by It has been shown to be a smaller-scale example of some of the most luminous quasars in a binary system containing a superstar and a likely black hole, which together are a source of intense X-rays. the universe.
The new results, from an international team that used NASAand Imaging X-ray Polarimetry Probe spacecraft (IXPE), described how X-ray binary system located about 24,000 light year away in our The Milky Way Galaxy increasing its X-ray emission in a funnel-shaped cavity that surrounds the probable black hole.
The system, Cygnus X-3, was discovered in the early 1970s when radio telescopes spotted powerful jets almost disappearing from it. speed of light. The radio emission from these jets lasts for a few days, before turning off, only to turn on again later.
The origins of jets were, at the time, mysterious. The system has been described as an “astronomical puzzle,” which isn’t helped by the fact that we can’t even see Cygnus X-3 in visible light; it is blocked by thick dust in the plane of our galaxy. During the 1970s, radio astronomers at observatories around the world coordinated by telephone to try to find Cygnus X-3 as it powered on or off.
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Over the years, additional observations at radio, infrared and X-ray wavelengths allowed astronomers to determine that Cygnus X-3 is an X-ray binary system involving the transfer of matter between a supermassive star and a compact object orbiting a common center. of gravity. The compact object is either a neutron star or, more likely, a black hole with a mass about five times greater than the the mass of our sun. The massive star is a Wolf-Rayet star – a rare phase a supergiant stars go under, in which they radiate large, powerful winds that begin to take large chunks of their outer covering in space. The material blown on the wind from this Wolf-Rayet star is feeding an accretion disk that spirals around the compact object.
However, Cygnus X-3 on luminosity Hard to believe. The flow of matter on a dense object like a black hole is governed by a property called the Eddington Limit. If the accretion rate is high enough, the accretion disk becomes a log file — the material ends up as a backup, the disk grows dense and so hot that the amount of radiation spilling out can stop the inflow of fresh material. In this way, black holes can control their own growth, and some of the material is scattered back in the radio emitting jets.
However, some of the most shining quasar – galaxies with extremely active supermassive black holes at their core – they appear to be breaking the Eddington Limit, in that their luminosity is very high but they appear to be still accreting matter. And Cygnus X-3 seems to fall into this category, albeit on a smaller scale.
Now, a team led by Alexandra Veledina from the University of Turku in Finland has used IXPE to measure the degree of polarization in the X-ray light coming from Cygnus X-3. They found that the degree of polarization is high enough that it can only be explained by X-rays scattered from inside a funnel-shaped cavity at the core of the accretion disk.
“We have discovered that the dense object is surrounded by a covering of dense, opaque material,” said Veledina in a. statement. “The light we observe is a reflection of the inner funnel walls formed by the surrounding gas, like a cup with a mirror inside.”
An opaque envelope raised by a funnel-shaped cavity is typical of quasars described as ‘ULXs’ — ultra-luminous X-ray sources. The scale of amplification as a result of the X-rays spreading out from inside the funnel cavity is also consistent with ULXs.
“ULXs are usually seen as luminous spots in the images of distant galaxies, with their emission amplified by the focusing effects of a funnel around the compact object, acting like a megaphone,” said study team member Juri Poutanen from the University of Turku . “However, because of the long distance to these sources … they appear to be relatively faint to X-ray telescopes.”
Learning about ULXs in quasars has therefore been difficult, but astronomers can use the much closer Cygnus X-3 as a model to better understand the distant ULXs.
“Our discovery has revealed a bright counterpart of these distant ULXs that reside within our own galaxy,” said Poutanen.
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Cygnus X-3’s outbursts are erratic due to the Wolf-Rayet star’s elliptical orbit around the compact object, which means it is sometimes more dense and more material falls in the wind onto the likely black hole. IXPE was able to see that when Cygnus X-3 is in its ULX phase – when the amount of streaming material is at its maximum – the polarization level reaches 24.9%, but when the system is less active, the polarization drops to 10.4% . This suggests that the structure of the funnel changes in response to larger or smaller amounts of addition. If the crediting rate drops too low, the funnel can collapse completely, only to rebuild itself when crediting increases again, Veledina’s team predicts.
The team is now planning further observations to try to catch this drop happening, which would indicate that the polarity would drop to almost zero, indicating that X-ray emission is coming directly. from the hot gas on the surface of the accretion disk and not indirectly. by circulation within the funnel.
The results were published on 21 June in the journal Natural Astronomy.
