Whenever you look up at the night sky and see the stars your eyes detect visible light given off by
stars and galaxies. Some of this light has spent millions of years travelling across space until it
reached your eye. This is just a small part of the spectrum of electromagnetic radiation that exists.
By studying the radio waves given off by objects in space we can see a totally different picture.
This difference can tell us a lot about what might be going on around the object.
Let’s dive in and examine some of the strange objects radio astronomy is revealing.
Radio waves were first detected from space in the 1930’s but few scientist took the
discovery seriously. The development of RADAR in the second world war led to
improvements in antennas and electronics. This allowed many scieneits to later use
this equipment to investigate the radio signals coming from space.
The quality of the images we can detect has vastly changed over these years
and Australia has spearheaded work to map the entire sky using radio telescopes.
These have revealed some very strange objects.
In order to try and understand what these images might tell us
it is important to understand how these radio waves might have been generated.
There are essentially two forms of radio emission; thermal and non-thermal.
Thermal emissions are created by the motion of charged objects such as molecules and atoms.
As all mater has some heat energy stored in it, atoms vibrate,
emitting electromagnetic radiation. The more energy that is stored,
the more the atoms vibrate and the greater the amount of radiation emitted.
If a gas is heated, eventually the energy will be enough to kick out one or more
electrons orbiting the atom. The atom is ionised and gains a positive charge
and the electron is freed. These electrons continuously interact with the plasma
and will undergo accelerations which causes them to emit electromagnetic radiation.
Another form of thermal emission is due to the spin of the electrons when they are bound to
an atoms. Atoms can undergo random collisions which can impart energy to electrons which can
sometimes cause their spin state to invert. They can later release this energy by flipping back.
This creates a radio wave of a very specific wavelength. An electron in a neutral hydrogen
atom, produces radio waves of 21cm wavelength via this process. As hydrogen is one of the most
abundant elements in the universe this 21cm hydrogen line was one of the first emissions
detected from space and continues to be a key wavelength for astonomers to observe.
Non-thermal sources of radio waves include synchrotron radiation,
in which electrons moving near the speed of light get accelerated in strong magnetic fields.
Lets examine some of those peculiar Radio sources
Dancing Ghosts
PKS 2130-538 is what they term a complex source which has 2 radio galaxies. It had previously
been observed but the images did not contain the detail that is revealed in these new images.
It is believed that it shows radio lobes of two host galaxies,
one of which is the bright galaxy at the centre of the curved northern radio bridge,
at a redshift of 0.0781. This is the brightest galaxy of the cluster Abell 3785.
The other galaxy is the bright galaxy near the southeast end, at a redshift of 0.0763.
They are not sure if there is any interaction between these two galaxies at this stage and also
identify a thin stream of emission labelled as 3 extending eastward from the NE bright region. Both
its dynamic origins and particle history don’t fit naturally into existing radio galaxy models.
If we examine the images I do see what they label as 3 as possibly extending further across
making almost a sin wave. If we examine this image then the brightness represents the intensity
and colour represents the spectral index. Here you can see a clear difference in spectral index
between one side of the sine wave and the other. I also see quite a lot of symmetry
about the two large lobes but then there would be no central galaxy associated with these but
this is something we did briefly discuss when we looked at Peratt’s concept of galactic evolution.
The interesting point is the amount of movement we see in the lobes. There are other examples
of these types of lobes being bent at very strange angles. This implies that something
in between these galaxies is moving the lobes. Making it appear like they are being blown away.
Double lobed Radio Galaxy
Previous Radio images of this double-lobed radio AGN only showed an indistinct extended
source corresponding to the nucleus the new images reveal much more details.
Again here we see an example of the jets being bent by an intergalactic wind. The detail in the
image also reveals that the eastern jet is split into two whereas the western jet breaks down
into a number of blobs, accompanied by a large diffuse area of emission to the est of the source.
Dying Radio galaxy In the image, we can
see two diffuse clouds of radio emissions whose origins are unclear. The most likely hypothesis
is that they represent the remnants of a classical double-lobed radio galaxy
in which the central engine has switched off. Leaving a remnant galaxy.
Strange Radio Galaxy with no obvious host galaxy In this image, we see two bright patches and
diffuse tails, presumably blown to the east? What is strange in this image is that there is
no obvious host galaxy at the centre. The bright southern lobe is coincident with a quasar. One
suggestion is that they may be two radio galaxies that appear incredibly similar in size and shape.
There is however to evidence for a cluster of galaxies at this location.
Odd Radio Circles I have previously covered the strange case of
what appear as giant radio circles with no clear identification. At this stage, they still do not
understand what these circles might be and whether there are several different classes of them.
Giant Radio Galaxies
These are radio galaxies where their projected linear size is greater than 1 Mpc.
These are truly colossal giants if this size is correct. An example of this is Abel3391/95.
This also happens to contain the longest ever gas filament between these two clusters of galaxies.
We see several examples of these giant radio lobes and once more see most of them are bent in some
way or shape possibly due to the movement of the intergalactic medium. One thing to bear in mind
here is that these are higher redshift galaxies so this may play a role in appearing larger if
we assume a large part of the redshift is due to some intrinsic component rather than a movement
away from us. A quick search of high redshift radio galaxies does reveal that they do not
all appear to be these galactic giants so there may indeed be a case for giant radio galaxies.
The USS Jellyfish
Spanning 1.2 million light-years, the strange entity lies in Abell 2877
which is a cluster of galaxies thought to lie about 340 million light-years from Earth.
The USS stands for Ultra Steep Spectrum
and refers to the radio waves that make up the jellyfish shaped space entity. They have dubbed
this the first known example of a polypheonix - a radio source of immense complexity and mystery.
Usually, these sorts of clouds are associated with the output from active galactic nuclei
but the USS Jellyfish is far from any of these. It gives of very specific, very low-frequency
radio waves and renders it almost invisible to normal radio telescopes. The odd thing is that
although the radio waves are very low frequency it is incredibly bright at these frequencies.
So they propose that it must have been emitted from an AGN and travelled a great
distance. The problem is that this would mean it would have to be exceptionally old
and should have faded over this time. Some suggest that it might have been re-energised by a shock
that was exceptionally weak, but then the radio emisiion shouldn’t be so bright.
The scientist believed they would find more objects similar to the USS Jellyfish
once they worked out the kind of radio signature they were looking for.
The problem is that this search reveals that the USS Jellyfish
seems to be a totally unique object with no others like it anywhere in our observable universe!