北京大学科维理天文与天体物理研究所

Featured Science

LAMOST reveals the secret of lithium-rich stars

A recent study revealed the actual evolutionary stage of lithium-rich stars by the Chinese astronomers is published in the Nature Astronomy on Oct.5. Yutao Zhou, the LAMOST Fellow from the department of astronomy at PKU, is involved in this study as the co-first author. By combining the LAMOST spectra with the asteroseismic data from Kepler, they find that most lithium-rich stars are located at the evolutionary stage of red clump instead of the red giant branch as previously thought. The findings challenge the previous theories of lithium enrichment, which is vital to resolve the problem of lithium origin.

Galactic Census Reveals Origin of Most "Extreme" Galaxies

Astronomers have found that the key to understanding galaxies with "extreme" sizes, either small or large, may lie in their surroundings. In two related studies, an international team found that galaxies that are either "ultra-compact" or "ultra-diffuse" relative to normal galaxies of comparable brightness appear to reside in dense environments, i.e., regions that contain large numbers of galaxies. This has led the team to speculate that these "extreme" objects could have started out resembling normal galaxies, but then evolved to have unusual sizes through interactions with other galaxies.

Runaway Star Might Explain Black Hole's Disappearing Act

"This new study is a great example of how flexibility in observation scheduling allows NASA and ESA missions to study objects that evolve relatively quickly and look for longer-term changes in their average behavior," said Michael Loewenstein, a coauthor of the study and an astrophysicist for the NICER mission at the University of Maryland College Park and NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland. "Will this feeding black hole return to the state it was in before the disruption event? Or has the system been fundamentally changed? We're continuing our observations to find out.” Two KIAA astronomers, Prof. Luis Ho and Ruancun Li, also participated in this discovery.

Quasar Monster Black Hole Found in the Early Universe

Astronomers have discovered the second most distant quasar ever found, using the international Gemini Observatory and Cerro Tololo Inter-American Observatory (CTIO), Programs of NSF’s NOIRLab. It is also the first quasar to receive an indigenous Hawaiian name, Pōniuā’ena. The quasar contains a monster black hole, twice the mass of the black hole in the only other quasar found at the same epoch, challenging the current theories of supermassive black hole formation and growth in the early Universe.

Feeling the drag

Within a hierarchically evolving Universe, binary black holes (BBHs) are expected to form through galaxy mergers. How these BBHs merge is, however, still under debate. Xian Chen and collaborators show that Poynting–Robertson (PR) drag, a radiative process whose effects are observed in the interaction between the Sun and dust in our Solar System, is applicable to BBHs and can play an important role in shrinking their orbits sufficiently for them to merge.

Off the beaten path: a new framework for cold filament formation in galaxy clusters

Mon, 2020-05-04Using state-of-the-art radiation-hydrodynamic simulations, KIAA postdoctoral fellow Dr. Yu Qiu and collaborators proposed a new framework for cold gas filament formation, shedding light on how cold gas exists immersed in the hot, X-ray-emitting plasma permeating galaxy clusters.