X-ray emission of stars

X-ray emission of stars (exemplification for the Sun)

Background and actual explanation

X-ray astronomy studies interstellar gas heated to millions of degrees around extreme environments like black holes, neutron stars, and colliding galaxies. Million degree gas can be found throughout the universe. In x-ray binary systems, a neutron star or black hole – the very dense remnant of a deceased massive star – is orbiting another star and stealing gas from its companion. The intense gravity of a neutron star or black hole accelerates the spiraling gas to high speeds, heating the material in the disk to extreme temperatures, and causing it to glow in x-ray light.

Here are some example of sources of X ray in Universe and their interpretation. In the constellation Scorpius, the source Scorpius X-1, turned out to be a neutron star, 9000 light-years away, orbiting another star. Superheated gas falling onto the neutron star was releasing 60,000 times more energy just in x-rays than all the wavelengths of light emitted by the sun.

Cygnus X-1 is not just an x-ray binary, but the first confirmed observation of a black hole—the remnant core of a supermassive star whose gravity is so intense that it can no longer emit light. At a distance of 6100 light-years from Earth, Cygnus X-1 is the black hole companion to a blue supergiant.

Although the first cosmic X-rays were detected from the Sun in the 1940s, the field of X ray astronomy developed only after the satellite era due to the telescopes installed on Earth-orbiting satellites .

Surveys using the Einstein Observatory have shown that all stars are X-ray sources at some level. The level of X-ray power from many of these stars cannot be explained by the old models for the turbulent outer layers of stars and therefore a new model was proposed.

As far in case of a star much of the energy is transferred from core to photosphere by gas convection, these motions will generate sound waves. It was suggested that the dissipation of these sound waves is the source of heat for the solar corona. Elegant theories were formulated, and many detailed calculations involving hours of computer time were performed to demonstrate the validity of this concept, which went under the general name of acoustical heating.

Unfortunately neither this explanation is satisfactory when, for example, the Alpha Centauri star system is analyzed. An X-ray photograph of the Alpha Centauri star system shows that all three stars in the system have hot coronas. Visually, the system consists of a star much like our Sun (a G type star), a nearby companion K type star which is slightly smaller and cooler than the Sun, and a very small M type dwarf star. The acoustical heating model predicts that the G type star should be more than 10 times brighter in X-rays than the K type star, but the observations show just the opposite. The K star is the stronger X-ray source of the two.

These examples show that the standard theory for the origin of hot coronas around stars is inadequate. It is now accepted that magnetic fields must play a key role in the X ray emission by stars.

As the Skylab X-ray photograph shows, the X-ray emission from the Sun comes from groups of hot magnetized loops. The Sun's outer atmosphere is so hot that it emits much light in the X-ray band, which was unexpected. X-rays are usually emitted from objects having a temperature in the millions of degrees, not the mere thousands of degrees of the Sun's surface. Evident there are hot spots on the solar surface, showing that areas above the Sun's surface really do reach millions of degrees. But possibly more puzzling is the broader X-ray glow surrounding the Sun.

Scientists still try to connect X ray emission with such local magnetic fields (or supposed induced electric currents) found in the region where the flares take place.

Even this theory of the origin of X-ray coronas around stars is still in a rudimentary stage and soon has to be discarded.....

Proposed interpretation

I am sure that in few years all these non-senses with black holes and matter of temperature of millions of degrees filling all the ,,visible universe” will become history and a regrettable error of science.

In case of our galaxy we cannot have a black hole in the galaxy nucleus and with the actual instrumentation we can see that matter is not moving in nucleus as it must when a black hole would be there. Of course, some papers were published based on the idea that motion of individual stars in our galactic center are strongly distorted and only a ,,black hole” could do such a job due to its huge mass. People interested in this topic can find enough data searching in Internet even after animation of this effect made by UCLA with data sets obtained from the W. M. Keck telescope. On the other hand the same black hole refute to accrete matter which we know it exist in its vicinity and of course refute to give a strong emission in X ray. So we have to accept that ,,our black hole “ in our galactic center is a bit more special....it is not hungry and has no pleasure to engulf more matter to the desperation of actual theoreticians …

Of course we have to accept that violent and extreme events take place in Universe, but most of these have got a false interpretation and we are exaggerating the size of the events because the scale of universe is not proper calibrated too.

