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5th January 2014, 22:33
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Triple star system 'can reveal secrets of gravity'
5 January 2014 Last updated at 19:18
By James Morgan
Science reporter, BBC News, Washington DC
http://news.bbcimg.co.uk/media/images/72074000/jpg/_72074046_triple_system_nrao.jpg
The pulsar (L) is orbited by a hot white dwarf star (C) both of which are orbited by a cooler, distant white dwarf (R)
Astronomers have discovered a unique triple star system which could reveal the true
nature of gravity.They found a pulsar with two white dwarfs all packed in a space
smaller than Earth's orbit of the Sun.The trio's unusually close orbits allow precise
measurements of gravity and could resolve difficulties with Einstein's theories.
The results appear in Nature journal and will be presented at the 223rd American
Astronomical Society meeting.
"This triple system gives us a natural cosmic laboratory far better than anything found
before for learning exactly how such three-body systems work and potentially for
detecting problems with general relativity that physicists expect to see under extreme
conditions," said Scott Ransom of the US National Radio Astronomy Observatory (NRAO) in Charlottesville, VA.
"This is a fascinating system in many ways, including what must have been a
completely crazy formation history, and we have much work to do to fully understand it."
Pulsars emit lighthouse-like beams of radio waves that rapidly sweep through space as
the stars spin on their axes.They are formed after a supernova collapses a burnt-out
star to a dense, highly magnetised ball of neutrons.Using the Green Bank Telescope, the
astronomers discovered a pulsar 4,200 light-years from Earth, spinning nearly 366
times per second.Such rapidly-spinning bodies are called millisecond pulsars - and are
used by astronomers as precision tools for studying gravitational effects and other
phenomena.Subsequent observations showed the pulsar is in a close orbit with a white
dwarf star, and that pair is in orbit with another, more-distant white dwarf.
http://news.bbcimg.co.uk/media/images/72074000/jpg/_72074373_r1600345-green_bank_radio_telescope,_west_virginia-spl.jpg
Green Bank radio telescope, West Virginia Green Bank is 100m wide - the world's
largest fully steerable radio telescope Three-body systems are keenly studied because
they allow competing theories of gravity to be tested. But until now the only known
triple system containing a millisecond pulsar was one with a planet as the outer
companion, causing only weak gravitational interactions.
"This is the first millisecond pulsar found in such a system, and we immediately
recognised that it provides us a tremendous opportunity to study the effects and nature
of gravity," Prof Ransom said.
"The gravitational perturbations imposed on each member of this system by the others
are incredibly pure and strong."
By precisely timing the arrival of the pulses, the scientists were able to calculate the
geometry of the system and the masses of the stars.The pulsar's inner white-dwarf
companion has an orbital period of less than two days, while the outer dwarf has a
period of almost a year.The system gives the scientists the best opportunity yet to look
for violations of the equivalence principle described by Einstein - which states that the
effect of gravity on a body does not depend on the nature or internal structure of that body.
This was famously illustrated by Galileo's dropping of two balls of different weights from
the Leaning Tower of Pisa, and Apollo 15 Commander Dave Scott's dropping of a
hammer and a falcon feather while standing on the Moon in 1971.Rather than drifting to
the ground, the feather plummeted, falling as fast as the hammer. Without air
resistance to slow the feather, both objects hit the lunar dust at the same time.
"While Einstein's theory of general relativity has so far been confirmed by every
experiment, it is not compatible with quantum theory," said Prof Ransom.
"Because of that, physicists expect that it will break down under extreme conditions."
High-precision timing of the pulsar's "lighthouse" flashes will let astronomers hunt for
deviations in the equivalence principle at a sensitivity several orders of magnitude
greater than ever before, said astronomer Prof Ingrid Stairs of the University of British Columbia.
"Finding a deviation would indicate a breakdown of general relativity and point us
toward a new, correct theory of gravity," she said.
