Cygnus X-1: A Black Hole and Its Companion
| Polish version is here |
Virtually everyone has heard of black holes, even those with little interest in astronomy. However, few truly understand the nature of these objects. A black hole is essentially a region of spacetime from which nothing can escape due to the force of gravity—not even light or information. According to the general theory of relativity, the formation of a black hole requires a sufficiently large mass compressed into a small enough volume. A black hole is surrounded by a mathematically defined boundary known as the event horizon, which marks the point beyond which nothing can escape into the surrounding space. Simplified models suggest that black holes emit no radiation, which is why they are referred to as “black” holes. However, quantum field theory predicts that black holes emit radiation similar to that of a perfect blackbody, with a non-zero temperature. This temperature is inversely proportional to the black hole’s mass, making it extremely difficult to observe in the case of stellar-mass black holes or larger ones.
Stellar-mass black holes form as a result of the gravitational collapse of very massive stars at the end of their life cycle. Another category is supermassive black holes, which have masses exceeding millions of solar masses.
Since black holes cannot be observed directly, their presence is inferred from their interactions with surrounding matter and electromagnetic radiation, including light. Observing a black hole is particularly convenient when it is part of a binary or multiple system, accompanied by a visible star that is much more accessible to our instruments. One such system is Cygnus X-1.
Observations
May 10, 2024, around 10:00 PM – Katowice (Poland)
urban conditions, very high level of light pollution
The sky that night was slightly hazy, and the humidity in the air did not encourage prolonged observation.
Cygnus X-1 is an X-ray binary system discovered in 1964, located in the constellation Cygnus. This system is situated 6,070 light-years from Earth and is the strongest source of X-rays visible from Earth.
The system consists of the star HDE 226868, a blue supergiant (visible in Photo 1), and a black hole. The components of this binary system orbit each other at a distance of 0.2 astronomical units, making it a relatively compact stellar system. The black hole has a mass of 15 M☉ and is measured to rotate at approximately 800 revolutions per second.
The intense radiation—including X-rays—is most likely produced by the process of accretion, in which matter is pulled from the visible star by the black hole’s gravitational forces. As this matter falls toward the black hole, it accelerates and becomes extremely heated—particles accelerated to relativistic speeds emit radiation.
Near the Cygnus X-1 system, observers can spot the characteristic nebula designated as number 101 in the Sharpless catalog, also known as the Tulip Nebula.
Photo 1 Parameters:
- ZWO Seestar s50
- Total exposure time: 4 minutes (stack of 24 RAW frames at 10s each)
- A filter was used to reduce the effects of artificial light pollution and atmospheric glow
Further readings:
- Substyk M., Atlas nieba 2000.0, AstroCD, 2021, str. 22
- Susskind L., The black hole war: my battle with Stephen Hawking to make the world safe for quantum mechanics, Little, Brown, Nowy Jork, 2008
- Hawking S.W., A brief history of time, Bantam Books, Nowy Jork, 1998
Marek Ples