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
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
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
“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.