In a groundbreaking achievement, China's Einstein Probe (EP) astronomical satellite has, for the first time in human history, detected soft X-ray signals from an explosion in the early universe. This monumental discovery opens a new window into the young cosmos, providing unprecedented insights into the universe's formative years.
Published recently in the journal Nature Astronomy, the findings stem from observations made on March 15, 2024. On that day, the Wide-field X-ray Telescope aboard the EP satellite captured a faint pulse of soft X-ray emissions from a burst event designated EP240315a. Exhibiting rapid brightness fluctuations, the burst persisted for over 17 minutes before gradually fading away.
Subsequent international observations confirmed that EP240315a originated from the distant early universe. Remarkably, the signal from this explosion took 12.5 billion years to reach Earth, meaning it occurred when the universe was only 10 percent of its current age.
\"This is just the beginning,\" said Yuan Weimin, principal investigator of the EP mission and a researcher at the National Astronomical Observatories of the Chinese Academy of Sciences (CAS). \"The discovery showcases the remarkable potential of the EP in detecting cosmic explosions from the early universe.\"
Scientists classify X-rays based on their energy levels: soft X-rays have lower energy, while hard X-rays possess higher energy. The detection of soft X-ray signals from such a distant explosion is unprecedented, marking a significant milestone in astronomical research.
The discovery of EP240315a also sparked international collaboration. The EP team partnered with Dr. Roberto Ricci from the University of Rome Tor Vergata in Italy. Dr. Ricci initiated long-term radio band monitoring of this gamma-ray burst (GRB) using the Australia Telescope Compact Array. His three-month radio observations confirmed that EP240315a's energy output aligns with the characteristics of a GRB, specifically designated as GRB240315C.
\"These results show that a substantial fraction of fast X-ray transients may be associated with GRBs,\" said Dr. Ricci. \"Sensitive X-ray monitors, such as the EP, can pinpoint them in the distant universe. Combining the power of X-ray and radio observations hands us a new way to explore these ancient explosions even without detecting their gamma rays.\"
However, mysteries remain. Typically, in GRB events, X-rays appear tens of seconds before gamma rays. In the case of EP240315a, the X-rays arrived more than six minutes earlier—an anomaly that has never been observed before.
\"Such a long delay challenges our understanding,\" said Sun Hui, an associate researcher at the National Astronomical Observatories of CAS and one of the study's co-first authors. Gao He, a co-corresponding author from Beijing Normal University, added that this discovery offers a fresh perspective and could lead to a re-evaluation of existing GRB models.
GRBs are among the most powerful explosive phenomena known in the universe, typically originating from the explosion of massive stars. The ability to detect and study such events from the early universe not only enriches our understanding of cosmic evolution but also demonstrates the cutting-edge capabilities of China's astronomical instruments.
The success of the EP satellite in capturing EP240315a heralds a new era in high-energy astrophysics. As scientists continue to analyze this event and others like it, we can anticipate further breakthroughs that will illuminate the mysteries of the cosmos.
Reference(s):
China's astronomical satellite detected explosion from early universe
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