There is always something new and exciting happening in the field of black hole research.
Albert Einstein first published his book in which he explains: the theory of general relativity – who postulated black holes – in 1922. One hundred years later, astronomers laid out the actual images of the black hole at the center of the Milky Way. In a recent article, a team of astronomers describes another exciting new discovery: the first “sleeping” black hole observed outside the galaxy.
I am an astrophysicist who has studied black holes — the most dense objects in the universe — for nearly two decades. Dormant black holes are black holes that emit no discernible light. So they are notoriously hard to find. This new discovery is exciting because it provides insight into the formation and evolution of black holes. This information is essential for understanding gravitational waves as well as other astronomical events.
What exactly is VFTS 243?
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VFTS 243 is a binary system, which means that it is composed of two objects that revolve around a common center of gravity. The first object is a very hot blue star with 25 times the mass of the sun, and the second a black hole nine times more massive than the sun. VFTS 243 is located in the Tarantula Nebula in the Large Magellanic Cloud, a satellite galaxy of the Milky Way about 163,000 light-years from Earth.
The black hole in VFTS 243 is considered dormant because it emits no detectable radiation. This is in stark contrast to other binary systems in which: strong X-rays are detected from the black hole.
The black hole is about 54 kilometers in diameter and dwarfs the energetic star, which is about 200,000 times larger. Both rotate rapidly around a common center of gravity. Even with the most powerful telescopes, the system visually appears to be a single blue dot.
Finding sleeping black holes
Astronomers suspect that there are hundreds of such black hole binary systems that do not emit X-rays, hiding in the Milky Way and the Large Magellanic Cloud. Black holes are most easily visible when they are stripping matter from a companion stara process known as “feeding”.
Feeding produces a disk of gas and dust that surrounds the black hole. As the material in the disk falls inward toward the black hole, friction heats the accretion disk to millions of degrees. These hot disks of matter emit an enormous amount of X-rays. The first black hole to be detected in this way is the famous Cygnus X-1 System.
Astronomers have known for years that VFTS 243 is a binary system, but whether the system is a pair of stars or a dance between a single star and a black hole was unclear. To determine what was true, the team studying the binary used a technique called spectral unbundling. This technique separates the light from VFTS 243 into its component wavelengths, which is similar to what happens when white light enters a prism and the different colors are produced.
This analysis showed that the light from VFTS was 243 from a single source, not two separate stars. Because there was no detectable radiation from the star’s companion, the only possible conclusion was that the second body in the binary star is a black hole, and thus the first dormant black hole found outside the Milky Way Galaxy.
Why is VFTS 243 important?
Most black holes with masses less than 100 suns are formed by the collapse of a massive star. When this happens, there is often a huge explosion known as a supernova.
The fact that the black hole in the VFTS 243 system is in a circular orbit with the star is strong evidence that there was no supernova explosion that might otherwise have occurred. kicked the black hole out of the system – or at the very least disrupted the orbit. Instead, it seems that the ancestor immediately collapsed to form the black hole without explosion.
The massive star in the VFTS 243 system will only live for another 5 million years — the blink of an eye in astronomical timescales. The star’s death should result in the formation of another black hole, turning the VFTS 243 system into a binary black hole.
To date, astronomers have detected nearly 100 events in which binary black holes merge and produced ripples in space-time. But how these binary black hole systems form is still unknown. That is why VFTS 243 and similar yet-to-be-discovered systems are so important for future research. Perhaps nature has a sense of humor – because black holes are the darkest objects in existence and do not emit light, yet they illuminate our fundamental understanding of the universe.