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The formation of stars and planets is accompanied not only by the build-up of matter, namely accretion, but also by its expulsion in the form of highly supersonic jets that can stretch for several parsecs 1,2 . As accretion and jet activity are correlated and because young stars acquire most of their mass rapidly early on, the most powerful jets are associated with the youngest protostars 3 . This period, however, coincides with the time when the protostar and its surroundings are hidden behind many magnitudes of visual extinction. Millimetre interferometers can probe this stage but only for the coolest components 3 . No information is provided on the hottest (greater than 1,000 K) constituents of the jet, that is, the atomic, ionized and high-temperature molecular gases that are thought to make up the jet's backbone. Detecting such a spine relies on observing in the infrared that can penetrate through the shroud of dust. Here we report near-infrared observations of Herbig-Haro 211 from the James Webb Space Telescope, an outflow from an analogue of our Sun when it was, at most, a few times 10 4 years old. These observations reveal copious emission from hot molecules, explaining the origin of the 'green fuzzies' 4-7 discovered nearly two decades ago by the Spitzer Space Telescope 8 . This outflow is found to be propagating slowly in comparison to its more evolved counterparts and, surprisingly, almost no trace of atomic or ionized emission is seen, suggesting its spine is almost purely molecular., (© 2023. The Author(s).)

The X-ray source known as GRS1915+105 belongs to a group dubbed 'microquasars'. These objects are binary systems which sporadically eject matter at speeds that appear superluminal, as is the case for some quasars. GRS1915+105 is also one of only two known binary sources thought to contain a maximally spinning black hole. Determining the basic parameters of GRS195+105, such as the masses of the components, will help us to understand jet formation in this system, as well as providing links to other objects which exhibit jets. Using X-ray data, indirect methods have previously been used to infer a variety of masses for the accreting compact object in the range 10-30 solar masses (M middle dot in circle). Here we report a direct measurement of the orbital period and mass function of GRS1915+105, which allow us to deduce a mass of 14 +/- 4 M middle dot in circle for the black hole. Black holes with masses >5-7 M middle dot in circle challenge the conventional picture of black-hole formation in binary systems. Based on the mass estimate, we interpret the distinct X-ray variability of GRS1915+105 as arising from instabilities in an accretion disk that is dominated by radiation pressure, and radiating near the Eddington limit (the point where radiation pressure supports matter against gravity). Also, the mass estimate constrains most models which relate observable X-ray properties to the spin of black holes in microquasars.

Hundreds of circumstellar disks in the Orion nebula are being rapidly destroyed by the intense ultraviolet radiation produced by nearby bright stars. These young, million-year-old disks may not survive long enough to form planetary systems. Nevertheless, the first stage of planet formation-the growth of dust grains into larger particles-may have begun in these systems. Observational evidence for these large particles in Orion's disks is presented. A model of grain evolution in externally irradiated protoplanetary disks is developed and predicts rapid particle size evolution and sharp outer disk boundaries. We discuss implications for the formation rates of planetary systems.

Young stars are thought to accumulate most of their mass through an accretion disk, which channels the gas and dust of a collapsing cloud onto the central protostellar object. The rotational and magnetic forces in the star-disk system often produce high-velocity jets of outflowing gas. These jets can in principle be used to study the accretion and ejection history of the system, which is hidden from direct view by the dust and dense gas of the parent cloud. But the structures of these jets are often too complex to determine which features arise at the source and which are the result of subsequent interactions with the surrounding gas. Here we present infrared observations of a very young jet driven by an invisible protostar in the vicinity of the Horsehead nebula in Orion. These observations reveal a sequence of geyser-like eruptions occurring at quasi-regular intervals and with near-perfect mirror symmetry either side of the source. This symmetry is strong evidence that such features must be associated with the formation of the jet, probably related to recurrent or even chaotic instabilities in the accretion disk.