Astronomers have witnessed a handful of galaxies undergoing sudden, rapid transformations from weak, lethargic states to ferociously bright quasars. The incredibly fast transitions, occurring over a few months, could be caused by an entirely new type of black hole activity in the center of these galaxies.
The study, published in the Astrophysical Journal on Sept. 18, details the observation of six low-ionization nuclear emission-line region (LINER) galaxies caught "turning on" within a period of nine months. LINER galaxies are a common fixture in the cosmos and astronomers have long debated how they form and where their light is coming from. Some believe a weak supermassive black hole at the center gives them their unique properties, but others hypothesize star formation outside the galactic center is the reason for their luminosity.
Using the Zwicky Transient Facility (ZTF), a new camera installed at the Palomar Observatory in California in 2018, the team of researchers examined a number of LINER galaxies. The ZTF is able to detect cosmic phenomena that rapidly change in brightness, as well as objects like asteroids, giving astronomers another way to study mysterious LINER galaxies and any aberrant transitions. In addition, the team followed up their observations by studying data from the Hubble, Spitzer and Swift telescopes and a handful of US-based observatories.
Poring over the data, they discovered the LINER galaxies underwent transitions from their "wimpy" state to exceptionally energetic galaxies, known as quasars, much faster than expected.
"Theory suggests that a quasar should take thousands of years to turn on, but these observations suggest that it can happen very quickly. It tells us that the theory is all wrong," said Suvi Gezari, an associate professor of astronomy at the University of Maryland and co-author of the research paper, in a statement.
Quasars are so energetic and bright because of supermassive black holes at their center. The black holes can be billions of times more massive than the sun and they are voracious beasts, attracting gas, dust and debris to circle them with their huge gravitational pull. It's this field of circling debris and the debris falling into the black hole that makes quasars so extremely bright. Some can be thousands of times brighter than our home galaxy, the Milky Way.
But why did the LINER galaxies spotted by the team switch so dramatically from wimpy to wow? That is a puzzle still to be solved and why the researchers suggest this is an all-new type of black hole activity. However, the data helps confirm that LINER galaxies can host supermassive black holes.
In addition, the team noted only gas and debris closest to the galactic center in the studied LINER galaxies was lighting up, whereas other quasars have demonstrated brightness at far greater distances from their center.
Perhaps, they hypothesize, we've caught the moments before and after a quasar's birth. It provides astronomers with an exciting new way to map galactic evolution.
"It's surprising that any galaxy can change its look on human time scales," said Sara Frederick, University of Maryland graduate student and first author on the paper. "These changes are taking place much more quickly than we can explain with current quasar theory."