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A possible direct exposure of the Earth to the cold dense interstellar medium 2–3 Myr ago

Cold, dense clouds in the interstellar medium of our Galaxy are 4–5 orders of magnitude denser than their diffuse counterparts. Our Solar System has most likely encountered at least one of these dense clouds during its lifetime. However, evidence for such an encounter has not been studied in detail yet. Here we derive the velocity field of the Local Ribbon of Cold Clouds (LRCC) by modelling the 21 cm data from the HI4PI survey, finding that the Solar System may have passed through the LRCC in the constellation Lynx 2–3 million years ago. Using a state-of-the-art simulation of the heliosphere, we show that during the passage, the heliosphere shrinks to a scale of 0.22 au, smaller than the Earth’s orbit around the Sun. This would have put the Earth in direct contact with the dense interstellar medium for a period of time and exposed it to a neutral hydrogen density above 3,000 cm−3. Such a scenario agrees with geological evidence from 60Fe

The Nearby Star Clusters Come from Only Three Places

Most of the star clusters in our neighbourhood come from only three star-forming regions, according to the story told by Gaia data.

Most nearby young star clusters formed in three massive complexes

Efforts to unveil the structure of the local interstellar medium and its recent star-formation history have spanned the past 70 years (refs. 1–6). Recent studies using precise data from space astrometry missions have revealed nearby, newly formed star clusters with connected origins7–12. Nonetheless, mapping young clusters across the entire sky back to their natal regions has been hindered by a lack of clusters with precise radial-velocity data. Here we show that 155 out of 272 (57%) high-quality young clusters13,14 within 1 kiloparsec of the Sun arise from three distinct spatial volumes. This conclusion is based on the analysis of data from the third Gaia release15 and other large-scale spectroscopic surveys. At present, dispersed throughout the solar neighbourhood, their past positions more than 30 million years ago reveal that these families of clusters each formed in one of three compact, massive star-forming complexes. One of these fami

Galactic Bloodlines: Many Nearby Star Clusters Originate from Only Three "Families"

An international team of astronomers led by the University of Vienna has deciphered the formation history of young star clusters, some of which we can..

How Often Do Supernovas Strike Earth? | Scientific American