From Sundqvist et al. 2012, showing generic X-ray line profile (tau_0=2.5) with absorption computed from LDI models vs. a smooth CAK wind. More info in paper.

Hot Monster Stars: Live Fast, Die Young


Off course, the most important thing for YOU to first realize is that the hot stars I study are those falling in the second and third categories -- in contrast to those in the first, and evidently preferred, one -- of our all-favorite and lovely search engine. But anyway, let's raise the level to this century and begin now, shall we:


During their short but energetic lives, stars with hot surfaces and masses many times that of the sun light up galaxies like our Milky Way through their high luminosities and intense radiation fields. Unlike the sun -- which will shine for some 5 billion more years -- such massive stars exhaust the nuclear fusion-fuel in their cores within only a few million years, after which they end their lives in catastrophic giant supernova explosions. Together with the stellar winds discussed below, these suoernovae disperse nuclear-processed heavy elements into the inter-stellar medium and thereby chemically enrich the sites where the next generation of stars and planets are formed.

The evolutionary paths of these stars toward their final destiny, however, are highly regulated by the huge amounts of mass that are being driven away from their surfaces. Indeed, a very massive star born with 100 solar masses or above may through stellar winds shed much more than half of this before it dies. Together with the escaping stellar photons, the energy and momentum of these powerful massive-star winds carve speculator giant bubbles in the neighborhoods of these stars, and their pushing on and heating of cold interstaller clouds also regulates the formation of new generations of stars. And once the star stops burning, which of the many types of astronomical supernovae it then ends its life as -- e.g. as a hydrogen poor or rich one, or perhaps as a pair-instability one, or perhaps even as a hypernova emitting fiercely in highly energetic gamma-rays -- depends critically on the quantitative amount of mass that has been lost until the time of explosion.



Winds from massive stars: Get blown away by Starlight

For stable massive stars with hot surfaces, scattering of spectral-line photons transfers momentum from the star's intense ultra-violet radiation field to the stellar plasma. For such stars, this radiation field is so strong that it provides an upward pushing force so strong that it overcomes the downward pull of gravity. Consequently stellar plasma is accelerated outwards in a so-called stellar wind, so that ultimately the gas escapes the star with velocities that can reach 1000 km/s or even more.


Through such starlight-powered winds, these massive monsters loose about an earth-mass to interstellar space during every year of their lives!


As a reference, this is about 100 000 000 times more than the sun looses every year through its solar wind — it’s good for us the sun’s wind is pretty weak, otherwise the Earth would be pretty inhospitable :-)

To be continued, with more details on various aspects of these line-radiation driven winds…..