Observations by the East Asian VLBI Network have revealed periodic motions in the jet emanating from the center of the elliptical galaxy M87−specifically, a precessional motion with a cycle of approximately 11 years and a lateral wobble with a cycle of about 0.9 years. An international research team from Kogakuin University, the National Astronomical Observatory of Japan (NAOJ), Bunkyo University, the Korea Astronomy and Space Science Institute (KASI), Central China Normal University, Nagoya City University, and Kyung Hee University hypothesized that these periodicities could be caused by the orbital motion of a second black hole revolving around the supermassive black hole at the center of M87. They theoretically derived the possible mass range of this hypothetical secondary black hole. Recently, the NANOGrav collaboration suggested that gravitational waves emitted by supermassive black hole binaries may have been detected as a “gravitational wave background” permeating the universe. Motivated by this, the research team focused on M87 as a promising candidate to explore this phenomenon. Their findings offer important guidance for future observational strategies aimed at directly testing the existence of supermassive black hole binaries.