The Gaia spacecraft was launched by the European Space Agency in 2013 and since then it regularly monitors the position of over a billion stars in our galaxy with unprecedented precision. An organization that includes several hundred scientists across Europe (including Israel), processes the data coming from the spacecraft and makes it available for use by the community One of the teams, including a Tel Aviv University research group led by Prof. (Emeritus) Zvi Maza from the School of Physics and Astronomy, focuses on the study of double stars discovered from the spacecraft data. Recently, the organization published a list of more than a quarter of a million double stars, one of which is a black hole – one of the rarest celestial objects in the universe, the holiday around them, including a black hole located 1500 light years from Earth.
invisible partner
The team of researchers from Tel Aviv University, which also includes Dr. Sahar Shaf (now at the Weizmann Institute), Dr. Simhon Feigler and Dr. Dolev Bashi, developed a technique to identify double stars in which one of the partners is a black hole. It is very difficult to detect black holes, Because light cannot penetrate the strong gravitational force in the black hole’s surroundings. When such a “dead” black hole is in a binary system with an ordinary star, the motion of the visible star is used to measure the mass of the invisible partner and prove that it is indeed a black hole. In recent years, published Several proposals for identifying black holes are still in binary systems, but in all cases difficult questions arose that undermined the reliability of the identification.
The recently published Gaia data made it possible to identify a small number of stars whose movement across the plane of the sky indicates the existence of a dead black hole as a partner. A few months ago, an international team, which includes the research group from Tel Aviv University, discovered the first black hole, Gaia BH1, which is 1500 light years away. Dedicated ground-based observations conducted intensively in recent months have now confirmed the existence of Gaia BH2, a second black hole about 4000 light-years away. Both black holes are 10 times heavier (each) than our sun.
“This is an exciting discovery,” says Prof. Zvi of the ZA. “The first combination of its kind between the observations from the ground, and the spacecraft data, proves beyond any doubt that we have discovered two dormant black holes. Their relative proximity to us shows that the number of silent black holes in space is large, and the spacecraft’s data that continues to flow will lead to the discovery of many such objects, as various theoretical works indeed expected. I am proud that our research group got to participate in processing the Gaia data, and then tracking the discovered candidates, a first-of-its-kind combination that resulted in the identification of two relatively close black holes. I hope that the discovery will lead to a deeper understanding of how such a double system is formed, a process whose details are currently not understood.”