Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World‘s team of editors and reporters
Gigantic X-ray “tsunami” spotted near galaxy cluster
A giant wave of hot gas twice the size of the Milky Way has been discovered using NASA’s Chandra X-ray Observatory, radio observations and computer simulations. The wave is located near the Perseus galaxy cluster – one of the most massive nearby groupings of galaxies that spans 11 million light-years. It is the brightest cluster in terms of X-ray emissions because most of its observable matter is a gas that is so hot (tens of millions of degrees) it only glows with X-rays. Chandra has observed a variety of features in the gas, including a concave “bay” wave. If this structure was a result of bubbles launched by the central galaxy’s supermassive black hole, it would emit radio waves. However, observations by the Karl G Jansky Very Large Array in the US showed no such signal. It also could not be the result of “sloshing” gas as it arcs in the wrong direction. To work out the wave’s origin, Stephen Walker from NASA’s Goddard Space Flight Center in the US and colleagues compared high-resolution observational data with computer simulations of merging galaxy clusters. The resulting simulation begins with a large galaxy cluster (Perseus) that has settled into a “cold” (30 million degrees) central region surrounded by a zone of gas three times hotter. A small galaxy cluster then skirts the larger relative, causing a gravitational disturbance that churns up the gas and creates an expanding spiral of cold gas. Roughly 2.5 billion years later, the gas has spread 500,000 light-years from the centre and massive waves, such as the bay, form and roll at its periphery for hundreds of millions of years before dissipating. In the Monthly Notices of the Royal Astronomical Society, the scientists suggest that the waves are giant Kelvin–Helmholtz waves – which occur when there is a velocity difference at the interface of two fluids, such as wind blowing over water.
First light for European X-ray Free Electron Laser
The European X-ray Free Electron Laser (European XFEL) in Hamburg, Germany, has achieved first light. Last month, engineers at the facility sent electrons down the facility’s 2.1 km-long superconducting linear accelerator for the first time. After being accelerated, electrons have now been sent through “undulators” to produce X-rays with a repetition rate of one pulse per second. When fully commissioned, the European XFEL will generate pulses of X-rays 27,000 times per second with each pulse lasting less than 100 fs (10–13 s). This will allow researchers to create “movies” of processes such as chemical bonding and vibrational energy flow across materials. Engineers will now continue commissioning the European XFEL – including increasing the facility’s repetition rate – ready for first users in September.
Survey highlights UK–Europe science collaboration
Scientists in the UK have strong collaborations with their European counterparts, according to a survey carried out by the UK National Academies. The Academy of Medical Sciences, British Academy, Royal Academy of Engineering and the Royal Society asked more than 1286 fellows and grant recipients about their international collaborations and mobility. They found that 95% had travelled to Europe and 87% collaborated with their European colleagues, while 58% of respondents had spent a year or more working abroad, 64% of whom went to North America. Meanwhile, a separate survey carried out by the Royal Society of 1285 UK-based scientists found that 72% had trained or worked abroad, while 80% of non-UK national researchers that were working in the UK were from the European Union or North America. The Royal Society survey also reported that women are less likely to work abroad than men. Some 39% of men say they had spent more than three years working outside of the UK compared to 25% for women.