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Thursday, March 15, 2018

The approach is completely new detectors of gravitational waves

Gravitational waves, which have recently experienced the LIGO collaboration emerged after the two black holes, each of which had a mass 30 times greater than the mass of the Sun are merged together the result is an impressive collision. But the so-called gravitational waves are very weak and cover a wide range of frequencies and therefore require different detection technologies. And to be able to fully explore this phenomenon, we need other types of detectors than are used today.

A new study by experts from the NANOGrav consortium of astronomers shows that in the near future low-frequency gravitational waves can be detected with existing radio telescopes.

“We can detect this signal, if we have the ability to control a fairly large number of pulsars scattered across the sky, explains in a press release, lead author of the new work Stephen Taylor (Stephen Taylor) from the jet propulsion Laboratory of NASA. — If we see the same rejection of all of them, and it will be irrefutable proof”.

Pulsars are rapidly rotating neutron stars with strong magnetic fields that remain after the explosion of a massive star as a supernova. Taylor and his colleagues were looking for ways to use these powerful sources of radiation for the detection of signals from low-frequency gravitational waves, which are formed by the collision the more massive objects than those with which the team worked LIGO. For example, in the collision of two galaxies, each of which contains a supermassive black hole billions of times exceeds Sun mass.

Such black holes will eventually be for a while to rotate relative to each other and slowly get closer to a full merger in an even more massive object. In the process of rotation they create a gravitational disturbance of the surrounding space-time that spread in all directions in the form of weak signals, like vibrations on the web.

When these waves reach our planet, they push it, causing a small deviation with respect to distant pulsars. Fluctuations caused by a single merger of supermassive black holes, can pass through space near the Earth for several months or even years. That is, to discover them, requires years of observation.

Pulsars emit “pillars” of radio waves. Their rapid rotation causes the Earth emanating from the pulsar radio emission by the radio telescopes is perceived as a quick “blink” of a star. All this is reminiscent of the work of the lighthouse. The majority of pulsars “signals” earthlings several times per second, but some spin hundreds of times faster. The time of arrival of such signals is strictly periodic and predictable fashion, so that existing devices can measure them accurately to the ten millionth fraction of a second. This can be used to determine extremely small changes relative to the position of the Earth caused by gravitational waves.

“It’s not just about the collision of galaxies, says Joseph Lazio (Joseph Lazio), co-author of an article published in this week’s edition of The Astrophysical Journal Letters. We think that many systems contain dual supermassive black holes, and perhaps we will be able to detect them. Observing pulsars, we can get a feel for how these massive objects slowly spiral closer to each other”.

Now American scientists, United by the NANOGrav project, see 54 of the pulsar in the sky above the Northern hemisphere, and are open to cooperation with colleagues from other continents to increase the number of observed sources.

It should be noted that shortly before the collision of black holes gravitational waves become too short to catch with the help of pulsars. In this case, the assistance can come in the space laser interferometers. Experts from the European space Agency with participation of colleagues from NASA are developing a detector eLISA, which may become the first milestone for a network of registrars of gravitational waves, placed in orbit of the planet.

The essence of the technology is that two objects are loose on the move in space at a constant distance from each other. They must be isolated from all pressures except gravity. In the future, a systematic weak fluctuations of these facilities are planned to determine the shortest gravity waves. And while scientists needed to find out whether two objects so accurately maintain their relative positions.

To test the viability of this idea in 2015 in the space was removed the test probe LISA Pathfinder. Finally, the project team reported the first successful tests of the system, which is still believed not all experts.

Inside a spacecraft placed two five-pound cube of gold and platinum, installed at a distance of 38 centimeters from each other. While moving the probe in space at a distance of 1.5 million kilometers from Earth, these cubes released from the anchorages, and measured their relative position with high precision laser sensors, which detect any deflection with an accuracy of one millionth of a millimeter. The device should adjust its position by thrusters that constantly Cuba remained exactly in its center.

“Everything works exactly as we had planned. It’s a kind of magic, and rare to see such in the career of the experimenter,” says principal investigator Stefano Vitale (Stefano Vitale) from the University of Trento.

In addition to the successful testing of LISA Pathfinder further funding for the project space of the detector depended on whether gravitational waves registered by ground detectors. Thus, the past February was for researchers especially good month.


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