And that seems like a good place to close down the live blog. What a fantastic day. It has been full of unalloyed joy at the ingenuity of human beings and our ability to develop technology to help us perceive the Universe.
We now know that 1.3 billion years ago, two gigantic black holes collided. For a brief moment, they gave out more energy that all the stars in the whole universe put together, and that set the very fabric of spacetime rippling. Those ripples have traveled through space ever since.
They arrived at Earth on 14 September 2015 and disturbed the detectors in the LIGO observatory by no more than one thousandth the width of a proton, the particle that makes up the heart of a hydrogen atom.
The fact that this minuscule movement was detected means that a whole new era has opened up. One in which we will be able to look into the hearts of stars, watch the most cataclysmic events in the universe unfold, and eventually see the moment of the big bang itself.
And all of this follows from a prediction of Albert Einstein’s 100 years ago, from a set of equations he developed originally to help him sort out a small discrepancy in the orbit of planet Mercury.
Of course, today belongs to the thousand plus researchers who work on LIGO and the other gravitational wave detectors around the globe, but it also belongs to Einstein, true genius.
Today is not the end of a search, but a beginning. It is the beginning of gravitational wave astronomy, prepare for the wonders to come.
Still got questions about today’s monumental discovery? Leave them in the comments here and Prof Jon Butterworth will answer them tomorrow between 14:00-15:00 GMT.
Arvanitaki also says that today’s detection shows that there could be thousands of detections a year with the fully sensitive LIGO and Virgo observatories. Truly a new era is opening up.
Arvanitaki now explains that there are experiments to try to detect gravitational waves by measuring the ultra-precise time pulses that comes from the spinning hearts of dead stars called pulsars.
Boyle now talking about the proposed eLISA space-based gravitational wave observatory. He explains that a space-based observatory would see different frequencies of gravitational waves than ground-based ones. In other words, we need space- and ground-based observatories.
Surely, the detection today gives the expensive space-based observatories a huge boost.
Turok says that now we know gravitational waves exist, future gravitational wave observatories will be able to see the signals coming from the big bang itself. He suspects that the technology may be 20-30 years away but one day, he says, we will be able to see the moment of the universe’s formation.
Bring it on!
Lehner says that astronomy to date has been like watching people come out from a movie and trying to guess the story by the look of their faces. Now, he says, gravitational waves allow us to look inside the theatre and read the plot.
Boyle is reminding us that after the advent of radio astronomy we say a lot of new types of objects in the Universe. Could we see ‘wilder’ stuff now that gravitational wave astronomy has begun?
Asimina Arvanitaki, Perimeter Institute, is now talking that perhaps gravitational waves will allow us to make progress in our search for dark matter. Dark matter is the so-far hypothetical particles that are thought to hold galaxies together in the Universe.
Lehner suggests that the discover today is so revolutionary that perhaps we should start a new calendar AGW – After Gravitational Waves. Welcome to year zero AGW!
Turok makes a philosophical point that there is something very mysterious about the Universe, and it is that we can understand it. It is astounding that we are sitting here today discussing a cataclysmic event that took place 1.3 billion years ago.
He says that it is an amazing prospect to wonder what use we may one-day be able to put gravitational waves – and not just for observing the Universe. He draws the analogy to radio waves. They were a curiousity when discovered, now we use them to transmit information.
Interesting to ponder and speculate...
Lehner explains that LIGO is just the start. Soon it will be joined by Virgo and Italy, and in a few years there are two more gravitational wave observatories that are due to come on line. The more detectors we have, the better we will be able to pinpoint the location of the gravitational wave sources.
Boyle explains that the slightly different detection times in the two LIGO detectors gives much confidence that this is a real signal, because it confirms that gravitational waves travel at the speed of light.
Latham Boyle, Perimeter Institute, says that the detection is possible because of a series of ingenious experimental ideas that gradually filter out all other extraneous signals. The development and improvements of these instruments has taken almost fifty years.
Talk about playing the long game!
Luis Lehner, a faculty member from Perimeter Institute says that todays signal is the confirmation that black holes exist. We have inferred their existence before, but the gravitational wave signal itself comes directly from the black hole.
He also says that the detection is ‘screaming’ that gravitational waves exist because it is such a strong signal.
He traces today’s triumph all the way back to Michael Faraday, the great Victorian experimenter. Faraday wonder how fast gravity travelled through the Universe. Einstein calculated that the speed would be the speed of light. Today, we know that is true.
Neil Turok, director of the Perimeter Institute, says that it is almost too difficult to put into words the importance of today’s discovery.
