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 of these 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.

FRBs – Fast Radio Bursts – are enigmatic, millisecond-lasting pulses of radio waves that send us out Reaching billions of light years away and within a thousandth of a second with hundreds of millions of solar luminosities apparently being able to release as much energy as our sun does in months. 2007 the first was discovered and since then over 150 more, but an identifiable source was never found. Until recently, astronomers were completely in the dark as to what effect might be hidden behind the FRBs. Now the problem seems to be about to be resolved.

Hawking’s cosmic time bombs Transient radio events are difficult to track down, but could provide insight into a wide variety of astrophysical processes. For example, radio pulses lasting just a few milliseconds from cosmological distances could be evidence of merging neutron stars or evaporating black holes in miniature format. According to some hypotheses, the latter are said to have originated during the Big Bang (so-called primordial black holes) and could be responsible for dark matter. Black holes emit Hawking radiation and gradually lose mass as a result. Usually it takes the ages of 07 65 years (10 56 times as long as our universe already exists), until a black hole of several solar masses has completely evaporated.

The evaporation process due to the Hawking radiation accelerates with decreasing mass and the last few 100 Tons disintegrate explosively, with the entire mass being converted into radiation in less than a second. In today’s universe, black holes are only formed in core collapse supernovae or neutron star mergers, which add at least 3-5 solar masses (the solar mass is about 2 10 30 kg), but in the elemental force of the Big Bang Mini black holes of any size can be created. According to Steven Hawking’s theory, those with an initial mass of around one billion tons should today, 13, 8 billion years after the Big Bang, gradually evaporating – if they exist.

Recycled radio data In search of the signals of such events, Duncan Lorimer and his student David Narkevic 2007 rummaged through archived measurements of 64 Meter diameter Parkes radio telescope in Australia. These were observations with which millisecond pulsars in the Magellanic Clouds, two satellite galaxies of the Milky Way in just under 200. 000 light years distance, should be tracked. Thanks to the multibeam receiver used 07 of neighboring reception lobes corresponding to the number of target fields. Your signals were every millisecond in each 85 Frequency channels with a bandwidth of 3 MHz each with one bit resolution (signal or no signal) have been recorded. That makes 3 MHz 96 = 205 MHz, which is in the 1.4 Gighertz band lay. The search for pulsar signals relied on the periodicity of the pulses in order to search for weak, periodic signals with the help of Fourier transform and computer support. The search was therefore blind to non-periodic signals. In search of exactly such, Lorimer and Narkevic took another look at the data.

The Parkes Radio Telescope in Australia. The first fast radio bursts were discovered with this device.

(Image: CSIRO, CC BY 3.0)

And they found something. At the 24. July 1500 at 21: 50 h CEST, the radio telescope had recorded a signal of less than 5 ms (five thousandths of a second) coming from a direction 3 ° south of the center of the Small Magellanic Cloud. However, it evidently did not come from the Magellanic Cloud, but from further away – much further away.

The Lorimer burst FRB 010724, in the top right inset as an amplitude diagram and in the Background plotted as a radio spectrum over time (“dynamic spectrum”). On the x-axis the time in milliseconds from 10: 50: 01, 63 World time (2h back behind CEST), the frequency in gigahertz on the y-axis. Each pixel corresponds to a frequency channel of 3 MHz width in the y-direction (total 96 channels) over a period of one millisecond in x-direction. Black points are detections (mostly noise). The Lorimer burst starts at the highest frequency, lasts approx. 5 pixels, and then falls in a parabolic shape to lower frequencies (the parabola results when you turn the diagram around 90 ° to the left and then mirror it on a vertical line, so that the frequency axis is from left to right grows). From the shape of the parabola, as described in the text, the distance can be estimated using the “dispersion measure”. The height of the black line gives information about the energy, the width about the duration, and the combination of both results in the power

(Image: DR Lorimer et al., ArXiv)

Lorimer and Narkevic could tell by how the signal, which later became FRB 010724 would be called (for “Fast Radio Burst from 21. 07. 01 “), developed over time. In a plasma, i.e. a gas in which some of the electrons can move freely, radio waves of different frequencies run at different speeds. The effect is very similar to that of light, which passes through media such as glass or water at different speeds depending on the frequency; This leads in particular to the fact that light of different colors is refracted to different degrees if it hits an interface at an angle, such as the surface of a raindrop, which gives us the rainbow.

