Bonus comic!

Yahoo! Einstein was right again! :D We now have our first detection of gravitational waves! 



What are Gravitational Waves?

Today, the National Science Foundation (NSF) announced the detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of ground-based observatories. But…what are gravitational waves? Let us explain:

Gravitational waves are disturbances in space-time, the very fabric of the universe, that travel at the speed of light. The waves are emitted by any mass that is changing speed or direction. The simplest example is a binary system, where a pair of stars or compact objects (like black holes) orbit their common center of mass.

We can think of gravitational effects as curvatures in space-time. Earth’s gravity is constant and produces a static curve in space-time. A gravitational wave is a curvature that moves through space-time much like a water wave moves across the surface of a lake. It is generated only when masses are speeding up, slowing down or changing direction.

Did you know Earth also gives off gravitational waves? Earth orbits the sun, which means its direction is always changing, so it does generate gravitational waves, although extremely weak and faint.

What do we learn from these waves?

Observing gravitational waves would be a huge step forward in our understanding of the evolution of the universe, and how large-scale structures, like galaxies and galaxy clusters, are formed.

Gravitational waves can travel across the universe without being impeded by intervening dust and gas. These waves could also provide information about massive objects, such as black holes, that do not themselves emit light and would be undetectable with traditional telescopes.

Just as we need both ground-based and space-based optical telescopes, we need both kinds of gravitational wave observatories to study different wavelengths. Each type complements the other.

Ground-based: For optical telescopes, Earth’s atmosphere prevents some wavelengths from reaching the ground and distorts the light that does.

Space-based: Telescopes in space have a clear, steady view. That said, telescopes on the ground can be much larger than anything ever launched into space, so they can capture more light from faint objects.

How does this relate to Einstein’s theory of relativity?

The direct detection of gravitational waves is the last major prediction of Einstein’s theory to be proven. Direct detection of these waves will allow scientists to test specific predictions of the theory under conditions that have not been observed to date, such as in very strong gravitational fields.

In everyday language, “theory” means something different than it does to scientists. For scientists, the word refers to a system of ideas that explains observations and experimental results through independent general principles. Isaac Newton’s theory of gravity has limitations we can measure by, say, long-term observations of the motion of the planet Mercury. Einstein’s relativity theory explains these and other measurements. We recognize that Newton’s theory is incomplete when we make sufficiently sensitive measurements. This is likely also true for relativity, and gravitational waves may help us understand where it becomes incomplete.

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Second Gravitational Wave Discovered!

Scientists at LIGO have just detected gravitational waves for the second time ever!

This is exciting news as it signals that the first detection wasn’t merely a fluke but that we are in fact on the right track to interacting with such phenomena regularly.

What is a gravitational wave? It’s a literal “jiggle” in spacetime caused by a dramatic event like the collision of two large black holes.

This effectively busts wide open a new field of astronomy: gravitational-wave astronomy!

Many space scientists rely on either rovers, spacecraft, optical, radio or even infrared observatories (or some combination) etc. Well now it seems plausible to expect more astronomers to specialize in the interaction between gravitatyand the fabric of spacetime itself.

Considering things like black holes, dark energy and dark matter leave all have considerable gravitational marks and yet hold many secrets back from light, it could stand to reason we now sit on the threshold of a new era in astronomy.

For now though a new door has opened and it’s time to explore

(Image credit: LIGO/T. Pyle)


Scientists just announced the discovery of a second gravitational wave signal

Gravitational waves are ripples through space-time that happen when something like a star collapses or two black holes merge. The discovery of the second one was announced in San Diego by the Laser Interferometer Gravitational Wave Observatory (LIGO) which utilized extraordinary technological measures to find the signal. 

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Scientists from the Laser Interferometer Gravitational-Wave Observatory (LIGO) will make a major research announcement on Thursday, at 10:30 a.m. Eastern Time, at a press conference hosted by the National Science Foundation. Unfortunately, the press conference is for media only, so there will be no live streaming events.* Nevertheless, we’re skeptically excited about tomorrow. If the rumors are true, and gravitational waves have been discovered, it would mean that the most elusive prediction of Einstein’s theory of relativity is right, gravitational radiation exists, and that these waves can be detected. Finding gravitational waves would be a monumental scientific discovery, it would kick-start a new era for gravitational-wave astronomy!

