Lisa, all about the NASA-ESA mission to search for new gravitational waves

Green light for Lisa. if Scientific Programs Committee DaleEuropean Space Agency (Jesus) is already only officially release him Help yourself To start the task, its name is an abbreviation for Space antenna laser interferometer: This is the first ever research and discovery project Gravitational waves Directly from space Help yourself It is a crucial step to move to the operational phase of the mission: with this approval, the space agency essentially acknowledges that Concept Lisa's technology is advanced enough that she then moves on to the next stage, which is selecting the contractors who will actually build the vehicles and tools. Construction is scheduled to begin in January 2025, and launch is expected to take place in the middle of the next decade. For the task, among other things, You will also participate NASA like “Collaborative partner”. Let's try to understand what it is and how it will work.

What are gravitational waves?

Gravitational waves are one Disturbances of time and place The “fabric” of which the universe is made, according to Einstein's theory of relativity) which arises as a result of the acceleration of one or more mass objects (two black holes or two rotating stars, for example), propagating at the speed of light and locally modifying the geometry of space and time. Its existence follows directly from the field equations in general relativity, and indeed it does Einstein himself predicted it in 1918But it took nearly a century before we could observe them and confirm indisputably that they actually existed. At least this Two reasonsThe first is that the force of gravity is much weaker than the other fundamental forces (electromagnetism, strong nuclear, and weak nuclear), even if it affects much greater distances, and therefore in order to feel its effects we must have very high accuracy. And sensitive. the The second reason is more subtle: Basically, whatever instrument you use to try to measure this disturbance in spacetime Itself Given this disorder, it is as if we wanted to try to measure how much the table leg had shortened using a measuring tape which would also have shortened at the same time. These difficulties, as we said, delayed the experimental observation of gravitational waves by about a century compared to the time of their theoretical prediction. But in the end we managed to use some Interferometersequipment capable of measuring the minimum discrepancy in the path traveled by two waves of light: in this way it is possible to understand whether space-time has been distorted due to the influence of a gravitational wave, Slowing down one beam of light relative to another.

The eureka moment (and subsequent moments)

At 11.50 a.m. on 14 September 2015, the interferometers were measured Hanford H Livingstonethousands of kilometers away, were discovered, simultaneously and with great precision, Signal of the first gravitational waves ever observed by humansResulting from the collision of two large black holes about a billion and a half years ago. The data captured were extraordinarily consistent with those predicted by Einstein's general relativity equations: if gravitational waves were subtracted from the detected effect, the remaining signal was consistent with background statistical noise. This landmark observation was followed by many others: two years later, for example, the “eyes” of the Ligo interferometers, in the United States, Virgo, in Italy, and the telescopes of the Eso Observatory, in Chile, made another observation. A gravitational wave signal, this time created by the collision of two waves Neutron stars. In a sense, it was a more important discovery, because, unlike… black holes (which emit no radiation – or no radiation at all), and neutron stars are accompanied by the emission of luminous radiation and heavy elements, including Gold, platinum and uranium: A mine of data that scientists rushed to analyze and which reveals many of the secrets of the universe.

The future: research from space

What is still missing, and what is right? Lisa's goal is to observe gravitational waves directly from space. “Lisa is a feat that has never been attempted before – He explained Nora LutzgendorfESA Project Leader – Using laser beams over distances of up to several kilometres, we are now able to detect gravitational waves generated by cosmic events involving star-sized objects, such as supernova explosions, collisions of ultra-dense stars or black holes, using ground-based instruments. To expand our capabilities, it is necessary to move into space.”. LISA consists of three different vehicles, which will be launched on board an Ariane 6 rocket, which will be placed in orbit to form an equilateral triangle with a side length of two and a half million kilometers, that is, approximately six times the distance between Earth and Earth. The moon is tall which will “exchange” laser beams. Each of the three vehicles will have inside a pair of gold and platinum cubes (so-called test blocks) which will float in a special chamber.. The concept is always the same: gravitational waves will adjust the distance between the cubes on board each vehicle in a barely perceptible way, Lasers Therefore, they will take slightly different times to move along both sides of the triangle. When devices detect this discrepancy, it means that there will be a gravitational wave passing through. To give an idea about How weak are gravitational waves?And how sensitive these tools are, just think that the change in the distances between the cubes is only a few billionths of a millimeter, compared to the two and a half million kilometers that the laser travels. “Since the distances traveled by LISA lasers are much greater than those traveled by lasers in ground-based interferometers – Lutzgendorf says again – And because of admiration hardware stability, “We will be able to detect gravitational waves at frequencies much lower than is possible on Earth, which will give us the possibility of studying events at very different levels.”.