A team led by Professor Xiaofeng Wang from the Department of Physics at Tsinghua University has discovered a rare blue large-amplitude pulsator (BLAP) using the Tsinghua-Ma Huateng Sky Survey Telescope (TMTS). This star, dubbed TMTS-BLAP-1, is located approximately 8,800 light-years from Earth. It exhibits a luminosity 110 times that of the Sun and a surface temperature six times higher. The detailed observations and analysis of TMTS-BLAP-1 reveal that it is a 0.7 solar mass hot subdwarf, a type of star where the hydrogen envelope has been stripped away, leaving a dense, hot core. This finding is significant as it provides a key clue to understanding the physical mechanisms behind BLAPs, which are a class of rare, high-temperature pulsating stars with unusually large amplitudes and extremely short periods. BLAPs were first reported in 2017 by the Optical Gravitational Lensing Experiment (OGLE), which monitors about a billion stars. Only 14 stars have been confirmed as BLAPs since then. These stars are characterized by their surface temperatures, which are 5 to 7 times hotter than the Sun, and their ability to change brightness by more than 20% in just half an hour due to their rapid expansion and contraction. The scarcity of BLAPs and the limited observational data have led to significant debates among astronomers regarding their physical origins. Two primary theories exist: one suggests that BLAPs are pre-white dwarfs with helium cores that have stopped burning and will eventually evolve into helium-core white dwarfs; the other posits that BLAPs are hot subdwarfs in binary systems, where the hydrogen envelope has been stripped away, and they are currently burning helium in their cores. The TMTS is a uniquely designed multi-barrel optical survey telescope funded by the Ma Huateng Foundation and supported by Tsinghua University's Physics Talent Class. It is capable of conducting high-frequency observations of the night sky, with a cadence of less than a minute, which has significantly expanded the detection of short-timescale variable celestial objects. Over a two-year period, TMTS has collected short-timescale light curve data for over 10 million stars, including TMTS-BLAP-1, which has a pulsation period of just 18.9 minutes. This makes it the BLAP with the shortest known pulsation period. To further investigate TMTS-BLAP-1, the team conducted continuous spectroscopic observations using the 10-meter Keck Telescope in Hawaii. These observations revealed that TMTS-BLAP-1 shares similarities with BLAPs that have low surface gravity and helium-rich envelopes, leading the team to classify it as a low-gravity BLAP. By analyzing long-term optical monitoring data from international surveys, the researchers discovered that TMTS-BLAP-1's pulsation period is increasing at a rate of 2.5 seconds per millennium. This finding challenges the prevailing models of BLAPs and suggests that the star is in a rapid evolutionary phase known as the "Hertzsprung Gap," where it is undergoing the ignition of helium in its shell. The Hertzsprung-Russell diagram and the period change rate-period diagram were used to support these findings. These diagrams show the evolutionary stages of hot subdwarfs, including the central helium burning phase and the shell helium burning phase. The data for TMTS-BLAP-1 aligns well with the shell helium burning model, which had previously been overlooked in the context of BLAPs. This alignment provides strong evidence that TMTS-BLAP-1 is a hot subdwarf currently in the process of igniting helium in its shell, a phase that is crucial for understanding the evolution of stars and the potential progenitors of Type Ia supernovae. The research, titled "An 18.9-minute Blue Large-Amplitude Pulsator Crossing the ‘Hertzsprung Gap’ of Hot Subdwarfs," was published in the journal *Nature Astronomy* on September 29. Professor Xiaofeng Wang is the corresponding author, and Dr. Jie Lin, a postdoctoral researcher at Tsinghua University since 2019, is the first author. The study also involved significant contributions from researchers such as Chengyuan Wu and Tao Wu from the Yunnan Observatories of the Chinese Academy of Sciences, Hiran Xu from the Australian National University, Petr Nemeth from the Astronomical Institute of the Czech Academy of Sciences, and the team led by Professor Alex Filippenko from the University of California, Berkeley. This discovery not only sheds light on the physical mechanisms behind BLAPs but also has implications for the broader field of stellar astrophysics, particularly in refining theories of stellar pulsation and evolution. Additionally, understanding the nature of BLAPs could provide insights into the origins of Type Ia supernovae, which are important for measuring cosmic distances and studying the expansion of the universe. The project received funding from the National Natural Science Foundation of China, the Ma Huateng Foundation, the Beijing Academy of Science and Technology "Beijing Scholar" project, and the Xplorer Prize. For more details, the full paper can be accessed at: https://www.nature.com/articles/s41550-022-01783-z.