New survey finds 'Peter Pan' radio galaxies that may never grow up

New survey finds 'Peter Pan' radio galaxies that may never grow up
An artist’s impression of a galaxy within which lies a supermassive black hole. The black hole drives enormous outflows of plasma from the galaxy’s core which produce prodigious amounts of radio emission. In this image, the outflows travel toward the upper left and lower right. Credit: ESA/Hubble, L. Calçada (ESO)

A team of astronomers has doubled the number of known young, compact radio galaxies—galaxies powered by newly energized black holes. The improved tally will help astronomers understand the relationship between the size of these radio sources and their age, as well as the nature of the galaxy itself.

In particular, it will help astronomers understand why there are so many more young radio galaxies than old.

"We do not understand how radio galaxies evolve," says Joseph Callingham, a postdoctoral fellow from the Netherlands Institute for Radio Astronomy (ASTRON) and lead author on the paper describing the result.

"For a long time, we thought all evolved into . However, we have now found far too many small galaxies relative to the large ones. This suggests some never make it to the 'adult phase'."

In a survey of ninety thousand radio galaxies, the astronomers identified 1500 compact galaxies among them. The results are described in a paper published 20 February in the Astrophysical Journal.

"These compact galaxies used to be as rare as hen's teeth," says Prof. Bryan Gaensler, a co-author on the paper and Director of the Dunlap Institute for Astronomy & Astrophysics, University of Toronto. "But now we've been able to discover a huge number of new cases. This breakthrough will let us begin to study the overall properties of these unusual and important objects."

A radio galaxy is a galaxy that shines brightly at radio wavelengths. A super-massive black hole—typically with the mass of millions of Suns—powers this outpouring of energy.

Gas and dust fall into the black hole, releasing vast amounts of energy. The energy is focused into two jets of particles, travelling in opposite directions at nearly the speed of light. As the jets blast through the galaxy, each generates its own lobe or hot-spot of radiation as it interacts with the gas in the galaxy.

According to one model, compact radio sources are young because the jets have not had time to reach far beyond the central black hole. The hot-spots are relatively close together and we see them as compact sources. Over time, the jets reach farther out into the galaxy and even beyond its confines; the hot-spots are farther from each other, and we see a more extended, double-lobed source.

In this simple model, the overabundance of young, compact radio galaxies raises the question: why don't young, compact radio galaxies mature into old, extended radio ?

However, another model argues that the relationship between the age and observed size of a radio galaxy is not so straightforward. That's because a compact source may be compact, not because it's young, but because gas within the galaxy is dense enough to prevent the jets from extending far from the central black hole; i.e. it remains compact despite it's age.

"This study shows that it is possible a dense environment near the heart of the galaxy hinders and stops galaxy growth," says Callingham, who did much of the research as a PhD student with the Australian Centre for All-shy Astrophysics (CAASTRO).

The astronomers made the discovery using data gathered with the Murchison Wide-field Array (MWA), an interferometric radio telescope in the Western Australian outback. The discovery was possible because, unlike conventional radio telescopes that observe tiny patches of the sky at a time, the MWA sweeps large areas of the sky and is capable of observing across a broader range of wavelengths.

Explore further

Hotspots in an active galactic nucleus

More information: J. R. Callingham et al. Extragalactic Peaked-spectrum Radio Sources at Low Frequencies, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/836/2/174
Journal information: Astrophysical Journal

Citation: New survey finds 'Peter Pan' radio galaxies that may never grow up (2017, March 8) retrieved 14 October 2019 from
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Mar 08, 2017
"For a long time, we thought all small galaxies evolved into massive galaxies. However, we have now found far too many small galaxies relative to the large ones. This suggests some never make it to the 'adult phase'."

Suggests...only to the committed merger maniac.

Alternatively, star clusters with intermediate black hole cores eventually grow from within into larger and larger clusters, dispersing more and more stars radially outward therefrom, until the cluster can be instead classified as a small galaxy itself. For this model, it is only natural that many more clusters would exist than larger galaxies, since the original source of the clusters themselves is largely the larger galaxies themselves, from which they are born from the supermassive cores through ejection.

Mar 08, 2017
As we have already seen that very old galaxies are discovered at the greatest distances yet imaged and young galaxies are abundant nearby it does point to a universe much older than 14 billion years and in continual rolling evolution.

30 Years ago it was routinely claimed that old galaxies only existed nearby and young galaxies only existed at great distances, but Hubble's first deep field imaged two galaxies, both of the mature older types.

It was also assumed, as in the 1st edition of Hawking's 'A Brief History of Time', that the universe curved in on itself so there is no matter horizon; travel in any direction long enough and you return to your starting point. But by the 2nd edition he refuted the curved universe as the measured evidence does not support it, so the universe now has an infinite extent and so can not be smaller in the past. The Big Bang, then, is a local phenomena, not a universal one...and the evidence in support is stacking up...

Mar 09, 2017
@RobertKarlStonjek the universe now has an infinite extent and so can not be smaller in the past.

This is a misunderstanding of the nature of an expanding space, the best description I can find with a brief search can be found here: which says;

"...the overall size of the universe was infinitely big to begin with and continues to remain infinitely big as time goes on".

Mar 09, 2017
" Australian Centre for All-shy Astrophysics (CAASTRO)"

Heheh I wish some of the loons here were more shy with their "physics".

Apr 09, 2017
If the universe is infinite in extent (infinite & flat) then it can not have finite properties such as a finite age, a finite matter-energy content etc. The infinite universe modelled in the past was a curved universe, but no curvature has been discovered.

An infinite flat universe is not compatible with a Big Bang model that includes the entire universe occupying a small finite extension. All we can say is that the local universe is currently expanding and so must have been more compact in the past.

There is nothing to misunderstand here. In an infinite universe the distance between objects can also be infinite and so the time taken for these objects collide is also infinite regardless of their speed (including the speed of space-time expansion of contraction if we run the clock backwards

As for the link, I never said anything about the universe 'expanding into' anything. The matter horizon was traditionally solved by the curved universe model.

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