A team of astronomers has discovered new young and compact radio galaxies , doubling the number of them known until now. This will help to understand the relationship between these radio sources and their ages, as well as the nature of the galaxies themselves, as there are many more young radio galaxies than old ones. “At the moment we don’t understand how radio galaxies evolve,” explains Joseph Callingham of the Netherlands Institute for Radio Astronomy (ASTRON).
” We have long believed that all small galaxies became giant galaxies . However, we have found far too many small galaxies compared to large ones. This suggests that they may never reach adulthood.”
In a survey of 90,000 radio galaxies, astronomers identified 1,500 compacts among them. “These compact galaxies used to be very rare. But now we have been able to discover a large number of new cases. This will allow us to begin to study the global properties of these unusual and important objects,” according to Professor Bryan Gaensler of the University of Toronto
A radio galaxy is a galaxy that glows at radio wavelengths. A supermassive black hole, normally with a mass equivalent to millions of Suns, fuels its emission of energy . Gas and dust fall into the black hole, releasing enormous amounts of energy. The energy is located in two jets of particles that travel in opposite directions at almost the speed of light. As the jets pass through the galaxy, they each generate their own lobe or zone of radiation when they interact with galactic gas.
A proposed model to explain why compact radio galaxies do not evolve to large radio galaxies indicates that the gas in the galaxy is so dense that it prevents the jets from straying too far from the central black hole. That is, it remains compact despite its age. “This study shows that it is possible for a dense environment near the heart of the galaxy to stunt its growth,” says Callingham.
Credit: ESA / Hubble, L. Calçada (ESO)
