“Baffling” -Radio Galaxies Would Take Several Million Years to Cross at Speed of Light


Radio Galaxy


“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 of the Center for Astrophysics and Planetary Science at University of Kent, about the biggest objects in the universe, so-called giant radio galaxies, some 22 times the size of the Milky Way, that stretch across a large part of the Universe.

The biggest objects in the universe

In 2019, 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. Conventional wisdom says 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. At that time, galaxies were growing and supermassive black holes were violently expelling enormous amounts of gas and energy. This matter accumulated into pairs of reservoirs, which formed these enormous objects, some twenty-two times the size of the Milky Way, that even moving at the speed of light, it would take several million years to cross.

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.

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Powered by twin jets 

Radio galaxies have long been known to be powered by twin jets which coming directly from the nucleus and going to the lobes, inflating their lobes and creating 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.

‘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.’

Avi Shporer, Research Scientist, MIT Kavli Institute for Astrophysics and Space Research via University of Kent. Avi was formerly a NASA Sagan Fellow at the Jet Propulsion Laboratory (JPL).

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



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