Posts Tagged ‘Gravitational Waves

LIGO, A Passion for Understanding

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… a film by Kai Staats


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April 21, 2014 at 10:58 pm

Hunting Gravitational Waves with Lasers

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April 11, 2014 at 6:17 pm

Evidence of cosmic inflation expands universe understanding

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March 19, 2014 at 12:45 pm

Gravitational Waves Help Us Understand Black-Hole Weight Gain

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Supermassive black holes: every large galaxy’s got one. But here’s a real conundrum: how did they grow so big?

Gravitational waves distort space, altering the regular signals from pulsars received by the CSIRO Parkes Radio Telescope. (Credit: Swinburne Astronomy Productions)

Gravitational waves distort space, altering the regular signals from pulsars received by the CSIRO Parkes Radio Telescope. (Credit: Swinburne Astronomy Productions)

A paper in today’s issue of Science pits the front-running ideas about the growth of supermassive black holes against observational data — a limit on the strength of gravitational waves, obtained with CSIRO’s Parkes radio telescope in eastern Australia.
“This is the first time we’ve been able to use information about gravitational waves to study another aspect of the Universe — the growth of massive black holes,” co-author Dr Ramesh Bhat from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) said.
“Black holes are almost impossible to observe directly, but armed with this powerful new tool we’re in for some exciting times in astronomy. One model for how black holes grow has already been discounted, and now we’re going to start looking at the others.”
The study was jointly led by Dr Ryan Shannon, a Postdoctoral Fellow with CSIRO, and Mr Vikram Ravi, a PhD student co-supervised by the University of Melbourne and CSIRO.
Einstein predicted gravitational waves — ripples in space-time, generated by massive bodies changing speed or direction, bodies like pairs of black holes orbiting each other.
When galaxies merge, their central black holes are doomed to meet. They first waltz together then enter a desperate embrace and merge.
“When the black holes get close to meeting they emit gravitational waves at just the frequency that we should be able to detect,” Dr Bhat said.
Played out again and again across the Universe, such encounters create a background of gravitational waves, like the noise from a restless crowd.
Astronomers have been searching for gravitational waves with the Parkes radio telescope and a set of 20 small, spinning stars called pulsars.
Pulsars act as extremely precise clocks in space. The arrival time of their pulses on Earth are measured with exquisite precision, to within a tenth of a microsecond.
When the waves roll through an area of space-time, they temporarily swell or shrink the distances between objects in that region, altering the arrival time of the pulses on Earth.
The Parkes Pulsar Timing Array (PPTA), and an earlier collaboration between CSIRO and Swinburne University, together provide nearly 20 years worth of timing data. This isn’t long enough to detect gravitational waves outright, but the team say they’re now in the right ballpark.
“The PPTA results are showing us how low the background rate of gravitational waves is,” said Dr Bhat.
“The strength of the gravitational wave background depends on how often supermassive black holes spiral together and merge, how massive they are, and how far away they are. So if the background is low, that puts a limit on one or more of those factors.”
Armed with the PPTA data, the researchers tested four models of black-hole growth. They effectively ruled out black holes gaining mass only through mergers, but the other three models are still a possibility.
Dr Bhat also said the Curtin University-led Murchison Widefield Array (MWA) radio telescope will be used to support the PPTA project in the future.
“The MWA’s large view of the sky can be exploited to observe many pulsars at once, adding valuable data to the PPTA project as well as collecting interesting information on pulsars and their properties,” Dr Bhat said…

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October 21, 2013 at 12:35 pm

The Quantum Enhanced LIGO Detector Sets New Sensitivity Record

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Recent progress in generating quantum states of squeezed vacuum has made it possible to enhance the sensitivity of the 4 km gravitational wave detector at the LIGO Hanford Observatory to an unprecedented level. LIGO, the Laser Interferometer Gravitational-wave Observatory, operates large Michelson interferometers with the goal of detecting gravitational waves from black holes, neutron stars, supernovae, and remnants of the Big Bang. Albert Einstein predicted the existence of gravitational waves as part of his general relativity theory. They are extremely faint and instruments with exquisite sensitivity are required to detect them. For example, two binary neutron stars, which are spiraling into each other, and located in the Virgo galaxy cluster will produce a signal no bigger than one thousandth of a proton radius.

The Heisenberg uncertainty principle states that we can’t know both the position and the velocity of a quantum particle perfectly–the better we know the position, the worse we know the velocity, and vice versa. For light waves, the Heisenberg principle tells us that there are unavoidable uncertainties in amplitude and phase that are connected in a similar way. One of the stranger consequences of quantum theory is that there must be fluctuating electric and magnetic fields, even in a total vacuum. In a normal vacuum state, these “zero-point” fluctuations are completely random and the total uncertainty is distributed equally between the amplitude and the phase. However, by using a crystal with non-linear optical properties, it is possible to prepare a special state of light where most of the uncertainty is concentrated in only one of the two variables. Such a crystal can convert normal vacuum to “squeezed vacuum“, which has phase fluctuations SMALLER than normal vacuum! At the same time, the amplitude fluctuations are larger, but phase noise is what really matters for LIGO.

