What is is the interstellar medium? The interstellar medium is the space between stars and galaxies. This matter includes a collection of gas, dust and cosmic rays. It is a region of birth for stars.
By measuring a stars color we can determine its age. Blue stars are relatively short-lived compared to the redder stars. The blue stars die off over a period of a few hundred million years, but the redder stars continue to shine for billions of years. Therefore, as a star cluster ages, its color gradually shifts from blue to red.
Perhaps one of the most iconic images by Hubble, the above image of the Eagle Nebula shows large pillars of molecular gas and dust. In this region there are many young stars, the largest pillar in the image is about 3.86243exp13 kilometers or 24 trillion miles in size.
The above image shows area of young star formation.
These clouds are held together by self-gravity and by the intense pressure that builds up in between the clouds. This in effect causes these molecular clouds to collapse into a center, which draws gas towards inside the cloud. When the density is high enough the clouds end up fragmenting and collapsing into itself. From these clouds of dust and gas are born stars and planets.
The above is an area in our local Large Magellanic Cloud (LMC), where there is low-mass stars with giants beside it, known as LH 95 it is about 160,000 Ly away from Earth. The image was taken by Hubble's Advanced Camera for Surveys.
From these high detail Hubble images we are looking at regions of interstellar clouds. Self-gravity is a gravitational attracting among all parts of the same object. The sum of all these forces on every other particle is exerted towards the center. This gravity can be balanced by its own structural pressure similar to how Earth is made up from rocks, or by the outward force acting on the inward force creating a balance known as hydrostatic equilibrium. If either force is unstable the star can either expand outwards on inwards into itself. However in most clouds the internal pressure pushes outward more than inward.
|From the above simulation we can get an idea of where the highlighted grey blob is the Large Magellanic Cloud (LMC) and the milky way largely visible on the right.|
The densest coolest interstellar clouds are called molecular clouds because they are mainly composed of hydrogen molecules. Once these molecular clouds begin to collapse the innermost becomes a star and outer parts can become planets. The innermost part of cloud is called a protostar. The surface of a protostar is thousands of times larger then the Sun and as a result is also more luminous.
LRLL 54361 a binary protostar, it demonstrates some unknowns about star formation. The protostar emits a burst of light at intervals perhaps caused by the eccentric orbit that it may exhibit.