This is not a computer simulation. It's an actual time-lapse video taken over
four years by the Hubble—and scientists don't know its origin yet.
http://sploid.gizmodo.com/star-explosion-video-is-the-most-awesome-thing-i-have-e-1589138376
First, despite appearances, the cloud itself is not changing in these images!
It’s actually fairly static, with movement far too small to notice on this time-
scale. What you’re seeing is actually a pulse of light from the outburst moving
through the cloud, illuminating it. Light moves very rapidly, but the cloud is
huge, light years across. That means it takes a long time for light to cross it,
and over the years we’re just seeing different parts of the dust cloud lit. This
type of event is common in astronomy, and it’s called a light echo.
Second, although we’re not exactly sure what caused the outburst, the most like-
ly explanation is that two normal (but massive) stars merged together. An event
like this is pretty rare, but entirely possible. When that happens they form a
single, more massive star, which is unstable. It can undergo a huge paroxysm,
brightening by a factor of thousands, and also expand and redden. This all fits
what we see here; the dust cloud would’ve been part of the nebula that formed the
stars, and existed long before they did.
http://www.slate.com/blogs/bad_astronomy/2014/06/12/v838_mon_video_of_a_stellar_outburst.html
This behavior of ballooning to an immense size, but not losing its outer layers,
is very unusual and completely unlike an ordinary nova explosion.
The outburst may represent a transitory stage in a star's evolution that is rare-
ly seen. The star has some similarities to highly unstable aging stars called
eruptive variables, which suddenly and unpredictably increase in brightness.
V838 Monocerotis is located about 20,000 light-years away from Earth in the di-
rection of the constellation Monoceros, placing the star at the outer edge of our
Milky Way galaxy.
http://www.nasa.gov/multimedia/imagegallery/image_feature_784.html
Light echo
Rapidly brightening objects like novae and supernovae are known to produce a
phenomenon known as light echo. The light that travels directly from the object
arrives first. If there are clouds of interstellar matter around the star, some
light is reflected from the clouds. Because of the longer path, the reflected
light arrives later, producing a vision of expanding rings of light around the
erupted object.
In the case of V838 Monocerotis, the light echo produced was unprecedented and
is well documented in images taken by the Hubble Space Telescope. While the photos
appear to depict an expanding spherical shell of debris, they are actually formed
by the illumination of an ever-expanding ellipsoid with the progenitor star at one
focus and the observer at the other. Hence, despite appearances, the structures in
these photos are actually concave toward the viewer. In other words, the light is
reflecting dust that is mostly 'behind' the star, not in 'front' of it.
It is not yet clear if the surrounding nebulosity is associated with the star
itself. If that is the case, they may have been produced by the star in earlier
eruptions which would rule out several models that are based on single catastroph-
ic events. However, there is strong evidence that the V838 Monocerotis system is
very young and still embedded in the nebula from which it formed.
Interestingly, the eruption initially emitted at shorter wavelengths (i.e. was
bluer), which can be seen in the light echo: the outer border is bluish in the
Hubble images.
http://en.wikipedia.org/wiki/V838_Monocerotis