During the last observational run in 2009 and 2010, the LIGO gravitational wave detectors were limited by zero-point fluctuations over most of their frequency range. In 2011, a squeezing crystal and associated precision optics and controls were installed at the LIGO Hanford Observatory to test the idea of reducing the vacuum phase fluctuations. Squeezed vacuum was directed into the output of the large Michelson interferometer. As predicted, this was found to reduce the noise at frequencies above 200 Hz by a small but significant amount, as shown in the figure below. During that test, the LIGO Hanford interferometer achieved better sensitivity than any gravitational wave detector operated to date. This experiment was an important step, following excellent earlier results achieved at higher frequencies with the GEO600 detector in Germany, and shows how future gravitational wave detectors can be made even more sensitive by manipulating the quantum properties of light.

Measured improvement in the sensitivity of the LIGO Hanford gravitational wave detector from this study. The vertical axis indicates the detector noise level as a function of frequency, so the blue curve ("quantum-enhanced" using squeezed vacuum) is better (lower) than the red curve at frequencies above ~200 Hz.

Measured improvement in the sensitivity of the LIGO Hanford gravitational wave detector from this study. The vertical axis indicates the detector noise level as a function of frequency, so the blue curve (“quantum-enhanced” using squeezed vacuum) is better (lower) than the red curve at frequencies above ~200 Hz.

Since LIGO is currently in the middle of an ambitious upgrade–the Advanced LIGO project–the detector used in this experiment has been decommissioned. The Advanced LIGO design was set long before the current squeezed vacuum experiment. As a result, quantum enhancement technologies are currently not in its base plan. However, they are ready to be included in the first upgrades. The successful demonstration of squeezed vacuum technology offers another way for these detectors to become more sensitive and thereby reach out even farther into the Universe. – See more at:

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August 19, 2013 at 10:00 am


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Interfering atoms could help detect gravitational waves

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An artist's impression of gravitational waves from two orbiting black holes. (Courtesy: T Carnahan, NASA GSFC)

An artist’s impression of gravitational waves from two orbiting black holes. (Courtesy: T Carnahan, NASA GSFC)

Scientists in California have proposed a new type of gravitational-wave detector that is immune to laser noise – a problem that adds to the expense of current detector designs. The researchers believe that their proposal – a modified form of an atom interferometer – would be cheaper and easier to implement in space than current laser interferometers.
Gravitational waves are tiny perturbations in the curvature of space–time that arise from accelerating masses – according to Einstein’s general theory of relativity. The first hint that the waves exist was spotted in 1974 as a gradual decrease of the orbital period of the pulsar PSR B1913+16, which circles a neutron star. However, no-one has directly detected a gravitational wave. Such a discovery would provide confirmation of general relativity and also open a new field of gravitational-wave astronomy, in which distant objects could be studied by the waves they emit…
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May 3, 2013 at 8:53 pm


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Space-time waves may be hiding in dead star pulses

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Beating heart of galaxy mergers (Image: MPI for Gravitational Physics/W. Benger-ZIB))

Beating heart of galaxy mergers (Image: MPI for Gravitational Physics/W. Benger-ZIB))

by Lisa Grossman
TAKE the pulse of the universe, and its invisible wrinkles become visible. The first direct evidence of Einstein’s gravitational waves, may already exist in records of light pulses from rapidly spinning dead stars.

Crucially, we may uncover those waves as early as 2013. New research suggests that we’ve underestimated the rate at which black holes merge, and how that changes the light from pulsars.

Gravitational waves are produced by massive, accelerating objects, such as two black holes spinning towards each other (see diagram). The heavier the black holes are, and the faster they’re moving, the more powerful those waves. As they move, the waves stretch and squash space-time like the folds of an accordion. Measuring the waves would be a powerful test of general relativity, and would offer a new wavelength for probing the universe.

But finding traces of the waves is a big challenge, in part because we haven’t had the right tools. A proposed space-based detector was cancelled due to lack of funds, and our best Earth-based detector, LIGO, is closed until 2014 for a major upgrade. Once it is running, LIGO may need another four to five years to collect enough data.

In the meantime, wave hunters have been watching for subtle changes in the timing of pulsars. These dense cores of dead stars sweep the sky with beams of radio waves ejected from their poles. If the beams point directly at Earth, the pulsars appear to blink at exceptionally regular intervals. But when a gravitational wave goes by, it distorts space-time so that the pulsar and Earth bounce towards or away from each other, changing the distance that the pulsar’s light has to travel and making its beat irregular.

Pulsar timing is most sensitive to the larger waves coming from supermassive black holes in the centres of merging galaxies. But galaxies are merging all the time, so the universe is too noisy for a lone pulsar to give a definitive signal, says Sean McWilliams of Princeton University.

Instead, observers use an array of well-characterised pulsars to see if their beats all vary in tandem – a sure sign of a passing gravitational wave. So far, this pulsar timing technique has been coming up empty. But that may be because we haven’t been looking at the data the right way, McWilliams says.

