black holes, gravitational waves, n other stuff like that

Swift kick from a supernova could knock a black hole askew
Gravitational wave detection hints at unexpected power from star explosion

https://www.sciencenews.org/article/swift-kick-supernova-could-knock-black-hole-askew

Gravitational waves are providing new hints about how black holes get their kicks.

The Advanced Laser Interferometer Gravitational-Wave Observatory’s detection of spacetime ripples from two merging black holes on December 26, 2015, indicated that one black hole was spinning like a tilted top as it orbited with its companion (SN: 7/9/16, p. 8). That off-kilter spin could mean that the stellar explosion that produced the black hole gave it a strong kick, physicist Richard O’Shaughnessy and colleagues report in a paper in press in Physical Review Letters.

Scientists aren’t sure how black holes like those detected by LIGO pair up (SN Online: 6/19/16). Two neighboring stars may have obliterated themselves in a pair of explosions called supernovas, producing two black holes. But that scenario should lead to black holes that spin in the same plane as their orbit. It would take a sizeable jolt from the supernova, of about 50 kilometers per second, to account for the cockeyed spin, the researchers conclude.

Computer simulations of supernovas predict smaller black hole boosts, making for a cosmological conundrum. “This will be a serious challenge for supernova modelers to explain,” O’Shaughnessy, of the Rochester Institute of Technology in New York, said June 5 in a news conference in Austin, Texas, at a meeting of the American Astronomical Society.

Get ready for our first image of a black hole
The Event Horizon Telescope will peer into the space immediately surrounding our galaxy’s supermassive black hole.

http://www.astronomy.com/news/2017/04/first-image-of-a-black-hole

Previous observatories have captured images of the region around our galaxy’s supermassive black hole, but they’re not exactly high-resolution pictures. The Event Horizon Telescope aims to outstrip the quality of all previous images by far.

Astronomers have brought a telescope online that’s (virtually) the size of Earth. Dubbed the Event Horizon Telescope, it’s aiming to achieve something that’s never been done before: imaging the space around a black hole all the way down to its event horizon.

One of its targets is Sagittarius A*, or Sgr A* for short. Sgr A* is the supermassive black hole in the center of the Milky Way, with a mass of approximately 4 million Suns. Because it’s so massive and so (relatively) close at a distance of 25,600 light-years, it’s the largest black hole visible in our sky. But large is a relative term as well — current estimates place the size of the black hole at 100 Astronomical Units (AU) or less. One AU is the average distance between Earth and the Sun, 93 million miles (150 million kilometers). Some estimates even indicate that the black hole could be as small as the distance between Mercury and the Sun, just 28 million miles (46 million km).

When astronomers “see” black holes, they are actually seeing light from a disk of material around the black hole, which is sitting beyond the event horizon. Anything within the event horizon itself is truly invisible, as that marks the point at which even light cannot travel fast enough to break free of the black hole’s gravity and escape. But currently, astronomical instruments don’t have the resolution to really see the disk closely or image its structure.

This is why every “image” ever shown of a black hole in a news article or textbook is an artist’s rendering, rather than an actual picture. But that’s all about to change.

The Event Horizon Telescope makes use of a technique called Very Long Baseline Interferometry (VLBI) that requires several telescopes observing the same object from different locations to create highly detailed images of very, very small sections of the sky. The farther apart the telescopes are located, the greater the detail they can achieve. The Event Horizon Telescope will link eight radio telescopes around the world, including the Atacama Large Millimeter/submillimeter Array in Chile, the Caltech Submillimeter Observatory in Hawaii, the Large Millimeter Telescope Alfonso Serrano in Mexico, the South Pole Telescope in Antarctica, and other facilities in France and Spain to utilize the longest baselines possible. By creating a truly Earth-sized telescope, the project should be capable of imaging the space around a black hole in exquisite detail.

This will allow astronomers to study not only the structure of the disk around the black hole, but also to test general relativity, get a better look at how the black hole actually feeds on material, and maybe even determine how the outflows and jets that are so common among black holes are actually created.

