These two black holes are rare because of the great distance that separates them from their star, preventing them from swallowing it. This also makes it difficult to detect them, which is why we have had to wait for Gaia’s work to find out about them.
ESA’s Gaia probe has found two black holes very close to Earth. And the best thing is that this is not the only thing that makes them special, because they seem to be very different from others that have been observed before. Called Gaia BH1 and Gaia BH2, their biggest difference from other black holes is their distance from their companion star. Binary systems consisting of a black hole and a star are quite common. Many have already been discovered, but they are usually so close that the black hole continually gobbles up material that robs the star, generating a great deal of energy.
Thanks to that, they are easily detectable by instruments capable of detecting X-rays or radio waves. But in this case that was not what was detected. Gaia perceived a small wobble in the star, which possibly would have been imperceptible to the cameras of other similar probes. This wobble seemed to correspond to the gravitational effect of a very massive object, such as a black hole. This needed to be confirmed with other observations at NASA’s Chandra X-ray Observatory and the South African MeerKAT radio telescope. Thus, it was confirmed that, even though they were black holes, they were practically not dragging material from the star. Therefore, yes, they are special in many ways.
two new black holes These two black holes are located 1,560 and 3,800 light years from Earth. It may seem like a lot. However, if we take into account that the closest one that has been found so far is 1,011 light-years from the solar system and that our galaxy covers an area of 105,000 light-years, we can get an idea of how close they are. But that is not the only peculiarity of these black holes, as we have already seen. It is striking that they are very far from their companion star. For example, Gaia’s BH2 orbits the black hole every 1,277 days. That indicates that they are approximately 714 million kilometers away. If we take another binary system as an example, the one formed by Cygnus X-1 and its companion star, in this case the time it takes for the star to orbit is 5.6 days.
The difference is clear. So in systems like Cygnus X-1, it’s easy for much of the material from the star to intrude on the black hole’s event horizon. That is to say, that distance from which nothing can escape from him. Thus, little by little, it feeds on the star. But in this case that does not happen. The activity is practically non-existent because the distance is enormous. And that shows us that we could be facing a new type of black hole.
The situation will have to be studied further. Perhaps Gaia will find more such cases. At the moment, we will not be able to see the data from its last 66 months of complete observations until, at least, the end of 2025.