A recent study published in the journal Physical Review letters suggests that the overwhelmed phase transition of the first kind in the early Universe can explain the signals of gravitational waves observed using pulsar arrays (PTAS). These gravitational waves are ripples in space-time caused by powerful cosmic events, such as the merger of black holes. For the first time, they were discovered by the Ligo Observatory in 2016, confirming the predictions of Albert Einstein made almost a century before.
Recently, the Nanograv Observatory (North American Nanohertz Observatory for Gravitational Waves) recorded the presence of Stochastic Background of gravitational waves (Stochastic Gravitational Wave Background, SGWB) using pulsar arrays. SGWB differs in that it is isotropic, spreading evenly in all directions, indicating a uniform distribution of its sources throughout the universe. This discovery prompted scientists from the research group, whose work is described in the article in Physical Review Letters, to study the possible origin of these waves.
The first conclusions and assumptions
Professor Yunchen Wu, one of the co-authors of the study, noted that the study of the early Universe is limited by the period after the formation of the cosmic microwave background (CMB). “Gravitational waves are currently the only method of studying a very early universe,” he said. Professor Lay added that in recent years, heavily overlapped phase transitions of the first kind are widely considered as a possible SGWB source. “The new signal observed by PTAS may indicate such a transition, which is a very exciting opportunity,” added Professor Peter Atron.
The essence of phase transitions of the first kind
The first kind phase transitions are transitions in which the system passes between different phases sharply and unevenly. An example of such a transition is the freezing of water. “Water can remain in a liquid state even at a temperature below the freezing point, and then with slight agitation suddenly turns into ice. The key feature is that the system remains in this phase for a long time at a temperature below the transition,” explained Professor Wu.
Electroweak interaction is a unified