If we make an analogy, we are going to talk here about the heavyweights of the galaxy, that is to say of the highest category of boxing applied to astronomy. We are going to encounter a titanic galaxy, the largest ever discovered to date and whose dimensions are difficult to assimilate.
Alcioneo, the largest galaxy in the universe
It’s called Alcyoneus and is a giant radio galaxy, a type of galaxy that is characterized by the emission of large quantities of radio waves from the lobes of its supermassive black holes.
Located approximately 3 billion light-years from Earth, Alcyonea spans 16 million light-years, a size that puts it at the top of the largest galaxies in the universe.
To give you an idea, our own galaxy, the Milky Way, is about 100,000 light years across, which means Alcyonea is about 160 times larger.
Besides its size, another factor makes Alcyonea particularly fascinating: its structure. The galaxy’s radio lobes extend in opposite directions from its core, eventually forming an elegant symmetry.
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These lobes are the result of jets of charged particles ejected at speeds close to light from the central supermassive black hole, which, by interacting with the intergalactic medium, expand and emit radio waves which outline the shape of the galaxy.
How do you calculate the size of a galaxy?
Calculating the size of a galaxy is a complex task that involves several astronomical techniques. In the case of giant radio galaxies like this, astronomers mainly observe radio waves that can be picked up by LOFAR (Low-Frequency Array) radio telescopes.
The first thing an astronomer does is identify the radio lobes, which are the most distant areas of the galaxy, and then measure the distance between these lobes to determine their overall size. This process requires careful analysis to ensure that the measurements are accurate and that the emissions are indeed coming from the galaxy in question.
Other types of measurement techniques
In addition to radio observations, astronomers also use visible light, infrared and x-rays to calculate the size of galaxies. Each method provides unique information about the structure and composition of galaxies, leading to a better understanding of their dimensions and characteristics.
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For example, visible light allows us to see stars in the galaxy, while infrared observations reveal the presence of dust and gas. X-rays, on the other hand, make it possible to identify high-energy regions, such as black holes. By combining this data, astronomers can get a more precise and complete idea of the size and structure of the galaxy.
