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Cluster and Double Star see star crack during massive 'starquake'(Forwarded)



 
 
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Old September 22nd 05, 04:37 PM
Andrew Yee
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Default Cluster and Double Star see star crack during massive 'starquake'(Forwarded)

ESA News
http://www.esa.int

21 September 2005

Cluster and Double Star see star crack during massive 'starquake'

Unique data obtained by ESA's Cluster and the joint Chinese/ESA Double
Star missions provided the first evidence of cracks on a neutron star's
crust. The cracks were caused during the initial phase of the biggest
'starquake' on a neutron star ever recorded.

On 27 December 2004, the radiation from an extremely powerful explosion
on the surface of neutron star SGR 1806-20 reached Earth and lasted more
than the record time of six minutes.

During the first 200 milliseconds, the amount of energy released was
equivalent to what our Sun radiates in 250 000 years, making this the
brightest event originating outside our Solar System and being recorded
on Earth.

SGR 1806-20 is a 'magnetar', a class of neutron star characterised by an
ultra-high magnetic field. SGR 1806-20 is located at around 50 000
light-years from Earth on the far side of our galaxy, the Milky Way in
the direction of the constellation Sagittarius.

A similar blast within 10 light-years of our planet would have destroyed
Earth's ozone layer and be similar to a major nuclear blast.
Fortunately, the closest known magnetar is 13 000 light-years away.

Several scientific satellites observed the giant flare experienced by
SGR 1806-20, including ESA's gamma-ray observatory, Integral. At its
peak, the intensity of the explosion was hundreds of times stronger than
any other observed so far.

For the first fractions of a second (200 milliseconds) the blast blinded
almost all instruments on gamma-ray satellites that were observing that
region of the sky.

However, the particle detectors on board the flotilla of Cluster and
Double Star satellites, designed to study Earth's magnetosphere, were
able to observe the blast for its whole duration without being blinded.

"The unique Cluster and Double Star data provide the first evidence of
three separate timescales within the first 100 milliseconds of this
event," said Prof. Steve Schwartz, lead author of the results, from
Imperial College London. "It is based on the characteristics of these
timescales, combined with theoretical models, that we could draw a
scenario on what happened in SGR 1806-20."

Schwartz and colleagues provide the first observational evidence that
the giant flare was produced when the crust of the magnetar could no
longer plastically compensate the internal magnetic stress and finally
cracked.

One of the three timescales even allowed the estimation of the fracture
size: about five kilometres across. This is a significant size
considering that SGR 1806-20 has been estimated to be a sphere of only a
few tens of kilometres in diameter.

Schwartz combined its findings with other results on the SGR 1806-20
starquake obtained by Italian astronomer Gianluca Israel, from
INAF-Osservatorio Astronomico di Roma, and colleagues.

These results, based on NASA's Rossi X-ray Timing Explorer data,
revealed the presence of quasi-periodic oscillations in the energy
emitted by the neutron star towards the end of its super-blast.

"These oscillatory modes are likely to be associated with global seismic
oscillations. In particular, the large crustal fracturing inferred by us
can easily excite oscillation modes with characteristic frequencies in
the range we observed," commented Schwartz.

Therefore Cluster and Double Star, though designed to study the various
boundary layers of Earth's magnetosphere, have not only enabled to
directly estimate crustal properties of magnetars, they have also linked
interior magnetic processes and their external consequences during giant
flares.

For more information:

Steve Schwartz, Space and Atmospheric Physics Group
Blackett Laboratory, Imperial College London
E-mail: s.schwartz @ imperial.ac.uk

Philippe Escoubet, ESA Cluster Project Scientist
E-mail: philippe.escoubet @ esa.int

The findings presented here appear in the 16 June 2005 issue of the
Astrophysical Journal, in an article titled “A g-ray giant flare from
SGR1806-20: evidence for crustal cracking via initial timescales” by SJ
Schwartz, S Zane, RJ Wilson, FP Pijpers, DR Moore, D Kataria, TS
Horbury, AN Fazakerley, PJ Cargill, (ApJ, 627:L129–L132, 2005).

The findings on the quasi-periodic oscillations of SGR 1806-20 appear in
the 27 June 2005 issue of the Astrophysical Journal, in an article
titled “Discovery of rapid X-ray oscillations in the tail of the SGR
1806-20 hyperflare” by GL Israel, T Belloni, L Stella, Y Rephaeli, DE
Gruber, P Casella, S Dall'Osso, N Rea (ApJ, 628:L53–L56, 2005).

Results from Cluster and Double Star are presented at the “Third Double
Star and Tenth Cluster Workshop”, taking place 19-23 September 2005 at
ESA's European Space Research and Technology Centre (ESTEC), the
Netherlands.

More about...

* ESA's gamma-ray astronomy mission
http://www.esa.int/SPECIALS/Integral/index.html
* Cluster factsheet
http://www.esa.int/esaSC/SEMYN5T1VED_index_0.html
* Double Star factsheet
http://www.esa.int/esaSC/SEMUX5WO4HD_index_0.html

Related articles

* From 'macro' to 'micro' -- turbulence seen by Cluster
http://www.esa.int/esaSC/SEM18O808BE_index_0.html
* Cluster's new view of near-Earth space
http://www.esa.int/esaCP/ESA6VTTM5JC_index_0.html
* Star eats companion
http://www.esa.int/esaSC/SEMWSAA5QCE_index_0.html
* Stars: Neutron stars, pulsars and magnetars
http://www.esa.int/esaSC/SEMK2Z7X9DE_index_0.html
* How the Sun affects us on Earth
http://www.esa.int/esaSC/SEML7BS1VED_index_0.html
* Observations: Seeing in the gamma-ray wavelengths
http://www.esa.int/esaSC/SEM3A2T1VED_index_0.html

Related links

* ESA's Space Weather pages
http://www.esa.int/spaceweather
* Science & Techology in-depth
http://sci.esa.int/science-e/www/obj...objectid=37944

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaSC/SEMERY7X9DE_index_1.html]
Artist's impression of cracks on a neutron star's surface.

Credits: NASA

[Image 2:
http://www.esa.int/esaSC/SEMERY7X9DE...html#subhead1]
SGR 1806-20, the neutron star which underwent a super-powerful explosion
in December 2004, is located in the direction of the constellation of
Sagittarius, 50 000 light-years from Earth.

Credits: NASA

[Image 3:
http://www.esa.int/esaSC/SEMERY7X9DE...html#subhead2]
This animation shows cracks being formed on the surface of a 'magnetar',
a class of neutron star characterised by an extremely high magnetic
field. Cracks form in the first phase of a massive 'starquake', when the
star's crust can no longer compensate for the internal magnetic stress.

Credits: NASA
 




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