs of galaxies. Their study is published this week in Nature 3 . The researchers used a version of the Alcock–Paczynski test, which relies on identifying symmetrical objects in space and using them as 'standard spheres'. Any distortions in space caused by the expansion of the cosmos would cause the most distant standard spheres to appear asymmetrical. "This provides a similar level of accuracy to supernovae," says Marinoni. "It's a direct proof of dark energy." Object lessons For example, if the universe is expanding outwards due to dark energy, distant objects will appear elongated along the line of sight from Earth, because Earth and the objects are being propelled away from one another along that direction. Several groups have tried to apply the test, for example by considering clusters of galaxies as the standard spheres, but largely failed because they could not measure distant objects with sufficient accuracy. To get round this, Marinoni and Buzzi instead studied the distribution in orientations of pairs of galaxies that orbit each other. In a Universe without dark energy, that distribution is expected to be spherically symmetrical - in other words, the number of galaxy pairs oriented in any particular direction should be the same. The researchers found that the farther away the galaxy pairs were, the more asymmetrical the distribution was, with more galaxy pairs oriented along the line of sight from Earth. The pattern matched what would be expected in a flat Universe expanding due to dark energy. The reliability of the test depends on the assumption that the distribution in orientations of galaxy pairs doesn't change depending on their distance from Earth - an idea that is largely untested. But researchers are still excited by the result. "It's a very clever idea, it's unexpected, and it's going to take a while to determine whether it's accepted or not," says Charles Alcock, director of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and co-proposer, in 1979, of the test Marinoni and Buzzi used 4 . "This is a cool new tool. It's another indication that everything is consistent," says Anthony Tyson, who studies cosmology at the University of California, Davis. Tyson adds that he is sceptical about some of the assumptions underlying theories of dark energy, so he finds independent efforts to confirm its presence extremely valuable. "For those of us who are doubters, it's making us think twice," he says. Future surveys of distant objects are planned, for example using the European Space Agency's planned Euclid space telescope, and the Wide Field Infrared Survey Telescope, a proposed mission that was the top recommendation of the US National Academy of Sciences Decadal Survey of Astronomy and Astrophysics. Marinoni says he hopes these will find further remote pairs of galaxies that can be analysed to pin down the nature of dark energy, perhaps even enough to overtake the accuracy offered by studies of type Ia supernovae. Were samples of protein from a fossilized T. Rex contaminated? Wikimedia / David Monniaux More doubt has clouded claims that dinosaur protein has been sequenced. Now a long-time critic has called for an independent review of the 2007 studies of ancient protein from a fossilized Tyrannosaurus rex after fresh analysis revealed traces of ostrich haemoglobin in the original samples. In the contentious papers, researchers identified seven fragments from a protein called collagen 1 , found in connective tissue, and said their sequences most closely matched the chicken version of the protein 2 . The samples came from the fossilized femur of a T. Rex . As well as further strengthening the evidence for the link between dinosaurs and birds, the findings would make the protein the oldest ever to be sequenced - by around 68 million years. The work, published in Science , garnered headlines worldwide and met with considerable scepticism at the time. Now Martin McIntosh, a mass spectrometrist at the University of Washington in Seattle, says he has identified ostrich haemoglobin protein in a cache of 48,000 protein spectra released last September by John Asara, whose lab at Beth Israel Deaconess Medical Center in Boston analysed the original samples. McIntosh suspects the samples were somehow contaminated with proteins from modern species. But Asara and colleagues are standing by their results and reject claims that their protein was tainted. Dinosaur debate McIntosh's findings came to light on 23 February at the sixth annual meeting of USHUPO - part of the international Human Proteome Organisation - in San Diego, California. In the course of a lecture, Pavel Pevzner, a computational biologist at the University of California, San Diego, cited McIntosh's work and called for an independent review of the original results. He said his analysis provides statistical support for two of seven collagen proteins the Science authors said were from T. rex . But now the contamination issue has raised new concerns about the validity of the earlier findings. It was not the first time that Pevzner had criticized the findings. Before Asara made the protein spectra available in September, Pevzner had publicly called for their release, arguing the statistical accuracy of the initial results couldn't be verified without them. Pevzner and his colleagues also penned a critical technical comment on the statistical questions in Science last August 3 . In an earlier technical comment in January last year, 27 authors had written that they couldn't verify collagen proteins in the samples 4 , and a separate study last spring asserted the proteins are from slime mould 5 . McIntosh also wrote a technical comment for Science , suggesting contamination on the basis the haemoglobin spectra - but it was rejected. Peer reviewers said that one fragment of ostrich haemoglobin was not enough to suggest contamination had occurred. McIntosh accepts that his paper doesn't prove contamination, but still believes the samples may be tainted. Close to an ostrich Asara is sticking by the findings, though his team reported in a follow-up paper in 2007 that there was no statistical support for one of the fragments 6 . He told Nature News it is "statistically unlikely" that only one ostrich peptide would show up if there was contamination, especially since sediment and reagents from his experiments had no trace of it. He claims that work he hopes to publish soon also rules against contamination. Last May, he and Mary Schweitzer, the palaeontologist at North Carolina State University in Raleigh who provided him with the samples from the femur, published another Science article showing that further comparison of the ancient proteins to those of existing species - like ostrich and crocodile - confirmed their work 7 . Meanwhile, the controversy rumbles on. When Pevzner polled his audience at the USHUPO meeting, none of the several dozen researchers present indicated support for the T. rex collagen results. Asara was in the room, but did not respond. Marshall Bern, a computational biologist at the Palo Alto Research Center in California who was not at the meeting, said he leaned in support of Asara's collagen analysis. "Asara has met Pevzner's test," says Bern. "All this scrutiny makes the two proteins [that Pevzner verified] look good. And I'm not ready to discount the other five. Contamination is now the issue." The two lead authors of the controversial papers say they may accept a review of the work - depending on its form. "We agree independent verification of our findings is critical to their acceptance," Asara told Nature News , adding collaborations are already under way. Schweitzer agrees. "If a review looked at everything, I would support it," she says.