The Perimeter Institute is now broadcasting their discussion of today’s discovery. Watch in the viewer above.
And here are the detected signals compared to the theoretical curves. But fitting these curves precisely, astronomers and physicists have been able to calculate the masses of the colliding black holes, pegging each at around 30 times the mass of the Sun.
Here is the graph that confirmed the detection. The same gravitational wave signal, captured by two different detectors, is superimposed on each other and displayed at the press conference in Washington DC, earlier today. The oscillating lines are as Einstein predicted a century ago.
Interest in the paper announcing the results took down the server at Physical Review Letters! They are back online now.
Updated
Gravitational waves have been detected
On 14 September 2015 at 9:50 GMT, the two detectors of the newly upgraded Laser Interferometer Gravitational Wave Observatory (LIGO) detected a signal.
It was unambiguously a gravitational wave signal because it matched the predictions from Einstein’s general theory of relativity almost precisely.
A gravitational wave is a ripple in the invisible fabric of the universe, called the spacetime continuum. The particular ripple moved the LIGO detectors by about one thousandth the width of a proton (the tiny particle found at the heart of a hydrogen atom).
It was generated by two black holes that collided 1.3 billion light years away. The masses of the individual black holes were large, at around 36 and 29 times the mass of the Sun each. They were just 150km across each, and collided at half the speed of light.
The merger formed a single black hole of 62 solar masses. The missing three solar masses of matter were transformed into the energy that powered the gravitational waves detected by LIGO.
This transforms the way in which we can observe the Universe, and is expected to lead to the discovery of unanticipated celestial objects.
The Perimeter Institute for Theoretical Physics, Ontario, Canada, will be hosting a live panel at 18:00 GMT to discuss the implications of today’s discovery. We’ll be webcasting that too so stay tuned!
Here’s another nice explainer of how gravitational waves are produced, this time provided by the European Space Agency.
Updated
The final question of the webcast press conference is whether LIGO has seen other signals. Gonzalez answers very carefully placing the emphasis back on the signal announced today. As she finishes one of her fellow panellists quips ‘that didn’t even sound rehearsed’.
Hmmm. What should we make of that?
According to New Scientist, who have done some sleuthing in publicly available observatory logs, LIGO may be investigating another two signals, detected in December 2015.
Let’s wait and see.
Perhaps Radiohead were the first to detect gravitational waves:
Kip Thorne confirms that, sadly, this detection does nothing to bring us any closer to being able to perform time travel. Shame.
Also, and slightly more scientifically, it does not bring us any closer to a quantum theory of gravity, which would be needed if we are to understand what happens inside a black hole, or at the moment of the big bang, the origin of the Universe.
Rainer Weiss laments NASA’s decision to pull of the space-based gravitational wave observatory LISA, and praises Europe’s determination to ‘go it alone’ with the eLISA mission and LISA Pathfinder. But he hopes for a new collaboration.
This reaction from Jon Butterworth:
On the one hand, this was expected. We know that mass bends space and time, and so when mass moves it really should cause ripples in space and time, in much the same way that a gymnast moving on the surface of a trampoline causes ripples in the cloth.
On the other hand... Well, there are several other hands actually.
Read all of Jon’s instant analysis here.
Thorne says that we expect to see more signals from similar sources within the next year. Tweeks and improvements will advance LIGO’s sensitivity by about three times. He promises, “A huge richness of gravitational wave signals in LIGO.”
We’re into the Q&A at the press conference now. Gonzalez says they originally checked very hard that this wasn’t a test (a blind injection). Because they saw it so soon after the detectors were switched on, they were suspicious that it was a test. It was not. She repeats it again: this signal is real.
Updated
Professor Dame Jocelyn Bell Burnell, President of The Royal Society of Edinburgh (RSE) and renowned astrophysicist, responds to today’s news:
I’d like to extend my warmest congratulations to all the Scottish scientists involved, including past and present members of the University of Glasgow and of the RSE Fellowship. This is a truly momentous discovery, opening up a totally new spectrum and providing a new way to observe the universe.
These waves were predicted by Einstein a hundred years ago in his theory of general relativity. It has taken decades of highly skilled innovative technical developments, on the part of scientists in Glasgow and elsewhere, to build equipment capable of detecting movements smaller than the nucleus of the atom.
I look forward to the detection of further gravitational wave sources, the opening up of this new field of astronomy, and the discoveries predictable and unpredictable that will come from it. Like many of my generation I wasn’t sure I would live to see this day, and am delighted to be around to congratulate those who have achieved this magnificent result.
