Andrew Yee[_1_]
May 4th 07, 05:06 PM
ESA Science News
http://sci.esa.int
3 May 2007
Has SOHO ended a 30-year quest for solar ripples?
The ESA-NASA Solar and Heliospheric Observatory (SOHO) may have glimpsed
long-sought oscillations on the Sun's surface. The data will reveal details
about the core of our star and it contains clues on how the Sun formed, 4.6
thousand million years ago.
The subtle variations reveal themselves as a miniscule ripple in the overall
movement of the solar surface. Astronomers have been searching for ripples
of this kind since the 1970s, when they first detected that the solar
surface was oscillating in and out.
The so-called 'g-modes' are driven by gravity and provide information about
the deep interior of the Sun. They are thought to occur when gas churning
below the solar surface plunges even deeper into our star and collides with
denser material, sending ripples propagating through the Sun's interior and
up to the surface. It is the equivalent of dropping a stone in a pond.
Unfortunately for observers, these waves are badly degraded during their
passage to the solar surface. By the time g-modes reach the exterior, they
are little more than ripples a few metres high.
To make matters more difficult, the g-modes take between two and seven hours
to oscillate just once. So, astronomers are faced with having to detect a
swell on the surface that rises a metre or two over several hours.
Now, however, astronomers using the Global Oscillation at Low Frequency
(GOLF) instrument on SOHO think they may have caught glimpses of this
behaviour. Instead of looking for an individual oscillation, they looked for
the signature of the cumulative effect of a large number of these
oscillations.
As an analogy, imagine that the Sun was an enormous piano playing all the
notes simultaneously. Instead of looking for a particular note (middle C for
instance) it would be easier to search for all the 'C's, from all the
octaves together.
In the piano their frequencies are related to each other just as on the Sun,
one class of g modes are separated by about 24 minutes.
"So that's what we looked for, the cumulative effect of several g modes,"
says Rafael A. Garcia, DSM/DAPNIA/Service d'Astrophysique, France. They
combined ten years of data from GOLF and then searched for any hint of the
signal at 24 minutes. They found it.
"We must be cautious but if this detection is confirmed, it will open a
brand new way to study the Sun's core," says Garcia.
Until now, the rotation rate of the solar core was uncertain. If the GOLF
detection is confirmed, it will show that the solar core is definitely
rotating faster than the surface.
The rotation speed of the solar core is an important constraint for
investigating how the entire Solar System formed, because it represents the
hub of rotation for the interstellar cloud that eventually formed the Sun
and all the bodies around it.
The next step for the team is to refine the data to increase their
confidence in the detection. To do this, they plan to incorporate data from
other instruments, both on SOHO and at ground-based observatories.
"By combining data from space (VIRGO and MDI, on SOHO) and ground (GONG and
BiSON) instruments, we hope to improve this detection and open up a new
branch of solar science," says Garc.
Notes for editors
The findings are published in the 4 May 2007 edition of the journal Science,
in the article: "Tracking solar gravity modes: the dynamics of the solar
core", by R. Garcia, S. Turck-Chieze, S. Jimenez-Reyes, J. Ballot, P. Palle, A.
Eff-Darwich, S. Mathur, J. Provost.
For more information:
Rafael A. Garcia
DSM/DAPNIA/Service d'Astrophysique, France
Email: Rafael.Garcia @ cea.fr
Alan Gabriel, SOHO GOLF Principal Investigator
Institut d'Astrophysique Spatiale, Universite Paris XI, France
Email: Gabriel @ ias.u-psud.fr
Bernard Fleck, ESA SOHO Project Scientist
Email: Bfleck @ esa.nascom.nasa.gov
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMOZPU681F_index_1.html ]
http://sci.esa.int
3 May 2007
Has SOHO ended a 30-year quest for solar ripples?
The ESA-NASA Solar and Heliospheric Observatory (SOHO) may have glimpsed
long-sought oscillations on the Sun's surface. The data will reveal details
about the core of our star and it contains clues on how the Sun formed, 4.6
thousand million years ago.
The subtle variations reveal themselves as a miniscule ripple in the overall
movement of the solar surface. Astronomers have been searching for ripples
of this kind since the 1970s, when they first detected that the solar
surface was oscillating in and out.
The so-called 'g-modes' are driven by gravity and provide information about
the deep interior of the Sun. They are thought to occur when gas churning
below the solar surface plunges even deeper into our star and collides with
denser material, sending ripples propagating through the Sun's interior and
up to the surface. It is the equivalent of dropping a stone in a pond.
Unfortunately for observers, these waves are badly degraded during their
passage to the solar surface. By the time g-modes reach the exterior, they
are little more than ripples a few metres high.
To make matters more difficult, the g-modes take between two and seven hours
to oscillate just once. So, astronomers are faced with having to detect a
swell on the surface that rises a metre or two over several hours.
Now, however, astronomers using the Global Oscillation at Low Frequency
(GOLF) instrument on SOHO think they may have caught glimpses of this
behaviour. Instead of looking for an individual oscillation, they looked for
the signature of the cumulative effect of a large number of these
oscillations.
As an analogy, imagine that the Sun was an enormous piano playing all the
notes simultaneously. Instead of looking for a particular note (middle C for
instance) it would be easier to search for all the 'C's, from all the
octaves together.
In the piano their frequencies are related to each other just as on the Sun,
one class of g modes are separated by about 24 minutes.
"So that's what we looked for, the cumulative effect of several g modes,"
says Rafael A. Garcia, DSM/DAPNIA/Service d'Astrophysique, France. They
combined ten years of data from GOLF and then searched for any hint of the
signal at 24 minutes. They found it.
"We must be cautious but if this detection is confirmed, it will open a
brand new way to study the Sun's core," says Garcia.
Until now, the rotation rate of the solar core was uncertain. If the GOLF
detection is confirmed, it will show that the solar core is definitely
rotating faster than the surface.
The rotation speed of the solar core is an important constraint for
investigating how the entire Solar System formed, because it represents the
hub of rotation for the interstellar cloud that eventually formed the Sun
and all the bodies around it.
The next step for the team is to refine the data to increase their
confidence in the detection. To do this, they plan to incorporate data from
other instruments, both on SOHO and at ground-based observatories.
"By combining data from space (VIRGO and MDI, on SOHO) and ground (GONG and
BiSON) instruments, we hope to improve this detection and open up a new
branch of solar science," says Garc.
Notes for editors
The findings are published in the 4 May 2007 edition of the journal Science,
in the article: "Tracking solar gravity modes: the dynamics of the solar
core", by R. Garcia, S. Turck-Chieze, S. Jimenez-Reyes, J. Ballot, P. Palle, A.
Eff-Darwich, S. Mathur, J. Provost.
For more information:
Rafael A. Garcia
DSM/DAPNIA/Service d'Astrophysique, France
Email: Rafael.Garcia @ cea.fr
Alan Gabriel, SOHO GOLF Principal Investigator
Institut d'Astrophysique Spatiale, Universite Paris XI, France
Email: Gabriel @ ias.u-psud.fr
Bernard Fleck, ESA SOHO Project Scientist
Email: Bfleck @ esa.nascom.nasa.gov
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaSC/SEMOZPU681F_index_1.html ]