Using NASA’s Chandra X-ray Observatory, ESA’s XMM-Newton and three radio telescopes (the Giant Metrewave Radio Telescope, the Low Frequency Array, and the Karl G. Jansky Very Large Array), astronomers have observed the huge galaxy cluster merger Abell 2256.
This composite image shows at least three galaxy clusters colliding in a jumbled scene. The resulting giant galaxy cluster, known as Abell 2256, resembles a grainy, pixilated, sky blue cloud topped with licks of flaming red hair. The cloud is adorned with red shapes and streaks, and set against a black background heavily dotted with colorful specks. The image combines X-ray, radio, optical, and infrared data. Image credit: NASA / CXC / University of Bolonga / Rajpurohit et al. / ESA / XMM-Newton / LOFAR / ASTRON / NCRA / TIFR / GMRT / NSF / NRAO / VLA / Pan-STARRS.
Galaxy clusters contain thousands of galaxies of all ages, shapes and sizes.
Typically, these structures have a mass of about one million billion times the mass of the Sun.
At one point in time they were believed to be the largest structures in the Universe — until they were usurped in the 1980s by the discovery of superclusters.
However, clusters do have one thing to cling on to; superclusters are not held together by gravity, so galaxy clusters still retain the title of the biggest structures in the Universe bound by gravity.
Collisions and mergers are the primary ways galaxy clusters grow, and can cause them to act as giant particle accelerators.
“Galaxy clusters contain enormous reservoirs of superheated gas, with temperatures of several million degrees Fahrenheit,” said University of Bologna astronomer Kamlesh Rajpurohit and colleagues.
“Only X-ray telescopes like Chandra and XMM can see this hot gas.”
The radio emission in Abell 2256, which is located 780 million light-years away in the constellation of Ursa Minor, arises from an even more complex set of sources.
“The first are the galaxies themselves, in which the radio signal is generated by particles blasting away in jets from supermassive black holes at their centers,” the astronomers said.
“These jets are either shooting into space in straight and narrow lines (those labeled ‘C’ and ‘I’ in the image) or slowed down as the jets interact with gas they are running into, creating complex shapes and filaments (‘A,’ ‘B,’ and ‘F’).”
“Source F contains three sources, all created by a black hole in a galaxy aligning with the left-most source of this trio.”
“Radio waves are also coming from huge filamentary structures (labeled ‘relic’), mostly located to the north of the radio-emitting galaxies, likely generated when the collision created shock waves and accelerated particles in the gas across over two million light-years.”
“Finally, there is a ‘halo’ of radio emission located near the center of the collision,” they added.
“Because this halo overlaps with the X-ray emission and is dimmer than the filamentary structure and the galaxies, another radio image has been produced to emphasize the faint radio emission.”
According to the team, the halo emission may be caused by the reacceleration of particles by rapid changes in the temperature and density of the gas as the collision and merging of the clusters proceed.
“This model, however, is unable to explain all the features of the radio data, highlighting the need for more theoretical study of this and similar objects,” the authors said.
Their findings apepar in two papers in the Astrophysical Journal and the journal Astronomy & Astrophysics.
K. Rajpurohit et al. 2022. Deep Low-frequency Radio Observations of A2256. I. The Filamentary Radio Relic. ApJ 927, 80; doi: 10.3847/1538-4357/ac4708
K. Rajpurohit et al. 2022. Deep low-frequency radio observations of Abell 2256. II. The Ultra-Steep Spectrum Radio Halo. A&A 669, A1; doi: 10.1051/0004-6361/202244925
Source : Breaking Science News