Astronomers received a unique image of a neutron star. As stated in the press release, this is one of the most detailed “snapshots” of such an object in the history of astronomy. Scientists helped the plasma cloud, which played the role of a natural lens.
The achievement is described in a scientific article published in the journal Nature by a team led by Robert Main of the University of Toronto.
Radio pulsars are neutron stars emitting a narrow radio beam. This radiation is received by terrestrial telescopes. The neutron star rotates its axis, and the ray describes the circle. When it is aimed exactly at the telescope, it fixes a bright pulse of radio emission. Then the beam turns away, and the “radio” arrives until the next full turn. For the telescope, all this looks like a series of bright pulses repeating through the same time interval. Hence the name of this class of celestial bodies is pulsars.
Neutron stars are unique objects. With a mass comparable to the solar mass, their diameter is measured in a few kilometers. Therefore, these bodies have an incredible density of hundreds of millions of tons per cubic centimeter. In addition, pulsars have a powerful magnetic field. All this makes the neutron star into a unique laboratory in which states of matter that are unattainable on Earth in the foreseeable future are realized.
Pulsar PSR B1957 + 20 has been of interest to astronomers for a long time. This is one of the most massive known neutron stars. Thus, in this case, nature herself put an experiment on “what is the maximum density the body can reach before it turns into a black hole”.
Unfortunately, an object a few kilometers in size can not be considered in detail from a distance of 6,500 light years. If, of course, nature itself does not come to the rescue.
The fact is that the PSR B1957 + 20 has a satellite – a brown dwarf. Recall that such bodies occupy an intermediate position between planets and stars. This is a huge ball of gas (in this case, its diameter is only three times less than the solar one), which, nevertheless, is not large enough for it to begin thermonuclear reactions. As a result, such a body does not radiate visible light.
Companion PSR B1957 + 20 is located in two million kilometers from it. This is about five times the distance between the Earth and the Moon, that is, very close to astronomical standards. Therefore, the period of circulation of the brown dwarf around the “master” is only nine hours. Moreover, the satellite is constantly turned to the pulsar by one side, like the Moon to the Earth.
The powerful gravity of a neutron star steals from a brown dwarf a substance that subsequently falls on a pulsar. Because of this, there is a constant flow of matter between the two bodies. Radiation “predator” warms it up to about six thousand degrees Celsius, that is, to the surface temperature of the sun. Therefore, the incident substance is a hot plasma (ionized gas). And plasma can focus radio waves, acting as a natural lens.
“The gas acts like a magnifying glass located just in front of the pulsar,” explains Maine in a press release from the study.
Of course, such a natural lens is very imperfect. The state of the plasma is constantly changing, and only in exceptional cases it really works like a magnifying glass.
This time the astronomers were lucky. Working with the data of the Arecibo radio telescope, they found that the plasma lens gave them incredibly detailed images of the areas in the pulsar’s atmosphere from which the ray is emitted. At some frequencies, the signal was amplified 70-80 times. The size of the revealed details was only about 10 kilometers. This is comparable with the distance from the emitting regions to the surface of the pulsar (about 20 kilometers) and with the diameter of the neutron star itself.
Recall that the distance between Earth and PSR B1957 + 20 is six and a half thousand light years. To see ten-kilometer details at this distance is like seeing a flea on a surface telescope on the surface of Pluto.
Astrophysicists still have to figure out what conclusions can be drawn about the structure of neutron stars based on such unique information. But the authors believe that they already hold the keys to at least one enigma of the cosmos in their hands. It’s about fast radio bursts, or fast radio bursts (FRB). We have repeatedly written about these bright and very short radio flares, the nature of which has not yet been solved.
Scientists knew what the PSR B1957 + 20 pulsar looks like, when it does not have a significant effect on the plasma cloud. Comparing it with fresh data, they revealed the details of the spectrum added by the “magnifying glass”. And it turned out that there is much in common with the spectrum of the rapid burst of FRB 121102. Recall that this is the only known of these flares, which from time to time repeats at the same point in the sky.
“Many of the observed properties of FRB can be explained if they are amplified by plasma lenses,” says Maine, “The pulses amplified by the lens that we found in our study show a significant similarity in properties with a repeated FRB burst, that a repeating FRB can be lent by plasma in its parent galaxy. ”
It is interesting that, according to independent observations, at least some of the fast radio bursts actually pass through a dense plasma cloud at the site of its origin.
The authors plan to continue to study PSR B1957 + 20 with the help of the main instrument of the Arecibo observatory in the hope that nature will give them a gift even at least several times.