Murchison Widefield Array (MWA): Radio galaxy discovery near Earth spurs more questions

A radio galaxy is a galaxy which is associated with jets of emission which show up in radio wavelengths. 

ICRAR Astronomers have worked out that these jets come from super massive black holes at the centres of these galaxies. 

The region around the black hole is also visible in the radio, and this shows up as a bright 'core' in between the wider plumes. 

Credit: Dr Natasha Hurley-Walker

Western Australia astronomers have discovered a radio galaxy near Earth by accident.

The previously unknown radio galaxy is considered quite close to Earth, and was discovered late last year.

ICRAR astronomer Dr Natasha Hurley-Walker spotted the galaxy while in a team meeting last year looking at a digital image captured by the Murchison Widefield Array (MWA).

"I just saw this thing out of the corner of my eye and thought, that doesn't look right and it turns out it is one of these radio galaxies and it is very, very faint and it is very nearby," she says.

But while astronomers consider the galaxy quite close, it is redshift 0.0178 from earth and would take 248 million light years to get there.

Dr Hurley-Walker says the radio galaxy, named NGC1434 after the galaxy it is in, is very large, which may explain why astronomers had not spotted it in the past.

It is not dissimilar to earth in that it has star formation going on, and it has what is called a dust blain, which suggests it has not been agitated by galaxies colliding (mergers).

"The interesting thing about the object I found is that it's being hosted by a spiral galaxy, like our own," she says.

"This is a very rare occurrence—this is only the fifth of this type to be discovered, and by far the faintest."

Because it is quite near earth, it means the galaxy is quite old, possibly forming within a billion years after the big bang.

Dr Hurley-Walker says the discovery is also intriguing because at some point in its history the central black hole switched off but the radio jets have persisted.

Jets are narrow beams of matter spat out at high speed from near a black hole.

"That is kind of unusual because normally when we see these things, they are usually still on, have been for quite some time and that tells us the jets have persisted for a very long time.

"[This] is kind of interesting because it tells us that the electrons out there must have been very hot originally so there could still be radiation now," she says.

She does not know why the black hole switched off.

But to unlock the reasons and to find out more, she says researchers will need to observe the galaxy's central core with a high-resolution instrument with a very narrow field of view.

ESO ALMA Turns Its Eyes to Centaurus A

A new image of the center of the distinctive galaxy Centaurus A, made with the Atacama Large Millimeter/submillimeter Array (ALMA), shows how the new telescope, which is still under construction, allows astronomers to see with unprecedented quality through the opaque dust lanes that obscure the galaxy's center.

Centaurus A is a massive elliptical "radio galaxy," (a galaxy that emits strong radio waves) and is the most prominent, as well as the nearest, radio galaxy in the sky. Its very luminous center hosts a supermassive black hole with a mass of about 100 million times that of the Sun.

As seen in visible light, a dark dusty band obscures the galaxy's center. This dust lane harbors large amounts of gas, dust and young stars. These features, together with the strong radio emission, indicate that Centaurus A is the result of a collision between a giant elliptical galaxy and a smaller spiral galaxy.

To see through the obscuring dust in the central band, astronomers need to observe using longer wavelengths of light, such as infrared light or radio waves.

The new ALMA observations, shown in a gradation of blue in this image, reveal the position and motion of clouds of gas in the galaxy.


They are the sharpest and most sensitive such observations ever made. ALMA was tuned to detect signals with a wavelength around 1.3 millimeters, emitted by molecules of carbon monoxide gas.

The motion of the gas in the galaxy causes slight changes to this wavelength, shown in this image as changes in color. Violet and dark-blue features trace gas coming towards us, while light-blue features depict gas moving away.

We can see that the gas to the left of the center is moving towards us, while the gas to the right of the center is moving away from us, indicating that the gas is orbiting around the galaxy.

The millimeter wavelength observations were made using super-sensitive radio receivers built by the National Radio Astronomy Observatory. In this image the ALMA observations are overlaid on an optical image of Centaurus A produced by the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory in Chile.

Construction of ALMA, on the Chajnantor Plateau in northern Chile, will be completed in 2013, when 66 high-precision antennas will be fully operational. Half of the antennas already are installed. Early scientific observations with a partial array began in 2011, and already are producing outstanding results. The ALMA observations of Centaurus A shown here were taken during the telescope's Commissioning and Science Verification phase.

Credit: ALMA (ESO/NAOJ/NRAO), T.A. Rector (University of Alaska Anchorage). Visible-light image: ESO