Cosmic Giants Inaugurate a New Era in Astronomy

Article announces the discovery of two novae of these galaxies in a small region of the sky

Some galaxies project jets of matter that start from their central region and extend far beyond the galaxy itself, through the intergalactic medium. In some cases, these jets, detected at radio frequencies, surpass extensions of hundreds of thousands or even millions of light years – they are the so-called giant radio galaxies, the largest individual objects that exist in the Universe.

Less than a thousand known since the first identified in 1974, these giant radio galaxies may ultimately be more common than previously thought and have been invisible to the limit sensitivity of the previous generation of radio telescopes, according to one. article1 published today in the scientific journal Monthly Notices of the Royal Astronomical Society and which had the collaboration of Jose Afonso, of the Institute of Astrophysics and Space Sciences (IA2) and the Faculty of Sciences of the University of Lisbon (Science ULisboa).

The article announces the discovery of two novae of these galaxies in a small region of the sky, something that would be said to be impossible in objects believed to be so rare.

On data recently collected with the new radio telescope MeerKAT, in South Africa, two opposing jets are visible in each of these galaxies, typical of galaxies with an active central core.3, but with impressive dimensions, stretching into intergalactic space many times the size of the part of the galaxy that emits in visible light.

“Part of the falling matter into the huge black hole that we find at the center of these active galaxies ends up being ejected far away”, explains José Afonso.

“Remaining bright at radio frequencies for millions and millions of years, this radio emission can be used as a record of active core activity throughout the galaxy's history. We've only been detecting 'the top of the iceberg' of the population of giant radiogalaxies, and such an important phase in a galaxy's life, the active galaxy phase, is probably much more common than we thought.”

These two newly discovered structures are therefore excellent targets to learn about the history and transformations that galaxies of this type have gone through, and even to understand how the center of our own Milky Way galaxy could eventually go through phases of much greater activity.

Located respectively at 2,1 and 3,8 billion light years, those two galaxies have dimensions of the order of seven million light years, which is more than 60 times the size of our galaxy. The study supports the hypothesis that, if they are more common, they are in fact ancient radiogalaxies, whose jets could grow for hundreds of millions of years.

Many will ultimately be still undiscovered, as they are very faint objects, but finally within range of the sensitivity of MeerKAT, a 64-antenna infrastructure opened in 2018 in South Africa and a forerunner of the future radio telescope Square Kilometer Array (BE).

In a sky survey carried out with the MeerKAT, the MIGHTEE survey, a project started in 2010 and which included José Afonso and other IA researchers, it was possible to identify the faint but long jets, including the characteristic terminal lobes where the material from the center of the galaxy is stopped by the gas that fills the intergalactic medium.

“In this work, we participated in the analysis of the images and we had to ensure that the radio transmission, along the entire length seen in the image, in fact belongs to a single structure, or jet”, says José Afonso. "I also tried to compare with previous results to see if this pair of giant radiogalaxies, in such a small area of ​​the sky, is such an unusual discovery, and yes, it is!"

The AI ​​researchers are exploiting the data from this survey to discover galaxies much further away than these, when the first galaxies appeared in the Universe. Jacinta Delhaize, a researcher at the University of Cape Town, South Africa, and first author of the article, says in a press release from that university: “We hope to reveal more of these giant galaxies in the MIGHTEE survey as it progresses. We also hope to find many more with the future telescope. Square Kilometer Array".

For José Afonso, the study of galaxies in radio frequencies will witness a revolution in the coming years. In 2019, AI investigators showed how it will be possible for telescopes like the SKA to reveal hundreds of these first giant galaxies in the history of the Universe.

“These two galaxies revealed now are much closer examples, but they will help us to optimize the techniques we are developing for the detection of the first monster galaxies. It is a very exciting period for our knowledge of galaxies in the Cosmos”, says José Afonso.

 

Author: Institute of Astrophysics and Space Science
© 2021 – Science in the Regional Press / Ciência Viva

 



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