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South Africa’s MeerKAT solves mystery of ‘X-galaxies’

Read time 3min 40sec
Source: SARAO
Source: SARAO

A team of astronomers from South Africa and the US have used the MeerKAT telescope to solve a longstanding puzzle in ‘X’-shaped radio galaxies.

This is according to the South African Radio Astronomy Observatory (SARAO), a facility of the National Research Foundation, responsible for managing all radio astronomy initiatives and facilities in SA.

Using the MeerKat telescope data, last month an international team of astronomers also uncovered unusual features in the radio galaxy ESO 137-006.

Launched in 2018, the South African MeerKAT radio telescope is a precursor to the Square Kilometre Array (SKA), which aims to answer fundamental astrophysical questions about the nature of objects in the Universe.

The MeerKAT is currently made up of 64 dishes, each 13.5m in diameter. However, it recently received R800 million funding from Germany and SA that will see it get an additional 20 dishes.

SARAO says many galaxies far more active than the Milky Way have enormous twin jets of radio waves extending far into intergalactic space.

It explains that normally these go in opposite directions, coming from a massive black hole at the centre of the galaxy.

However, SARAO says a few are more complicated and appear to have four jets forming an “X” on the sky.

Several possible explanations have been proposed to understand this phenomenon. These include changes in the direction of spin of the black hole at the centre of the galaxy, and associated jets, over millions of years; two black holes each associated with a pair of jets; and material falling back into the galaxy being deflected into different directions forming the other two arms of the “X”.

Exquisite new MeerKAT observations of one such galaxy, PKS 2014-55, strongly favour the latter explanation as they show material “turning the corner” as it flows back towards the host galaxy; the results have just been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society, says SARAO.

This work was carried out by a team from SARAO, the US National Radio Astronomy Observatory (NRAO), the University of Pretoria and Rhodes University.

According to SARAO, previous studies of these unusual galaxies lacked the high-quality imaging provided by the recently completed MeerKAT telescope.

This telescope array consists of 64 radio dishes located in the Karoo semi-desert in the Northern Cape province of South Africa.

Computers combined the data from these antennas into a telescope 8km in diameter, and provided images in the radio band of unprecedented quality for PKS 2014-55 which enabled solving the mystery of its shape.

Bernie Fanaroff, former director of the SKA South Africa project that built MeerKAT, and a co-author of the study, notes: “MeerKAT was designed to be the best of its kind in the world. It’s wonderful to see how its unique capabilities are contributing to resolving longstanding questions related to the evolution of galaxies.”

Lead author William Cotton of the NRAO says: “MeerKAT is one of a new generation of instruments whose power solves old puzzles even as it finds new ones – this galaxy shows features never seen before in this detail which are not fully understood.”

SARAO points out that further research into these open questions is already under way.

More about the image

The galaxy PKS 2014-55, located 800 million light years from Earth, is classified as ‘X-shaped’ because of its appearance in previous relatively blurry images. The detail provided in this radio image obtained with the MeerKAT telescope indicates its shape is best described as a ‘double boomerang’.

Two powerful jets of radio waves, indicated in blue, each extend 2.5 million light years into space (comparable to the distance between the Milky Way and the Andromeda galaxy, our nearest major neighbour). Eventually, they are ‘turned back’ by the pressure of tenuous intergalactic gas.

As they flow back towards the central galaxy, they are deflected by its relatively high gas pressure into the shorter, horizontal, arms of the boomerang. The background image shows visible light from myriad galaxies in the distant universe.

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