The giant telescope came online April 5 and will observe for about a week and a half, gathering data until April 14. In addition to imaging our relatively quiescent Sgr A*, it will also look at the more active supermassive black hole residing in Messier 87, a huge elliptical galaxy in the nearby Virgo Cluster. The amount of information obtained will be so immense that it’s too large to transfer digitally — it will be stored physically and taken to the Max Planck Institute in Germany, and the Haystack Observatory in Massachusetts for processing.

That will take time. But in a few months, we may finally have our first picture of the region immediately around a supermassive black hole.

Universe’s Largest Black Hole May Have An Explanation At Last

https://www.forbes.com/sites/startswithabang/2017/07/31/universes-largest-black-hole-may-have-an-explanation-at-last/#514ec55efc55

An ultra-distant quasar showing plenty of evidence for a supermassive black hole at its center. How that black hole got so massive so quickly is a topic of contentious scientific debate, but may have an answer that fits within our standard theories.

The brightest, most luminous objects in the entire Universe are neither stars nor galaxies, but quasars, like S5 0014+81.

The sixth brightest quasar known so far, its mass was determined in a 2009 study: 40 billion Suns.

The mass of a black hole is the sole determining factor of the radius of the event horizon, for a non-rotating, isolated black hole. Its physical size would have a radius that’s 800 times the Earth-Sun distance, or over 100 billion kilometers.

This makes it the most massive black hole known in the entire Universe, as massive as the Triangulum galaxy, our local group’s third largest member.

It shines so brightly because large amounts of matter are falling into the center via an accretion disk, getting accelerated and producing light.

If this quasar were 18 million times as far away as our Sun (280 light years from Earth), it would shine as bright in the sky as our life-giving star does.

If it were located just 280 light years away, it would shine as brightly as our Sun does in the sky.

Instead, S5 0014+81 is over 22 billion light years away; we see it as it was just 1.6 billion years after the Big Bang.

Simulations of various gas-rich processes, such as galaxy mergers, indicate that the formation of direct collapse black holes should be possible. A combination of direct collapse, supernovae, and merging stars and stellar remnants could produce a young black hole this massive.

The biggest ‘big idea’ that JWST has is to reveal to us the very first luminous objects in the Universe, including stars, supernovae, star clusters, galaxies, and luminous black holes. To date, however, no one has a plan to detect distant, ultramassive, but inactive black holes.

Its activity gives it away; more massive, inactive black holes may exist.

Gravitational waves are helping us crack the mystery of how pairs of black holes form

http://theconversation.com/gravitational-waves-are-helping-us-crack-the-mystery-of-how-pairs-of-black-holes-form-82789

A tiny disturbance in space became an enormous scientific discovery when LIGO amazingly managed to register it early on the morning of September 14, 2015. This was the first ever observation of a “gravitational wave” – a minute ripple in the structure of spacetime itself – predicted by Albert Einstein a century ago. The signal came from two black holes merging more than a billion light years away, and reached our planet on that very morning.

The detection ushered in a whole new era of astronomy. Two more detections followed (and a third likely one), all from mergers of pairs of black holes. Already, these measurements are starting to help scientists unravel some of the universe’s best-kept secrets. Our new study, published in Nature, shows just how close we are to working out how pairs of black holes form.

The black holes studied by LIGO – each weighing in at between 10 and 30 times the mass of the sun – collide while moving at half the speed of light, twisting space and time as they do so. The merger of two black holes releases more energy in a fraction of a second than all of the stars in the visible universe combined.

However, by the time the spacetime distortions, travelling at the speed of light for more than a billion years, get to the Earth, the ripples are very weak indeed – stretching and squeezing space by less than one part in 1021. That means they make the mirrors in the LIGO detector move by less than a thousandth of the size of an atomic nucleus. No wonder gravitational waves have been so hard to detect.

The incomplete science of black holes

Black holes are infinitely dense remnants of massive stars. Studying them provides astrophysicists with a glimpse into the lives of these stars. And one of the key questions puzzling us since the first gravitational wave detection is: how did these heavy black hole pairs get close enough to merge?

Unravelling the history of how merging black holes formed is important – it can help us to understand the mysterious ageing of massive stars and interactions in dense stellar environments.

