Most Distinct Image Of The Center Of The Milky Way Captured By South African Radio Telescope

Driven by the desire for the understanding that a mere glimpse into the vast and luminous universe can yield, billions of dollars have been spent developing more and more sophisticated telescopes capable of capturing electromagnetic radiation from myriads of lightyears away.

In keeping with this trend, the MeerKAT, a radio telescope consisting of an array of 64 antennas, was constructed in South Africa as the first part of an international project to build the most sensitive radio telescope yet. The telescope has already captured the most distinct image to date of the center of the Milky Way galaxy.

What is MeerKAT?

On Friday the 13^th of July, 2018, the MeerKAT telescope in South Africa was inaugurated by the Deputy President David Mabuza. During the inauguration, a panoramic image captured by the telescope was revealed, showing the clearest image yet collected of the centre of the Milky Way galaxy, in the area surrounding the supermassive black hole.

Image of the centre of the Milky Way galaxy. Image source: SARAO.

The First Light image collected by MeerKAT spans 2 ° by 1 °, and shows an area of 1000 by 500 lightyears of the universe at the centre of the galaxy. The radio frequencies collected were 900 – 1670 MHz, and in the image shown above, the intensity of the radio waves collected are indicated by the brighter yellow-white light. This image shows regions of births and deaths of stars occurring at the centre of the galaxy, as well as magnetized filaments located only near the supermassive black hole. The filaments are of special note, as their origin is as yet unknown, but the image captured by MeerKAT shows what seem to be some sources of the filaments, which have never been observed before and may shed some light on the origins of the filaments.

Originally termed the Karoo Array Telescope (KAT) for its location in the Karoo region of South Africa, the radio telescope was meant to be composed of 20 receptors. However, the budget was expanded, allowing for a total of 64 receptors to be built, and the name of the telescope changed to MeerKAT, meaning ‘more of KAT’, and shares its name with a small mammal that lives in the region.

MeerKAT is a radio telescope, operated by the South African Radio Astronomy Observatory (SARAO), that forms the first stage of a larger international project called the Square Kilometre Array (SKA). MeerKAT is composed of 64 receptors and has taken 10 years and billions of South African Rand to build. The telescope is located outside of Carnarvon in South Africa. The receptors are within 8 km of one another and are all interconnected. Each receptor is 19.5 m tall and weighs 42 tons, and includes an antenna positioner (which is steerable and consists of the main reflector and sub-reflector), radio receivers, and digitizers.

The main reflector is the 13.5 m dish-shaped structure of the antenna, and is composed of 40 sheets of aluminum, while the sub-reflector is the smaller, 3.8 m, dish-shaped structure that is positioned facing the main reflector. The sub-reflector is composed of a single sheet of material. The design of the configuration of the reflectors is called the ‘Offset Gregorian’ because there are no struts between the dishes to interfere with incoming electromagnetic radiation. The lack of obscuring struts helps to improve the sensitivity and performance quality of the telescope.

The radio receivers receive the collected radio waves and the digitizers convert the radio frequency (RF) signal into a digital signal.

How Does a Radio Telescope Work?

Radio waves emitted from objects in space are collected by and bounced off of the main reflector into the sub-reflector, where the waves are focused into the receiver. The receiver captures the radio waves and amplify the signal, which is converted from a radio frequency (RF) signal into a digital signal. The digital signal is sent via fibre optic cable to a digital processor. The processor correlates all of the signals into an image of a certain portion of the sky. MeerKAT is capable of being accurately positioned, to within 0.007 of a degree under normal operating conditions. The range of motion of a receptor is from 15 to 88 ° in height, and -185 to +275 ° across the sky, with a reference point of north at 0 degrees.

The Centre of the Milky Way

Like most galaxies, at the centre of the Milky Way, a supermassive black hole (approximately 4 million times larger than the sun) dwells. Earth orbits the sun approximately 25 000 lightyears away from the centre of the Milky Way, on the other side of the constellation Sagittarius. Due to the position of the centre of our galaxy from Earth, our central supermassive black hole is called Sagittarius A*. Stars are not the only celestial objects lurking between Earth and Sagittarius A*; massive gas and/or dust clouds also fill the vacuum of space between us and the galaxy’s centre. Due to scattering, regular optical telescopes cannot be used to detect the centre of the Milky Way. Radio waves are able to travel through the clouds of dust and gas to reach our radio telescopes on Earth, but are weak and require as much sensitivity from the telescope as possible to form a clear image.

Future Directions for MeerKat

Some large survey projects of greater than 1000 hours have already been scheduled on MeerKAT. These projects include the observations of pulsars to help understand neutron stars, surveying hydrogen from the early universe, and investigating galaxies, dark matter, and supernovae. Up to 70 % of the available usage time on MeerKAT has been scheduled for the large survey projects, with the other 30 % allocated to smaller research projects.

While MeerKAT is a fully functional radio telescope itself, it also forms part of the first phase of the Square Kilometre Array (SKA), which will be called SKA-MID (the mid-frequency portion of SKA). Phase 1 of SKA will consist of both SKA-MID and SKA-LOW, and when combined with Phase 2, will be the most sensitive radio telescope in the world. SKA will be located across Africa and Australia, in the Southern Hemisphere, and should be complete by the year 2024.