The best thing about a day in my life on the lookout for gravitational waves is that I never know when it will begin.
Like many of my colleagues working for the Laser Interferometer Gravitational-Wave Observatory (LIGO), the morning of Monday, September 14, 2015 caught me completely off-guard. For years, we’ve been joking that Advanced LIGO would be so sensitive we might just detect one the very first day it turns on. In retrospect, it’s remarkable how close to reality that joke turned out to be.
LIGO is listening for gravitational waves – one of the last unproven predictions of Einstein’s theory of general relativity. In his view of the universe, space and time are fluid things that depend on an observer’s frame of reference. For example, time passes just a (very) little bit more slowly for those who work on the ground floor of an office building as compared to their peers on the 101st floor. Why? They’re deeper in Earth’s gravitational pull.
Einstein predicted that gravitational waves are formed when matter and energy warp space and time. Their effects – until now unseen – sound bizarre. As a gravitational wave passes by, an observer will see the distance between objects change. All around us space is oscillating, distances are changing and we are being stretched and squeezed by passing gravitational waves. Only the most extreme objects in the universe can bend space enough to produce ripples that are measurable here on Earth. The effect is so tiny that we fail to notice it even with the most sensitive measurements – but Advanced LIGO was designed to change all that by directly measuring tiny ripples in space itself.
Although Advanced LIGO had collected data off and on over the summer of 2015, September 14 was slated to be the first official day of its first observing run. From those who built and commissioned the advanced LIGO detectors to those who characterized and analyzed the data, we’d all been preparing for decades to make this kind of discovery, but I don’t know if any of us was truly ready for a detection – and on Day One, as luck would have it.
Hearing what we were listening for
Like others on the team, I should have been woken up in the middle of the night when LIGO heard that first gravitational wave – but it was so early in the run that I hadn’t even had a chance to enable my text message alerts! Instead, I read about the event, termed GW150914, on my phone as I walked to campus hours after it had been observed. It is difficult to describe the level of anticipation regarding a possible event. But I can say that if you have waited for over 12 years for such a discovery, as I have, it certainly is not something to take lightly when it happens.
Like everyone else at the time, though, I thought this signal was just a test of the analysis system, called a hardware injection. I spent the rest of the morning assuming as much. But minutes before a 2:00 p.m. seminar that same day, we received word from each LIGO observatory that no tests had been performed. My student, two postdocs and I all went to our seminar looking like we had seen a ghost! The rest of our colleagues in attendance were not part of LIGO, so we couldn’t say a word. Our silence stood for months to come.
The LIGO Scientific Collaboration (LSC), of which I am a member, is currently made up of more than 1,000 people from dozens of institutions and 15 countries worldwide. There are two LIGO instruments, one in Louisiana and one in Washington. And we work with the Virgo Collaboration that operates a detector in Italy and the GEO600 detector team in Germany. Since we are all so far apart, we met by teleconference so folks who are at the observatories and folks who are analyzing the data could all discuss what was happening and whether or not to share the information more broadly.
At first it was unclear which of many possibilities could be responsible for the GW150914 signal. It would have to be a major astronomical event that released immense amounts of energy – such as a binary merger, a nearby supernova or some completely unforeseen occurrence. Initial investigations indicated that it could be a binary black hole merger – two black holes that are driven to smash together as they release energy in the form of gravitational waves.
Over the next few weeks, we worked to assess the significance of GW150914. Its probability of being the real thing was simply off the charts and had virtually no plausible explanation as anything but a gravitational wave. There was just no way random noise could have caused such a loud, consistent signal between detectors that matched the expectation of general relativity so perfectly.
From then on, the collaboration shifted into high gear, preparing additional scientific publications to provide all the juicy details about the detection and interpretation of GW150914. We now know that gravitational waves can be measured, binary black holes exist and that there are perhaps far more detectable sources of gravitational waves than we had anticipated.
GW150914 stretched and squeezed our nearby space by about 1 part in 1021. This is equivalent to squeezing the entire Milky Way galaxy by a typical person’s height. As you might imagine, it is nearly impossible to measure such a small change in distance. To do so, LIGO uses high-power lasers, ultra high vacuum and some of the most advanced optics ever built.
The basic idea is simple: LIGO has two 4-km-long arms built at 90 degrees with respect to one another. A high-power laser beam is split in two to travel down each arm separately. When the laser gets to the end, it’s reflected back by a mirror. If one arm is longer than another, due to the change in space caused by a gravitational wave, then the laser light won’t arrive back at the same time in each arm.
We continuously record the recombined laser light; it encodes how the gravitational wave causes space to stretch and squeeze at frequencies that are very similar to what the human ear can hear. That’s why we often think of LIGO as listening to the universe. In fact, LIGO records its data as what’s basically an audio file. You can literally listen to the gravitational waves detected with LIGO using headphones.