There are two broad classes of scenarios that have been proposed so far. The first view holds that two massive stars were born as a pair. They may have interacted by raising tides on each other’s surface, in the way that the moon raises ocean tides on the Earth. Or they may have exchanged gas, with one star blowing off material into space and the other capturing some of it.

Eventually, each star collapsed into a black hole. If the black holes were close enough, then the gradual loss of energy from their orbits in the form of gravitational waves would cause the two black holes to spiral in and eventually merge. This scenario is known as isolated binary evolution.

The other option is that the two black holes formed independently, but did so in an environment where there were many stars closely packed together. In this scenario, known as dynamical formation, a sequence of gravitational interactions with other stars could bring the two black holes to orbit each other.

Numerical simulations of the gravitational waves emitted by the merger of two black holes, including spins (green arrow). NASA/wikipedia
We do not yet know which scenario is correct, but nature has provided an exciting hint. Black holes rotate around their own axes. We know from a few observations of stars orbiting black holes in our own galaxy and its immediate neighbours that sometimes black holes appear to be rapidly spinning. We think that if the black holes seen by LIGO were formed from stars already orbiting each other, these spins should be aligned with the orbit. But if the black holes formed by the gravitational influence of several other stars, the spins would be randomly oriented relative to the orbit – meaning they formed independently in a dense environment.

In a new paper, our team of scientists from the University of Birmingham in the UK and the Universities of Maryland and Chicago in the US, analysed the alignment of the spins and orbits of the merging black hole pairs detected by LIGO. It turns out that the phase of the gravitational waves measured is influenced by the spin of the black holes. A certain component of this spin – known as effective spin – is therefore imprinted in the data.

If this effective spin is large and positive, the black holes are rapidly spinning and rotating in the same direction as the orbit. If it’s large and negative, the black holes are rapidly counter-rotating with respect to the orbit. If it is near zero, then either the black holes’ spins are significantly misaligned with the orbit, or both black holes are spinning slowly.

The LIGO observations of merging black holes so far have found that the effective spin is consistent with zero for all but one observation. Therefore, we concluded that if the black holes are rapidly spinning, the data point to a lack of alignment – and that the black holes were not born from pairs of stars. It does indeed seem likely that the black holes could be rapidly spinning – observations in our galaxy after all suggest this is the case.

We suggest that with as few as ten additional detections, it may be possible to know for sure the origin of black hole pairs. However, it is possible that the merging black holes had a different evolutionary history to the black holes we’ve observed in our own galaxy, and are rotating slowly. If they are, many more observations would be required. Either way, the research goes to show just how important the discovery of gravitational waves really is – opening an entirely new window on the universe.

Supernova déjà vu, all over again
When astronomers saw a star explode they knew – thanks to Einstein – that they could watch it again a year later. Katie Mack explains.

https://cosmosmagazine.com/space/supernova-deja-vu-all-over-again

In late 2015, the Hubble Space Telescope turned toward a distant galaxy to watch the explosive demise of a doomed star. Supernova Refsdal was a replay, having already been seen and measured a year before. But between here and there was a region of space so crowded and mangled with galaxies, the exploding star’s light rays flowed through it like a river over rapids, twisting and bending along multiple paths. Hubble was watching another angle on the same explosion, from light rays that took the scenic route.

That light can split and bend is a familiar concept. Every time we look through a lens, see a reflection off glass, or watch the dance of sunlight underwater, we are watching light being bent or split by the matter through which it flows. In space, as long as it doesn’t run into anything, such as a galaxy, there’s no matter for light to flow through: it should travel in straight lines, unimpeded.

But thanks to Einstein we know it doesn’t. He hypothesised that when there’s matter nearby, empty space itself can bend, stretch and compress, carrying light beams along with it. In fact, this phenomenon of gravitational lensing was one of the first pieces of evidence to support Einstein’s general relativity theory.

He recast gravity, not as a force but as a consequence of the distortion of space by massive objects such as stars or galaxies.

Imagine placing a bowling ball on the middle of a trampoline, and then rolling a tennis ball past it. The tennis ball won’t travel in a straight line, but will instead circle around or fall into the dent in the centre. This new picture of gravity explained why a planet orbits a star. It also predicted that light can’t pass by a massive object in a straight line. The path of light through curved space would bend, too.

