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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Star formation | 4/4 | https://en.wikipedia.org/wiki/Star_formation | reference | science, encyclopedia | 2026-05-05T13:33:42.282534+00:00 | kb-cron |
Stars of different masses are thought to form by slightly different mechanisms. The theory of low-mass star formation, which is well-supported by observation, suggests that low-mass stars form by the gravitational collapse of rotating density enhancements within molecular clouds. As described above, the collapse of a rotating cloud of gas and dust leads to the formation of an accretion disk through which matter is channeled onto a central protostar. For stars with masses higher than about 8 M☉, however, the mechanism of star formation is not well understood. Massive stars emit copious quantities of radiation which pushes against infalling material. In the past, it was thought that this radiation pressure might be substantial enough to halt accretion onto the massive protostar and prevent the formation of stars with masses more than a few tens of solar masses. Theoretical work has shown that the production of a jet and outflow clears a cavity through which much of the radiation from a massive protostar can escape without hindering accretion through the disk and onto the protostar. Present thinking is that massive stars may therefore be able to form by a mechanism similar to that by which low mass stars form. There is mounting evidence that at least some massive protostars are indeed surrounded by accretion disks. Disk accretion in high-mass protostars, similar to their low-mass counterparts, is expected to exhibit bursts of episodic accretion as a result of a gravitationally instability leading to clumpy and in-continuous accretion rates. Accretion bursts in high-mass protostars have been confirmed observationally. Detection of high-mass protostellar disk candidates around high-mass protostars is consistent with theories that the total mass of a protostar contributes to the properties of their protostellar disk. Several other theories of massive star formation remain to be tested observationally. Of these, perhaps the most prominent is the theory of competitive accretion, which suggests that massive protostars are "seeded" by low-mass protostars which compete with other protostars to draw in matter from the entire parent molecular cloud, instead of simply from a small local region. Magnetic properties of high mass binary systems show that the fields are more prominent at larger distances, possibly causing disk fragmentation. Other research shows that a stronger magnetic field can alter gas cloud fragmentation as well as increase the production of high-mass stars. However, this is still an active area of research. Another theory of massive star formation suggests that massive stars may form by the coalescence of two or more stars of lower mass. Contact binary systems are suggested as candidate sources of some massive star formations.
== Filamentary nature of star formation == Simulations suggest that star forming filaments are commonly created when a shock velocity passes through a cloud of gas. When shock velocity is high (
≳
{\displaystyle \gtrsim }
5 km/s) from Supernova or a H II region expanding the dominate filament creation process is molecular clouds being shock compressed. When shock velocity is less than 5 km/s, filaments form from converging gas moving within local magnetic fields. Filamentary structures in molecular clouds are important initial conditions for star formation. The spatial relationship between cores and filaments indicates that the majority of prestellar cores are located within 0.1 pc of supercritical filaments. This supports the hypothesis that filamentary structures act as pathways for the accumulation of gas and dust, leading to core formation.
Both the core mass function (CMF) and filament line mass function (FLMF) observed in the California GMC follow power-law distributions at the high-mass end, consistent with the Salpeter initial mass function (IMF). Current results strongly support the existence of a connection between the FLMF and the CMF/IMF, demonstrating that this connection holds at the level of an individual cloud, specifically the California GMC. The FLMF presented is a distribution of local line masses for a complete, homogeneous sample of filaments within the same cloud. It is the local line mass of a filament that defines its ability to fragment at a particular location along its spine, not the average line mass of the filament. This connection is more direct and provides tighter constraints on the origin of the CMF/IMF.
== See also == Accretion – Accumulation of particles into a massive object by gravitationally attracting more matter Champagne flow model Chronology of the universe – History and future of the universe Formation and evolution of the Solar System Galaxy formation and evolution – Subfield of cosmology List of star-forming regions in the Local Group – Regions in the Milky Way galaxy and Local Group where new stars are forming Pea galaxy – Possible type of luminous blue compact galaxy Star evolution – Changes to stars over their lifespansPages displaying short descriptions of redirect targets
== References ==