Interstellar shock waves, which can trigger star formation, may come from several sources.

'Contracting fragment' may have been triggered by M20. Nebula may compress interstellar clouds to greater densities, triggering star formation.

Shock waves driven out by high temperatures and pressures in an emission.

HH30, illustrating a real example of the bipolar flow, along with anДЄrtist's conception of a young star system.ДЄnother pair of outflow jets, HH1 and HH2, in the Jets fan out as the disk of nebular gas is blown away. Protostars within the Orion Molecular Cloud imaged by the Hubble Space Telescope.ДЇormation of bipolar jets due to intense heating and strong outflows.

Contracting fragment (between stages 1 and 2).

M20 (The Trifid Nebula), evidence for three broad phases of star formation.

We can observe it at various stages of evolution.

Period of cloud contraction is far too long for us to 'watch'. Observations of Cloud Fragments and Protostars

About 50 brown dwarfs seen at distance of 1,500 light years.

Hubble Space Telescope image in infrared of brown dwarfs in Trapezium of Orion Nebula. 10-15 percent of 'stars' in Orion are brown dwarfs.Faint specks are brown dwarf candidates.Infrared image of star cluster near Orion Nebula. Number of brown dwarfs in the Milky Way may be Jupiter is technically not a brown dwarf (0.001 solar masses). 012 solar masses (12 times Jupiter's mass). Star 'stays put' on the main-sequence, spending most of its life in one place.Stars will be slightly off-set from this band depending on the concentration of.Main-sequence band predicted for stars.Stars of different masses appear at different points Summary of the Evolution of a Solar-type Star Larger, but cooler, than Sun, resulting in somewhat lower luminosity. Repulsion of two positively charged protons (Hydrogen nuclei) cannot beДЄpproximate Time to Next Stage: 3 x 10 7 yr.Central temperature is still not hot enough for thermonuclear fusion.Characterized by violent surface activity and strong protostellar winds.This path from stage 4 to 6 is known as the.As the protostar moves beyond stage 4, it becomes a T Tauri star,.The collapsing cloud heats as it contracts. This early evolutionary track is known as the Kelvin-Helmhotz contraction.Prior to its reaching stage 4, a protostar. Protostar appears at the center of the fragment.ДЄpproximate evolutionary track of the collapse of an interstellar cloud fragment.Cloud has now shrunk to region the size of our Solar System.Several tens of thousands of years after the stage 2 fragment began toД¬ollapse, it becomes opaque at the center, and the The mass is dominately in the form of cold atomic and molecular gas, with some dust.ДЄpproximate Time to Next Stage: 2 x 10 6 yrД«reak up into tens, hundreds, or thousands of fragments.ДЄpproximate Time to Next Stage: 3 x 10 4 yrДЄt this phase the cloud is very diffuse, so heat is not trapped (except near the center) and temperatureДoes not build much ( except at the center).The cloud might contain thousands of times the Sun's mass. Very large interstellar cloud (spanning tens of parsecs) provides the initial Star formation begins when gravity begins to dominate over heat, causing a cloud to lose its The evolution of a star can be thought of as passing through H-R diagram is a useful way to summarize the observed properties of prestellar Eventually, if mass is sufficient to produce concentration, it becomes hot enough for nuclear burning (thermonuclear fusion).Д®ffect of magnetism - hinders contraction.Spin competes with inward pull of gravity. Much more than all the atoms contained in the Earth.For a 100 K cloud, roughly 10 57 atoms are required.It takes an enormous collection of particles to create the combined gravitational attraction required to hold them together.Heat generated in collapse opposes pull of gravity.Gravity only weakly influences interacting particles. Heating due to release of gravitational energy.Region of interstellar medium collapses under its own weight.

Stellar Nursery in Tarantula Nebula in Large Magellanic Cloud. Infrared image of the so-called Elephant Trunk Nebula.Д®xamples of Extragalactic Star Formation. Scores of young stars and protostars embedded in nebula.and bright emission nebula in the neighborhood excited by these bright stars.Accompanied by massive stars that died out long ago,.Together in a dense cloud of gas and dust. Most of the stars in our immediate cosmic neighborhood probably formed.Our Sun and the Solar System have survived such a violent environment of.Characterized by outbursts of activity and interstellar shock waves.The birthplace of stars are dense, violent nurseries.Observations of Cloud Fragments and Protostars.

Sequential star notes