|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Cannibal stars like their food hot, XMM-Newton reveals (Forwarded)
ESA News
http://www.esa.int 23 March 2006 Cannibal stars like their food hot, XMM-Newton reveals ESA's XMM-Newton has seen vast clouds of superheated gas, whirling around miniature stars and escaping from being devoured by the stars' enormous gravitational fields -- giving a new insight into the eating habits of the galaxy's 'cannibal' stars. The clouds of gas range in size from a few hundred thousand kilometres to a few million kilometres, ten to one hundred times larger than the Earth. They are composed of iron vapour and other chemicals at temperatures of many millions of degrees. "This gas is extremely hot, much hotter than the outer atmosphere of the Sun," said Maria Díaz Trigo of ESA's European Science and Technology Research Centre (ESTEC), who led the research. ESA's XMM-Newton x-ray observatory made the discovery when it observed six so-called 'low-mass X-ray binary' stars (LMXBs). The LMXBs are pairs of stars in which one is the tiny core of a dead star. Measuring just 15*20 kilometres across and comparable in size to an asteroid, each dead star is a tightly packed mass of neutrons containing more than 1.4 times the mass of the Sun. Its extreme density generates a powerful gravitational field that rips gas from its 'living' companion star. The gas spirals around the neutron star, forming a disc, before being sucked down and crushed onto its surface, a process known as 'accretion'. The newly discovered clouds sit where the river of matter from the companion star strikes the disc. The extreme temperatures have ripped almost all of the electrons from the iron atoms, leaving them carrying extreme electrical charges. This process is known as 'ionisation'. The discovery solves a puzzle that has dogged astronomers for several decades. Certain LMXBs appear to blink on and off at X-ray wavelengths. These are 'edge-on' systems, in which the orbit of each gaseous disc lines up with Earth. In previous attempts to simulate the blinking, clouds of low-temperature gas were postulated to be orbiting the neutron star, periodically blocking the X-rays. However, these models never reproduced the observed behaviour well enough. XMM-Newton solves this by revealing the ionised iron. "It means that these clouds are much hotter than we anticipated," said Díaz. With high-temperature clouds, the computer models now simulate much better the dipping behaviour. Some 100 known LMXBs populate our galaxy, the Milky Way. Each one is a stellar furnace, pumping X-rays into space. They represent a small-scale model of the accretion thought to be taking place in the very heart of some galaxies. One in every ten galaxies shows some kind of intense activity at its centre. This activity is thought to be coming from a gigantic black hole, pulling stars to pieces and devouring their remains. Being much closer to Earth, the LMXBs are easier to study than the active galaxies. "Accretion processes are still not well understood. The more we understand about the LMXBs, the more useful they will be as analogues to help us understand the active galactic nuclei," says Díaz. Notes to editors: The findings appear in Astronomy & Astrophysics (445, 179*195, 2006). The original article, 'Spectral changes during dipping in low-mass X-ray binaries due to highly-ionized absorbers', is by M. Díaz Trigo and A.N. Parmar (ESA, Noordwijk, The Netherlands), L. Boirin (Observatoire Astronomique de Strasbourg, France), M. Méndez and J.S. Kaastra (SRON, National Institute for Space Research, Utrecht, The Netherlands). For more information: Maria Diaz Trigo, ESA, ESTEC, Noordwijk, The Netherlands E-mail: mdiaz @ rssd.esa.int Arvind Parmar, ESA, ESTEC, Noordwijk, The Netherlands E-mail: arvind.parmar @ esa.int Norbert Schartel, ESA XMM-Newton Project Scientist, ESAC, Madrid E-mail: norbert.schartel @ sciops.esa.int More about... * XMM-Newton overview http://www.esa.int/esaSC/120385_index_0_m.html Related articles * 'Deep impact' of pulsar around companion star http://www.esa.int/esaCP/SEMK6HMVGJE_index_0.html * XMM-Newton scores 1000 top-class science results http://www.esa.int/esaCP/SEMAB0NZCIE_index_0.html * ESA's Integral and XMM-Newton missions extended http://www.esa.int/esaCP/SEM31GVLWFE_index_0.html * XMM-Newton sees 'hot spots' on neutron stars http://www.esa.int/esaCP/SEMLY9NQS7E_index_0.html * ESA is hot on the trail of Geminga http://www.esa.int/esaCP/SEMQB4YO4HD_index_0.html * XMM-Newton probes formation of galaxy clusters http://www.esa.int/esaCP/SEMDW5A5QCE_index_0.html * XMM-Newton's fifth anniversary in orbit http://www.esa.int/esaSC/SEMZ5CXJD1E_index_0.html IMAGE CAPTIONS: [Image 1: http://www.esa.int/esaCP/SEM7T6OVGJE_index_1.html] Artist's impression of a vast cloud of superheated gas whirling around an asteroid-sized cannibal star, part of a low-mass X-ray binary star system. The clouds, discovered by ESA's XMM-Newton space observatory, are composed of iron vapour and other chemicals at many millions of degrees and are located where the 'river' of matter from the companion star strikes the disc. The clouds periodically block the X-ray emission from the cannibal star and cause an X-ray 'blinking'. Credits: ESA [Image 2: http://www.esa.int/esaCP/SEM7T6OVGJE...html#subhead1] Artist's impression of XMM-Newton, ESA's Earth-orbiting x-ray observatory. Credits: ESA |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Most Milky Way Stars Are Single (Forwarded) | Andrew Yee | Astronomy Misc | 0 | January 30th 06 04:02 PM |
Most Milky Way Stars Are Single (Forwarded) | Andrew Yee | News | 0 | January 30th 06 03:37 PM |
Spitzer Reveals Unexpected Disks Around Interacting Stars (Forwarded) | Andrew Yee | News | 0 | January 10th 06 03:16 PM |
[sci.astro] Stars (Astronomy Frequently Asked Questions) (7/9) | [email protected] | Astronomy Misc | 0 | October 6th 05 02:36 AM |
Could galactic find be Andromeda's food? (Forwarded) | Andrew Yee | Astronomy Misc | 0 | January 9th 04 06:58 PM |