Black holes used to measure universe acceleration

Astronomers from Tel Aviv, Paris and Beijing maintain that the history of the expanding universe can be traced by watching a certain type of huge black hole.

The team, led by Jian-Min Wang of the the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, investigated the properties this type of active black holes that reside in the centers of many galaxies.

The mass of such black holes ranges from about a million to several billion times the mass of our sun. They can be observed when they accrete large amounts of gas from their surroundings, a situation that causes them to shine at levels of up to a thousand times the energy produced by a large galaxy containing 100 billion stars.

Astronomist Prof. Hagai Netzer of Tel Aviv University’s School of Physics and Astronomy and the Wise Observatory at the Raymond and Beverley Sackler Faculty of Exact Sciences, Dr. David Valls-Gabaud from Observatoire de Paris and Pu Du and Chen Hu from the Chinese institute worked on the discovery with Jian-Min Wang.

Their paper has just been published in Physical Review Letters.

“We live in an accelerating and expanding universe; a surprising discovery of the late 1990s for which the Nobel Prize was awarded to others in 2011. However, measuring the rate of acceleration at very large distances is very challenging and problematic,” the paper stated.

“Our new paper suggests a method, based on the properties of black holes, that will improve the accuracy of such measurements. The article illustrates how to implement the method over a wide range of distances that can be translated into measuring the rate of expansion of the universe at a very early age.”

The new method makes use of the properties of those black holes that accumulate gas at the highest possible rate and, therefore, are the most luminous black holes in their mass group. The paper shows that the amount of energy emitted in the process of this accretion is proportional to the black hole mass.

Thus, measuring the mass using well-established methods enabled the researchers to derive the amount of energy released in the vicinity of the black hole. Measuring the fraction of this radiation that reaches the Earth, using ground-based telescopes, can be used to derive the distance to the black hole and also the time in the history of the universe when the radiation was emitted. Such measurements over a range of distances can be used to derive the rate of acceleration of the universe, it said.

“The results allow us to analyze the requirements for using the method in future samples of active black holes, and to demonstrate that the expected uncertainty, given large enough samples, can make them into a useful, new cosmological ruler,” the paper conlcuded.