How a South African telescope found 2 galaxies no-one else could

South Africa’s MeerKAT telescope has discovered two giant radio galaxies, which are among the largest single objects in the Universe and previously thought to be quite rare.

Radio galaxies are so named because they release jets of electromagnetic radiation when charged particles interact with the strong magnetic fields caused by the supermassive black hole in the middle of the galaxy.

These jets are visible in the radio frequency spectrum. These are the frequencies between 10MHz and 100Ghz.

For comparison, FM radio in South Africa and most other places in the world operates at frequencies between 87.5MHz and 108MHz. Cellular networks around the world generally use frequencies between 700MHz and 3500MHz, Wi-Fi uses 2.4GHz and 5GHz, and DStv beams down a signal of between 10.7GHz and 11.5GHz from its satellites.

MeerKAT was the first radio telescope to detect these two “monster” galaxies, even though other advanced telescopes had scanned the exact same region of the sky.

The reason MeerKAT spotted these galaxies and others did not is that it has unprecedented surface brightness sensitivity, Jacinta Delhaize, a Research Fellow at the University of Cape Town, told MyBroadband.

Delhaize was the lead author on the paper about the discovery that was published in the Monthly Notices of the Royal Astronomical Society.

“The receivers are incredibly sensitive, even more so than they were designed to be,” she stated.

“The MeerKAT interferometer also has many different baselines, meaning it has excellent [ultraviolet] coverage.”

Delhaize explained that the radio emission from the jets of the galaxies is very diffuse. In other words, it has low surface brightness and is distributed over a large region of the sky.

“This ‘extended emission’ is impossible to detect if your telescope dishes are all spaced very far apart. You need some spaced closer together to be able to detect the extended emission.”

This means that the way MeerKAT was designed makes it sensitive to a wide range of spatial frequencies.

At the same time, MeerKAT has good angular resolution, albeit not as good as some other telescopes like the Very Large Array.

“We will have to wait for the SKA to have excellent surface brightness sensitivity plus excellent angular resolution,” Delhaize noted.

Taking everything together, MeerKAT has a combination of:

  1. Excellent sensitivity — allows it to detect faint signals.
  2. Excellent range of spatial scales — allows it to detect large-scale signals
  3. Good angular resolution — allows it to resolve fine details.

“This combination is unprecedented and makes MeerKAT the first telescope capable of easily detecting radio galaxies that are as extended and as faint as these two monsters,” said Delhaize.

The two giant radio galaxies found with the MeerKAT telescope. In the background is the sky as seen in optical light. Overlaid in red is the radio light from the enormous radio galaxies, as seen by MeerKAT. Left: MGTC J095959.63+024608.6. Right: MGTC J100016.84+015133.0. Credit: I. Heywood (Oxford/Rhodes/SARAO).
Part of the MIGHTEE radio map of the sky. A zoom in of each giant radio galaxy is shown in greyscale. The purple line traces around the radio emission from the giants. Image credit: I. Heywood (Oxford/Rhodes/SARAO).

Radio galaxies may be more common than first thought

The fact that MeerKAT detected these two large galaxies in a relatively small patch of sky suggests that such giant radio galaxies may actually be much more common than previously thought.

“We found these giant radio galaxies in a region of the sky which is only about four times the area of the full moon, though the galaxies are much further away and much larger than the moon,” Delhaize said.

“Based on our current knowledge of the density of giant radio galaxies in the sky, the probability of finding two of them in this region is extremely small. This means that giant radio galaxies are probably far more common than we thought!”

According to the South African Radio Astronomy Observatory, this gives astronomers further vital clues about how galaxies have changed and evolved throughout cosmic history.

The properties of the two giant radio galaxies are as follows:

Name MGTC J095959.63+024608.6 MGTC J100016.84+015133.0
Distance 2.08 billion light-years 3.8 billion light-years
Diameter 2.42 Mpc (7.9 million light-years) 2.04 Mpc (6.7 million light-years)

MeerKAT would kill your home Internet connection

MeerKAT requires peak network speeds of 20Gbps to transfer all the data it collects to researchers, the group lead for network engineering at the South African National Research Network (SANReN), Siju Mammen, told MyBroadband last year.

These bandwidth demands will only increase in the coming years.

MeerKAT will continue to expand as part of the first phase of the Square Kilometre Array project, and will eventually require as much as 10 terabits per second (Tbps) of bandwidth — five hundred times the bandwidth it currently uses.

Now read: Elon Musk’s Starlink project could cripple South Africa’s SKA telescope

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How a South African telescope found 2 galaxies no-one else could