Refraction of light in a vacuum The technical term for the different propagation speeds of Waves of different frequencies in a medium is “dispersion”. The vacuum of space is not completely empty, but filled with an extremely thin mixture of hydrogen and helium gas. This is partially ionized by the ultraviolet radiation of the stars: the UV photons have so much energy that they knock some electrons out of the hydrogen and helium atoms, which, due to the low particle density in the gas, cannot immediately be captured by another nucleus, such as that in the earth’s atmosphere below 85 Kilometers of altitude is the case (the ionosphere begins above this – that’s exactly why).

The empty space between the stars and galaxies is therefore filled with a plasma. In a plasma, the propagation delay of radio waves depends on the square of their frequency due to the dispersion in the plasma and linearly on the amount of free electrons passed through. The radio astronomers indicate their density in the so-called “dispersion measure” DM. DM is measured as the density of free electrons per cubic centimeter times the distance in parsecs (1 parsec or pc is the distance from which the astronomical unit, the distance earth-sun, under an angle of vision of one arc second, 1 / 3600 Angular degrees, appears; this is about 3, 26 light years). A distance of one million parsecs with an average of one free electron per cubic meter (1 cbm has a million cm³) would have a dispersion measure of 1 / cm³ pc. A common notation for this unit among astronomers is 1 pc / cc (parsec per cubic centimeter).

If you now know the difference in transit time of two radio frequencies, then the DM value follows, in which the distance is included if you know the electron density. In the Small Magellanic Clouds the 5 known pulsars have DM values ​​of 70, 76, 105, 125 and 205 pc / cc, where the last one in a HII Region, i.e. a star formation region in which young stars have ionized the hydrogen gas – the electron density is naturally very high locally there.

Greetings from JWD For “their” radio pulse, Lorimer and Narkevic measured a DM of 375 pc / cc. In the Small Magellanic Cloud, however, there is no HII region in the corresponding direction, and behind it there is just a lot of empty space with very little gas, let alone free electrons. The closest galaxy LEDA 010724 (redshift / distance: unknown) is 5 arc minutes south of the location of the Source in a reception lobe adjacent to the detection-reception lobe in which, however, no signal was measured. She won’t come with it t in question as a source galaxy. Based on the particle densities cited in other papers and the basic assumption that all atoms are ionized (which leads to the smallest possible distance estimate), Lorimer estimates the distance to be 1 gigaparsec (Gpc) – one billion pc or 3, 26 Billions of light years !

However, there could be a higher local DM value in the galaxy in question as well as in the Milky Way, which would then reduce the distance again. In the case of a galaxy similar to the Milky Way, the local DM component would be the estimated distance to 500 Mpc (1, 63 billions of light years) shrink. As is so often the case here, the astronomer is satisfied if he can at least state the correct magnitude.

How great would the luminosity of the source be in this case? The 1-bit digitizer only allowed a rough estimate by taking into account the number of those neighboring reception lobes that also deflected. The signal was therefore at 30 ± 10 Jansky (1 Jy = 10 – 26 W per square meter of reception area and hertz Bandwidth). With an approximate duration of 5 ms and a distance of 375 Mpc would result an energy of 10 33 Joules, released in 5 ms, corresponding to a power of 2 10 35 Watt – this applies under the assumption of an isotropic, that is, in all directions with the same Intensity followed release. That would be over 500 millions of sun luminosities or as much energy as the sun in 30 days over all frequencies!

With a duration of 5 ms, the source cannot have been greater than the distance that the light travels in this time , otherwise the pulse would be smeared over time due to the difference in transit time between the nearest and farthest point of the source. And 5 ms correspond to a light path of just once 1500 km.

A new class of objects According to Lorimer, the following compact sources could be considered: on the one hand the 2006 discovered rotating radio transients (RRATs), which apparently are pulsars with strongly fluctuating pulse intensity, so that despite a rotation period of 0.1 to 7 seconds only all 10 to 10. 000 seconds a pulse is observed. Or on the other hand, extremely strong individual giant pulses of a millisecond pulsar or a very young pulsar, in which a large number of incident particles have gotten into the magnetic field and swirled around the magnetic field lines – such pulses sometimes only last nanoseconds.

But even the brightest pulses of these two object classes are only ~ 6000 pc (~ 20. 000 LJ) or ~ 100. 000 pc