The 223rd AAS meeting runs from 5-9 January in Washington DC.
http://www.bbc.co.uk/news/science-environment-25598051
Triple star system 'can reveal secrets of gravity'
5 January 2014 Last updated at 19:18
By James Morgan
Science reporter, BBC News, Washington DC
http://news.bbcimg.co.uk/media/images/72074000/jpg/_72074046_triple_system_nrao.jpg
The pulsar (L) is orbited by a hot white dwarf star (C) both of which are orbited by a cooler, distant white dwarf (R)
Astronomers have discovered a unique triple star system which could reveal the true
nature of gravity.They found a pulsar with two white dwarfs all packed in a space
smaller than Earth's orbit of the Sun.The trio's unusually close orbits allow precise
measurements of gravity and could resolve difficulties with Einstein's theories.
The results appear in Nature journal and will be presented at the 223rd American
Astronomical Society meeting.
"This triple system gives us a natural cosmic laboratory far better than anything found
before for learning exactly how such three-body systems work and potentially for
detecting problems with general relativity that physicists expect to see under extreme
conditions," said Scott Ransom of the US National Radio Astronomy Observatory (NRAO) in Charlottesville, VA.
"This is a fascinating system in many ways, including what must have been a
completely crazy formation history, and we have much work to do to fully understand it."
Pulsars emit lighthouse-like beams of radio waves that rapidly sweep through space as
the stars spin on their axes.They are formed after a supernova collapses a burnt-out
star to a dense, highly magnetised ball of neutrons.Using the Green Bank Telescope, the
astronomers discovered a pulsar 4,200 light-years from Earth, spinning nearly 366
times per second.Such rapidly-spinning bodies are called millisecond pulsars - and are
used by astronomers as precision tools for studying gravitational effects and other
phenomena.Subsequent observations showed the pulsar is in a close orbit with a white
dwarf star, and that pair is in orbit with another, more-distant white dwarf.
http://news.bbcimg.co.uk/media/images/72074000/jpg/_72074373_r1600345-green_bank_radio_telescope,_west_virginia-spl.jpg
Green Bank radio telescope, West Virginia Green Bank is 100m wide - the world's
largest fully steerable radio telescope Three-body systems are keenly studied because
they allow competing theories of gravity to be tested. But until now the only known
triple system containing a millisecond pulsar was one with a planet as the outer
companion, causing only weak gravitational interactions.
"This is the first millisecond pulsar found in such a system, and we immediately
recognised that it provides us a tremendous opportunity to study the effects and nature
of gravity," Prof Ransom said.
"The gravitational perturbations imposed on each member of this system by the others
are incredibly pure and strong."
By precisely timing the arrival of the pulses, the scientists were able to calculate the
geometry of the system and the masses of the stars.The pulsar's inner white-dwarf
companion has an orbital period of less than two days, while the outer dwarf has a
period of almost a year.The system gives the scientists the best opportunity yet to look
for violations of the equivalence principle described by Einstein - which states that the
effect of gravity on a body does not depend on the nature or internal structure of that body.
This was famously illustrated by Galileo's dropping of two balls of different weights from
the Leaning Tower of Pisa, and Apollo 15 Commander Dave Scott's dropping of a
hammer and a falcon feather while standing on the Moon in 1971.Rather than drifting to
the ground, the feather plummeted, falling as fast as the hammer. Without air
resistance to slow the feather, both objects hit the lunar dust at the same time.
"While Einstein's theory of general relativity has so far been confirmed by every
experiment, it is not compatible with quantum theory," said Prof Ransom.
"Because of that, physicists expect that it will break down under extreme conditions."
High-precision timing of the pulsar's "lighthouse" flashes will let astronomers hunt for
deviations in the equivalence principle at a sensitivity several orders of magnitude
greater than ever before, said astronomer Prof Ingrid Stairs of the University of British Columbia.
"Finding a deviation would indicate a breakdown of general relativity and point us
toward a new, correct theory of gravity," she said.
The 223rd AAS meeting runs from 5-9 January in Washington DC.
http://www.bbc.co.uk/news/science-environment-25598051