The latest research indicates that our galaxy has at least one free black hole. This is the first object of its type observed in the Milky Way. Among the discoverers of this rare phenomenon are scientists from the Astronomical Observatory of the University of Warsaw, involved in the OGLE project.
Black holes are one of the most mysterious objects known to astronomy. These phenomena are extremely difficult to study and observe, especially when they occur alone and do not emit any signals. Scientists managed to find such a black hole and take measurements of it.
The technique of gravitational microlensing is used to observe non-luminous celestial bodies. It uses the property of massive objects to bend and focus rays of light. If the light reaching the Earth from a distant star encounters such a body on its way, the observer will see a characteristic, time-varying brightening of the source – it is the so-called the phenomenon of microlensing.
One of the most important research centers using the gravitational microlensing technique is the Astronomical Observatory of the University of Warsaw. Since 1992, it has been running the scientific project The Optical Gravitational Lensing Experiment (OGLE) under the leadership of Professor Andrzej Udalski. So far, as many as 22,000 microlensing phenomena have been discovered as part of the initiative.
On the trail of a black hole
The black hole brightening was first observed on June 2, 2011 by scientists from the OGLE program. The existence of the phenomenon was confirmed by another research project using the technique of gravitational microlensing, the New Zealand-Japanese Microlensing Observations in Astrophysics (MOA).
The facility was monitored regularly for the next nine years. Researchers collected 15,545 precise measurements of the brightness of the phenomenon. A team of astronomers from the Space Telescope Science Institute, who turned the watchful eye of the Hubble Space Telescope, also joined the observation. In this way, astrometric measurements of the phenomenon were made, possible due to the high mass of the object. The facility was also tested by an independent team of scientists from the University of California, Berkeley.
Several times more massive than the sun
As shown by the modeling results, the mysterious object could only be a free black hole hidden inside the Milky Way. Dr. Przemysław Mróz, a member of the OGLE team who participated in modeling the phenomenon, explains that the light of an ordinary star with such a mass would be easily registered. This indicates that we are dealing with a non-luminous object, that is, a free, stellar-mass black hole. Depending on their calculations, scientists estimate that the object has a mass from 4.2 to 7 times that of our sun.
The discovery of the first free black hole in the Milky Way is a breakthrough in the study of these rare objects. Scientists speculate that there are many more such objects in our galaxy, and future observations should enable the detection of more of them. Prof. Andrzej Udalski also explains that this discovery ends a certain stage in the development of the technique of gravitational microlensing.
– This method has so far been able to estimate the content of the so-called dark matter in the galaxy, discover extrasolar planetary systems and free planets. The discovery of a free black hole is the long-awaited conclusion of another fundamental research area – microlensing by very massive objects – says Udalski.
Main photo source: NASA, STScl, FECYT, IAC