“When we look far into the distant universe, we are observing objects way in the past – when they were young. We expected to find that these distant giants would appear as a comparatively small pair of vague lobes. To our surprise, we found that these giants still appear enormous even though they are so far away,” said astrophysicist Michael D. Smith at University of Kent. Conventional wisdom tells us that large objects appear smaller as they get farther from us, but this fundamental law of classical physics is reversed when we observe the distant universe.
Formation of Giant Radio Galaxies
Astrophysicists at the University of Kent simulated the development of the biggest objects in the universe to help explain how galaxies and other cosmic bodies were formed. By looking at the distant universe, it is possible to observe it in a past state, when it was still at a formative stage. At that time, galaxies were growing and supermassive black holes were violently expelling enormous amounts of gas and energy. The massive accretion disks around the supermassive black holes launched collimated jets of relativistic electrons and ions, creating pairs of bipolar lobes of intense radio emission. This matter accumulated into pairs of reservoirs, which formed the biggest objects in the universe, so-called giant radio galaxies. These giant radio galaxies stretch across a large part of the Universe. Even moving at the speed of light, it would take several million years to cross one.
Appeared Larger, Not Smaller
Smith, and student Justin Donohoe collaborated on the research. They expected to find that as they simulated objects farther into the distant universe, they would appear smaller, but in fact they found the opposite.
Radio galaxies have long been known to be powered by twin jets which inflate their lobes and create giant cavities. The team performed simulations using the Forge supercomputer, generating three-dimensional hydrodynamics that recreated the effects of these jets. They then compared the resulting images to observations of the distant galaxies. Differences were assessed using a new classification index, the Limb Brightening Index (LB Index), which measures changes to the orientation and size of the objects.
Hot Spots at the Outer Edges
‘We already know that once you are far enough away, the Universe acts like a magnifying glass and objects start to increase in size in the sky,” said Smith. “Because of the distance, the objects we observed are extremely faint, which means we can only see the brightest parts of them, the hot spots. These hot spots occur at the outer edges of the radio galaxy and so they appear to be larger than ever, confounding our initial expectations.’
The Last Word
In an email to The Daily Galaxy, Michael Smith, author of The Origin of Stars and Director, Centre for Astrophysics and Planetary Science at The University of Kent wrote:
“Radio galaxies are powered by supermassive black holes. The energy is transmitted through supersonic jets which channel the energy from the nucleus of a galaxy out to distances far beyond the normal bounds of a galaxy. If the jets remain intact, they are only stopped by a direct impact with the gas between the galaxies. The impact regions are detected as very intense regions of radio emission called hot spots.”
The composite NASA image of the intense radio lobes emitted from the supermassive black hole in the middle of the Galaxy Cygnus A is shown at the top of the page. X-ray is shown in blue, radio is red and visible light is yellow.
Image credit: Chandra Observatory image at the top of the page shows the nearby radio galaxy Centaurus A. X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Radio: NSF/NRAO/AUI/VLA