Science news in pictures
Science news in pictures
1/20 'Tiny vampires' existed millions of years ago
Scientists have discovered that microscopic 'vampire' amoebae existed hundreds of millions of years ago, and they may have been some of the first predators on Earth. By examining ancient fossils with an electron microscope, paleobiologist Susannah Porter from UC Santa Barbara discovered tiny holes which may have been drilled by vampiric microbes. The tiny creatures are believed to be the ancestors of modern Vampyrellidae amoebae, and punctured holes in their prey before sucking out the contents of their cells
2/20 Kepler 62f
An Earth-like planet orbiting a star 1,200 light years away could have conditions suitable for life, say scientists. Kepler 62f is about 40 per cent larger than the Earth and may possess surface oceans. It is the outermost of five planets circling a star that is smaller and cooler than the sun discovered by the American space agency Nasa's Kepler space telescope in 2013
3/20 Vegetables grow well in soil from Mars
Scientists have taken a leaf out of the script of The Martian by showing how easy it would be to grow your own veg on the Red Planet. In the hit Ridley Scott film, a stranded astronaut played by Matt Damon uses his botanical skills to cultivate potatoes. Now his success has been emulated by researchers in the Netherlands who harvested tomatoes, peas, rye, rocket, radish and cress raised on simulated Martian soil supplied by Nasa
4/20 Ancient Roman 'leisure complex' unearthed in Jerusalem
An ancient Roman estate complete with its own wine press and bathhouse has been unearthed in Jerusalem. A series of buildings dating back at least 1,600 years were discovered underneath the city's famous Schneller Orphanage which operated on the site from 1860 until the end of the Second World War, when it was turned into an army base. The ruins were discovered by archaeologists from the Israel Antiquities Authority who were excavating the site ahead of building new flats for the city's Orthodox Jewish community
5/20 Scientists discover possible new species of deep-sea octopus nicknamed 'Casper'
Scientists believe they may have found a new species of octopus likened in appearance to Casper, the friendly cartoon ghost. Researchers with the US National Oceanic and Atmospheric Administration made the discovery by chance as they searched the seabed on an unrelated mission collecting geological samples. Teams were operating an unmanned submarine on the Pacific Ocean floor at depths of more than four kilometres (two-and-a-half miles) in the Hawaiian Islands when they spotted the unusual creature
6/20 Black hole captured eating a star then vomiting it back out
Astronomers have captured a black hole eating a star and then sicking a bit of it back up for the first time ever. The scientists tracked a star about as big as our sun as it was pulled from its normal path and into that of a supermassive black hole before being eaten up. They then saw a high-speed flare get thrust out, escaping from the rim of the black hole. Scientists have seen black holes killing and swallowing stars. And the jets have been seen before.But a new study shows the first time that they have captured the hot flare that comes out just afterwards. And the flare and then swallowed star have not been linked together before
7/20 'Male and female brains' aren't real
Brains cannot be categorised into female and male, according to the first study to look at sex differences in the whole brain. Specific parts of the brain do show sex differences, but individual brains rarely have all “male” traits or all “female” traits. Some characteristics are more common in women, while some are more common in men, and some are common in both men and women, according to the study
8/20 Dog-sized horned dinosaur fossil found shows east-west evolutionary divide in North America
A British scientist has uncovered the fossil of a dog-sized horned dinosaur that roamed eastern North America up to 100 million years ago. The fragment of jaw bone provides evidence of an east-west divide in the evolution of dinosaurs on the North American continent. During the Late Cretaceous period, 66 to 100 million years ago, the land mass was split into two continents by a shallow sea. This sea, the Western Interior Seaway, ran from the Gulf of Mexico to the Arctic Ocean. Dinosaurs living in the western continent, called Laramidia, were similar to those found in Asia
9/20 Asteroid to skim past Earth on Halloween 2015
A huge asteroid is set to skim by Earth on Halloween, just three weeks after it was first spotted. The rock is travelling through space at 78,000 miles per hour, and will fly past the Earth at a distance of only 300,000 miles – only slightly further away than our moon, and easily close enough for Nasa to class it a potentially hazardous object. The asteroid is bigger than a skyscraper
10/20 Life on Earth appeared hundreds of millions of years earlier than previously thought
Life may have come to earth 4.1 billion years ago, hundreds of millions of years earlier than we knew. The discovery, made using graphite that was trapped in ancient crystals, could mean that life began "almost instantaneously" after the Earth was formed. The researchers behind it have described the discovery as “a potentially transformational scientific advance”. Previously, life on Earth was understood to have begun when the inner solar system was hit by a massive bombardment from space, which also formed the moon's craters
11/20 Earth could be at risk of meteor impacts
Earth could be in danger as our galaxy throws out comets that could hurtle towards us and wipe us out, scientists have warned. Scientists have previously presumed that we are in a relatively safe period for meteor impacts, which are linked with the journey of our sun and its planets, including Earth, through the Milky Way. But some orbits might be more upset than we know, and there is evidence of recent activity, which could mean that we are passing through another meteor shower. Showers of meteors periodically pass through the area where the Earth is, as gravitational disturbances upset the Oort Cloud, which is a shell of icy objects on the edge of the solar system. They happen on a 26-million year cycle, scientists have said, which coincide with mass extinctions over the last 260-million years
12/20 Genetically-engineered, extra-muscular dogs
Chinese scientists have created genetically-engineered, extra-muscular dogs, after editing the genes of the animals for the first time. The scientists create beagles that have double the amount of muscle mass by deleting a certain gene, reports the MIT Technology Review. The mutant dogs have “more muscles and are expected to have stronger running ability, which is good for hunting, police (military) applications”, Liangxue Lai, one of the researchers on the project. Now the team hope to go on to create other modified dogs, including those that are engineered to have human diseases like muscular dystrophy or Parkinson’s. Since dogs’ anatomy is similar to those of humans’, intentionally creating dogs with certain human genetic traits could allow scientists to further understand how they occur
13/20 Nasa confirms Mars water discovery
Nasa has announced that it has found evidence of flowing water on Mars. Scientists have long speculated that Recurring Slope Lineae — or dark patches — on Mars were made up of briny water but the new findings prove that those patches are caused by liquid water, which it has established by finding hydrated salts.
