Andrew Yee[_1_]
January 5th 07, 12:00 AM
Press and Media Relations
University of Warwick
Coventry, UK
For further information please contact:
Dr Boris Gsicke
Department of Physics, University of Warwick
Tel: 02476 574741
Richard Fern, Press Officer
University of Warwick
Tel: 024 76 574255
Peter Dunn, Press and Media Relations Manager
Communications Office, University of Warwick,
Tel: 024 76 523708
PR82 PJD
18th December 2006
Metal Ring Round White Dwarf Solves Missing Planets Puzzle
Astrophysicists at the University of Warwick have found an unusual ring of
metal-rich gas orbiting very close around a white dwarf star. The presence
of the ring helps solve a problem for astronomers who, up till now, have
been puzzled by the apparent absence of planets around white dwarf stars.
Their research is published today in the Friday December 22nd edition of the
journal Science.
The research team led by Dr Boris Gsicke and Professor Tom Marsh from the
University of Warwick's Department of Physics found this unusual gas disc
around a relatively young white dwarf star called SDSS1228+1040. It is
located in the constellation Virgo and it is around 463 light years distant
from our solar system. The star became a white dwarf around 100 million
years ago, and is still fairly hot with a surface temperature around 22,000
degrees.
The team observed double-peaked emission lines superimposed on the white
dwarf's starlight caused by iron, magnesium and calcium from material in the
vicinity of the star. This indicated that they were dealing with a disc of
metal-gas orbiting close around the star (around 1.2 solar radii or roughly
half a million miles). The observations also show that we are looking nearly
edge-on to the ring around the white dwarf.
The likely origin of the disc is an asteroid, of at least 50 kilometres in
size, which approached close enough to the star to be broken up by tides
generated from the gravitational forces of the white dwarf. Those disrupted
remains then entered a close orbit around the star and is evaporated by the
radiation from the white dwarf.
White dwarfs begin as a star similar to our sun (or a star up to 8 times
bigger than our sun). Late in the star's life it swells into a red giant
probably destroying any inner planets at orbits such as those of Mercury and
Venus and pushing out other planets and asteroids to a more distant orbit
than before.
Here is a link to some simple diagrams explaining this:
http://deneb.astro.warwick.ac.uk/phsdaj/public_html/SDSS1228+1040/
In the evolution of what is today a white dwarf, the progenitor of
SDSS1228+1040 will have destroyed all planetary material out to a distance
of 1000 solar radii (roughly 500 million miles), but asteroids still exist
today at larger distances. To destabilise an asteroid from an orbit that far
out, it needs the gravitational force of a larger object, such as a
relatively massive planetesimal, or a genuine planet. While the presence of
asteroids around white dwarf has been hypothesized before, the case of
SDSS1228+1040 provides the first clear proof of the debris of a planetary
disc around a white dwarf, and provides an example of what our own Solar
system may look like in around 5 to 8 billion years.
This "metal" disc around SDSS1228+1040 appears to be relatively rare. Before
their study, three white dwarfs, out of a study of a few hundred, were
suggested to be surrounded by planetary debris material. However, in none of
those three cases could a definite proof of an asteroid origin be made due
to the lack of information on the geometry and the chemical abundance of the
material found in the vicinity of these stars. As part of their study, the
Warwick team investigated data for 500 additional white dwarfs without
finding conclusive evidence for another system harbouring such a disc. The
rarity of such a ring made from a disrupted asteroid tells us that the
majority of planetary systems may look quite different from our own Solar
system. They may not have asteroid belts at all, or not as far out as it is
the case in the Solar system, or they may not have planets at such great
distances as Mars or Jupiter. This conclusion is consistent with the current
knowledge on extrasolar planets found around others stars similar to the
Sun, where the vast majority of the exo-planets are in very close orbits
around their host stars.
Notes for editors
1. A Podcast interview with Dr Gsicke and Professor Marsh is available here:
http://www2.warwick.ac.uk/newsandevents/audio/?podcastItem=white_dwarf.mp3
2. Science have told us that copies of the full embargoed Science paper can
only be distributed only by Science's AAAS Office of Public Programs on
1-202-326-6440 or
3. The research was based on observations obtained on the 4.2m William
Herschel Telescope on La Palma.