Image Credit: S. Larson

* The press conference will be live streamed via the @NSF YouTube channel: https://www.youtube.com/user/VideosatNSF/live

NASA Astronomy Picture of the Day 2016 February 11 

LIGO Detects Gravitational Waves from Merging Black Holes 

Gravitational radiation has been directly detected. The first-ever detection was made by both facilities of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Washington and Louisiana simultaneously last September. After numerous consistency checks, the resulting 5-sigma discovery was published today. The measured gravitational waves match those expected from two large black holes merging after a death spiral in a distant galaxy, with the resulting new black hole momentarily vibrating in a rapid ringdown. 

A phenomenon predicted by Einstein, the historic discovery confirms a cornerstone of humanity’s understanding of gravity and basic physics. It is also the most direct detection of black holes ever. The featured illustration depicts the two merging black holes with the signal strength of the two detectors over 0.3 seconds superimposed across the bottom. Expected future detections by Advanced LIGO and other gravitational wave detectors may not only confirm the spectacular nature of this measurement but hold tremendous promise of giving humanity a new way to see and explore our universe.


This week we learned that a prediction made by the brilliant, staggeringly counter-intuitive theory of general relativity, formulated by Albert Einstein 100 years ago, has been confirmed.

A billion light-years across the universe, two massive black holes spiraled round and round each other, ever closer, ever faster, until they merged in an extremely brief but tremendous explosion of energy. In that fraction of an instant, more power was produced than that of all the stars in the cosmos, sending subtle ripples in the space-time continuum, of which we are a part, in all directions. A billion years later, on September 14, 2015, these disturbances were intercepted by detectors on Earth, marking the first time we have ever witnessed a gravitational wave.

This is the immense triumph of 50 years of scientific inquiry and technological experimentation, and a watershed in the history of human knowledge.

A new window on the cosmos has just opened. We will be peering through it forevermore.

LIGO: Gravitational Waves Detected 100 Years After Einstein’s Prediction

Gravitational Waves: The Big Discovery

My PhD is in materials physics for the next generation of gravitational wave detectors. That’s a fancy way of saying I spend a lot of time in a lab trying to understand the behaviour of pieces of sapphire, silicon and silica. One day this will help to inform the design of a huge machine which will be used to observe wobbles in space. The sapphire and silica both look like glass, the silicon is shiny and dark grey.

This is a sapphire disc suspended on two very thin tungsten fibres.

Those space wobbles, or gravitational waves, as my boss prefers me to call them, are caused by huge, violent events going on out in the cosmos. Things like colliding black holes and exploding stars. It’s dramatic stuff. Turns out that’s because you need a whole lot of energy to make space wobble even a teeny tiny bit.

When there is enough energy to make waves, the waves are really small. So they’re really hard to detect. Einstein predicted them about 100 years ago and even he thought we’d never be able to find them because they’d be too small. However, scientists are tenacious. Here’s a rough timeline (after the fancy picture):

