Scientists from the University of Bath (UK) have developed a new method for locating extremely rare extragalactic objects – quasars.
Astrophysicists hope their method of detecting changing-look quasars (CLQs) will bring scientists one step closer to solving one of the universe’s greatest mysteries. Namely, how supermassive black holes grow. Quasars are thought to be responsible for regulating the growth of supermassive black holes and their host galaxies.
A quasar is a region of impressive luminosity in the center of the galaxy, fed by a supermassive black hole. It is the largest type of black hole, with a mass billions of times the mass of our Sun. There is also a supermassive black hole in the center of the Milky Way. Quasars are formed when gaseous matter is pulled by gravity towards a supermassive black hole. When the gas approaches it, it forms an acreation disc. Energy is released from it in the form of electromagnetic radiation, and it is this that creates the luminosity of the quasar.
Quasars that change in appearance quickly switch between high and low luminosity, and scientists have yet to figure out why. When the brightness decreases, the quasar becomes too dim to be seen against the backdrop of its parent galaxy. That is why it is difficult for scientists to find either him or the supermassive black hole with which he is associated.
The new detection method will allow researchers to find quasars that are undergoing drastic changes in luminosity, and, therefore, to conduct a more complete census of supermassive black holes. The next step will be to study the causes of luminosity switching to give scientists a better understanding of the growth of supermassive black holes. In turn, this will help scientists trace the chain of events that lead to the growth of galaxies. It is the release of energy from supermassive black holes that can influence their fate.
Previous attempts to identify CLQ-type quasars relied on variability in a wide range of wavelengths – the method of photometric variability. The problem is that it transmits quasars with lower luminosity. Researchers at the University of Bath used spectroscopic data to assess changes in very small wavelength ranges. This allowed them to detect CLQ-type quasars, which were not detected by photometry. Using this technique, astrophysicists have discovered four changing quasars a million light-years from Earth. They were all too dim to be detected by photometry.