The background is filled with bright
orange-red clouds of varying density. Towards the top-left several
large, pale blue stars with prominent cross-shaped spikes are scattered.
A small, tadpole-shaped dark patch floats near one of these stars. More
of the same dark, dense gas fills the lower-right, resembling black
smoke. A bright yellow star and a smaller blue star shine in front of
this. Credit: ESA/Hubble & NASA, R. Sahai
Just in time for the festive season, this new Picture of
the Week from the NASA/ESA Hubble Space Telescope features a glistening
scene in holiday red. This image shows a small region of the well-known nebula
Westerhout 5, which lies about 7000 light-years from Earth. Suffused
with bright red light, this luminous image hosts a variety of
interesting features, including a free-floating Evaporating Gaseous
Globule (frEGG). The frEGG in this image is the small tadpole-shaped
dark region in the upper centre-left. This buoyant-looking bubble is
lumbered with two rather uninspiring names — [KAG2008] globule 13 and
J025838.6+604259.
FrEGGs are a particular class of Evaporating Gaseous
Globules (EGGs). Both frEGGs and EGGs are regions of gas that are
sufficiently dense that they photoevaporate less easily than the less
compact gas surrounding them. Photoevaporation occurs when gas is
ionised and dispersed away by an intense source of radiation — typically
young, hot stars releasing vast amounts of ultraviolet light. EGGs were only identified fairly recently, most notably at the tips of the Pillars of Creation,
which were captured by Hubble in iconic images released in 1995. FrEGGs
were classified even more recently, and are distinguished from EGGs by
being detached and having a distinct ‘head-tail’ shape. FrEGGs and EGGs
are of particular interest because their density makes it more difficult
for intense UV radiation, found in regions rich in young stars, to
penetrate them. Their relative opacity means that the gas within them is
protected from ionisation and photoevaporation. This is thought to be
important for the formation of protostars, and it is predicted that many
FrEGGs and EGGs will play host to the birth of new stars.
The frEGG in this image is a dark spot in the sea of red
light. The red colour is caused by a particular type of light emission
known as H-alpha emission. This occurs when a very energetic electron
within a hydrogen atom loses a set amount of its energy, causing the
electron to become less energetic and this distinctive red light to be
released.
Links
Source: ESA/Hubble/potw
![[KAG2008] globule 13](https://cdn.spacetelescope.org/archives/images/large/potw2251a.jpg){kind=link}