The first time gravitational lensing was observed, it rocked the scientific world. Einstein’s theory predicted that stars in the same part of the sky as the sun would appear to be shifted from their true positions, as the light passing by the sun would be curved around by its distortion of space.

During the next total solar eclipse, when the moon blocked out the sun’s light, astronomers were able to see the background stars and measure the difference, exactly as predicted, between the stars’ charted positions and where they appeared. A famous New York Times headline proclaimed “Lights All Askew in the Heavens.” Einstein became an overnight sensation and our understanding of the nature of space and time changed forever.

SOMETIMES THAT DISTORTION CAN BE SO EXTREME AND COMPLEX THAT WE SEE MULTIPLE IMAGES OF THE SAME GALAXY, AS IF LOOKING THROUGH WARPED, UNEVEN GLASS.

These days, astronomers can use gravitational lensing to magnify distant galaxies, helping us see and study the far reaches of the Universe. In some cases, it can help us measure the shape of space itself on the largest scales. It can also map out invisible dark matter: anything that has mass distorts space and bends the light behind it, giving away its presence.

Sometimes that distortion can be so extreme and complex that we see multiple images of the same galaxy, as if looking through warped, uneven glass. Light originally travelling off to one side might be pulled through a strongly curved part of space to reach us from another angle. Because a curved path is longer than a direct one, there can be a delay between two images of the same distant light source.

When astronomers discovered Supernova Refsdal, they knew to be ready for a replay, because they saw another image of the host galaxy, but in that one the supernova had yet to go off. It involved a fortuitous alignment: the very distant host galaxy, where the supernova occurred, and a giant cluster of galaxies in between. The combined gravity of an entire cluster turned space into a distorting lens between the supernova’s host and us, making the host appear to be in several places behind it.

After the combined gravity of the cluster split the image, a single galaxy acted as another lens, splitting one of the resulting mirages four more times. When the original supernova was seen in 2014, it was seen there, in quadruplicate, framing the interloper galaxy like a cross. In another part of the cluster, because the light had taken a longer route, the doomed star was still intact. Astronomers calculated the light travelling on that path would take about a year more. And then they saw the explosion, again, right on time.

Neutron star collision showers the universe with a wealth of discoveries

After two neutron stars slammed together, scientists detected gravitational waves, a burst of gamma rays and a glow from ejected material, shown in this artist’s conception.

https://www.sciencenews.org/article/neutron-star-collision-gravitational-waves

WASHINGTON — Two ultradense cores of dead stars have produced a long-awaited cosmic collision, showering scientists with riches.

The event was the first direct sighting of a smashup of neutron stars, which are formed when aging stars explode and leave behind a neutron-rich remnant. In the wake of the collision, the churning residue forged gold, silver, platinum and a smattering of other heavy elements such as uranium, researchers reported October 16 at a news conference in Washington, D.C. Such elements’ birthplaces were previously unknown, but their origins were revealed by the cataclysm’s afterglow.

“It really is the last missing piece” of the periodic table, says Anna Frebel, an astronomer at MIT who was not involved in the research. “This is heaven for anyone working in the field.” After the collision, about 10 times the Earth’s mass in gold was spewed out into space, some scientists calculated.

Using data gathered by about 70 different observatories, astronomers characterized the event in exquisite detail, releasing a slew of papers describing the results. A tremor of gravitational waves, spotted by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, on August 17, provided the first sign of the cataclysm.

“Already it is transforming our understanding of the universe, with a fresh narrative of the physics of stars in their death throes,” said France Córdova, director of the National Science Foundation, which funds LIGO.

A sequence of various types of electromagnetic radiation followed that gravitational trill, like musical instruments taking turns in a symphony. A burst of gamma rays segued into a glow of visible and infrared light, first spotted about 12 hours after the smashup. More than a week later, as those wavelengths faded away, X-rays crescendoed, followed by radio waves.

Combining gravitational waves with light from a neutron star merger is a long-held dream of astrophysicists. “The picture that you can put together by having all of those sources is synergistic,” says LIGO spokesperson David Shoemaker of MIT. “You can make inferences that otherwise would be impossible.”