IMAGE CAPTION:
[http://mms.warwick.ac.uk/mms/getMedia/813BAD2C89CDF30F004484FB1169F8B7.jpg
(3.97MB)]
Ring around white dwarf. Credits: Mark A. Garlick
University of Warwick
Coventry, UK
For further information please contact:
Dr Boris Gsicke
Department of Physics, University of Warwick
Tel: 02476 574741
Richard Fern, Press Officer
University of Warwick
Tel: 024 76 574255
Peter Dunn, Press and Media Relations Manager
Communications Office, University of Warwick,
Tel: 024 76 523708
PR82 PJD
18th December 2006
Metal Ring Round White Dwarf Solves Missing Planets Puzzle
Astrophysicists at the University of Warwick have found an unusual ring of
metal-rich gas orbiting very close around a white dwarf star. The presence
of the ring helps solve a problem for astronomers who, up till now, have
been puzzled by the apparent absence of planets around white dwarf stars.
Their research is published today in the Friday December 22nd edition of the
journal Science.
The research team led by Dr Boris Gsicke and Professor Tom Marsh from the
University of Warwick's Department of Physics found this unusual gas disc
around a relatively young white dwarf star called SDSS1228+1040. It is
located in the constellation Virgo and it is around 463 light years distant
from our solar system. The star became a white dwarf around 100 million
years ago, and is still fairly hot with a surface temperature around 22,000
degrees.
The team observed double-peaked emission lines superimposed on the white
dwarf's starlight caused by iron, magnesium and calcium from material in the
vicinity of the star. This indicated that they were dealing with a disc of
metal-gas orbiting close around the star (around 1.2 solar radii or roughly
half a million miles). The observations also show that we are looking nearly
edge-on to the ring around the white dwarf.
The likely origin of the disc is an asteroid, of at least 50 kilometres in
size, which approached close enough to the star to be broken up by tides
generated from the gravitational forces of the white dwarf. Those disrupted
remains then entered a close orbit around the star and is evaporated by the
radiation from the white dwarf.
White dwarfs begin as a star similar to our sun (or a star up to 8 times
bigger than our sun). Late in the star's life it swells into a red giant
probably destroying any inner planets at orbits such as those of Mercury and
Venus and pushing out other planets and asteroids to a more distant orbit
than before.
Here is a link to some simple diagrams explaining this:
http://deneb.astro.warwick.ac.uk/phsdaj/public_html/SDSS1228+1040/
In the evolution of what is today a white dwarf, the progenitor of
SDSS1228+1040 will have destroyed all planetary material out to a distance
of 1000 solar radii (roughly 500 million miles), but asteroids still exist
today at larger distances. To destabilise an asteroid from an orbit that far
out, it needs the gravitational force of a larger object, such as a
relatively massive planetesimal, or a genuine planet. While the presence of
asteroids around white dwarf has been hypothesized before, the case of
SDSS1228+1040 provides the first clear proof of the debris of a planetary
disc around a white dwarf, and provides an example of what our own Solar
system may look like in around 5 to 8 billion years.
This "metal" disc around SDSS1228+1040 appears to be relatively rare. Before
their study, three white dwarfs, out of a study of a few hundred, were
suggested to be surrounded by planetary debris material. However, in none of
those three cases could a definite proof of an asteroid origin be made due
to the lack of information on the geometry and the chemical abundance of the
material found in the vicinity of these stars. As part of their study, the
Warwick team investigated data for 500 additional white dwarfs without
finding conclusive evidence for another system harbouring such a disc. The
rarity of such a ring made from a disrupted asteroid tells us that the
majority of planetary systems may look quite different from our own Solar
system. They may not have asteroid belts at all, or not as far out as it is
the case in the Solar system, or they may not have planets at such great
distances as Mars or Jupiter. This conclusion is consistent with the current
knowledge on extrasolar planets found around others stars similar to the
Sun, where the vast majority of the exo-planets are in very close orbits
around their host stars.
Notes for editors
1. A Podcast interview with Dr Gsicke and Professor Marsh is available here:
http://www2.warwick.ac.uk/newsandevents/audio/?podcastItem=white_dwarf.mp3
2. Science have told us that copies of the full embargoed Science paper can
only be distributed only by Science's AAAS Office of Public Programs on
1-202-326-6440 or
3. The research was based on observations obtained on the 4.2m William
Herschel Telescope on La Palma.
IMAGE CAPTION:
[http://mms.warwick.ac.uk/mms/getMedia/813BAD2C89CDF30F004484FB1169F8B7.jpg
(3.97MB)]
Ring around white dwarf. Credits: Mark A. Garlick