Therefore, for the moment, I will start with a common sense explanation for the X ray emission in case of our Sun. A lot of other stars emit X ray in the same manner based on the same simple mechanism.

In case of our Sun we have a quite constant glow of X ray emission around Sun like a glow and we have from time to time flares of X ray emitted around solar spots.

As we have presented in another paper, Sun is made of a special kind of fluid (I will invent a name for this state of matter later). Not only is like a ,,fluid” at 6000K or even more, but it keeps the atoms in the same state they exist on the Earth. It means the electrons are orbiting atoms nucleus on the same orbits they do on Earth at 293K.

As a boiling fluid, it can present a quiet boiling or a violent boiling depending on amount of energy to be transferred due to its internal cycle and how the transfer of energy is made.

In case of a violent boiling what we see as mass ejections are splashes of fluid released due to an higher amount of heat which cannot be transferred in a regular way.

When this mass of fluid is ejected, it encounters the void space and very low pressure in the solar atmosphere. Part of matter ejected can fall back on the Sun but most of the ejected matter is instantly vaporized.

There are three factors dictating the vaporization: low pressure, high temperature and atomic mass. Although these are completely new direction of study and we haven't experienced such phenomena on Earth, I will make some analogies in order to have an idea about what is happen.

If you put water into a vacuum at room temperature on Earth, it will boil, even though it won't get any hotter. If you released water into interplanetary space, it would flash boil and evaporate more or less instantly. In fact in order to evaporate from liquid to gas, water needs to take some energy from the surroundings or to cool down in case of liquid water released in interplanetary space.

When instead of water, the experiment is performed with a mixture of fluids having different atomic or molecular masses, there is a discrimination against higher molecular mass, which vaporize slower and its molecules get lower speeds.

When a splash of solar matter leaves the Sun, due to the extremely low pressure it will start evaporate in solar atmosphere and in the same time it will cool down a bit. Therefore it is normal that solar atmosphere in the vicinity of Sun is a bit colder than Solar surface.

There is no analogy possible to explain what happen during this evaporation. Not only atoms vaporize instantly but due to the hot temperature electrons are stripped away from nuclei and it can be considered that at this step solar wind is generated. For hydrogen and helium, as far their ionization energies are low (11 eV for H and 24 eV for the second electron of helium), the recombination process is not possible and they get ejected in space as free electrons, protons and alfa particles.

For higher mass elements, they can lose a variable number of electrons because due to the greater charge of the nucleus, these species can remain with some electrons around nucleus.

For the generation of X ray during this process, I will make an analogy with well known phenomena already studied and applied in different field of science.

When a beam of accelerated electrons or protons are directed toward a solid target a detector of X ray will measure a flux of this radiation as in fig. 1

Figure 1 Generation of X ray by a solid target

The mechanism of X ray generation is well understood. We will discus here only the generation of X ray by accelerated electrons but processes are similar in case of proton beams. There are two different atomic processes that can produce X-ray photons. One is called Bremsstrahlung and the other is called K-shell emission. They can both occur in heavy atoms. Bremsstrahlung is generated when negatively charged electron slows down after swinging around the target material nucleus and this energy loss produces X-radiation with a continuous spectrum like in fig. 2

Figure 2. Bremsstrahlung emission by electron nuclei interaction

K-shell emission radiation or even L shell emission in case of more heavier atoms are based on a different mechanism. An incoming electron can give a K-shell electron enough energy to knock it out of its energy state. Then, a electron of higher energy (from an outer shell) can fall into the K-shell. The energy lost by the falling electron shows up in an emitted x-ray photon as in fig. 3. Meanwhile, higher energy electrons fall into the vacated energy state in the outer shell, and so on. K-shell emission produces higher-intensity x-rays than Bremsstrahlung, and the x-ray photon comes out at a single wavelength.

