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XMM-Newton sees 'hot spots' on neutron stars (Forwarded)
ESA News
http://www.esa.int 25 April 2005 XMM-Newton sees 'hot spots' on neutron stars Thanks to data from ESA's XMM-Newton spacecraft, European astronomers have observed for the first time rotating 'hot spots' on the surfaces of three nearby neutron stars. This result provides a breakthrough in understanding the 'thermal geography' of neutron stars, and provides the first measurement of very small-sized features on objects hundreds to thousands light-years away. The spots vary in size from that of a football field to that of a golf course. Neutron stars are extremely dense and fast-rotating stars mainly composed of neutrons. They are extremely hot when they are born, being remnants of supernovae explosions. Their surface temperature is thought to gradually cool down with time, decreasing to less than one million degrees after 100 000 years. However, astrophysicists had proposed the existence of physical mechanisms by which the electromagnetic energy emitted by neutron stars could be funnelled back into their surface in certain regions. Such regions, or 'hot spots', would then be reheated and reach temperatures much higher than the rest of the cooling surface. Such peculiar 'thermal geography' of neutron stars, although speculated, could never be observed directly before. Using XMM-Newton data, a team of European astronomers have observed rotating hot spots on three isolated neutron stars that are well-known X-ray and gamma-ray emitters. The three observed neutron stars are 'PSR B0656-14', 'PSR B1055-52', and 'Geminga', respectively at about 800, 2000 and 500 light-years away from us. As for normal stars, the temperature of a neutron star is measured through its colour that indicates the energy the star emits. The astronomers have divided the neutron star surfaces into ten wedges and have measured the temperature of each wedge. By doing so, they could observe rise and fall of emission from the star's surface, as the hot spots disappear and appear again while the star rotates. It is also the first time that surface details ranging in size from less than 100 metres to about one kilometre are identified on the surface of objects hundreds to thousands light-years away. The team think that the hot spots are most probably linked to the polar regions of the neutron stars. This is where the star's magnetic field funnels charged particles back towards the surface, in a way somehow similar to the 'Northern lights', or aurorae, seen at the poles of planets which have magnetic fields, such as Earth, Jupiter and Saturn. "This result is a first, and a key to understand the internal structure, the dominant role of the magnetic field treading the star interior and its magnetosphere, and the complex phenomenology of neutron stars," says Patrizia Caraveo, of the Istituto Nazionale di Astrofisica (IASF), Milan, Italy. "It has been possible only thanks to the new capabilities provided by the ESA XMM-Newton observatory. We look forward to applying our method to many more magnetically isolated neutron stars," concludes Caraveo. However, there is still a puzzle for the astronomers. If the three 'musketeers' are predicted to have polar caps of comparable dimensions, why then are the hot spots observed in the three cases so different in size, ranging from 60 metres to one kilometre? What mechanisms rule the difference? Or does this mean some of the current predictions on neutron stars magnetic fields need to be revised? The result, by Andrea De Luca, Patrizia Caraveo, Sandro Mereghetti, Matteo Negroni (IASF) and Giovanni Bignami of CESR, Toulouse and University of Pavia, is published in the 20 April 05 issue of the Astrophysical Journal (http://www.journals.uchicago.edu/ApJ, vol. 623:1051-1069). For more information please contact: Patrizia Caraveo, IASF, Milan, Italy Tel: +39 02 2369 9326 E-mail: pat @ mi.iasf.cnr.it Norbert Schartel, ESA XMM-Newton Project Scientist Tel: +34 91 8131 184 E-mail: norbert.schartel @ sciops.esa.int More information * XMM-Newton overview http://www.esa.int/esaSC/120385_index_0_m.html IMAGE CAPTIONS: [Image 1: http://www.esa.int/esaCP/SEMLY9NQS7E_index_1.html] This is an X-ray image of the neutron star 'Geminga', as taken by XMM-Newton on 5 April 2002. It lies about 500 light-years away from Earth. Credits: ESA [Image 2: http://www.esa.int/esaCP/SEMLY9NQS7E...html#subhead1] The left panel shows X-ray emitting regions from three neutron stars, 'PSR B0656-14', 'PSR B1055-52' and 'Geminga', nicknamed the 'three musketeers', as measured by ESA's XMM-Newton, down to scale. While the majority of the neutron stars surfaces emit at temperatures between 500 000 and 700 000 degrees Celsius, smaller spots have significantly higher temperatures, well above one million degrees Celsius. The dimensions of the hot spots are different for the three stars. The right panel shows how the emitting surface of each star varies while the star rotates (note that the hotter and the cooler surface are not drawn to scale). From the animation, the hot spots for PSR 1055 and Geminga disappear for a fraction of the star rotation, while for PSR 0656 the hot spot is always in sight. This offers a new clue to understanding neutron star geometry. Credits: IASF [Image 3: http://www.esa.int/esaCP/SEMLY9NQS7E...html#subhead2] This is an X-ray image of the neutron star 'PSR B0656-14', as taken by XMM-Newton on 23 October 2001. It lies about 800 light-years away from Earth. Credits: ESA [Image 4: http://www.esa.int/esaCP/SEMLY9NQS7E...html#subhead3] This is an X-ray image of the neutron star 'PSR B1055-52', as taken by XMM-Newton on 14 and 15 December 2000. It lies about 2000 light-years away from Earth. Credits: ESA |
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In message , A. Yee
writes ESA News http://www.esa.int 25 April 2005 XMM-Newton sees 'hot spots' on neutron stars Thanks to data from ESA's XMM-Newton spacecraft, European astronomers have observed for the first time rotating 'hot spots' on the surfaces of three nearby neutron stars. First? Wasn't this also reported last year? http://www.esa.int/esaSC/Pr_15_2004_s_en.html -- Remove spam and invalid from address to reply. |
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Jonathan Silverlight wrote:
In message , A. Yee writes ESA News http://www.esa.int 25 April 2005 XMM-Newton sees 'hot spots' on neutron stars Thanks to data from ESA's XMM-Newton spacecraft, European astronomers have observed for the first time rotating 'hot spots' on the surfaces of three nearby neutron stars. First? Wasn't this also reported last year? http://www.esa.int/esaSC/Pr_15_2004_s_en.html Wow, so the first paragraph is wrong! It wasn't for the first time. Same scientist though (who should have known it wasn't the first time...). Well they did find two other nuetron stars with hot spots (besides Geminga). |
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