New giant ‘radio galaxies’ help shed light on the history of the universe
What’s new
Many galaxies have supermassive black holes in their midst. When large amounts of interstellar gas start to orbit and fall into the black hole, the black hole becomes ‘active’: huge amounts of energy are released from this region of the galaxy.
In some active galaxies, charged particles interact with the strong magnetic fields near the black hole and release huge beams, or ‘jets,’ of radio light. The radio jets of these so-called ‘radio galaxies’ can be many times larger than the galaxy itself and can extend vast distances into intergalactic space. Think of them like jets of water from a whale’s blowhole, a thin column extending into a cloudy plume at the end.
We found these giant radio galaxies in a region of sky that’s about four times the area of the full Moon. Based on what we currently know about the density of giant radio galaxies in the sky, the probability of finding two of them in a region this size is extremely small – only 0.0003%. So, it’s possible that giant radio galaxies – those that emit the beams, or jets of light described above – may actually be more common than we previously thought.
These aren’t the first radio galaxies astronomers have discovered. Many hundreds of thousands have already been identified. But only around 800 have radio jets bigger than 700 kilo-parsecs in size, or around 22 times the size of the Milky Way. These truly enormous systems are called ‘giant radio galaxies’.
Our new discoveries are more than 2 Mega-parsecs across: about 6.5 million light years or about 62 timesthe size of the Milky Way. Yet they are fainter than others of the same size. That’s what makes them harder to see.
Clues
We suspect that many more galaxies like these should exist, because of the way we think galaxies should grow and change over their lifetimes. And that’s one question we hope this discovery can help to answer: how old are giant radio galaxies and how did they get so enormous?
Now, telescope technology is making it possible to put these and other theories to the test. MeerKAT is the best of its kind in the world because of the telescope’s unprecedented sensitivity to faint and diffuse radio light. This capability is what made it possible for us to detect the giant radio galaxies. We could see features that haven’t been noticed before: large-scale radio jets coming from the central galaxies, as well as fuzzycloud-likelobes at the end of the jets.
The fact that only very few radio galaxies are so gigantic has always been a bit of a mystery. It is thought that the giants are the oldest radio galaxies, which have existed for long enough (several hundred million years) for their radio jets to grow outwards to these enormous sizes. If this is true, then many more giant radio galaxies should exist than are currently known. And that’s important because radio jets can influence the star formation of their host galaxy. Essentially, they might ‘kill’ their galaxy by blowing out all the gas and preventing the formation of new stars.
The MIGHTEE survey continues, and we hope to uncover more of these giant galaxies as it progresses. We also expect to find many more with the Square Kilometer Array: construction of this transcontinental telescope is due to start in South Africa and Australia in 2021 and continue until 2027. Science commissioning observations could begin as early as 2023.
The Square Kilometer Array is also expected to reveal larger populations of radio galaxies, revolutionizing our understanding of galaxy evolution.
This article byJacinta Delhaize, SARAO Postdoctoral Research Fellow,University of Cape Townis republished fromThe Conversationunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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