Surprising blow-outs from massive stars throughout the Milky Way
INTEGRAL's spectrometer SPI was used to measure the speed at which
hot gas ejected by massive stars in the inner regions of the Milky
Way moves. The speed turns out to be surprisingly high: the motion
is about 200 km/s faster than the speed at which the Milky Way
rotates and in the same direction. The velocity measurement is
done using the Doppler shift of the gamma rays emitted by Aluminium-26,
a radioactive isotope that is produced in massive stars and blown out
into interstellar space where it decays after a lifetime of one million
years.
The results are shown in the above picture where the gamma-ray-measured
velocities (crosses, including error bars) are compared with other
objects in our Galaxy. For comparison, different models are shown
(blue solid, red dotted, and green dashed lines), as well as the
velocity information from molecular gas as seen in CO (colour scale
overlay). The picture is a refinement of work that has previously
been featured in the INTEGRAL
POM of October 2010,
relative to which the precision of the velocity measurements has been
improved.
This means that a large fraction of this gas can move at high speed
for a long time and therefore over long distances before it is stopped
when it encounters other gas. From this, it is deduced that the massive
stars that eject the Aluminium-26 are probably located on the leading
edge of the spiral arms, and blow most of their ejecta over large
distances into the regions between the spiral arms. This observation
helps to understand how stars and supernovae drive the long-term
development of the interstellar gas in our Milky Way. How the gas is
enriched with freshly-produced atomic nuclei and recycled into
next-generation stars and how this affects the large-scale flows of
gas in the Galaxy are fundamental issues in astrophysics.