Dr Ed Daw has been researching gravitational waves with LIGO since 1998. He works in the Physics at the University of Sheffield, and sends the following reaction.
Discoveries of this importance in Physics come along about every 30 years. A measure of its significance is that even the source of the wave - two black holes in close orbit, each tens of times heavier than the sun, which then collide violently, has never been observed before, and could not have been observed by any other method. This is just the beginning.
Imagine that your T.V. had only ever received one channel on which the shows were all rather similar to each other. One day a second one appeared which showed completely different programs, like nothing that had ever been broadcast on the old channel. Wouldn’t you want to switch over? By detecting this signal, LIGO has effectively tuned in to a new channel - a completely new way of observing the Universe.
Gravitational waves are so completely different from light, we’re probably only just beginning to understand how they reflect and shape our Universe. For example, a gravitational wave will propagate almost completely unaltered through entire planets, star systems, galaxies....how different is that from the radio waves that your mobile phone picks up - even getting too close to a building can disrupt those signals. Light, or more generally electromagnetic waves are so much more vulnerable to interference than gravitational waves.
Gravitational waves are so different than light that Thorne is sure that we will see great surprises in the Universe.
We have only seen spacetime like the surface on a calm ocean until now, says Thorne. Now, we are seeing a storm!
The ‘storm’, meaning the collision of the black holes, lasted for just 20 milliseconds. In that brief moment, it generated 50 times the power of all the stars in the Universe put together.
It was the equivalent of taking three stars, each the size of the Sun, and annihilating them into pure energy. Wow!
Updated
Please note: it was 14 September 2015 (not 12 September 2015 as I stated earlier) that the signal was seen.
Kip Thorne, co-founder of LIGO and the scientist who inspired the movie Interstellar, is speaking now about the long road to building LIGO.
The excitement is beginning to spread through the astronomy and physics communities.
Listen to two black holes colliding
This is the real sound of two gigantic black holes colliding at half the speed of light: the chirp detected by LIGO that signals the gravitational waves.
Rainer Weiss, MIT, now talking about Einstein’s original prediction of gravitational waves, way back in 1916.
Updated
“This is the first of many to come,” says González. We can now listen to the Universe.
The signal came from the Southern sky, in the rough direction of the Magellanic clouds, the satellite galaxies of the Milky Way. At 1.3 billion light years away, however, it is very far beyond the Magellanic clouds, deep in intergalactic space somewhere.
The signals correspond very well indeed to a theoretical model produced by Einstein’s relativity. There is little to no ambiguity in this detection.
The tell-tale signal can be seen by just by eye rising above the noise of the detector. It was detected first in the LIGO Livingston detector. The clincher was that 7 milliseconds later the same signal was seen in the Hanford LIGO detector. The time delay was produced by the gravitational waves travelling in a particular direction.
LIGO’s detectors have arms that are 4 kilometres long for the laser beams to travel down.
Gabriela González, Louisiana State University, now speaking on behalf of the LIGO scientific collaboration. She is paying tribute to the whole collaboration, including the scientists at the Virgo gravitational wave detector in Italy.
We are going to see things that we never knew existed, predicts Reitze, who goes on to call LIGO a ‘scientific moonshot’, likening it to the Apollo moon landings of the 1960s.
Being 1.3 billion light years away means that these black holes collided 1.3 billion years ago. The gravitational waves have been travelling through space for 1.3 billion years. When they arrived at Earth on 12 Sept. 2015, they caused the LIGO machinery to move by 1/1000 of the width of a proton particle. LIGO detected it. Amazing.
This detection is proof that binary black hole systems can exist. Each black hole was about 150km in diameter. Each contained 30 solar masses and was accelerated at about half the speed of light. That is what collided. “It’s mindboggling,” says Reitze.
Too true!
The two black holes are indeed about 30 solar masses. They are about 1.3 billion light years away.
What’s exciting is what comes next, says Reitze. He likens it to Galileo using a telescope for the first time.
It was “exactly” what Einstein’s theory predicted for two colliding black holes.
The signal was detected on September 12, 2015.
Gravitational waves HAVE indeed been detected.
Two colliding black holes produced the gravitational waves.
David Reitze, executive director of LIGO is speaking now.
“We have detected gravitational waves. we did it.”
France Córdova is introducing the press conference. She says that LIGO was a big risk because it was so expensive.
The Press Conference is beginning
Here we go. The panellists are taking their seats...
The press conference is nearly ready to start. Before they switched to the ambient noise of the room, they were playing some pretty celebratory jazz over the livefeed. Don’t know whether that’s a clue to their announcement!