That detailed picture revealed the inner workings of neutron star collisions and the source of brief blasts of high-energy light called short gamma-ray bursts. Researchers also calculated how fast the universe is expanding and tested the properties of the odd material within neutron stars.

For astrophysicists, “this event is the Rosetta stone,” says LIGO member Richard O’Shaughnessy of the Rochester Institute of Technology in New York.

LIGO’s two detectors, located in the United States, registered an unmistakable sign of the upheaval: A shimmying of space itself that continued for about 100 seconds before cutting off. It was the strongest and longest series of spacetime ripples LIGO had ever seen. At that point, scientists knew they had something big, says LIGO member Vicky Kalogera of Northwestern University in Evanston, Ill. “The e-mails that were circulated said, ‘Oh my God, this is it.’”

That vibration was an indication of a cosmic crash: Whirling round each other as if on an ill-fated merry-go-round, two orbiting neutron stars spiraled closer and closer, until they converged. The neutron stars, whose masses were between 1.17 and 1.60 times that of the sun, probably collapsed into a black hole, although LIGO scientists were unable to determine the stars’ fate for certain. LIGO has previously spotted mergers of swirling black holes with masses tens of times that of the sun (SN Online: 9/27/17); the smaller masses of the orbiting duo pointed the finger at neutron stars. And because black holes aren’t expected to emit light, the fireworks show that followed solidified the case for neutron stars.

LIGO’s sister experiment in Italy, Advanced Virgo, saw only a faint signal. That relatively weak detection helped narrow down where the convulsion occurred to “a part of the sky that was a blind spot of Virgo,” Kalogera says. That constrained the site to within a region of about 30 square degrees in the southern sky.

Just 1.7 seconds after the gravitational wave signal, NASA’s Fermi space telescope spotted a glimmer of gamma rays in the same neighborhood of the sky. Meanwhile, other telescopes swung into action, picking up a glow where none had been before. “We saw what looked like a new star,” says astronomer Edo Berger of Harvard University, who led a team that spotted the light with the DECam on the Blanco telescope in Chile. Berger’s was one of several teams that observed the blast’s light. That detection pinpointed the galaxy NGC 4993, 130 million light-years from Earth in the constellation Hydra, as the collision site. “There was this moment of disbelief: Wow, we actually did it. We found it,” Berger says.

That afterglow also revealed an amazing story of stellar alchemy: With the stars’ death came the birth of elements. As the collision spurted neutron-rich material into space, a bevy of heavy elements formed, through a chain of reactions called the r-process (SN: 5/14/16, p. 9). In this process, which requires an environment crammed with neutrons, atomic nuclei rapidly gobble up neutrons and decay radioactively, thereby transforming into new elements, before resuming their neutron gorgefest. The r-process is thought to produce about half of the elements heavier than iron.

Scientists detected the characteristic glow of this process, called a kilonova, in follow-up observations. “Until this event, we had never directly seen anywhere in nature these heavy elements being forged. Now we have,” says Brian Metzger, a theoretical astrophysicist at Columbia University. “It is a feeling like you’ve discovered some kind of secret of nature.”

Previously, astrophysicists disagreed about where the r-process occurs: Two top candidates were exploding stars called supernovas (SN: 2/18/17, p. 24) and neutron star mergers. Although scientists can’t yet say whether all r-process elements are produced in neutron star mergers, the amount such collisions should produce appears large enough to explain the abundances found in the universe.

Additional riches were revealed by gamma rays. Scientists spotted a phenomenon called a short gamma-ray burst, a brief spurt of high-energy light, less than two seconds long. Such paroxysms are relatively common, appearing in the sky about 50 times a year. But finding their source is “a long-standing problem in astrophysics,” says theoretical astrophysicist Rosalba Perna of Stony Brook University in New York. The detection clinched it: Short gamma-ray bursts come from neutron star tête-à-têtes.

By studying how the neutron stars spiraled inward, astrophysicists also tested the “squishiness” of neutron star material for the first time. This extreme substance is so dense that a teaspoonful of it would have a mass of around a billion metric tons, and scientists don’t fully understand how it responds when squeezed, a property known as its “equation of state.” Measuring this property could give scientists a better understanding of the strange material. Although the results couldn’t pin down whether the neutron stars were squishy, some theories that predicted ultrasquishy neutron stars were ruled out.

