SA finds radio galaxies

MEERKAT: TELESCOPE IN KAROO MAKES EXCITING DISCOVERIES

Although millions are known to exist, only about 800 giants have been found.

Two giant radio galaxies have been discovered with South Africa’s powerful MeerKAT telescope, located in the Karoo region. Radio galaxies get their name from the fact that they release huge beams, or “jets”, of radio light. These happen through the interaction between charged particles and strong magnetic fields related to supermassive black holes at the galaxies’ hearts.

These giant galaxies are much bigger than most of the others in the universe and are thought to be quite rare.

Although millions of radio galaxies are known to exist, only around 800 giants have been found.

This population of galaxies was previously hidden from us by radio telescopes’ limitations. But the MeerKAT has allowed new discoveries because it can detect faint, diffuse light which previous telescopes were unable to do.

Our discovery, published in the Monthly Notices of the Royal Astronomical Society, gives astronomers further clues about how galaxies have changed and evolved throughout cosmic history. It is also a way to understand how galaxies may continue to change and evolve – and even to work out how old radio galaxies can get.

The giant radio galaxies were spotted in new radio maps of the sky created by one of the most advanced surveys of distant galaxies. The team working on it has included astronomers from around the world, including SA, the UK, Italy and Australia.

Called the International Gigahertz Tiered Extragalactic Exploration IGHTEE survey, it involves data collected by SA’s impressive MeerKAT radio telescope.

MeerKAT consists of 64 antennae and dishes, and started collecting science data in early 2018.

It will ultimately be incorporated into the Square Kilometre Array, an intergovernmental radio telescope project spearheaded by Australia and SA.

The galaxies in question are several billion light years away. The discovery of enormous jets and lobes in the IGHTEE map allowed us to confidently identify the objects as giant radio galaxies.

Their discovery means that a

clearer understanding of the evolutionary pathways of galaxies is beginning to emerge. This is tantalising evidence that a large population of faint, very extended giant radio galaxies may exist.

This may help us understand how radio galaxies become so huge and what sort of havoc supermassive black holes can wreak on their galaxies.

Many galaxies have supermassive black holes in their midst. When large amounts of interstellar gas start to orbit and fall in towards the black hole, the black hole becomes “active” – huge amounts of energy are released from this region of the galaxy.

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 – may actually be more common than we previously thought.

These are not 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”.

More clues about how galaxies have evolved