Education Activities To Accompany Chandra Data Analysis Software
Cen X-3 & Clocks in the Sky
Conclusion
It is rather remarkable that such a simple set of observations can tell us so much about the nature of the Cen X-3 binary star system. But we still have not found out how it works. Now, we must use our imagination and knowledge of astronomy and physics to come up with a model of the system.
First, we need to figure out what type of object can radiate such a prodigious amount of x-rays. This problem was solved in the 1960’s, when “pulsars” were first discovered. Only a neutron star can do this; an object so dense that the entire mass of the Sun would be need to occupy a volume no bigger than Manhattan. But why would it vary every five seconds?
If an object has an intense magnetic field, trillions of times more powerful than that of the Earth, particles streaming in from the companion star could be trained into a powerful stream of material that would be concentrated at the magnetic poles. This is very similar to what happens when aurorae (the “Northern Lights”) are produced on the Earth. The Sun spews forth particles from a solar storm, and the Earth catches them, and focuses them along the magnetic field lines towards the poles, where they give off the eerie light of an aurora. Now, if this magnetic field in the neutron star is not lined up with the rotation axis of the star, the “hot spots” at the magnetic poles would fly past our sight every revolution of the star, much like a lighthouse beacon illuminates the shoreline as it spins around.
So our picture is this: there are two stars in the system, a tiny dense one that is responsible for the x-rays we see, and a companion, which in this case turns out to be a supergiant star (one that would swallow up the Sun, Mercury, Earth and Mars if it were placed in the center of our solar system!) They revolve around each other every 2.1 days. The supergiant companion provides the “fuel” that the neutron star catches in its intense gravitational field. Then the magnetic field takes over, and funnels the material toward the magnetic poles of the neutron star. As these poles come into view, the intense x-rays emitted from the hot material are seen as “pulses” of radiation every 4.8 seconds.
So are we done? Not really. How did these diverse stars come to be associated with each other? The neutron star is at the end of its evolutionary path, but the supergiant is a very young star. How can exist at the same time, in the same place in the sky? As is usual with our probing of the mysteries of the Universe, as soon as we answer one question, another one pops into view, even more fascinating than the first. But for now, we must be content with our new found understanding of Cen X-3, and leave for another day the story about the evolution of these strange “clocks in the sky”.
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