This is an artist’s impression of two neutron stars in orbit around each other. Eventually they will collide and merge into one. The swirls represent the gravitational waves. Image credit: NASA
  • 1916: Albert Einstein publishes a Review Article on General Relativity, it is suggested that gravitational waves are a result of general relativity but it’s not clear that they will be directly detectable.
  • 1955: Joseph Weber, an American physicist, takes a sabbatical to work with John Archibald Wheeler. He develops an early design for a gravitational wave detector that takes the form of a large aluminium bar. If a gravitational wave passes the bar, it should cause it to ring.
  • 1968: Joseph Weber claims to have “good evidence” of a detection but others point out that his equipment should not be able to detect waves so small. The claim remains controversial.
  • 1972: A “Weber bar” is sent to the Moon with Apollo 17.
  • 1974: Hulse and Taylor discover a binary pulsar. A pulsar is a kind of neutron star which sends out radio waves periodically as it spins. This one was orbiting a different star. Hulse and Taylor observed it for a long time.
  • 1983: Hulse and Taylor published a paper saying that the period of the pulses from their pulsar was changing. That the system must be losing energy. From their measurements, the only known way for this energy to be lost was through gravitational waves.
  • 1992: Kip Thorn, Ronald Dreever and Rainer Weiss cofound LIGO: The Laser Interferometric Gravitational Wave Observatory. This is a new kind of gravitational wave detector which uses a laser to measure the position of mirrors 4 kilometers away. The measurements are very precise. If a gravitational wave passes the detector the mirrors will move and that movement will be picked up. There are to be three detectors: One in Livingston, Louisiana and two in Hanford in Richland, Washington.
  • 1993: Hulse and Taylor receive the Nobel Prize for Physics for the first indirect detection of gravitational waves.
  • 1993: The Virgo detector, similar to LIGO is founded in Italy, with collaborators in France, The Netherlands, Poland and Hungary. It gets final approval in 1994.
  • 1995: Construction of the GEO600 detector begins. This again is similar to LIGO but has shorter arms. It will become the test bed for many new technologies
  • 1995: The TAMA project begins in Japan. Like GEO600, this is another, smaller interferometric detector. Again, it was a test bed used for developing technologies
  • 2002: The LIGO detectors are built and the search with this kind of detector begins. It continues until 2010, when they are shut down for upgrades that will make the detectors even more sensitive.
  • 2003: TAMA stops taking data but is still used as a testing facility.
  • 2003: MiniGRAIL is built. This is a bar-type detector, with one obvious difference: Instead of being a bar, it’s a sphere. It is operated at cryogenic temperatures to improve sensitivity.
  • 2003: The construction of the Virgo detector is completed.
  • 2005: A different approach is taken with “pulsar timing.” This is more like the original indirect detection made by Hulse and Taylor. The Parkes Pulsar Timing Array begins collecting data.
  • 2006: CLIO, the Cryogenic Laser Interferometry is built in the Kamioka mine in Japan, it will pave the way for KAGRA.
  • 2007: Virgo starts taking data
  • 2008: The Deci-Hertz observatory is proposed. It would be a space based observatory run by Japan.
  • 2009: LIGO India, or IndIGO, is proposed.
  • 2010: The LCGT (Large Scale Cryogenic Gravitational Wave Telescope) is approved in Japan.
  • 2011: Virgo is decommissioned so that upgrades can be made to improve sensitivity. Advanced Virgo is planned to go online in 2016.
  • 2011: NASA announces that it will be unable to fund LISA due to funding limitations. ESA now needs to fund it alone which requires scaling down the mission. The scaled down version is originally called NGO (the New Gravitational-wave Observatory) but is later renamed eLISA.
  • 2012: LCGT is renamed KAGRA (the Kamioka Gravitational Wave Detector).
  • 2014: BICEP2 reports a detection of gravitational waves which is later retracted when it is discovered that a different effect has been overlooked.
  • 2015: The first “Advanced LIGO” observing run begins in September. Sensitivity is now four times higher than for initial LIGO. On 14th September a signal is detected.
  • 2015: The LISA Pathfinder mission is launched in December. The launch is successful but it won’t be until February 2016 that we find out whether or not everything is working as it should be.
  • 2016: A press conference is held on 11th February (today!) announcing the first direct detection of gravitational waves. The detection was made by LIGO.
  • 2016, but 30 seconds later: The whole gravitational waves community celebrates.

Sometimes it takes a full century and literally thousands of scientists to make something happen. Sometimes science is just hard and there’s no getting away from that but in the end really amazing things can be achieved. Not that this is the end, really. This is actually just the beginning.

Mostly people do astronomy by making observations, or by running computer models based on those observations and some scientific theories that they want to test. People don’t often go to space to do experiments and they certainly don’t do experiments on actual stars and planets. So astronomy is an observational science. It’s about watching carefully to see what happens.

The Western leg of LIGO Hanford. A laser beam runs all the way down that 4 km arm and bounces off a suspended fused silica mirror at the far end, then it runs all the way back. Image from Wikipedia.

Normally people watch with light. That’s just how telescopes work. It might be a telescope that picks up the same range of light as the human eye, or it might be a telescope that picks up radio waves, or it might be a telescope that picks up something else, but it’s all light (except when it’s neutrinos, but that’s another story altogether). Thing is, whilst stars make light and planets reflect it so we can see them, not everything in space glows or shines. Black holes, for example, definitely don’t. If it doesn’t glow or shine we have to get creative because ordinarily telescopes won’t pick it up.

However, black holes are heavy, they have mass. That’s true of a lot of the other stuff in space that doesn’t shine too. Anything with mass works with gravity and so, in the right circumstances it should produce some kind of gravitational wave signature. Eventually, the goal is to be able to observe a wide range of these signatures, to understand them   and to use them to do new astronomy. When we get to that stage we’ll see things no one has ever seen before, using gravitational waves instead of light.

These are oxidised silicon blocks. This photograph is not in black and white.

So the first detection is significant not only because its been a long time coming, or because it’s yet another piece of evidence for Einstein being one smart cookie, but because it leads us that little bit further along in understanding our Universe.

To read more about this stuff I strongly recommend checking out the blog posts by other scientists in the collaboration. Notably, the following: