The magnetic field lines force fast-moving electrons into helical paths, causing them to spray out polarized x-rays known as synchrotron radiation. “We will get a result, as long as we launch,” he predicts.Īlso in the mission’s sights are magnetars, stellar remnants like pulsars, but with even more powerful magnetic fields, 100 million times stronger than any magnet made on Earth. Each theory predicts the x-ray polarization signal should vary with the timing of the pulses in a way IXPE should be able to distinguish. Weisskopf says rival theories of beam generation suggest the x-rays originate in different locations on the pulsar: all across its surface, at its poles, or in its atmosphere. These city-size remnants of dead stars spin frenetically, sometimes hundreds of times per second, emitting beams of radio waves, x-rays, and other radiation that sweep past Earth like a lighthouse beacon. Imaging many trails and their spread tells observers how polarized the light is, and in which direction. An x-ray hitting a gas atom knocks out an electron that tends to shoot off in the direction of polarization, leaving a visible trail. (X-rays penetrate standard telescope mirrors.) Sensors provided by the Italian Space Agency detect the x-rays and their polarization in a layer of dimethyl ether gas. Each telescope is a cylinder containing two dozen concentric shells that focus x-rays through grazing reflections. IXPE will spend at least 2 years scrutinizing cosmic x-ray sources with three identical telescopes-cheaper than one big one and a hedge against failures. However, magnetic conditions at their birth or interactions on their journey can polarize the photons by forcing those oscillations into the same plane. Typically, the photons’ own magnetic and electric fields oscillate perpendicularly to their path, but in random directions. X-rays are emitted when gas is heated up to hundreds of millions of degrees Celsius and ionized to produce plasma, a roiling soup of electrons and ions. Weisskopf says he proposed dedicated x-ray polarimetry missions several times before succeeding with IXPE, a $190 million mission that is set to launch on 9 December from the Kennedy Space Center in Florida on a SpaceX Falcon 9 rocket. Since then, the questions such x-rays might answer have piled up, but no mission has set out to measure them-in part because the data from that first sensor suggested there might be too few to be worth the effort. NASA’s Orbiting Solar Observatory 8, launched in 1975, detected a smattering of polarized x-rays from a single source, the Crab nebula, Weisskopf says. “The community has been waiting for this for a long time,” says x-ray astronomer Feryal Özel of the University of Arizona, who is not part of the project. “We’re just trying to find out how do you produce these x-rays anyway,” says principal investigator Martin Weisskopf of NASA’s Marshall Space Flight Center. By detecting how intense magnetic fields in collapsed stars and black holes align, or polarize, the x-rays they emit, the Imaging X-ray Polarimetry Explorer (IXPE) could reveal how those objects spew out radiation in the first place. Next week, NASA will launch a small mission with an ambitious task: to peer into some of the universe’s most violent objects for clues to how they work.
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