The neutron stars’ union also gave researchers the opportunity to gauge the universe’s expansion rate, by measuring the distance of the collision using gravitational waves and comparing that to how much the wavelength of light from the galaxy was stretched by the expansion. Scientists have previously measured this property, known as the Hubble constant, through other means. But those measurements are in disagreement, leaving scientists scrambling to explain the discrepancy (SN: 8/6/16, p. 10).

Now, scientists have “a totally different, independent measurement,” says LIGO collaboration member Daniel Holz of the University of Chicago. The new measurement indicates that distantly separated galaxies are spreading apart at about 70 kilometers per second for each megaparsec between them. It falls squarely between the two previous estimates: 67 and 73 km/s per megaparsec. Though this collision can’t yet resolve the debate, future mergers could help improve the measurement.

“These are all just unbelievable, major advances,” Holz says. “It’s really been this insane thrill.”

The excitement has yet to die down. Take it from astronomer Ryan Foley of the University of California, Santa Cruz, whose team was the first to spot visible light from the merger: “This is certainly the biggest discovery of my career and probably will be the biggest discovery of my entire life.”

Neutron stars collide, solve major astronomical mysteries
Produces light and gravitational waves, confirms collisions produce fast gamma ray bursts, heavy elements.

https://arstechnica.com/science/2017/10/neutron-stars-collide-solve-major-astronomical-mysteries/

We’ve been extremely lucky. The LIGO and VIRGO detectors only operated simultaneously for a few weeks, but they were a remarkably busy few weeks. Today, those behind the joint collaboration announced that they’ve observed the merger of two neutron stars. And, because neutron stars don’t swallow everything they encounter, the gravitational waves were accompanied by photons, including an extended afterglow. So dozens of telescopes, and many in space, had representatives involved in the announcement.

The number of major astrophysical issues cleared up by this collision is impressive. The collision was simultaneously detected with the Fermi space telescope, confirming that neutron star mergers produce a phenomenon known as a short gamma-ray burst. The gravitational waves were detected nearly simultaneously with the gamma ray burst, confirming that they move at the speed of light. And heavy elements like gold were detected in the debris, indicating that these mergers are a source of elements that would otherwise be difficult to produce in a supernova.

Finally, the gravitational waves from this event were detected over a period of roughly 100 seconds, which should allow a detailed analysis of their production.

Meet the neutrons

Neutron stars are the product of supernovae where the star doing the exploding doesn’t have sufficient mass to form a black hole. The object that forms instead crushes one or two solar masses down to an object with a diameter of about 20km. At these densities, individual atoms are crushed out of existence, and the entire star becomes a single chunk of neutrons—and possibly other exotic particles (quark matter stars have been proposed but not yet confirmed to exist). In cases where two massive stars both go supernova, it’s possible to form binary systems where two neutron stars orbit each other.

We’ve known about binary neutron star systems for years, including some that were inspiralling toward a collision. Theoreticians have been busy proposing what they would look like and how they would behave once the merger took place, but the simultaneous detection of the event in gravitational and electromagnetic waves has been essential to confirm a number of the theoreticians’ ideas.

For that to happen, we needed to get lucky in two ways. Since neutron stars are substantially less massive than black holes, the events are weaker, and we’d only detect them if they were closer. In this case, the merger took place 130 million light years from Earth, something astronomers are calling a “relatively close distance.” (For context, that “relatively close distance” means the event took place shortly after the ancestors of marsupials and placental mammals went their separate ways.)

We also needed LIGO and VIRGO in operation simultaneously. As shown by a diagram in the gallery above, having a third detector has radically shrunk the area of sky that contains a gravitational wave source. Thus, we have a high degree of certainty that the gamma ray burst was produced by the same source as the gravitational waves.