Observers depend on theoretical predictions of how often galactic black holes merge to calculate how large and complex a signal they should expect amid the noise. Current analysis methods look for a smooth data curve, based on the known merger rate. But in 2010, observers noticed that galaxies in the centres of clusters were gaining mass much faster than expected, hinting that these galaxies are growing via more frequent mergers.

Based on this new rate, McWilliams and colleagues calculated that the gravitational wave signal should be 3 to 5 times stronger ( than anticipated, and that the data curve should become more complex. If analysis methods are tuned to this new curve, the team thinks gravitational waves could even be waiting in data collected but not yet analysed.
gravitational waves1
“If the most optimistic predictions of McWilliams are correct, it could be announced next year,” says Maura McLaughlin of West Virginia University, who studies pulsar-timing.

In an independent paper, Alberto Sesana of the Albert Einstein Institute in Golm, Germany, made a similar, more conservative analysis of galaxy mergers and came to nearly the same conclusion: pulsar timing arrays should be able to catch the waves in the next 3 to 10 years (

Both models leave plenty of wiggle room, McLaughlin cautions, and the observing techniques being used now aren’t perfect. “There are lots of uncertainties,” she says. But the push to find gravitational waves is important, she adds.

“Once we have gravitational waves, we’ll have this completely different tool, and we can see things we’ve never seen before because they don’t emit light. It will be really revolutionary.”

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Read also: First Observation of Gravitational Waves is ‘Imminent’

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December 8, 2012 at 6:23 pm

First Observation of Gravitational Waves is ‘Imminent’

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Gravitational wave strain and strain sensitivity for a 5 year observation with PTAs

Gravitational waves are ripples in the fabric of spacetime caused by cataclysmic events such as neutron stars colliding and black holes merging.

The biggest of these events, and the easiest to see, are the collisions between supermassive black holes at the centre of galaxies. So an important question is how often these events occur.

Today, Sean McWilliams and a couple of pals at Princeton University say that astrophysicists have severely underestimated the frequency of these upheavals. Their calculations suggest that galaxy mergers are an order of magnitude more frequent than had been thought. Consequently, collisions between supermassive black holes must be more common too.

That has important implications for the ability of today’s gravitational wave observatories to see them. There is an intense multi-million dollar race to be first to spot gravitational waves but if McWilliams and pals are correct the evidence may already be in the data collected by the first observatories.

The evidence that McWilliams and co rely on is various measurements of galaxy size and mass. This data shows that in the last 6 billion years, galaxies have roughly doubled in mass and quintupled in size.

Astrophysicists know that there has been very little star formation in that time so the only way for galaxies to grow is by merging, an idea borne out by various computer simulations of the way that galaxies must evolve. These simulations suggest that galaxy mergers must be far more common than astronomers had thought.

That raises an interesting prospect–that the supermassive black holes at the centre of these galaxies must be colliding more often too. McWilliams and co calculate that black hole mergers must be between 10 and 30 times more common than expected and that the gravitational wave signals from these events are between 3 and 5 times stronger.

That has important implications for astronomers’ ability to see these signals. Astrophysicists are intensely interested in these waves since they offer an entirely new way to study the cosmos.

One way to spot them is to measure the way the waves stretch and squeeze space as they pass through the Earth, a process that requires precise laser measurements inside machines costing hundreds of millions of dollars.

The most sensitive of these machines is called LIGO, the laser Interferometer gravitational wave observatory in Washington state, which is currently being upgraded although it is not due to reach its design sensitivity until 2018-19.

Another method is to monitor the amazingly regular radio signals that pulsars produce and listen for the way these signals are distorted by the stretching and squeezing of space as gravitational waves pass through the Solar System.

So-called pulsar timing arrays largely rely on existing kit for monitoring pulsars and so are significantly cheaper than bespoke detectors.

Of course, everyone has assumed that the more sensitive bespoke detectors such as LIGO will be the first to see gravitational waves, although not until the end of the decade.

But all that changes if gravitational waves turn out to be stronger than thought. And that’s exactly what McWilliams and co predict. In fact, they say the waves are so strong that current pulsar monitoring kit ought to be capable of spotting them. “We calculate…that the gravitational-wave signal may already be detectable with existing data from pulsar timing arrays,” say the Princeton team.

Pulsars timing arrays are also increasing in sensitivity. If McWilliams and co are correct, this makes the detection of gravitational waves a near certainty within just a few years. Their most pessimistic estimate is that pulsar timing arrays will have nailed this by 2016.

“We expect a detection by 2016 with 95% confidence,” they say.

That’s an extraordinary prediction and a rather refreshing one, given the general reluctance in science to nail your colours to a particular mast.

The first direct observation of gravitational waves will be one of the most important breakthroughs ever made in astronomy; the discoverer a shoe-in for a Nobel Prize.

So the stakes could not be higher in this race and this time there is a distinct chance of an outside bet taking the honours.

Ref: The Imminent Detection Of Gravitational Waves From Massive Black-Hole Binaries With Pulsar Timing Arrays

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November 26, 2012 at 3:57 pm