Astronomers to Use Pulsars to Detect Gravitational Waves Created by Super-Massive Black Holes

6a00d8341bf7f753ef0134850fc301970c-320wi Last year, an international team of scientists discovered a promising way to fine-tune pulsars into the best precision time-pieces in the Universe and provide astronomers with a new tool to study the powerful gravitational forces that shaped the universe.

Pulsars–incredibly fast spinning collapsed stars–have been studied in great detail since their discovery in 1967.

Pulsars rank at or near the top of freaky phenomena found in our Universe. In the early 1930s, California Institute of Technology astrophysicist, Fred Zwicky, an immigrant from Bulgaria, focused his attention on a question that had long troubled astronomers: the appearance of random, unexplained points of light.

It occurred to Zwicky that if a star collapsed to the sort of density found in the core of atoms, the result would be an unimaginably compacted core: atoms would be crushed together with their electrons squeezed into the nucleus, forming neutrons and a neutron star, with a core so dense that a single spoonful would weigh 200 billion pounds. But there's more, Zwicky  concluded: with the collapse of the star there would be  huge amounts of leftover energy that would result in a massive explosion,  the biggest in the known universe that we called today supernovas.

Most neutron stars house incredibly large magnetic fields. If they are spinning rapidly they make fabulous clocks, cosmic radio beacons we call pulsars. Pulsars can keep time to an accuracy better that one microsecond per year. Some pulsars generate more than 1000 pulses per second, which means, as Lawrence Krauss wrote in The Physics of Star Trek, that an object with the mass of the Sun packed into an object 10 to 20 kilometers across is rotating over 1000 times per second, or more that half the speed of light!

The extremely stable rotation of these 'cosmic clocks' has enabled astronomers to discover the first planets orbiting other stars and provided stringent tests for theories of the Universe.

However, slight irregularities in their spin have puzzled scientists and significantly reduced their usefulness as precision tools.

Astronomers have observed that pulsar spin rates slow very gradually over time. Last year, a team, led by the University of Manchester's Professor Andrew Lyne, used decades-worth of observations to determine that pulsars actually exhibit two different rates of spin change, not one as previously thought, and switch between them abruptly. The team also discovered that these variations are associated with changes in the pulsar's appearance that can be used to 'correct' for the shifts.

"Humanity's best clocks all need corrections, perhaps for the effects of changing temperature, atmospheric pressure, humidity or local magnetic field," says Lyne. "Here, we have found a potential means of correcting an astrophysical clock."

The discovery makes pulsars better tools for detecting gravitational waves–mysterious, powerful ripples which have not yet been directly observed, although widely believed to exist. The direct discovery of gravitational waves, which cause the distortion of space, could allow scientists to study the Universe shortly after the Big Bang and other violent events such as the merging of super-massive black holes.

"Many observatories around the world are attempting to use pulsars in order to detect the gravitational waves that are expected to be created by super-massive binary black holes in the Universe," says University of British Columbia astronomer Ingrid Stairs. "With our new technique we may be able to reveal the gravitational wave signals that are currently hidden because of the irregularities in the pulsar rotation."

"These changes are associated with a change in the shape of the pulse, or tick, emitted by the pulsar," says George Hobbs of the Australia Telescope National Facility. "Because of this, precision measurements of the pulse shape at any particular time indicate exactly what the slowdown rate is and allow the calculation of a 'correction'. This significantly improves their properties as clocks.

As stated by Professor Michael Kramer of the Max Planck Institute for Radioastronomy and the University of Manchester: "These results give a completely new insight into the extreme conditions near neutron stars and also offer the potential for improving our already very precise experiments in gravitation."

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