The two neutron stars that merged here have a relatively low mass: they were estimated at about 1.1 to 1.6 times the mass of the Sun, compared to black holes that have been greater than 20 solar masses. This means that the neutron stars spent more time orbiting at a close distance before merging. This allowed the detection of gravitational waves for nearly 100 seconds; black hole mergers have produced detectable waves for only a fraction of a second. This should provide a nice test of our understanding of gravitational wave production.

Let there be light

LIGO-VIRGO’s analysis software is programmed to do a quick-and-dirty analysis of data for possible sources and send out an alert to telescopes to allow them to perform observations of the area of sky where an event may be taking place. In this case, however, the telescopes also got an alert from NASA’s Fermi Space Telescope, which specializes in catching high-energy events. Fermi has a gamma-ray burst monitor, and it picked up an event about two seconds after the gravitational wave signal arrived. This increased the precision with which we could map the source of the event, and telescopes of every sort sprung into action. More than 70 have provided observations that went into today’s announcement.

The rapid redirection of so much hardware caught people’s attention, and people quickly figured out that this was likely to mean the detection of a neutron star merger. So today’s announcement had been expected since shortly after the event took place in August.

Even before these telescopes got involved, however, the Fermi detection told us two things. One is that, as theoreticians had predicted, gravitational waves appear to travel at the speed of light. There’s still some imprecision in the measurements that could allow them to travel close, but not quite, to the speed of light, but the new measurements mean that it would have to be very, very close.

The second thing is that it nails down neutron star collisions as the source of some gamma-ray bursts. Gamma rays are the highest energy photons we can detect, and so we knew some powerful event must be producing them. Theoreticians had pointed the finger at neutron star mergers, but that had been a difficult thing to confirm, since it was often impossible to identify a counterpart to the bursts that was detectable at lower-energy wavelengths, plus we’d only be looking at debris produced by the event, not its source. The gravitational waves, by contrast, leave no doubt that the source was a neutron star merger.

Then there were the observations of the debris. This picked up the presence of gold and other heavy elements in the debris, which again, clears up an outstanding mystery. Some heavy elements are readily formed in the environment created by a supernova, meaning it’s easy to explain their abundance in the cosmos. But others can only form through pathways that involve the rapid ingestion of multiple neutrons—so fast that the atom doesn’t have time to rearrange to accommodate the previous neutrons it had absorbed. Supernovae aren’t thought to provide an environment that’s sufficiently neutron-rich for this to occur.

Neutron stars obviously would, but they keep their matter gravitationally crushed into its exotic state. What would be needed is for some event to liberate some of the matter that was otherwise trapped in these stars. Again, theoreticians had pointed to neutron star collisions as providing that opportunity, as the collisions would blast some debris out into space in a phenomenon that has picked up the term “kilonova.” But it hadn’t been confirmed until this point.

It’s an incredible wealth of information. As LIGO spokesman David Shoemaker put it in a statement, “From informing detailed models of the inner workings of neutron stars and the emissions they produce, to more fundamental physics such as general relativity, this event is just so rich. It is a gift that will keep on giving.” Plus it hints that further events of this sort will add to our understanding. Though they might not be as detailed, Laura Cadonati, another LIGO scientist, says that events of this proximity should only occur by chance once every 80,000 years. If we see more like this one, then the theoreticians will have yet another mystery to explain.

“It is tremendously exciting to experience a rare event that transforms our understanding of the workings of the Universe,” said France A. Córdova, director of the National Science Foundation. The organization she now runs took a multimillion dollar risk that the LIGO detector would bring us to this point. If the recent Nobel Prizes to the LIGO team didn’t already validate that risk, then this set of discoveries surely does.

There are two press conferences about to happen, and several papers will be released shortly. If any contain important information, we’ll have further coverage.

UPDATES:

Researchers are saying that the resulting object is either one of the heaviest neutron stars yet observed, or the lightest black hole. Data is ambiguous at this point, but they’re hoping further observations will sort this out.

The neutron stars have been orbiting each other for 11 billion years, as their stars went supernova early in the Universe’s history. The second explosion sent the neutron stars on an erratic orbit through their galaxy through this entire time.

A 16-inch telescope could have picked up the source, meaning that these events will be in the range of amateur astronomers. Plans are to open the LIGO trigger system notifications to the public, letting the amateurs in on the earliest observations.

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