EVIDENCE OF ACCRETION-GENERATED X-RAYS IN THE YOUNG ...

violent. For example, radiation pressure of nearby stars can compress gas to create
an over-density of material in part of the cloud, which can start the collapse of part or
all of the cloud. Supernovae send out shockwaves that ripple through the interstellar
medium. When a pressure wave comes in contact with an interstellar cloud, a shock
forms as the high-speed wave slams into the slower-moving cloud, creating a region
of high over-density. Gravitational encounters between galaxies can lead to large
amounts of gas being stripped from each galaxy as they perform their gravitational
tango, leading to tidal tails millions of light-years long. As the gas clouds of one
galaxy are stretched and compressed by the gravitational influence of the interacting
galaxies, over-densities arise in the gas. This often gives rise to massive amounts of
star formation all at once, prompting astronomers to know many of these interacting
bodies as “starburst galaxies.”
In order to start the process of core collapse, even with all of the listed ingredients
and trigger mechanisms, the Jean’s stability must be overcome (Eq. 1.1).
dP
dr
= G⇢Menc
r 2
(1.1)
Equation 1.1 shows that the outward pressure P in a volume over a given distance
r is determined by the gravitational force that is trying to collapse the mass enclosed
inside the given volume (Menc) withacertaindensity⇢. In an “inert” cloud, the
thermal pressure (and other internal forces such as support from a magnetic field) of
the material is in balance with the gravitational force. In order to start the collapse
of the cloud, the external trigger mechanism must apply enough force so that the
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