It turns out that the first black hole discovered by scientists is much larger than previously thought

It turns out that the first black hole discovered by scientists is much larger than previously thought

This benefits astronomers.

An international team of researchers – including astronomers from the University of Amsterdam – has discovered that the Cygnus X-1 black hole is much larger than previously thought. It is not 15 solar masses but at least 21 solar masses. You can read this in the magazine Science. Cygnus X-1’s revised mass is causing some excitement among astronomers. The gap between small stellar holes and intermediate black holes narrowed again with this discovery.

Cygnus X-1 is a black hole, whose existence was first suggested in the 1960s. Geiger counters were aboard a rocket launching in the wild at the time, as they captured a large amount of X-rays that appeared to be coming from a black hole. X-rays are created by an extremely heavy star orbiting the black hole, from which the black hole extracts gas. This creates a disk accumulation around the black hole. The material in this disc is greatly heated, which causes x-rays to appear. While that might sound like a very logical story today, it was different in the 1960s; Black holes were a purely theoretical phenomenon and not everyone was convinced that Cygnus X-1 was a black hole. And it stayed that way for a while. Stephen Hawking, for example, bet in 1974 that Cygnus X-1 was not a black hole. However, it did return to it in 1990. Today, Cygnus X-1 is known as the first black hole that the scientific community had – in the end – approved of its widespread existence.

Distance: distance
Scientists now take a closer look at the black hole using Very long base arrayA radio telescope of ten dishes scattered across the United States. Based on observations, they determined the distance between the black hole and the Earth. When asked, Professor Sera Markov of the University of Amsterdam explains: “We have benefited from a phenomenon called“ parallax. ”“ If you extend your arms to something far away and lift your thumb up and close one eye alternately and then the other, it looks as if your thumb is moving relative to the distant object. If you know the angle of apparent motion and the distance between your eyes, you can use trigonometric geometry to calculate the distance from your thumb. In our case, the thumb is the radio emission emitted by Cygnus X-1, and the far object in the background is a quasar that also emits radio waves, but is billions of light-years away. And the eyes are the radio telescopes on Earth. ”In the above example, the eyes are alternately closed. With radio telescopes, this is handled a little differently. Markov explains:“ When you look at Cygnus X-1 from different places in Earth’s orbit, it’s in Reality is like looking at your thumb alternately with one eye on the other. ”The distance to Cygnus X-1 is enormous (approximately 7,000 light-years) and the change in position in the sky is small even with a distance between the“ two eyes ”comparable to the diameter of Earth’s orbit. But with a network of radio telescopes we can measure very precisely the position – and thus also the change in it caused by parallax. ”For example, researchers discovered that Cygnus X-1 is 20 percent more away from Earth than previously thought.

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Then the researchers took another step forward and also calculated the mass of the black hole. “If you know the mass of the companion star (which you can deduce from its optical light), as well as the distance between that star and the black hole and the star’s orbital cycle, you can determine the mass of the black hole. Calculate the orbital time very precisely from the differences in the star’s optical light,” Markov explains. , But to calculate the star’s mass and the distance from the black hole, you need to know how bright the star really is (because the mass depends on the brightness of these types of stars). “But to determine how bright the star is, you need to know the distance between the Earth and the star.” When our measurements showed that this distance was greater than expected, it automatically indicated that the mass of both the black hole and the companion star should be, “said Dr. Phil Uttley, also associated with the University of Office. It is also much larger than expected. ”Amsterdam.

On the right you see a black hole pulling gas from an accompanying heavy star. This creates a disk buildup. The jets – which are a collector stream of gas perpendicular to the plane in which the accretion disk rotates – are also visible. Photo: ICRAR.

Smaller hole
Calculations indicate that Cygnus X-1 is about 21 solar masses heavy. This is much heavier than the 15th Sun’s mass that was previously attributed to the black hole. Cygnus X-1 will appear in the books right now as the heaviest stellar black hole has been observed without gravitational wave detectors. With the new mass, a stellar black hole – which astronomers greatly delight – is crawling closer to intermediate black holes (30 to 40 solar masses). “Intermediate black holes are located between stellar black holes and the supermassive black holes that we find in the very core of galaxies,” Utley says. It remains unclear how intermediate black holes form – which have been regularly discovered in recent years thanks to the gravitational waves emitted during the merging of these black holes. It is thought to start with massive stars orbiting each other, developing into black holes, and then merging into heavier black holes. But researchers don’t know exactly how all of this works. Cygnus X-1 might be able to provide more insights into this. In terms of mass, the black hole appears to face medium black holes and around the black hole a heavy star has not yet transformed into a black hole, which then merges with the existing black hole. “Cygnus X-1 is only halfway in terms of mass, but also in evolution,” Markov said.

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So the researchers hope Cygnus X-1 will help improve theoretical models. “There are many different models that Cygnus X-1 fits in,” Utley said. How massive stars form binary systems that evolve into black holes and how these black holes eventually merge together is an important part of stellar evolution. Cygnus X-1 is particularly interesting, due to the presence of many relatively heavy elements in the gas of this system. Systems like these are thought to have more powerful winds that carry the most gas and loosen up the resulting black holes here. But the larger mass we found indicates that this is not the case and that the winds are not able to carry the gas away. This may have implications for the evolution of massive stars, which are dictated by the force of the winds these stars generate. We are also interested in how black holes “capture” energy and convert it, for example, into winds and jet currents that accelerate particles and ionize the environment. We believe that over time these processes gave rise to galaxies as we know them today, paving the way for successive generations of stars. But all of these models have to be tested. ”Cygnus X-1 is very suitable for this thanks to this research. Because ideally you test models with a system that you have a lot of data and know, for example, how far away from Earth is, how much the black hole weighs, and how heavy the star is Companion, and the distance between the companion star and the black hole. “Cygnus X-1 was the first black hole to be discovered and is, in many ways, the primary black hole for testing all these theories.”

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The search will undoubtedly get a tail end. “Theorists trying to understand massive stars will undoubtedly adjust their models in light of these findings to explain the effects of less efficient winds and heavier black holes,” Markov said. “Here in Amsterdam, we are more interested in the black hole and how it affects matter in the surrounding accretion disk and generates jet streams. During this research, we also collected a lot of data about other wavelengths (especially X-ray measurements), so the big challenge now is to integrate All this data and discovering the secrets that Cygnus X-1 still holds for us. “

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