In the vastness of the Universe, some discoveries remind us how much we still have to learn. A recent study on Cosmic Horseshoe, a gravitational lensing phenomenon, is a striking example.
Cosmic Horseshoe, discovered in 2007, is a system where a massive foreground galaxy distorts and amplifies the light from a distant galaxy, creating an almost perfect Einstein ring. This rare configuration offers a unique window into the properties of the involved galaxies.
Cosmic Horseshoe, showing the Einstein ring formed by gravitational lensing.
Credit: NASA/ESA/Hubble
A team of researchers, led by Carlos Melo-Carneiro, has revealed the presence of an ultra-massive black hole at the heart of the lensing galaxy, forming the Einstein ring LRG 3-757. With an estimated mass of 36 billion times that of the Sun, this black hole upends current expectations and models.
Ultra-massive black holes, although poorly defined, are generally considered to have a mass greater than 5 billion times that of our Sun. Their discovery in galaxies like LRG 3-757 raises questions about their formation and evolution.
The MBH-sigmae relation, which links the mass of supermassive black holes to the velocity dispersion of stars in their host galaxy, is a valuable tool for astronomers. However, the black hole in Cosmic Horseshoe significantly deviates from this relation, suggesting different evolutionary processes.
Several hypotheses are proposed to explain this deviation, including past galactic mergers or feedback effects from active galactic nuclei. These scenarios could explain how the black hole could reach such a mass without a corresponding stellar velocity dispersion.
Future missions, such as Euclid and the Extremely Large Telescope, promise to expand our understanding of these cosmic giants. These tools will allow detailed study of thousands of gravitational lenses, offering new perspectives on galaxy and black hole evolution.
This study, published on
arXiv, paves the way for a better understanding of the most massive black holes in the Universe and their role in cosmic evolution.
What is gravitational lensing?
Gravitational lensing is a phenomenon where the light from a distant object is deflected and amplified by the gravity of a massive object located between that object and the observer. This phenomenon, predicted by Einstein's theory of general relativity, allows astronomers to study very distant objects that would otherwise be invisible.
The distortion of light can create multiple images, arcs, or even complete rings, as in the case of Cosmic Horseshoe. These effects are used, among other things, to measure the masses of the lensing objects and to study the distribution of dark matter in the Universe.
Gravitational lenses are also valuable tools for testing gravity theories and exploring the Universe at remote epochs. They have enabled the discovery of very ancient galaxies and the study of the expansion of the Universe.
How is the mass of a black hole measured?
The mass of a supermassive black hole is often estimated by observing the motion of stars or gas around it. In distant galaxies, where these direct observations are difficult, astronomers use empirical relations, such as the MBH-sigmae relation.
This relation links the mass of the black hole to the velocity dispersion of stars in the galactic bulge. A high velocity dispersion generally indicates a more massive black hole. However, this method has its limitations, as shown by the case of the ultra-massive black hole in Cosmic Horseshoe.
Other methods include observing accretion disks or jets emitted by active black holes. Each method has its advantages and disadvantages, and astronomers often combine several techniques to obtain the most accurate estimates.