14/20 Bees in the Rocky Mountains are evolving shorter tongues
With warmer summers, flowers in the Rockies have become shallower and more suited to shorter-tongued bees
15/20 The majority of the UK public believe in aliens
The titular alien character from 2011's 'Paul' - a poll has found the majority of the public in Britain, Germany and the US believe that intelligent life is out there in the universe
16/20 Researchers discover 'lost world' of arctic dinosaurs
Scientists say that the new dinosaur, known as Ugrunaaluk kuukpikensis, “challenges everything we thought about a dinosaur’s physiology”. Florida State University professor of biological science Greg Erickson said: “It creates this natural question. How did they survive up here?”
17/20 Scientists find exactly what human corpses smell like
New research has become the first to isolate the particular scent of human death, describing the various chemicals that are emitted by corpses in an attempt to help find them in the future. The researchers hope that the findings are the first step towards working on a synthetic smell that could train cadaver dogs to be able to more accurately find human bodies, or to eventually developing electronic devices that can look for the scent themselves.
18/20 The Syrian civil war has caused the first ever withdrawal from the 'doomsday bank'
Researchers in the Middle East have asked for seeds including those of wheat, barley and grasses, all of which are chosen because especially resistant to dry conditions. It is the first withdrawal from the bank, which was built in 2008. Those researchers would normally request the seeds from a bank in Aleppo. But that centre has been damaged by the war — while some of its functions continue, and its cold storage still works, it has been unable to provide the seeds that are needed by the rest of the Middle East, as it once did.
19/20 A team of filmmakers in the US have made the first ever scale model of the Solar System in a Nevada desert
Illustrations of the Earth and moon show the two to be quite close together, Mr Overstreet said. This is inaccurate, the reason being that these images are not to scale.
20/20 Academics claim a full bladder makes for a better liar
People lie more convincingly if they have a full bladder, according to research by academics at California State University. Iris Blandón-Gitlin's team asked 22 students to lie to a panel of interviewers. Half were given 700ml to drink before the interview and the other half, just 50ml. The students with the full bladders showed fewer signs that they were lying and their untrue answers were longer and more detailed, meaning interviewers were less able to detect that they were telling porkies. PM David Cameron has previously attested to giving speeches on a full bladder.
Colliding black holes and neutron stars are some of LIGO’s primary targets, though we also search for supernovae, spinning isolated neuron stars and gravitational waves left over from the birth of the universe. The LIGO detectors, for the most part, are sensitive to sources all over the sky, which means a single detector can’t tell from which direction a gravitational wave arrived. However, using multiple detectors we can localize the source. All the gravitational wave detectors across the globe work together to make observations of the same signals at the same time (within tens of milliseconds).
I’m part of a team that is searching for merging neutron stars and black holes in near real time. We hope to know within seconds that a gravitational wave has reached the Earth. With this knowledge, we can inform other astronomers who can point their telescopes in the direction of the event in the hope that the gravitational wave will have an electromagnetic counterpart. Having information from both channels is a bit like having both sound and picture when watching a film. The movie would be far less interesting with only one and not the other.
Unlike many telescopes, LIGO can observe at any time of day, though it is sensitive to environmental noise that’s often caused by human beings working nearby. Observing at night tends to be easier, when most people are in bed. The team I work with is always on call. If a gravitational wave event is detected, we should know within a minute and receive a call to our cellphones as well as a text message with details about the event – just as happened on September 14.
Beginning of a new era
Detecting this first gravitational wave event has changed the world. It confirms the last great prediction of a revolutionary theory that’s now over 100 years old. But it doesn’t stop there. We’re still listening for more gravitational waves; soon Advanced LIGO will detect them regularly – and each one will tell us something new about the universe.
As observations become commonplace, we will enter a new era of gravitational wave astronomy and start to map out just how black holes and neutron stars are born, evolve and eventually die. Someday we might even be surprised to detect something we never expected. From now on, every time my phone rings, that’s what I will be hoping for.