The nearest black hole to Earth,Sagittarius A^(*)(Sgr A^(*)),with its intense gravitational field,provides a unique opportunity to explore black hole mysteries.Over the past few decades,monitoring of the S2 star has p...The nearest black hole to Earth,Sagittarius A^(*)(Sgr A^(*)),with its intense gravitational field,provides a unique opportunity to explore black hole mysteries.Over the past few decades,monitoring of the S2 star has provided extensive valuable data that can be utilized to examine various gravity theories and black hole paradigms.This paper focuses on the most intriguing objects in astronomy,spinning black holes,and investigates the effects of spin on orbital motion.By applying the Markov Chain Monte Carlo algorithm to publicly available observational data of the S2 star,our findings indicate that current data fail to constrain the spin of Sgr A^(*).Simulated stars with smaller semi-major axes reveal that the direction of Lense-Thirring precession aligns with the spin direction of Sgr A^(*).Additionally,by incorporating the cosmological constant,which accounts for the expansion of the universe,into our analysis,we establish an upper limit of Λ■7.3×10^(-34) km^(-2) on the cosmological constant at the lo confidence level.Future long-term monitoring of S-cluster stars,combined with enhanced observational precision,may enable the determination of the spin of Sgr A^(*)and further tighten the bound on the cosmological constant.展开更多
Numerical simulation is an important tool that is helpful for us to understand the process of structure formation in the universe. However, many simulation results of cold dark matter （CDM） halos on a small scale ar...Numerical simulation is an important tool that is helpful for us to understand the process of structure formation in the universe. However, many simulation results of cold dark matter （CDM） halos on a small scale are inconsistent with observations： the central density profile is too cuspy and there are too many substructures, Here we point out that both the problems may be connected with a hitherto unrecognized bias in the simulated halos. Although CDM halos in nature and in simulation are both virialized systems of collisionless CDM particles, gravitational encounter cannot be neglected in the simulated halos because they contain many fewer particles. We demonstrate this by two numerical experiments, showing that there is a difference on the microcosmic scale between the natural and simulated halos. The simulated halo is more akin to globular clusters where gravitational encounter is known to lead to such drastic phenomena as core collapse. Such an artificial core collapse process appears to link the two problems together in the bottom-up scenario of structure formation in the ACDM universe. The discovery of this bias also has implications on the applicability of the Jeans theorem in galactic dynamics.展开更多
基金Supported by the National Natural Science Foundation of China(12275034,12347101)。
文摘The nearest black hole to Earth,Sagittarius A^(*)(Sgr A^(*)),with its intense gravitational field,provides a unique opportunity to explore black hole mysteries.Over the past few decades,monitoring of the S2 star has provided extensive valuable data that can be utilized to examine various gravity theories and black hole paradigms.This paper focuses on the most intriguing objects in astronomy,spinning black holes,and investigates the effects of spin on orbital motion.By applying the Markov Chain Monte Carlo algorithm to publicly available observational data of the S2 star,our findings indicate that current data fail to constrain the spin of Sgr A^(*).Simulated stars with smaller semi-major axes reveal that the direction of Lense-Thirring precession aligns with the spin direction of Sgr A^(*).Additionally,by incorporating the cosmological constant,which accounts for the expansion of the universe,into our analysis,we establish an upper limit of Λ■7.3×10^(-34) km^(-2) on the cosmological constant at the lo confidence level.Future long-term monitoring of S-cluster stars,combined with enhanced observational precision,may enable the determination of the spin of Sgr A^(*)and further tighten the bound on the cosmological constant.
文摘Numerical simulation is an important tool that is helpful for us to understand the process of structure formation in the universe. However, many simulation results of cold dark matter （CDM） halos on a small scale are inconsistent with observations： the central density profile is too cuspy and there are too many substructures, Here we point out that both the problems may be connected with a hitherto unrecognized bias in the simulated halos. Although CDM halos in nature and in simulation are both virialized systems of collisionless CDM particles, gravitational encounter cannot be neglected in the simulated halos because they contain many fewer particles. We demonstrate this by two numerical experiments, showing that there is a difference on the microcosmic scale between the natural and simulated halos. The simulated halo is more akin to globular clusters where gravitational encounter is known to lead to such drastic phenomena as core collapse. Such an artificial core collapse process appears to link the two problems together in the bottom-up scenario of structure formation in the ACDM universe. The discovery of this bias also has implications on the applicability of the Jeans theorem in galactic dynamics.
