When looking for lost keys, there are several possible search strategies. You can walk from room to room, looking around all horizontal surfaces, hoping to notice your missing ligament. This strategy is based on the assumption that the keys are prominently displayed; if it turns out that the keys were covered with a newspaper or fell behind the sofa, then the strategy will be fruitless. So what is the best search strategy?
Scientists have faced a similar problem while "hunting" for gravitational waves - "ripples" of space-time - emanating from the side of rapidly rotating neutron stars. These stars are the densest objects in the universe and, if they are not perfectly spherical, emit a very faint "buzz", or continuous stream of gravitational waves. If scientists hear this "buzz", they will be able to better understand the structure of the neutron star and other features of extreme states of matter. Until now, however, our very sensitive "ears" - four-kilometer detectors using powerful lasers - have "heard" nothing.
Part of the problem is choosing a search strategy, similar to choosing a strategy for finding lost keys. Most previous studies have used a room-to-room approach, looking for a continuous background of gravitational waves in as many different locations as possible. With this approach, one and the same region of space is subject to only a "cursory" observation, and therefore there is a possibility of missing the weak gravitational-wave "buzz" of pulsars.
In a new study, a team led by postdoc researcher Karl Wette of the Australian National University's ARC Center of Excellence for Gravitational Wave Discovery (OzGrav) tried to "guess where the keys should lie" by correlating pulsar radio zones and zones gravitational-wave "buzz". However, after 6000 hours of detailed "listening" to one narrow region of outer space in the hope of detecting gravitational waves from the pulsars, the authors did not "hear" anything.
"This time our guess was not confirmed, but we will continue to" listen "to gravitational waves in other areas of space," - said Vette.
The work was published in the journal Physical Review D.