The lack of detected gravitational waves coming from supermassive objects like galaxies can be attributed to several reasons:
Signal Strength: Gravitational waves from supermassive objects produce weaker signals compared to compact binary systems, which are the primary sources of gravitational wave detections thus far. Supermassive black holes at the centers of galaxies, for example, generate continuous gravitational waves due to their asymmetrical motion. However, these signals are relatively weak and challenging to detect with the current sensitivity of gravitational wave detectors.
Frequency Range: The frequency range of gravitational waves emitted by supermassive objects is lower compared to those produced by binary systems. The sensitivity of gravitational wave detectors, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo detector, is optimized for detecting higher-frequency gravitational waves. Supermassive objects generate gravitational waves at lower frequencies, requiring detectors with lower-frequency sensitivity, such as the proposed Laser Interferometer Space Antenna (LISA), to have a better chance of detection.
Distance: Supermassive objects are typically located at significant distances from us, within galaxies millions or billions of light-years away. Gravitational waves become weaker as they propagate through space, and by the time they reach us, their signal strength is further diminished. This makes it challenging to detect gravitational waves originating from supermassive objects due to their weakened state by the time they reach Earth.
Instrumentation: The technology and sensitivity of gravitational wave detectors have significantly advanced over the past few decades. The first direct detection of gravitational waves was made in 2015, and since then, the detectors have undergone improvements. With each upgrade, the sensitivity and range of detection have improved, increasing the chances of detecting weaker signals from supermassive objects in the future.
It's important to note that efforts are underway to detect gravitational waves from supermassive objects. Future missions like LISA, a space-based gravitational wave observatory planned for launch in the 2030s, are specifically designed to detect lower-frequency gravitational waves, including those from supermassive black holes. These missions, along with advancements in technology and analysis techniques, may enhance our ability to detect gravitational waves from supermassive objects in the coming years.