Neutron Stars in Binary Systems


You've now completed your own unique analysis of raw X-ray data for a binary star system, GX301-2! According to a paper published by M.G Watson, R.S. Warwick, and R.H.D Corbet, scientists studying this system, GX301-2 is a binary with a neutron star and a massive supergiant star named Wray 977, which is at least 35 times more massive than our Sun. They orbit around each other with a period of 41.5 days, with a highly elliptical orbit as below.

Supergiant Wray 977

In other words, the two stars are sometimes close to one another, sometimes far away.

You may have noticed that the spectrum for GX301-2 is not as smooth as HT Cas. In fact, the light curve doesn't look much like the theoretical light curves in which you practiced finding the period and size of component stars. The period you have found is actually the period of theX-ray "flares" from this system. The flare happens because the neutron star is varying distances from the supergiant. Supergiants have superwinds of particles flowing off their surface. When the neutron star comes nearer the supergiant Wray 977, it accretes the particles from the wind too fast, and energy comes off the neutron star's accretion disk in the form of an X-ray flare.

Both HT Cas and GX201-2 are in the later evolutionary stage of the binary system (about 20-30 seconds into the animation) that will later result in the complete destruction of Wray 977 and the formation of a fast pulsar or, if too much mass is accreted, a black hole.

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