Tag Archives: gravitational wave

Gravitational waves might be created at the centre of most galaxies

Gravitational waves may be forged by the ungodly forces at the center of galaxies, a new study suggests.

Sagittarius A*, the black hole at the centre of our own galaxy. This image was taken with NASA’s Chandra X-Ray Observatory.

Gravitational waves have recently taken the world by storm. After they were first predicted by Einstein a century ago, it took a hundred years and a groundbreaking project which involved an extremely complex experiment setup and over a thousand scientists’ work to prove their existence. Now, researchers are working hard to understand as much as they can about these elusive waves.

Gravitational waves are small ripples in space-time that spread across the universe. The problem with them (and the reason why they’re so hard to detect) is that they’re only formed by extremely powerful interactions, and even then, they have an extremely low amplitude — in fact, their amplitude is so low that Einstein thought we’d never be able to detect them. They were first observed thanks to a pair of black holes which drew closer and closer to each other before ultimately merging. Since then, astronomers have discovered gravitational waves an additional four times. Every episode involved a pair of merging black holes.

Recent data has shown that these events are fairly common, but we still don’t know much about how black hole pairs end up in this scenario in the first place. Furthermore, in order for these events to lead to observable gravitational waves, they need to be in very specific orbits (either very close or very eccentric).

PhD student Joseph Fernandez at Liverpool John Moores University reports that these events might be even more common than we thought, and might be aided by black holes such as the ones found towards the center of our galaxy. Along with his colleagues, Fernandez found that the orbits of these binary black-hole systems can be changed by the black hole that lies in the center of most galaxies, including our own.

Using prediction models, they showed that black hole binaries which wouldn’t merge in the lifetime of the universe can become tight and eccentric under the gravitational influence of other massive black holes, such as the ones at the center of most galaxies. In 10% of all cases, the merger time is reduced by a factor of over 100 — which explains why we have been able to observe several such instances, and also predicts there will be many more occurrences in the future.

The process also flips the binary system orbital plane, making the BHs orbit in the opposite direction to their initial conditions. This could be used as a smoking gun to allow astronomers to identify when the phenomenon is taking place.

The findings haven’t peer-reviewed yet and will be presented at the European Week of Astronomy and Space Science in Liverpool.

Physicists report new, solid observation of gravitational waves

It’s pretty much official now: there are gravitational waves. A collaboration between the LIGO Lab and the Virgo interferometer collaboration just reported the first joint detection of gravitational waves, adding much more weight to previous detection events.

Image credits: NASA/Ames Research Center/C. Henze.

Virgo had just been switched on

It’s not the first time gravitational waves had been detected. Physicists had recorded three previous events, offering serious proof to support the hypothesis first proposed by Albert Einstein a hundred years ago. Both the LIGO and Virgo detectors picked up the same event — a binary black hole system colliding. Together, the two observers provided 3D detail of the gravitational warping caused by the collision. To make things even more exciting, this comes just after Virgo had been switched on. It basically observed gravitational waves on its trial run.

“This is just the beginning of observations with the network enabled by Virgo and LIGO working together,” says David Shoemaker of MIT, LSC spokesperson. “With the next observing run planned for Fall 2018 we can expect such detections weekly or even more often.”

“It is wonderful to see a first gravitational-wave signal in our brand new Advanced Virgo detector only two weeks after it officially started taking data,” says Jo van den Brand of Nikhef and VU University Amsterdam, spokesperson of the Virgo collaboration. “That’s a great reward after all the work done in the Advanced Virgo project to upgrade the instrument over the past six years.”

Gravitational waves are basically ripples in the curvature of spacetime, generated in certain gravitational interactions. They propagate as waves outward from their source, at the speed of light. However, in order for us to observe them, we need dramatic interactions between the most massive objects we know of: black holes. Even these dramatic events send only a tiny observable wobble, which require finely tuned detectors, the likes of which only LIGO and Virgo provide. That two facilities, functioning independently, confirmed the same thing is highly encouraging.

“Little more than a year and a half ago, NSF [National Science Foundation] announced that its Laser Gravitational-Wave Observatory had made the first-ever detection of gravitational waves resulting from the collision of two black holes in a galaxy a billion light-years away,” says France Córdova, NSF director. “Today, we are delighted to announce the first discovery made in partnership between the Virgo Gravitational-Wave Observatory and the LIGO Scientific Collaboration, the first time a gravitational-wave detection was observed by these observatories, located thousands of miles apart. This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our Universe.”

Thanks to slightly different fine-tuning, the two observers allow researchers to observe different characteristics of the waves. Specifically, Virgo’s arms are angled differently than the two Ligo detectors, which allows it to extract new information about the polarisation of gravitational waves. This is extremely important because previous observations from LIGO came from two detectors with a parallel orientation. Vigo’s arms come at a different angle (an intentional design feature), allowing researchers to get a more 3D view of what’s happening.

“It’s like if I give you just one slice of apple, you can’t guess what the fruit looks like,” said Prof Andreas Freise, a Ligo project scientist at the University of Birmingham. “When you see things from different angles, suddenly you can see the 3D shape as well,” he said. “Einstein’s theory of what [the waves] look like is pretty clear.”

Although Henri Poincaré first suggested that in analogy to an accelerating electrical charge producing electromagnetic waves, gravitational waves are tightly associated to Albert Einstein, who first predicted their existence in 1916, in his famous general theory of relativity. His mathematical equations showed that massive accelerating objects (namely neutron stars or black holes orbiting each other) would disrupt the fabric of space-time, sending waves in the process, much like a stone thrown into a pond sends ripple in the water. However, later on in his work, Einstein started to doubt their existence. In 1936, Einstein and Nathan Rosen submitted a paper to Physical Review in which they argued that the gravitational waves could not exist in the full theory of general relativity. The paper was anonymously reviewed by mathematician Howard P. Robertson, who pointed out some miscalculations within the paper. Furious, Einstein withdrew the paper, but ultimately, one of his assistants, who had been in contact with Robertson, convinced Einstein that the criticism was correct. They rewrote the paper, but with exactly the opposite conclusions, supporting the existence of gravitational waves.