A black hole gets a large corona first, and only after that it emits jets. This is revealed, among other things, by the heart beat graph that an international team of astronomers has made of a black hole and a star orbiting around each other. The team, led by Mariano Méndez from the University of Groningen (the Netherlands), published their results on 7 March in Nature Astronomy.
Just as the blood in a human heart cannot be in the atrium and in ventricles at the same time, a black hole also appears to first collect material and heat it up in a so-called corona, only then to spit it out in jets. 'It sounds logical, but there has been a debate for twenty years about whether the corona and the jet were simply the same thing. Now we see that they arise one after the other and that the jet follows from the corona,' says principal investigator Mariano Méndez (Kapteyn Institute, University of Groningen, the Netherlands). 'It was quite a challenge to demonstrate this sequential nature. We had to compare data of years with that of seconds, and of very high energies with very low ones.'
The researchers collected 15 years of data from several telescopes. Amongst others, they pointed the Rossi X-ray Timing Explorer at the black hole GRS 1915+105 from space about every three days and collected high-energy X-ray radiation from the corona. The astronomers combined the X-ray data with those of the Ryle Telescope. This is a collection of radio dishes about ninety kilometres north of London, which collect low-energy radio radiation from the jet of the black hole almost every day.
The black hole GRS 1915+105 is not an isolated black hole, but a double system consisting of a black hole and a normal star that circle around each other. This double system lies in our Milky Way at about 36,000 light years from us in the direction of the constellation Aquila. The black hole weighs about as much as twelve times our Sun, making it one of the heaviest known stellar black holes.
Now that the researchers have proven the sequence, there are still some unanswered questions. For example, the X-ray radiation that the telescopes collect from the corona contains more energy than can be explained by the temperature of the corona alone. The researchers suspect that a magnetic field provides extra energy. This magnetic field and the accompanying energy could also explain why jets are formed. If the magnetic field is chaotic, the corona heats up. If the magnetic field then becomes less chaotic, material can escape via the field lines into a jet.
The researchers suggest that the principle they demonstrated may also apply to heavier black holes, for example to the supermassive black hole at the centre of our Galaxy.
Reference: Mariano Méndez, Konstantinos Karpouzas, Federico García, Liang Zhang, Yuexin Zhang, Tomaso M. Belloni and Diego Altamirano: Coupling between the accreting corona and the relativistic jet in the micro quasar GRS 1915+105, Nature Astronomy, 7 March 2022.
Text: NOVA / Astronomie.nl
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