A cluster of galaxies is not trivial. The shocks, the turbulence, the energy, since all that matter and energy merge and interact. And we can see all the chaos and chaos as it happens.
A team of astronomers is observing the Abell 2255 cluster of galaxies with the European Low Frequency Radio Telescope (LOFAR), and their images show some details never before seen in this actively merging cluster.
A new study based primarily on LOFAR from observations of Abell 2255 has revealed the scope of the galaxy cluster and its emissions. The title of the article is “The beautiful disaster in Abell 2255”. The lead author is Andrea Botteon, from Leiden University in the Netherlands. The article will be published in The Astrophysical Journal.
“The image that emerges from our work is that of one of the most complex diffuse radio sources known to date.”
From the document “The beautiful disaster in Abell 2255”.
Abell 2255 is considered one of the most intricate objects in the sky when it comes to radio broadcasts, an ideal target for LOFAR. And these new LOFAR images only strengthen that conclusion. In their article, the authors write that “The image that emerges from our work is that of one of the most complex diffuse radio sources known to date.”
The LOFAR radio telescope is a geographically widespread array of around 20,000 small radio antennas in almost 50 countries. LOFAR’s total signal collection area can be up to 300,000 square meters (3.2 million square feet) depending on how the array is configured and used. All the collected signals are sent to a supercomputer for processing, but not in real time like other interferometers.
LOFAR’s observations have revealed some details that researchers have never seen before.
“We discovered the existence of numerous filaments within the halo emission that had not previously been seen.”
Andrea Botteon, lead author, Leiden University.
Like other galaxy clusters, Abell 2255 contains hundreds of galaxies. Galaxies span a vast area, spanning hundreds of light years, but are still gravitationally bonded. And there is more to the cluster than just galaxies.
The cluster also has a vast magnetic field and particles that move at relativistic speeds. When these particles interact with the magnetic field, they emit radiation in the radio band. LOFAR tunes in to those broadcasts.
Astrophysicists call these emissions a radio halo because they are spherical and smooth. Scientists think that halos are created when two galaxy clusters collide and the emissions come from the central region of the collision. That is the most accepted hypothesis, anyway, although there is still some uncertainty and some unknowns.
But the Abell 2255 halo is different. It lacks the smoothness of other halos radii.
In a press release, lead author Botteon said: “We discovered the existence of numerous filaments within the halo emission that had not been seen before. This was made possible by LOFAR, which has much more sensitivity and angular resolution. higher than the radio telescopes that have observed galaxy clusters in the past, and also because the discovered filaments emit most of their radiation at long radio wavelengths, precisely those detected by LOFAR Antennas.
This new study not only used LOFAR observations. They also used observations from another radio telescope, the Westerbork Synthesis Radio Telescope (WSRT). A comparison of images from both domains shows how powerful LOFAR is and the new details he discovered in Abell 2255.
The researchers already knew that Abell 2255 defies the trend for smooth, spherical radius halos. But this work only emphasizes Abell 2255’s unusual emission morphology. In their article, the authors write: “The new LOFAR data adds more complexity to our A2255 image, where large numbers of structures at various scales are embedded within the central diffuse emission “.
So what’s unique about Abell 2255 that the filamentary nature of its radio emission creates, unlike the smooth, spherical emissions of other galaxy clusters?
All radio halos come from the turbulence generated in the group gas by the merging groups. That is the hypothesis, anyway. These new observations may shed some light on the whole process.
“The filaments discovered by LOFAR could form exactly as a consequence of these turbulent movements,” says Gianfranco Brunetti of INAF-Bologna (Italy) and second author of the study. “Another possibility we are considering is that the filaments originate from the interaction between galaxies, which move at speeds of many hundreds of km / s within the cluster and the plasma that produces the radio emission from the halo.”
“The filamentary nature of the emission shows the importance of turbulent magnetic fields, as the emission bands are likely to follow the strands of the magnetic fields,” adds team member Marcus Brüggen of the University of Hamburg, Germany.
The research team thinks that some of the radio functions do not come from the center of the group. Some of them come from more distant regions of Abell 2255. And only a radio telescope like LOFAR can help untangle that.
Emissions from distant regions, rather than the cluster center, have their own story to tell.
According to astrophysicists, these emissions trace shock waves that propagate outward over great distances. Shock waves can accelerate energetic particles and can amplify magnetic fields. In the outer regions where these emissions come from, the hot intergalactic gas emits only weak radiation. So weak that instruments that perceive gamma rays and X-rays cannot really see them. But LOFAR is ideal to observe them.
And these detailed LOFAR observations are posing another question for astrophysicists: Do these emissions track the cosmic network connecting the galaxy clusters?
“To study how far the radio broadcast extends in the group, in recent months LOFAR has carried out an even deeper observation of Abell 2255,” says co-author Reinout van Weeren of Leiden University, The Netherlands. “One of the goals is to understand if the radio emission extends beyond Abell 2255 as well, tracing the gigantic cosmic network that connects the galaxy clusters in the Universe.”
But that question will have to wait for future studies to be addressed. And LOFAR probably also has a role to play in those consultations.
As the authors write in the conclusion of their article, “The analysis of
Other features in the system, such as the emission extended over a long distance from the center of the cluster, will be carried out in future works that will exploit deep (75 hr) and pointed LOFAR observations of the cluster. “
