The black hole that was ahead of its time

Dr. Benny Trachtenbrot, an Israeli researcher who is in post-doctoral training at the Swiss Institute of Technology ETH, led research involving observations of ancient black holes with the help of the giant Keck telescope in Hawaii. The observations were made with the help of a state-of-the-art instrument in the infrared field and indicated the discovery of a giant black hole residing in a fairly ordinary galaxy in the early universe.

In the center of most galaxies in the universe there is a huge black hole and it is accepted to think that in most cases in larger galaxies the black hole is more massive. A team of researchers from the ETH Institute of Technology in Switzerland discovered from observations of the early universe a medium-sized galaxy with an extremely large black hole that grew at a faster rate than the rate at which the galaxy in which it resides grew. The findings of the new study raise questions about the assumption that galaxies and the black holes at their center evolve together. The results of the research are published in the new issue of the prestigious journal Science.

Benny Trachtenbrot, an Israeli researcher who is in post-doctoral training at the Swiss Institute of Technology ETH led a study involving observations of ancient black holes with the help of the giant Keck telescope in Hawaii. The observations were made with the help of a state-of-the-art instrument in the infrared field and indicated the discovery of a giant black hole residing in a fairly ordinary galaxy in the early universe. Since the light emitted from the object, known as CID-947, traveled a very long way before reaching Earth, the scientists observe it as it was when the age of the universe was less than 2 billion years - about one seventh of its current age (which is a little less than 14 billion years).
From the analysis of the data collected in the observations, it became clear that the black hole at the center of CID-947 has a mass greater than the mass of the Sun by about 7 billion times, so that it is among the largest black holes observed so far. However, the discovery that surprised the scientists the most was that the mass of the black hole is only about 10 times smaller than the mass of the entire galaxy in which it resides. In the universe close to us (in space and time), most black holes have a mass 200 to 500 times smaller than the mass of the galaxies in which they reside. "Our measurements indicate that this is a galaxy with an extremely normal mass," explains Trachtenbrot, who completed his doctoral studies at Tel Aviv University. "We are witnessing a supermassive black hole system residing in a perfectly normal galaxy." The result was so surprising that the team decided that two of the researchers would measure the mass of the galaxy independently of each other. Both measurements led to the same conclusion.

What changed in the early universe?
Most of the galaxies in the universe, including our home galaxy - the "Milky Way" - contain massive black holes at their center whose mass is millions or even billions times greater than the mass of the Sun. "The gravity of black holes is so strong that nothing - not even light - can escape their pull. Einstein's theory of general relativity describes how these strange bodies distort space-time itself," explains astrophysicist Prof. Hagi Netzer from Tel Aviv University - an expert on massive black holes (who was not involved in the new study). Such black holes are discovered thanks to the radiation emitted by the hot gas that falls into them at high speeds.

Many observations made so far have shown that the greater the number of stars in a particular galaxy, the larger the black hole at its center. "This connection describes what is happening in the universe close to us, that is, the situation in our era" explains Trachtenbrot. This connection, as well as other evidence, has led the research community to hypothesize that the growth of black holes progresses in an integrated manner with the formation of new stars in galaxies. This is a fairly simple idea if we assume that a common reservoir of cold gas is responsible for creating stars and "feeding" the black hole at the center. However, many studies from recent years have raised the possibility that the radiation emitted from the approach of the black hole during its growth process can affect and even completely stop the formation of stars, by heating the gas throughout the galaxy. The new study shows that the two processes, the creation of stars in galaxies and the emission of radiation near the black hole, are not necessarily related to each other - at least not in the early universe.

"The significance of our discovery is that the black hole at the center of the galaxy CID-947 managed to grow much more efficiently than the growth rate due to star formation, contrary to the predictions of the models that focus on a parallel evolution." The researchers even concluded that while the black hole is approaching the end of the growth process, the rate of creation of new stars in the galaxy is still high and the galaxy will continue to grow even after the black hole stops being active. It seems that the radiation and particles emitted from the vicinity of the black hole during its growth, did not slow down the creation of stars. The researchers believe that objects like CID-947 may constitute the source population for the most massive galaxies observed in the local universe.

The new research - bibliographic information:
Trakhtenbrot B, Urry Megan C, Civano F, Rosario DJ, Elvis M, Schawinski K, Suh H, Bongiorno A, Simmons BD:
An Over-Massive Black Hole in a Typical Star-Forming Galaxy, 2 Billion Years After the Big Bang,
Science, volume 349 (Issue 6244), pages 168-171 (2015)

Thanks to Dr. Benny Trachtenbrot for the translation.