Introduction
A recent study led by a team from Keio University, including doctoral student Tatsuya Kotani and professor Tomoharu Oka, has provided groundbreaking insights into the temperature of the universe approximately 7 billion years ago. Utilizing data from the Atacama Large Millimeter/submillimeter Array (ALMA), the researchers have determined the temperature of the cosmic microwave background (CMB) at a redshift of z = 0.89, revealing a value of 5.13 ± 0.06 Kelvin. This measurement is nearly double the current CMB temperature of 2.7 K and marks a significant advancement in understanding the thermal history of the universe.
Filling a Gap in the Universe’s Thermal Timeline
The cosmic microwave background represents the residual radiation from the Big Bang, having cooled over time as the universe expanded. Accurate measurements of the CMB temperature at various epochs are crucial for validating standard cosmological models. While previous research has successfully established CMB temperatures for both the early universe and the present day, there has been a lack of precise data for intermediate epochs, particularly at a redshift of approximately 0.89. The findings published in The Astrophysical Journal by Kotani and his team provide essential data that supports the expected temperature evolution throughout cosmic history.
Molecular Absorption Lines to Track Ancient Heat
To ascertain the temperature from this distant epoch, the research team focused on light emitted by the quasar PKS1830–211, which is situated far beyond our Milky Way galaxy. As this light passed through a foreground galaxy, it interacted with cold gas containing hydrogen cyanide (HCN), which absorbed certain frequencies of light. These absorption lines function as indicators of the CMB temperature from that time period. The team specifically analyzed four rotational transitions of HCN to derive the excitation temperature profiles, taking into account various uncertainties such as the continuum covering factor and the non-uniform distribution of the absorbing gas. Employing a Monte Carlo simulation approach, they were able to refine their measurements with a high degree of accuracy.
Confirming the Big Bang Model with Unmatched Precision
The temperature measurement of 5.13 K aligns closely with the theoretical predictions of the Big Bang model, which posits that the CMB temperature scales with the factor (1 + z). The expected temperature at redshift 0.89 is 5.14 K, making the results from Kotani’s team remarkably consistent with theoretical expectations. This new measurement is noted for its precision, reducing the uncertainty of previous estimates significantly. The researchers addressed common issues seen in past studies by employing a rigorous analysis method that included a detailed uncertainty model, thus enhancing the reliability of their findings.
Groundwork for Deeper Exploration into Cosmic Evolution
Although this study focuses on a specific redshift, its implications extend far beyond this singular measurement. The methodology established for accurately measuring historical temperatures of the universe paves the way for future research into cosmic evolution. The potential for future observations targeting quasars at even higher redshifts could further enhance our understanding. Upcoming instruments, such as the Square Kilometre Array (SKA) and the next-generation Very Large Array (ngVLA), are anticipated to provide improved sensitivity and broaden the range of CMB measurements.
Conclusion
The precise measurement of the CMB temperature at z = 0.89 not only reinforces fundamental cosmological theories but also serves as a critical benchmark for future explorations of the universe's thermal history. This study exemplifies the ongoing efforts to deepen our understanding of cosmic evolution and the physical laws governing the universe, suggesting that as the universe expands, it cools in a manner consistent with established theoretical frameworks.