by neufer » Mon Jan 19, 2009 10:37 pm
Nereid wrote:Chris Peterson wrote:I'm not sure that gravitational redshift has been observed outside the laboratory.
I'm not sure if this would count, but in 2005 the Hubble Space Telescope was used to obtain a clean spectrum of Sirius B (the brightest and nearest white dwarf). This enabled the team to estimate the gravitational redshift of the photons detected (from the surface of the star).
Here is a Press Release about the observation, and
here is the arXiv preprint of the paper
("Hubble Space Telescope Spectroscopy of the Balmer lines in Sirius B").
This certainly seems reasonable to me - and should count as
gravitational redshift observed outside the laboratory .
http://en.wikipedia.org/wiki/Sirius
<<In 1915, Walter Sydney Adams, using a 60-inch (1.5 meter) reflector at Mount Wilson Observatory, observed the spectrum of Sirius B and determined that it was a faint whitish star. This led astronomers to conclude that it was a white dwarf, the second to be discovered. The diameter of Sirius A was first measured by Robert Hanbury Brown and Richard Q. Twiss in 1959 at Jodrell Bank using their stellar intensity interferometer.
In 2005, using the Hubble Space Telescope, astronomers determined that Sirius B has nearly the diameter of the Earth, 12,000 kilometers (7,500 miles), with a mass that is 98% of the Sun>>
While white dwarfs have a gravitational well a 1,000 times shallower than the gravitational well of a neutron star it is still 100 times deeper than that of our sun and a 6563 Angstrom White dwarf Balmer line will be gravitationally red shifted by a good of 3 Angstroms:
6563 Angstrom White dwarf Balmer line is to 3 Angstrom gravitational red shift as
6,371km earth like white dwarf radius is to 3km (1 solar mass) Schwartzchild radius.
Since we know the exact velocity of Sirius B to better than 1km/s from astrometry
we should know Doppler effects down to about 0.02 Angstroms and, hence,
should be able to estimate the mass of Sirius B to better than 1% accuracy.
6563 Angstrom White dwarf Balmer line is to 0.02 Angstrom Doppler shift as
300,000km/s velocity of light is to 1km/s astrometric accuracy Sirius B velocity determination.
http://en.wikipedia.org/wiki/File:White ... radius.jpg
<<[The white dwarf hydrogen/helium] atmosphere, the only part of the white dwarf visible to us, is thought to be the top of an envelope which is a residue of the star's envelope in the AGB phase and may also contain material accreted from the interstellar medium. The envelope is believed to consist of a helium-rich layer with mass no more than 1/100th of the star's total mass, which, if the atmosphere is hydrogen-dominated, is overlain by a hydrogen-rich layer with mass approximately 1/10,000th of the stars total mass. Although thin, these outer layers determine the thermal evolution of the white dwarf. The degenerate electrons in the bulk of a white dwarf conduct heat well. Most of a white dwarf's mass is therefore almost isothermal, and it is also hot: a white dwarf with surface temperature between 8,000 K and 16,000 K will have a core temperature between approximately 5,000,000 K and 20,000,000 K. The white dwarf is kept from cooling very quickly only by its outer layers' opacity to radiation.>>
[quote="Nereid"][quote="Chris Peterson"]I'm not sure that [b]gravitational redshift has been observed outside the laboratory[/b].[/quote]
I'm not sure if this would count, but in 2005 the Hubble Space Telescope was used to obtain a clean spectrum of Sirius B (the brightest and nearest white dwarf). This enabled the team to estimate the gravitational redshift of the photons detected (from the surface of the star).
[url=http://www.spacetelescope.org/news/html/heic0516.html]Here[/url] is a Press Release about the observation, and [url=http://fr.arxiv.org/abs/astro-ph/0506600]here[/url] is the arXiv preprint of the paper
("Hubble Space Telescope Spectroscopy of the Balmer lines in Sirius B").[/quote]
This certainly seems reasonable to me - and should count as
[b] gravitational redshift observed outside the laboratory [/b].
[quote] [b] http://en.wikipedia.org/wiki/Sirius [/b]
<<In 1915, Walter Sydney Adams, using a 60-inch (1.5 meter) reflector at Mount Wilson Observatory, observed the spectrum of Sirius B and determined that it was a faint whitish star. This led astronomers to conclude that it was a white dwarf, the second to be discovered. The diameter of Sirius A was first measured by Robert Hanbury Brown and Richard Q. Twiss in 1959 at Jodrell Bank using their stellar intensity interferometer.[b] In 2005, using the Hubble Space Telescope, astronomers determined that Sirius B has nearly the diameter of the Earth, 12,000 kilometers (7,500 miles), with a mass that is 98% of the Sun[/b]>>[/quote]
While white dwarfs have a gravitational well a 1,000 times shallower than the gravitational well of a neutron star it is still 100 times deeper than that of our sun and a 6563 Angstrom White dwarf Balmer line will be gravitationally red shifted by a good of 3 Angstroms:
6563 Angstrom White dwarf Balmer line is to 3 Angstrom gravitational red shift as
6,371km earth like white dwarf radius is to 3km (1 solar mass) Schwartzchild radius.
Since we know the exact velocity of Sirius B to better than 1km/s from astrometry
we should know Doppler effects down to about 0.02 Angstroms and, hence,
should be able to estimate the mass of Sirius B to better than 1% accuracy.
6563 Angstrom White dwarf Balmer line is to 0.02 Angstrom Doppler shift as
300,000km/s velocity of light is to 1km/s astrometric accuracy Sirius B velocity determination.
[quote][b] http://en.wikipedia.org/wiki/File:WhiteDwarf_mass-radius.jpg [/b]
<<[The white dwarf hydrogen/helium] atmosphere, the only part of the white dwarf visible to us, is thought to be the top of an envelope which is a residue of the star's envelope in the AGB phase and may also contain material accreted from the interstellar medium. The envelope is believed to consist of a helium-rich layer with mass no more than 1/100th of the star's total mass, which, if the atmosphere is hydrogen-dominated, is overlain by a hydrogen-rich layer with mass approximately 1/10,000th of the stars total mass. Although thin, these outer layers determine the thermal evolution of the white dwarf. The degenerate electrons in the bulk of a white dwarf conduct heat well. Most of a white dwarf's mass is therefore almost isothermal, and it is also hot: a white dwarf with surface temperature between 8,000 K and 16,000 K will have a core temperature between approximately 5,000,000 K and 20,000,000 K. The white dwarf is kept from cooling very quickly only by its outer layers' opacity to radiation.>>[/quote]