Gravitational waves are often said to be ripples like on a pond. In reality that are three-dimensional ripples as you can see in the animation below. In reality, the distortion are much smaller than the width of an atom.
Updated
Don’t forget that our very own Jon Butterworth will be here tomorrow to answer those nagging question you might still have about gravitational waves. I’ll publish the link for you at the end of today’s blog.
Ed Daw, Reader in Physics, University of Sheffield makes it sound easy to build a gravitational wave detector:
All you need to build a gravitational-wave interferometer is two light beams, travelling between pairs of mirrors down pipes running in different directions, say north and west. The effect of a passing gravitational wave should stretch space in one direction and shrink it in the direction that is at right angles. On Earth, that would cause the mirrors to swing by tiny amounts, so that the distance between one pair of mirrors gets smaller, while the other gets larger. The swinging is actually the mirrors responding to the stretching and compression of space-time, which is just amazing.
Easy-peasy then!
To summarise, the strong rumour is that at 3.30pm GMT, scientists from the LIGO gravitational wave observatory will announce that they have detected the signal of two black holes colliding.
The two black holes are rumoured to be larger than anyone would have expected at 30 times the mass of the Sun each. This in itself would be a great discovery as black holes of that size are highly unusual.
Stay tuned, we could be getting two great discoveries for the price of one: gravitational waves and bigger than expected black holes.
Updated
There is a nice explanation of the ‘inspiral’ gravitational wave signal given at the LIGO website. It explains that as two black holes (or other massive celestial objects) spiral towards each other just before a collision, they emit gravitational waves of increasing frequency. In the moments before the collision, the frequency rises sharply. The scientists refer to this sequence as the ‘chirp’.
The rumours suggest that it is the ‘chirp’ that has been identified in the signal that will be announced this afternoon.
You can hear the inspiral and chirp at this link. (Hands up if you think it sounds like something from a Jean-Michel Jarre song.)
LIGO is not the only gravitational wave observatory in the world. The Virgo instrument is situated near Pisa, Italy. It is currently offline for upgrades. When it returns to service later this year, it will detect the same gravitational wave signals that LIGO does.
With three detectors (two for LIGO and one for Virgo), astronomers will be able to fully triangulate their sources and known precisely where their signals are coming from.
Today’s announcement could be rather imprecise as far as direction is concerned because the scientists only have the two LIGO detectors to work with.
The gravitational wave observatory making today’s announcement is the Laser Interferometer Gravitational Wave Observatory (LIGO). It consists of a pair of detectors, one in Livingston, Louisiana and the other in Hanford, Washington.
Each detector uses laser beams to run in different directions in perfect synchrony. When gravitational waves passes through the detector, it knocks the laser beams out of synch and it is this interference that the scientists detect. The twist is that the disturbances are smaller than the width of an atom, so the equipment must be extraordinarily sensitive. It has taken scientists and engineers decades to get to this point. LIGO itself was founded in 1992.
Nice that this is outside the National Press Club in Washington DC.
The detection of gravitational waves has been likened to astronomers developing a whole new sense.
We have been able to see the universe ever since the first human looked upwards to the skies.
The advent of the telescope in 1610, started the process of using telescope to extend our sense of sight ever further into the Universe.
Gravitational waves are different however. They are not at all like light or any of the other ‘electromagnetic radiations’ such as radio waves, X-rays, infrared, ultraviolet rays.
Instead, they are ‘ripples’ in the fabric of the universe. This makes them more analogous to sounds, which can be thought of as ripples or waves in the air.
Researchers can even turn the simulated gravitational wave signals into audible sounds. If you are Professor Daniel Price, Monash University, Australia, you then put those sounds in a piece of music and call it ‘A gravitational wave symphony’.
The simulated gravitational wave signals are the oscillating sounds that increase in frequency until they abruptly stop with a ‘chirp’. These are the tell-tale signals for which gravitational wave astronomers search.
Welcome to the gravitational universe
Welcome to our coverage of today’s gravitational wave announcement, coming from Washington DC at 10.30am ET / 3.30pm GMT. In calling the press conference, the National Science Foundation played it coy. Officially they have only said that the briefing will “update the scientific community on efforts to detect” gravitational waves.
Unofficially, the rumours are rife that the announcement will be an actual detection. If so, then our view of the universe changes forever, and we have a whole new way to study the celestial objects.
The ability to detect gravitational waves will not just be bring us new views of objects that we can already see, but will allow us to detect and study objects and events that are currently completely hidden from view.
We have to wait and see if physics and astronomy is about to change forever. We will be here from now on to pull together all the news and expert reaction as we get it.
