An article published in “The Astrophysical Journal” reports the confirmation of three pairs of supermassive black holes in close proximity to the point that we will see them merge in a future that is near from an astronomical point of view. A team of researchers led by Dr. John Silverman of the Kavli Institute for the Physics and Mathematics of the Universe used three observatories on Mount Maunakea in Hawaii: the Subaru Telescope, the Keck Observatory, and the Gemini Observatory to examine a huge amount of quasars in search of traces of a dual center, and among 421 candidates they confirmed three. These are rare cases, to the point that the estimate is that 0.3% of quasars are dual with two supermassive black holes on a collision course.
Quasars are the brightest objects in the universe. Their extremely intense electromagnetic emissions allow them to be observed even billions of light-years away. However, those emissions make it difficult to detect activity such as a galaxy merger, as the light from the stars of the two merging galaxies is too dim compared to that of the active galactic nucleus to be visible. Even the activity of two quasars is difficult to resolve when the two supermassive black holes that power them are close. The combination of suitable instruments can overcome these obstacles.
Galaxy mergers are common, but astronomer John Silverman’s team calculated that dual quasars with the two black holes on a collision course make up just 0.3% of the total. Those processes are important in the evolution of galaxies and are among the most important studies for the astronomers who deal with them, so the researchers looked for ways to recognize dual quasars.
The researchers used observations made with the Hyper Suprime-Cam (HSC) mounted on the Subaru telescope to observe the 34,476 quasars in the Sloan Digital Sky Survey. Initially, the research concerned the type of galaxies hosting quasars, but observations showed traces of two optical sources at the center of some of them that suggested their dual nature.
421 candidates were found among the quasars, but it was necessary to verify that there weren’t external sources that altered the images. John Silverman’s team used the Keck Observatory’s Low Resolution Imaging Spectrometer (LRIS) and the Gemini Observatory’s Near-Infrared Integral Field Spectrometer to examine the candidates. The result was the confirmation of three dual quasars.
The image (Courtesy Silverman et al. Shows SDSS J141637.44+003352.2, one of the confirmed dual quasars, approximately 4.6 billion light-years away. The two quasars are approximately 13,000 light-years apart. The bottom panels show the optical spectroscopies.
The combination of the use of various instruments made it possible to identify objects that weren’t easy to observe in detail due to the combination of their distance and intense brightness. This will help to better study the evolution of those quasars and the galaxies that host them. The pairs of supermassive black holes will merge, and this will also generate gravitational waves.