Figure 3. Discrete X ray spectrum

This X ray radiation is a "characteristic" of the element. The resulting characteristic spectrum is superimposed on the continuum spectrum. An atom remains ionized for a very short time (about 10^-14 second) and thus an atom can be repeatedly ionized by the incident electrons which arrive about every 10^-12 second.

These are well known facts and now is it high time to see how these things work in case of solar flares. In solar atmosphere there is a low concentration of both electrons and positive species: protons, alfa particles, ionised heavier species like magnesium, iron, sodium, sulfur, neon, silicon, carbon, nitrogen etc. When a solar flare is generated, the incoming flux of protons and electrons resulted from vaporization bombard these heavier species from solar atmosphere and generate X rays due to mainly Bremsstrahlung but also K shell emission is possible. Even the concentration of heavy species is low, as far the bombardment is strong and an X ray can be emitted in about 10^-14 second, a simple calculation can show how many cycles can an atom perform in one second. For Bremsstrahlung the process of X ray generation can be considered continuous as far incoming charged particle interact with another nucleus …..

Also the heavy species contained in the splashed material take part in this process and in fact the splashed material and the region around it after vaporization becomes like a torch in X ray and UV radiation.

A strong magnetic field in the vicinity cannot accelerate the charged particles, but it can make help the process of X ray generation because the electrons and positive species have opposite motion in magnetic field. This will increase the probability of clashing and X ray generation in some cases or diverge the trajectory in other cases and in the later case, particles can return back to the Sun.

Beside these well known mechanism which can explain the generation of X ray flares in Sun and stars, there is still a new effect which can generate X ray radiation. Until now we have considered that a heavy nucleus as target is necessary for the X ray generation.

But in the special condition from Sun atmosphere we have to accept that even small species like proton and alfa particles can generate Bremsstrahlung during interaction with electrons like in fig 4.

Figure 4. Electron proton or alfa particle interaction and X ray release.

As far evaporation, hot temperature and strong local magnetic field force the electron to smash into proton and alfa particles, but the temperature is to high to allow the recombination process and formation of neutral atoms (hydrogen, helium), the result of this interaction will be a release of X rays. In fact for some stars or even for our Sun this third possibility can overrun the other ,,terestrial like X ray generation modes”. Of course this aspect will be clarified soon …......

The existence of a strong magnetic field will increase the probability of electron collision with positive species. As it is observed in fig 5., electron and positive particles have a spiral motion around magnetic field line, but in opposite directions - in the configuration presented in fig 5, electrons rotate counter clockwise and positive charges clockwise.

The broader X-ray glow visible surrounding the Sun during quite activity has the same origin only at a smaller scale. So with this problem solved, a lot of scientists will have no subject of much discussion and debate.

A base X ray glow has to be present in each star, independent on the temperature of the star. An this has to be called ,,cold X ray”, because has no thermal origin. So a lot of stars has to be declassified and their temperature to be droped ...sometimes dramatically …..

On the other hand a lot of stars can emit huge quantities of X ray radiation and to have the same real temperature like our Sun. Only an accelerated cycle and some solar spots due to a excess of energy necessary to be released and.... we are fooled with ,, million degree temperatures...”

Last but not least the temperature of external layers of Sun need a radical reconsideration. If the concept of temperature is biased and with simple experiments made on Earth it can be proved that concept of kinetic temperature is absurd, how can someone infer that corona temperature is millions of Kelvins. In a gas discharge tube the temperature of gas is not thousands of degrees although that gas according to kinetic molecular theory moves with high speed and emit light also. For the fact that Sun emits in X ray it is not necessary a temperature of millions of degrees too. There is already an article about temperature concept in the Thermodynamic section and soon the topic will be extended. The link:

http://pleistoros.com/index.php/en/books/thermodynamic/temperature-concept

Figure 5 Opposite rotation of charged particles in magnetic field