“A” Sources

The “A” sources were the brightest extra-solar radio sources first discovered when radio astronomy was in its pioneering stages. They were named after the constellation within which the source was found followed by the letter “A”. When they were first discovered astronomers were not entirely certain which astronomical objects they were associated with. It was only later, when they were identified against optical counterparts, that this association could be made and so many of the “A” sources are also known by other names.

Cassiopeia A is the only “A” source not visible from the Murchison Radio Observatory. It is a supernova remnant approximately 11,000 light-years away.

Centaurus A is one of the closest radio galaxies to the Earth (10-16 million light-years away). In RACS we primarily see the inner radio lobes of this galaxy, which are powered by jets from a supermassive blackhole at its centre. The radio galaxy extends much further out than the image below and is about 8 degrees in extent (16 times the angular extent of the full moon)

Centaurus A

Cygnus A is one of the strongest radio sources in the sky. It is a distant radio galaxy approximately 756 million light-years from Earth.

Fornax A is a radio galaxy about 60 million light-years from Earth.

Hercules A (also known as 3C 348) is a distant radio galaxy approximately 2.1 billion light-years away.

Hydra A (also known as 3C 218) is a radio galaxy situated approximately 840 million light-years from Earth.

Pictor A is a radio galaxy around 485 million light-years away.

Puppis A is a supernova remnant (the remains of an exploded star) approximately 7000 light-years away.

Sagittarius A* is a bright radio source at the Galactic Centre of the Milky Way. It is associated with a supermassive black hole and is approximately 26,700 light-years from Earth.

Sagittarius A*

Taurus A is a radio source associated with the Crab Nebula (also known as Messier 1, or M1). The Crab Nebula is a supernova remnant that is believed to be associated with a supernova observed by Chinese astronomers in the year 1054.

Taurus A (Crab Nebula)

Taurus A (Crab Nebula)

Virgo A (also known as Messier 87, M87 or NGC 4486) is a supergiant elliptical galaxy approximately 16.4 million light-years away.

Virgo A (M87)