Detecting Gravity Waves Directly in Space-Sciencetimes

“Ladies and gentlemen. We have detected gravitational waves. We did it!”

According to Einstein’s general theory of relativity, a gravitational wave that propagates at the speed of light and warps surrounding space-time is an energy wave that occurs when an object with mass undergoes rapid acceleration. The existence of these gravitational waves is well known in theory, but it was not easy to measure. On February 11, 2016, there was a big news of astronomy that really made the world buzz. It was the first mankind to successfully observe the gravitational wave predicted by Einstein more than 100 years ago. The announcement above is “Ladies and gentlemen. We have detected gravitational waves. We did it! Prof. Dr. David Reitze’s message begins with Professor Prof. Dr. David Reitze’s message, “We have found the gravitational waves, everyone!” there was.

Dr. Marco Drago, a physicist at the Max Planck Institute for Gravity Waves in Hannover, Germany, who was part of a joint team of the laser interferometer Gravity Wave Observatory (LIGO) and the Virgo team, said that the waveforms measured by the first detectors will not be true Judged. After more than a month of more detailed statistical analysis, it was found that the merger of a pair of black holes and the resulting single black hole were consistent with the theoretical predictions of the gravitational waves produced. This is a strong test of the theory of general relativity and is the first observation of a binary black hole merger, and it is also the result of indicating the existence of a stellar mass black hole binary system.

The above detection was made in the first year of the LIGO detector’s mission, so the prospect is very bright. The so-called gravitational wave observation era has wide open. As of October 29, 2020, more than 50 gravitational wave observation signals were officially compiled.

Limitations of current gravitational wave discovery

Currently, the discovery of gravitational waves mainly uses the phenomenon of laser interference. The principle of the equipment is basically the same as that of the Michelson interferometer. The gravitational wave is detected through the phase change of the laser passing through two vacuum pipes of approximately 4 km placed at right angles. When the distance that the completely coherent laser travels is changed due to the oscillation of space, the interference fringes change accordingly, and through this, it is possible to measure the oscillation as small as the diameter of the atomic nucleus. It is very encouraging that the range of gravitational waves is quite wide. For reference, the black hole binary, the first to discover gravitational waves, is 1.3 billion light-years away from Earth.

One limitation of LIGO is that black holes with masses of the order of the Sun or slightly larger are the main targets for observation. In addition, the influence of various meteorological phenomena (mainly earthquakes, waves, wind, etc.) occurring on the earth becomes more important as it goes to the low frequency band, and for this reason, low frequency bands below 1 Hz cannot be observed from the earth. How can we observe gravitational waves that are difficult to observe from the ground, e.g. from a supergiant black hole that is hundreds of times the mass of the Sun?

And the European Space Agency’s LISA (Laser Interferometer Space Antenna) mission

To this end, the European Space Agency came out. With the aim of observing the gravitational waves generated in giant black holes, which are hundreds of times the mass of the Sun, we plan to measure the gravitational waves generated mainly when very large objects in the galactic unit collide with each other. The basic operating principle is the same as that of the LIGO detector.

However, the European Space Agency’s mission LISA (Laser Interferometer Space Antenna), which will be launched in space, will exchange lasers while operating three spacecraft equipped with interferometric gravity wave detectors in a 25 million km long triangular flight. Through this, the phase difference that changes due to the gravitational wave is recorded. Considering that it is already in a vacuum, there is also an advantage that even a pipe is not required.

The stability of the interferometer-based gravitational wave detector is mainly determined by the vibration of the device, the surface conditions such as the material of the mirror, and the stability of the light source.Seismic noise caused by the vibration of various devices is the most interfering with the discovery of the gravitational wave. It is one of the big factors. However, there is also the advantage that there are relatively few disturbing factors appearing on Earth in space. As a result, the LISA mission aims to detect gravitational waves in the 0.001-0.1 Hz band.

Success of LISA Pathfinder and preparation for full-fledged LISA mission

The strong will of the European Space Agency’s above mission can be seen in the LISA Pathfinder (SMART-2), the second mission of ESA’s Horizon 2000+ program. The LISA project was actually aiming to launch as early as 2018. However, in 2011, NASA was pulled out of the plan due to funding problems, and the European Space Agency, under pressure of funding, changed its name to eLISA and called for a reduction in the project.

Meanwhile, in December 2015, the “Compass” LISA Pathfinder, developed with the aim of demonstrating the technology necessary for successful observation of LISA, was launched and the overall technology was verified. The LISA Pathfinder also had a small interferometer with a length of 38 cm, which makes it difficult to detect gravitational waves in a very short path. However, many of the LISA Pathfinder’s preliminary tours have been incredibly successful, as they have achieved far more stable results than originally intended. Through this, the European Space Agency concluded that it is possible to detect gravitational waves in outer space through LISA.

The above results contributed greatly to the further upgrade of eLISA, and the space laser interferometer, which was renamed LISA, is scheduled to be launched in 2034, and plans to focus on reliably detecting gravitational waves in space afterwards. Observing the merger of the largest black holes in the universe means getting closer to the history of the universe. In addition, LISA will be able to serve as a guide for terrestrial detectors that will remain active even after launch. This is why the LISA mission is expected.

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