The invisible radiation of the universe / Geektimes

The pages are still empty, but it is strangely clear that all words are already written in invisible ink and only pray for visibility.
 – Vladimir Nabokov

The beautiful images of deep space – from distant galaxies to stars, clusters, nebulae in our Galaxy – have one common property.

Light! Specifically, electromagnetic radiation. This light does not always gets in the visible spectrum, but it is her we are most familiar. No wonder: the greatest source of energy for us is the same as for the cluster at the top, NGC 3603.

The light emanating from these stars – as well as the light emanating from all the stars – Strongly depends on the temperature of the stars. The hotter it is, the more blue or even ultraviolet light will emanate from it, and the colder it is, the more red or even the infrared region it will go.

The colors are exaggerated

But not every star looks like our Sun, or a little colder, or a bit hotter than it. Some stars are thousands of times more massive, while others are only a tiny part of the mass of the Sun.

Therefore, the fate of the stars is very diverse.

The vast majority of known to us Stars get their energy from wherece the Sun takes it – from nuclear fusion it is not the only source of energy for the stars of the universe.

In addition to the nuclear reactions that emit this energy, a huge amount of energy is stored in gravity

During compression or collapse ajor weight happens and does not happen, a few interesting things. Space-time outside the mass – what was outside the original star, until the collapse – does not change. Its energy does not change, the curvature does not change, the gravitational potential does not change, etc.

But in the space-time that was originally inside the object, and after collapse or compression was outside, the absolute value of the negative Gravitational potential energy. And this energy must go somewhere.

It, for example, can turn into light – this is what happens to white dwarfs. They are comparable in mass with the Sun, but in size with the Earth, and from them emanates a large amount of light, the source of energy for which is only gravitational compression.

For example, if a white dwarf appeared on the place of the Sun, It would still be 400 times brighter than our full moon!

But not every shrunken or collapsed object was one star in its solar system. Many of them, like the brightest stars in our sky, are double systems. The dual system, two stars, or starlike object, orbit each other. Over time, these orbits do not remain stable, because of gravity they decrease, and the stars fall in a spiral to each other.

But this time with the decrease of the gravitational energy, . And I’m not just talking about visible light – they do not emit any light. Neither x-rays, nor infrared, nor radio waves, nothing.

And what kind of radiation should such a system emit?

Gravitational radiation, also known as gravitational Waves! These waves must propagate through space-time, and we can detect them not as light, but as a deformation of the measurements of objects when a gravitational wave passes through them!

. When spiraling the two objects together, a constantly accelerating emission of waves should be observed. The closer they are to each other, the shorter the period becomes. In the fusion phase, a catastrophic emission of both light (and, in the case of two white dwarfs, the appearance of a supernova is likely), and gravitational waves, followed by a calming phase of waves, should occur

This bold prediction of the general theory of relativity of Einstein. But we already observed, though not directly, one of the important aspects of this phenomenon.

By observing two pulsars (collapsed neutron stars) rotating around each other, we can predict a decrease in the orbital period of these stars. And for more than 30 years that have passed since the discovery of the first double pulsar, this is exactly what we were doing.

But we really needed to find these waves directly! So what do we do to discover them? For example, you can shoot from high-precision lasers at a known wavelength over long distances in different directions. This light is reflected from the mirrors and sent back, you collect the light received from both directions and look at the interference pattern.

Gravitational waves are extremely weak, so you need a very long base To obtain a large number of wavelengths, it is necessary to detect a change in 1/10 ²⁸ ) to detect a small shift of one of the two distances.

And on Earth there is such a project: laser-interferometric gravitational-wave Observatory, LIGO.

But LIGO on Earth, where we are not only limited in the possibilities of passing through laser beams, but also in protecting the experiment from surface vibrations.

It will be much easier to detect Gravity waves in space!

It is for this purpose that they develop a project of an improved space antenna using the principle of a laser interferometer, eLISA (formerly LISA). Unfortunately, because of the high cost of space projects, the problems with the NASA budget and the inability of ESA to afford such an object alone, a set of three spacecraft designed to be in orbit around the Earth at distances of 5 million km from each other will not be launched In the next ten years [ the estimated launch time to date – 2034; Approx. ].

The Universe always speaks to us in a language that we did not understand. And, as soon as we heard it, we immediately began to understand it!

So what does she tell us? How much, and where, white dwarfs, converging in a spiral. How many black holes are merging in remote galaxies. What is catastrophic emission of gravitational waves by combining two bodies. The universe tells us this right now. We need only listen, and we can catch this invisible radiation of the universe: gravitational waves!

Note. Perev: the translation was slightly reworked due to the fact that after its appearance, the ground project LIGO discovered gravitational waves. On February 11, 2016, the LIGO and Virgo collaborations announced the discovery of gravitational waves that occurred on September 14, 2015 at LIGO installations. The detected signal originated from the fusion of two black holes with masses of 36 and 29 solar masses at a distance of about 1.3 billion light-years from the Earth, while three solar masses went to radiation.