Thanks to ever better technology, innovative approaches and international cooperation, astronomy is flourishing. But while many observations help to refine or sort out theories, there are always discoveries that just don’t seem to fit. Mysterious signals, alleged violations of the laws of nature and – as yet – phenomena that cannot be explained. The public then likes to discuss whether there are traces of extraterrestrial intelligence, scientists know that in the end there is almost always a natural explanation. But the imagination is stimulated everywhere.

In a series of articles on heise online in the coming weeks we will present some such astronomical anomalies from a recently presented collection and explain why all attempts to explain them have failed so far.

In astronomy there are always observations that cannot be explained at first. While some suspect extraterrestrials behind it, others expect new insights into the nature of the universe. They are always exciting. heise online takes a look at some of these up to now inexplicable anomalies.

Cygnus OB2 is a star cluster where things get down to business. It consists of numerous, tightly packed young stars of the hottest spectral classes O and B, it contains the microquasar Cygnus X-3 and recently the second known case of a gamma-ray binary star system with a pulsar as a source was found there. Almost 17 years ago in the same area astronomers found a gamma ray source with no counterpart at other wavelengths. Where does the radiation in the teraelectron volt range come from?

Hammer-hard radiation Astronomical objects send electromagnetic radiation not only in the form of light with wavelengths between 400 and 800 nm (nanometers), but over a wide range of radio waves that are kilometers long for X-ray (10 nm down to 0, 005 nm) and the even shorter-wave gamma radiation. The energies of the photons at these wavelengths are so high that they can shatter atomic nuclei. Since they arrive more sporadically than as a continuous flow, you no longer specify their wavelength, but usually their energy in electron volts. Light photons have a few eV, X-ray photons between 100 and 10. 000. Carry photons of gamma radiation 100. 000 eV (100 keV) and more. Sometimes billions of times more.

Gamma radiation occurs in space during the following processes:

Nuclear reactions, such as the merger or the Decay of atomic nuclei. The sun draws most of its energy from gamma radiation, which is released during the nuclear fusion taking place inside, but does not penetrate outside; on the round 100. 000 The way to the sun’s surface, which takes years, is transformed into light and heat radiation. However, if a thermonuclear reaction ignites on the surface of a white dwarf in a nova, for example, unshielded gamma radiation is released. The same applies to the decay of radioactive elements in the gas cloud that is left behind by a supernova (supernova residual). The energies of the photons in nuclear reactions are in the range of 1 to 10 MeV ( Million eV). Pair annihilation of matter and antimatter. The positrons produced during nuclear reactions, the antiparticles of the electrons, annihilate each other on contact with electrons without a residue to form two gamma photons of 511 keV, the rest mass of electrons and positrons. This radiation is mainly received from the center of the Milky Way. It is possible that particles of dark matter also produce pair annihilation radiation, which, however, has not yet been proven with certainty. When extremely fast particles collide. In the process, new, unstable particles are often formed, some of which decay while emitting gamma rays. When charged particles (mostly the light, omnipresent electrons) are strongly accelerated, decelerated or deflected. This can happen in magnetic fields (synchrotron radiation), in the electric field of an atomic nucleus (bremsstrahlung) or in the electromagnetic field of a photon (Compton scattering). The magnetic fields of neutron stars are extremely strong (millions of Tesla) and can cause electrons whirling in them to emit gamma rays. Finally, high-energy particles can reflect oncoming photons and bring them to extremely high energies, analogous to a ball that is kicked against an oncoming fast train and ricochets off at a greatly increased speed (inverse Compton scattering) . This can happen anywhere where particles are accelerated to high speeds in magnetic fields or by high temperatures and there are abundant photons. This happens in hot accretion disks or jets, especially when neutron stars merge or hypernovae explode. This process is mainly responsible for gamma photons with the highest energies. Telescopes that do not look into the distance Gamma-ray astronomy from Earth is not easy. The gamma radiation does not reach the earth (luckily for us!). Hence, gamma-ray space telescopes such as Swift, Integral, and the Fermi gamma-ray space telescope have been shot into space. You feel radiation in the range of 400 keV = 10 5 eV and 10 GeV = 10 10 eV on.

One of the two 17 meters diameter MAGIC Cherenkov telescope at Roque de las Muchachos on La Palma, Canary Islands. The huge segment mirror bundles the light of the extremely weak Cherenkov flashes caused by high-energy gamma photons in the atmosphere onto a matrix of residual light amplifiers in the white box on the left, which here was apparently swiveled down to the pedestal for maintenance.