Researchers at the Center of Competence in Dark Matter Physics and the University of Western Australia have created a new type of gravitational wave detector. The instrument recently recorded two rare events that could be signals of dark matter. An alternative explanation: these are signals from primordial black holes or even the manifestation of external interference.
We add that these signals cannot be caught by most of the existing gravitational wave detectors. They have never registered before. The scientists published a report on the results obtained in the scientific journal Physical Review Letters.
Gravitational waves are changes in the gravitational field that propagate through space in the form of waves on the canvas of space-time. They appear due to the movement of massive objects, for example, black holes.
The existence of gravitational waves was predicted by general relativity over a century ago. Physicists managed to detect these very weak disturbances with the help of special ultrasensitive detectors only in 2015, for which they received the Nobel Prize in Physics in 2017.
The gravitational waves recorded in 2015 were a signal from a massive black hole created by the merger of two smaller black holes.
Since 2015, detectors have repeatedly recorded signals from gravitational waves. However, according to Australian scientists (the authors of the new detector), the current generation of gravitational wave detectors is capable of detecting only low-frequency waves. Methods for detecting high-frequency gravitational waves remain unexplored and extremely difficult in astrophysics, according to a press release from the University of Western Australia.
Just to register high-frequency gravitational waves, a detector was created at the Competence Center in the field of dark matter physics. The detector is a resonator of bulk acoustic waves based on a quartz crystal - a quartz generator.
A quartz disc vibrates at a high frequency when acoustic waves pass through it. A quartz crystal with piezoelectric properties converts acoustic vibrations into an electrical charge. This charge is taken by two electrically conductive plates pressed against a quartz disc. They transmit an electrical signal to a superconducting quantum interference device, which amplifies the signal so that a detector can pick it up.
This entire structure is placed inside several radiation shields that protect it from interference in the form of external electromagnetic radiation, and is cooled to almost absolute zero. Such a detector can detect signals from gravitational waves with frequencies in the megahertz range.
Australian scientists tested their detector for 153 days. This was the total duration of the two sessions of the experiment that the researchers conducted in May and November 2019.
During these sessions, a new gravitational wave detector recorded two rare high-frequency events. Signals with a frequency of about five megahertz were recorded on May 12 and November 27.
Where these signals came from is still unknown, but scientists suggest that dark matter candidates - particles that theorists call WIMPs - interacted with their detector in this way.
However, it is possible that the signal received by the detector is not a gravitational wave at all, but a manifestation of the presence of charged particles or the accumulation of mechanical stress in the detector, or a meteorite event, or an internal atomic process of the crystal, the authors of the detector say.
Despite the lack of certainty about the signals received, scientists from the Center of Competence in Dark Matter Physics and the University of Western Australia are optimistic.
"In this work, we have demonstrated for the first time that these devices can be used as highly sensitive gravitational wave detectors," says Michael Tobar of the University of Western Australia. high frequency gravitational waves at these frequencies, and we have plans to expand the capabilities of our detector to even higher frequencies that have not been seen in any other experiment before."
Scientists emphasize that the development of their applied technology could potentially provide the first detection of gravitational waves at such high frequencies.
In the next experiment, the researchers are going to use the same quartz detector together with the muon detector of cosmic particles.