Free Astronomy Magazine March-April 2015

T he animated simula- tion on the side shows the interaction between the winds of the two com- ponents of Eta Carinae during the months of the periastron passage. The spiralling tunnel is repre- sented by pink-red hues. [NASA's Goddard Space Flight Center/T. Gull et al.] conditions of the system, and their correct interpretation is essential for understand- ing the system itself. Gull’s team showed that when the two stars get closer to each other and Eta Carinae B starts to dive into the denser layers of the shell of gas fed by Eta Carinae A’s wind, that same gas absorbs the ultraviolet radiation of the former, pre- venting it from reaching the more rarefied layers, responsible for the emission of dou- bly ionized iron. The absence or presence of this type of radiation are therefore already very indicative of what’s happening in the star system: for instance, its intensity can be related to the pace at which Eta Carinae A loses mass, a pace that in the last three peri- astron passages showed to be constant, as confirmed by the ionized helium signal which remained unchanged. This conclusion does in fact attribute to Eta Carinae B the responsibility for the X-rays peaks measured in recent years; peaks which can now be interpreted as episodic increases in the mass loss by the smaller star, a matter that has so far remained con- troversial. Overall, there is still much more to understand about the dynamics govern- ing Eta Carinae, but the recent work by Ted Gull and colleagues has nevertheless paved the way for a thorough study of the next peri-astron passage. n ducing solid versions with an ordinary 3-D printer. In so doing, the researcher highlighted some spike- like protuberances in the gaseous flow along the edges of the tunnel. These protrusions, not yet acknowledged by direct observation, are attrib- uted to instabilities in the action of the winds during the months of closest approach between the two stars. Even more inter- esting are the conclusions drawn by Ted Gull and colleagues on some key observations that re- veal the inner workings of the Eta Carinae system, starting from specific forms of radiation emitted by it. This is the case of a blue light, detected by ground telescopes, produced by singly ionized helium atoms (i.e. deprived of an electron) and associated to the conditions of Eta Carinae A’s wind. Another key radia- tion, observed with the Space Telescope Imaging Spectrograph aboard Hubble, is that emitted by doubly ionized iron (thus deprived of two electrons), that is being generated in the regions where the gases emanated by the primary star are heated by the intense ultraviolet light of the second- ary. A third revealing radiation is represent- ed by the X-rays produced in the region where the winds of the two stars collide, creating shock waves that heat the gas up to hundreds of millions of degrees. Each variation in the intensity of those three forms of radiation is a direct consequence of the varying physical and/or geometric