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  main article image
  [28](Mark Myers/OzGrav ARC Centre of Excellence/Swinburne University of
  Technology)
  [29]SPACE

Astronomers Have Caught a Star Literally Dragging Space-Time Around With It

  MATTHEW BAILES & VIVEK VENKATRAMAN KRISHNAN, THE CONVERSATION
  31 JAN 2020

  One of the predictions of Einstein's [30]general theory of relativity
  is that any spinning body drags the very fabric of space-time in its
  vicinity around with it. This is known as "frame-dragging".

  In everyday life, frame-dragging is both undetectable and
  inconsequential, as the effect is so ridiculously tiny. Detecting the
  frame-dragging caused by the entire Earth's spin requires satellites
  such as the US$750 million Gravity Probe B, and the detection of
  angular changes in gyroscopes equivalent to just one degree every
  100,000 years or so.

  Luckily for us, the Universe contains many naturally occurring
  gravitational laboratories where physicists can observe Einstein's
  predictions at work in exquisite detail.

  Our team's research, [31]published today in Science, reveals evidence
  of frame-dragging on a much more noticeable scale, using a radio
  telescope and a unique pair of compact stars whizzing around each other
  at dizzying speeds.

  The motion of these stars would have perplexed astronomers in Newton's
  time, as they clearly move in a warped space-time, and require
  Einstein's [32]general theory of relativity to explain their
  trajectories.

  An illustration of frame dragging. (Mark Myers/OzGrav ARC Centre of
  Excellence) An illustration of frame dragging. (Mark Myers/OzGrav ARC
  Centre of Excellence)

  [33]General relativity is the foundation of modern gravitational
  theory. It explains the precise motion of the stars, planets and
  satellites, and even the flow of time. One of its lesser-known
  predictions is that spinning bodies drag space-time around with them.
  The faster an object spins and the more massive it is, the more
  powerful the drag.

  One type of object for which this is very relevant is called a
  [34]white dwarf. These are the leftover cores from dead stars that were
  once several times the mass of our Sun, but have since exhausted their
  hydrogen fuel.

  What remains is similar in size to Earth but hundreds of thousands of
  times more massive. White dwarfs can also spin very quickly, rotating
  every minute or two, rather than every 24 hours like Earth does.

  The frame-dragging caused by such a white dwarf would be roughly 100
  million times as powerful as Earth's.

  That is all well and good, but we can't fly to a white dwarf and launch
  satellites around it. Fortunately, however, nature is kind to
  astronomers and has its own way of letting us observe them, via
  orbiting stars called pulsars.

  IFRAME: [35]https://www.youtube.com/embed/GOb3MCAg9zM

  Twenty years ago, CSIRO's Parkes radio telescope discovered a unique
  stellar pair consisting of a white dwarf (about the size of Earth but
  about 300,000 times heavier) and a radio pulsar (just the size of a
  city but 400,000 times heavier).

  Compared with white dwarfs, pulsars are in another league altogether.
  They are made not of conventional atoms, but of neutrons packed tightly
  together, making them incredibly dense. What's more, the pulsar in our
  study spins 150 times every minute.

  This mean that, 150 times every minute, a "lighthouse beam" of radio
  waves emitted by this pulsar sweeps past our vantage point here on
  Earth. We can use this to map the path of the pulsar as it orbits the
  white dwarf, by timing when its pulse arrives at our telescope and
  knowing the speed of light. This method revealed that the two stars
  orbit one another in less than 5 hours.

  This pair, officially called PSR J1141-6545, is an ideal gravitational
  laboratory. Since 2001 we have trekked to Parkes several times a year
  to map this system's orbit, which exhibits a multitude of Einsteinian
  gravitational effects.

  Mapping the evolution of orbits is not for the impatient, but our
  measurements are ridiculously precise. Although PSR J1141-6545 is
  several hundred quadrillion kilometres away (a quadrillion is a million
  billion), we know the pulsar rotates 2.5387230404 times per second, and
  that its orbit is tumbling in space.

  This means the plane of its orbit is not fixed, but instead is slowly
  rotating.

How did this system form?

  When pairs of stars are born, the most massive one dies first, often
  creating a white dwarf. Before the second star dies it transfers matter
  to its white dwarf companion.

  A disk forms as this material falls towards the white dwarf, and over
  the course of tens of thousands of years it revs up the white dwarf,
  until it rotates every few minutes.

  Illustration of a white dwarf being spun-up by the transfer of matter
  from its companion. (ARC Centre of Excellence for Gravitational Wave
  Discovery) A white dwarf being spun-up by the transfer of matter from
  its companion. (ARC Centre of Excellence for Gravitational Wave
  Discovery)

  In rare cases such as this one, the second star can then detonate in a
  supernova, leaving behind a pulsar. The rapidly spinning white dwarf
  drags space-time around with it, making the pulsar's orbital plane tilt
  as it is dragged along. This tilting is what we observed through our
  patient mapping of the pulsar's orbit.

  Einstein himself thought many of his predictions about space and time
  would never be observable. But the past few years have seen a
  revolution in extreme astrophysics, including the [36]discovery of
  gravitational waves and the [37]imaging of a black hole shadow with a
  worldwide network of telescopes. These discoveries were made by
  billion-dollar facilities.

  Fortunately there is still a role in exploring general relativity for
  50-year-old radio telescopes like the one at Parkes, and for patient
  campaigns by generations of graduate students. The Conversation

  [38]Matthew Bailes, ARC Laureate Fellow, Swinburne University of
  Technology., [39]Swinburne University of Technology and [40]Vivek
  Venkatraman Krishnan, Scientific staff, [41]Max Planck Institute.

  This article is republished from [42]The Conversation under a Creative
  Commons license. Read the [43]original article.

  [p?c1=2&c2=10055482&cv=2.0&cj=1]

  Quantcast

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 34. https://theconversation.com/how-we-found-a-white-dwarf-a-stellar-corpse-by-accident-114089
 35. https://www.youtube.com/embed/GOb3MCAg9zM
 36. https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956
 37. https://theconversation.com/observing-the-invisible-the-long-journey-to-the-first-image-of-a-black-hole-115064
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 39. https://theconversation.com/institutions/swinburne-university-of-technology-767
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 43. https://theconversation.com/warp-factor-weve-observed-a-spinning-star-that-drags-the-very-fabric-of-space-and-time-130201

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