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Questions and Answers:
Professor Claude Canizares The questions in this interview were submitted by openDOOR readers in March. Of the twelve questions submitted, Prof. Canizares was asked to select three to answer here. While the imaging resolution of NASA's Chandra X-ray observatory is superior, I understand that ESA's XMM-Newton spacecraft actually features much higher collecting area and much higher resolution spectroscopy. I also understand that the real science is in the spectroscopy rather than the imaging, and that a large collecting area is crucial to working with far-away sources. Is MIT's Center for Space Research working also from data acquired by XMM-Newton? Is there a planned follow-on spacecraft? Is X-ray astronomy the main activity of MIT's Center for Space Research? question submitted by: Philippe Kletzkine, SM '83 Chandra and XMM-Newton are in fact very complementary missions, each with significant strengths and some weaknesses. Chandra has the best imaging resolution and also the best spectral resolution, and its energy range is wider for spectroscopy. XMM-Newton, as the questioner is aware, collects more photons, which may be critical for some observations. So many Center for Space Research (CSR) scientists are looking forward to combining data from both missions, althouhg we are concentrating much more on using Chandra for observations for which it is best suited. We are also working with many other X-ray astronomers on a new mission that would have much higher collecting area for spectroscopy, called Constellation-X. This is in the conceptual planning stages and new technology is being developed for telescopes and sensors. You can get more information on this mission from http://constellation.gsfc.nasa.gov/. The rotation of a pulsar sweeps the radiation-emitting magnetic pole past the observer like the rotating beacon of a lighthouse. Why is the magnetic axis not parallel to the rotational axis? What is the source of the angle, alpha? question submitted by: Charley Musselman, SM '75 It is possible for the magnetic and rotation axes to be parallel, but even for the earth the two are not precisely aligned. The magnetic field in a star is generated by a complex dynamo action that is driven by the differential rotation of different layers of the star, and again it is not likely that the field will be precisely aligned with the rotation axis. When the star collapses, the magnetic field is amplified greatly and "freezes" with the configuration it happened to have when the star finally collapses. Of course, we can only detect pulses in the case when the field and rotation are not perfectly aligned. I am not aware of any estimate of how many such cases exist but believe the prevailing opinion is that most systems would have some misalignment. If there is dark matter all over the universe, does this also mean it penetrates the earth? How would it influence us? question submitted by: Brian If dark matter exists in the form of elementary particles (some of which may be neutrinos and others may be a new, exotic particle), then they would indeed be streaming through the Earth and through us. Luckily, the very nature of this dark matter, namely something that interacts effectively only through its force of gravity, means that it has negligible effect on normal matter. It just flies right through without interacting. To give an example, we know that even neutrinos, which are produced in large quantity by the sun, stream through us without any noticeable effect. Only one in 500,000 neutrinos that pass through the whole Earth would interact. There are some attempts to detect the very rare interactions of such dark matter particles as a way of showing that they exist, but so far they have not seen anything. Someday, very sensitive instruments might be able to show the existence of such particles. |
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