So far, astrophysicists thought that super-massive black holes can only influence their immediate surroundings. A collaboration of scientists at the Heidelberg Institute for Theoretical Studies (HITS) and in Canada and the US now discovered that diffuse gas in the universe can absorb luminous gamma-ray emission from black holes, heating it up strongly.
A supermassive black hole is surrounded by a dust ring (torus). The collapse of gas onto the black hole launches an energetic jet of matter and radiation, which is transported over cosmological distances. A jet that is pointing into our direction is called a "blazar". copyright: ESA/NASA, the AVO project and Paolo Padovani
Simulated line forest of a quasar spectrum. The blue spectrum represents a universe without blazar heating, the red one a universe with blazar heating. It is evident that the additional heating process ionizes neutral hydrogen, implying less absorption of the UV light emitted by the quasar. Picture: HITS
This surprising result has important implications for the formation of structures in the universe. The results have just been published in "The Astrophysical Journal“ and „Monthly Notices of the Royal Astronomical Society”.
Every galaxy hosts a supermassive black hole at its center. Such black holes can emit high-energy gamma rays and are then called blazars. Whereas other radiation such as visible light and radio waves traverses the universe without problems, this is not the case for high-energy gamma rays. This particular radiation interacts with the optical light that is emitted by galaxies, transforming it into the elementary particles electrons and positrons.
Initially, these elementary particles move almost at the speed of light. But as they are slowed down by the ambient diffuse gas, their energy is converted into heat, just like in other braking processes. As a result, the surrounding gas is heated efficiently. In fact, the temperature of the gas at mean density becomes ten times higher, and in underdense regions more than one hundred times higher than previously thought.
A Journey into the Cosmic Youth
"Blazars rewrite the thermal history of the universe", emphasizes Dr. Christoph Pfrommer (HITS), one of the authors. But how can this idea be tested? In the optical spectra of quasars there is a plethora of lines, called the "line forest". The forest originates from the absorption of ultra-violet light by neutral hydrogen in the young Universe. If the gas becomes hotter, weak lines in the forest are broadened. This effect represents an excellent opportunity to measure temperatures in the early Universe, while it was still growing up.
The astrophysicists at HITS checked this newly postulated heating process for the first time with detailed supercomputer simulations of the cosmological growth of structures. Surprisingly, the lines were broadened just enough so that their properties perfectly matched those of the observed lines. "This allows us to elegantly solve a long-standing problem with the quasar data", says Dr. Ewald Puchwein, who conducted the large simulations on the supercomputer at HITS.
How Black Holes Influence the Formation of Galaxies
What are the further consequences of this new heating process? The forest of lines in the quasar spectra originates from density fluctuations in the Universe. In the course of cosmic evolution, the densest fluctuations collapse to form galaxies and galaxy clusters, as observed in the local Universe. Diffuse gas that is too hot cannot collapse. Hence, the formation of dwarf galaxies is slowed or even entirely suppressed. This could be the key to the solution of another long-standing problem in the theory of galaxy formation: why do we observe fewer dwarf galaxies in the vicinity of the Milky Way and in the underdense regions than predicted by cosmological simulations?
Prof. Volker Springel, scientific group leader at HITS, explains: "The process of blazar heating is especially exciting since this single effect is able to simultaneously solve several different puzzles in cosmological structure formation." The group plans to further improve their simulation models for a still deeper understanding of the nature of blazar heating and its implications for today's Universe.Press contact:
The Cosmological Impact of Luminous TeV Blazars III: Implications for Galaxy Clusters and the Formation of Dwarf Galaxies. C. Pfrommer, P. Chang, and A. E. Broderick, 2012, ApJ, in print, arXiv:1106.5505 http://arxiv.org/abs/1106.5505
The Cosmological Impact of Luminous TeV Blazars II: Rewriting the Thermal History of the Intergalactic Medium. P. Chang, A. E. Broderick, and C. Pfrommer, 2012, ApJ, in print, arXiv:1106.5504 http://arxiv.org/abs/1106.5504
The Cosmological Impact of Luminous TeV Blazars I: Implications of Plasma Instabilities for the Intergalactic Magnetic Field and Extragalactic Gamma-Ray Background. A. E. Broderick, P. Chang, and C. Pfrommer, 2012, ApJ, in print, arXiv:1106.5494 http://arxiv.org/abs/1106.5494
Dr. Peter Saueressig | idw
A new force for optical tweezers awakens
19.06.2019 | University of Gothenburg
View of the Earth in front of the Sun
19.06.2019 | Georg-August-Universität Göttingen
The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.
Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...
The well-known representation of chemical elements is just one example of how objects can be arranged and classified
The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...
Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.
Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...
Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.
The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...
Discovery by Brazilian and US researchers could change the classification of two species, which appear more akin to jellyfish than was thought.
The tube anemone Isarachnanthus nocturnus is only 15 cm long but has the largest mitochondrial genome of any animal sequenced to date, with 80,923 base pairs....
29.04.2019 | Event News
17.04.2019 | Event News
15.04.2019 | Event News
19.06.2019 | Physics and Astronomy
19.06.2019 | Information Technology
19.06.2019 | Materials Sciences