Black holes absorb light, making them impossible to observe directly. The easiest black holes to spot are those that form a binary star system, such as the Cygnus X-1 black hole, which is paired with a blue super giant. As the black hole and the star orbit around it, the black hole pulls matter away from the star and engulfs it, releasing x-rays in the process. Scientists can spot these X-rays and detect the presence of a black hole.
This technique only detects black holes that are close enough to their partner stars to retrieve material. It is thought that there are many, many more black holes that do not approach close enough to absorb material and produce x-rays, which make them darker and even more difficult to locate.
The new study demonstrates how to spot these smokier black holes using the example of a binary system consisting of a giant star, 2MASS J0521
To find a hidden black hole, scientists examined the Doppler shift of the stars and compared this to their brightness over time. A significant Doppler shift can indicate a strong source of gravity, and when a star's brightness increases and decreases according to a given pattern, it implies that there is a large object in the star's orbit that sometimes blocks its light. Taken together, these two indicators suggest a black hole.
After zeroing in 2MASS J05215658 + 4359220 as a prime candidate, scientists were able to determine that the object orbiting the star should have a mass about three times that of our Sun, indicating that it is probably small Black hole.
The next step in proving the usefulness of this approach is for the team to search for more hidden black holes using the same method. If successful, we could have a new tool for locating multiple black holes throughout our galaxy.
The results are published in the journal Science .