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Massive Galaxies May be Crucial for the Enrichment of Cosmic Metal in the Early Universe

What are the sources of early metals and how did they enrich the intergalactic medium (IGM) are among the most crucial questions in galaxy formation. Most of the previous searches in optical wavelengths indicate that the enrichment of cosmic metals is due to low-mass galaxies that are fainter than the current detection limit. Here, we report the discovery of a galaxy associated with a strong OI absorber at redshift of 6. The galaxy has a halo mass of four hundred billion solar mass, one or two orders of magnitude more massive than that expected from modern cosmological simulations. Our observations indicate that massive galaxies may be more important in transporting metals in the intergalactic medium (IGM) than predicted by simulations.

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DoA faculty reviews the statistical distribution of exoplanets

How do planetary systems form and evolve? It is a scientific question that astronomers have long been wondering and also a key step toward understanding the origin of life and human beings on Earth. Since the discovery of the first planet orbiting around a Sun-like star outside of the Solar System in 1995 (which was awarded the Nobel Physics Prize in 2019), the number of known exoplanets has grown to over 4000. This large sample has enabled many detailed studies into the statistical distribution of planets and has sharpened our understanding of the planet formation process.

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A new movie “The Great Learning” is now being shown in theaters all over China

One of the four main characters is Prof. Zheng Cai from the Department of Astronomy. It shows his move back from the US to China, and his push, together with his collegues, to build a 6.5m telescope in China. More information is available in Chinese [link].

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Tsinghua Astronomy's 20th anniversary ceremony

On April 24th, on the occasion of the 110th anniversary of Tsinghua University, a ceremony was held to celebrate the 20th birthday of Tsinghua Astronomy, Department of Astronomy (hereafter called DoA for short) at the Chuan Shan Academy—a classic and historical place.

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Forming planets by pebble accretion: a metallicity gradient emerges

Following our previous research efforts, we have conducted numerical calculations about the thermal evolution of the envelope of pebble-accreting protoplanets. These protoplanets emerge early, when the protoplanetary gas disk is still present. Due to the accretion of solids, their envelope becomes hot, sublimating the infalling pebbles and transforming mm-sized solid particles (“pebbles”) into a metal vapor (e.g, SiO2). This transformation greatly affects the thermodynamical evolution of the protoplanet. For example, planets end up with a small "core" but may still undergo runaway gas accretion due to the high molecular weight and small pressure scale height of the atmosphere.

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History of the Solar Nebula from Paleomagnetism

The solar system formed about 4.6 billion years ago. During that time, left-over materials of gas and dust orbited the proto-Sun and formed a disk known as the “solar nebula”. Through a sequence of growth by coagulation and accretion, dust in the solar nebula eventually grow to form our planetary system. The solar nebula is the counterpart of “protoplanetary disks”, which are commonly found around other young stars in the Milky Way. Magnetic fields are known to play a crucial role in the formation, evolution, and dynamics of protoplanetary disks, and hence the processes of planet formation. Currently, attempts to directly measure or infer magnetic field from protoplanetary disks from astronomical observations have been unsuccessful. On the other hand, ancient meteorites have the potential to record the magnetic field in the solar nebular when they formed, which can be deciphered from techniques in the field known as paleomagnetism.

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