Gravity probe LISA Pathfinder achieves best ever free fall

时间:2019-03-15 10:06:00166网络整理admin

ESA/ATG medialab A gravitational space experiment has received top marks for staying almost perfectly still – a feat that could one day be used to help probe the very nature of the universe itself. Inside the European Space Agency’s LISA Pathfinder spacecraft, launched last December, float two 2-kilogram cubes of gold and platinum, which are now experiencing the truest free fall ever achieved by human-made objects. LISA Pathfinder is designed to test the technology necessary for building a gravitational-wave observatory in space. Such waves, first predicted by Albert Einstein almost a century ago, are ripples in space-time, the fabric of the universe, caused by collisions between massive objects such as black holes. By Jacob Aron Researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first direct detection of gravitational waves earlier this year, but physicists also want to pick up these waves in space, free from the influence of Earth. This would allow them to see the gravitational universe in different frequencies to those of LIGO, and thus study different cosmic objects. ESA has long-term plans for a trio of spacecraft called LISA, which will fly 1 million kilometres apart and pick up any changes in distance between them caused by passing gravitational waves. Creating these probes is an immense technical challenge, because researchers must isolate their instruments from all outside forces apart from gravity. ESA thus started with a smaller experiment: “We decided we should learn to walk before we can run,” said ESA’s Fabio Favata at a press conference at the European Space Astronomy Centre near Madrid, Spain, this morning. LISA Pathfinder’s test cubes are just 38 centimetres apart, but accurately measuring the distance between them – to within a trillionth of a metre, or less than the width of an atom – involves the same principles. The cubes were released within the spacecraft shortly after launch, and are now in free fall together, meaning they are barely moving with respect to each other. The first results, released today, show that the spacecraft can measure the distance between the cubes down to the femtometre scale – 100 times better than planned. ESA–C.Carreau “We are able to measure the motion of these test masses with unprecedented precision,” said Martin Hewitson of the University of Hannover, Germany. “We didn’t know we were going to be able to do that.” The results mean that ESA has now tested the technology that will allow it to build the much larger observatory. “We’ve not only learned to walk, but actually to jog pretty well,” said Favata, meaning the technique for hunting gravitational waves is sound. “Thanks to LISA Pathfinder, we know that we have sufficient sensitivity to observe them from space, and therefore a new window to the universe has been opened.” The three LISA spacecraft are not set to launch until 2034, but the performance of LISA Pathfinder means there should be no technical obstacles to achieving the mission’s goals. “The most important message is, we can go with LISA,” said mission lead Stefano Vitale of the University of Trento, Italy. More on these topics: