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NSF/LIGO/Sonoma State University/A. Simonnet
NSF/LIGO/Sonoma State University/A. Simonnet

Astronomers Observe a New Kind of Massive Cosmic Collision for the First Time

NSF/LIGO/Sonoma State University/A. Simonnet
NSF/LIGO/Sonoma State University/A. Simonnet

For the first time, astronomers have detected the colossal blast produced by the merger of two neutron stars—and they've recorded it both via the gravitational waves the event produced, as well as the flash of light it emitted.

Physicists believe that the pair of neutron stars—ultra-dense stars formed when a massive star collapses, following a supernova explosion—had been locked in a death spiral just before their final collision and merger. As they spiraled inward, a burst of gravitational waves was released; when they finally smashed together, high-energy electromagnetic radiation known as gamma rays were emitted. In the days that followed, electromagnetic radiation at many other wavelengths—X-rays, ultraviolet, optical, infrared, and radio waves—were released. (Imagine all the instruments in an orchestra, from the lowest bassoons to the highest piccolos, playing a short, loud note all at once.)

This is the first time such a collision has been observed, as well as the first time that both kinds of observations—gravitational waves and electromagnetic radiation—have been recorded from the same event, a feat that required co-operation among some 70 different observatories around the world, including ground-based observatories, orbiting telescopes, the U.S. LIGO (Laser Interferometer Gravitational-Wave Observatory), and European Virgo gravitational wave detectors.

"For me, it feels like the dawning of a next era in astrophysics," Julie McEnery, project scientist for NASA's Fermi Gamma-ray Space Telescope, one of the first instruments to record the burst of energy from the cosmic collision, tells Mental Floss. "With this observation, we've connected these new gravitational wave observations to the rest of the observations that we've been doing in astrophysics for a very long time."

A BREAKTHROUGH ON SEVERAL FRONTS

The observations represent a breakthrough on several fronts. Until now, the only events detected via gravitational waves have been mergers of black holes; with these new results, it seems likely that gravitational wave technology—which is still in its infancy—will open many new phenomena to scientific scrutiny. At the same time, very little was known about the physics of neutron stars—especially their violent, final moments—until now. The observations are also shedding new light on the origin of gamma-ray bursts (GRBs)—extremely energetic explosions seen in distant galaxies. As well, the research may offer clues as to how the heavier elements, such as gold, platinum, and uranium, formed.

Astronomers around the world are thrilled by the latest findings, as today's flurry of excitement attests. The LIGO-Virgo results are being published today in the journal Physical Review Letters; further articles are due to be published in other journals, including Nature and Science, in the weeks ahead. Scientists also described the findings today at press briefings hosted by the National Science Foundation (the agency that funds LIGO) in Washington, and at the headquarters of the European Southern Observatory in Garching, Germany.

(Rumors of the breakthrough had been swirling for weeks; in August, astronomer J. Craig Wheeler of the University of Texas at Austin tweeted, "New LIGO. Source with optical counterpart. Blow your sox off!" He and another scientist who tweeted have since apologized for doing so prematurely, but this morning, minutes after the news officially broke, Wheeler tweeted, "Socks off!") 

The neutron star merger happened in a galaxy known as NGC 4993, located some 130 million light years from our own Milky Way, in the direction of the southern constellation Hydra.

Gravitational wave astronomy is barely a year and a half old. The first detection of gravitational waves—physicists describe them as ripples in space-time—came in fall 2015, when the signal from a pair of merging black holes was recorded by the LIGO detectors. The discovery was announced in February 2016 to great fanfare, and was honored with this year's Nobel Prize in Physics. Virgo, a European gravitational wave detector, went online in 2007 and was upgraded last year; together, they allow astronomers to accurately pin down the location of gravitational wave sources for the first time. The addition of Virgo also allows for a greater sensitivity than LIGO could achieve on its own.

LIGO previously recorded four different instances of colliding black holes—objects with masses between seven times the mass of the Sun and a bit less than 40 times the mass of the Sun. This new signal was weaker than that produced by the black holes, but also lasted longer, persisting for about 100 seconds; the data suggested the objects were too small to be black holes, but instead were neutron stars, with masses of about 1.1 and 1.6 times the Sun's mass. (In spite of their heft, neutron stars are tiny, with diameters of only a dozen or so miles.) Another key difference is that while black hole collisions can be detected only via gravitational waves—black holes are black, after all—neutron star collisions can actually be seen.

"EXACTLY WHAT WE'D HOPE TO SEE"

When the gravitational wave signal was recorded, on the morning of August 17, observatories around the world were notified and began scanning the sky in search of an optical counterpart. Even before the LIGO bulletin went out, however, the orbiting Fermi telescope, which can receive high-energy gamma rays from all directions in the sky at once, had caught something, receiving a signal less than two seconds after the gravitational wave signal tripped the LIGO detectors. This was presumed to be a gamma-ray burst, an explosion of gamma rays seen in deep space. Astronomers had recorded such bursts sporadically since the 1960s; however, their physical cause was never certain. Merging neutron stars had been a suggested culprit for at least some of these explosions.

"This is exactly what we'd hoped to see," says McEnery. "A gamma ray burst requires a colossal release of energy, and one of the hypotheses for what powers at least some of them—the ones that have durations of less than two seconds—was the merger of two neutron stars … We had hoped that we would see a gamma ray burst and a gravitational wave signal together, so it's fantastic to finally actually do this."

With preliminary data from LIGO and Virgo, combined with the Fermi data, scientists could tell with reasonable precision what direction in the sky the signal had come from—and dozens of telescopes at observatories around the world, including the U.S. Gemini telescopes, the European Very Large Telescope, and the Hubble Space Telescope, were quickly re-aimed toward Hydra, in the direction of reported signal.

The telescopes at the Las Campanas Observatory in Chile were well-placed for getting a first look—because the bulletin arrived in the morning, however, they had to wait until the sun dropped below the horizon.

"We had about eight to 10 hours, until sunset in Chile, to prepare for this," Maria Drout, an astronomer at the Carnegie Observatories in in Pasadena, California, which runs the Las Campanas telescopes, tells Mental Floss. She was connected by Skype to the astronomers in the control rooms of three different telescopes at Las Campanas, as they prepared to train their telescopes at the target region. "Usually you prepare a month in advance for an observing run on these telescopes, but this was all happening in a few hours," Drout says. She and her colleagues prepared a target list of about 100 galaxies, but less than one-tenth of the way through the list, by luck, they found it: a tiny blip of light in NGC 4993 that wasn't visible on archival images of the same galaxy. (It was the 1-meter Swope telescope that snagged the first images.)

A NEW ERA OF ASTROPHYSICS

When a new star-like object in a distant galaxy is spotted, a typical first guess is that it's a supernova (an exploding star). But this new object was changing very rapidly, growing 100 times dimmer over just a few days while also quickly becoming redder—which supernovae don't do, explains Drout, who is cross-appointed at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto. "We ended up following it for three weeks or so, and by the end, it was very clear that this [neutron star merger] was what we were looking at," she says.

The researchers say they can't be sure if the resulting object was another, larger neutron star, or whether it would have been so massive that it would have collapsed into a black hole.

As exciting as the original detection of gravitational waves last year was, Drout is looking forward to a new era in which both gravitational waves and traditional telescopes can be used to study the same objects. "We can learn a lot more about these types of extreme systems that exist in the universe, by coupling the two together," she says.

The detection shows that "gravitational wave science is moving from being a physics experiment to being a tool for astronomers," Marcia Rieke, an astronomer at the University of Arizona who is not involved in the current research, tells Mental Floss. "So I think it's a pretty big deal."

Physicists are also learning something new about the origin of the heaviest elements in the periodic table. For many years, these were thought to arise from supernova explosions, but spectroscopic data from the newly observed neutron star merger (in which light is broken up into its component colors) suggests that such explosion produce enormous quantities of heavy elements—including enough gold to put Fort Knox to shame. (The blast is believed to have created some 200 Earth-masses of gold, the scientists say.) "It's telling us that most of the gold that we know about is produced in these mergers, and not in supernovae," McEnery says.

Editor's note: This post has been updated.

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NASA, JPL-Caltech
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Space
It's Official: Uranus Smells Like Farts
NASA, JPL-Caltech
NASA, JPL-Caltech

Poor Uranus: After years of being the butt of many schoolyard jokes, the planet's odor lives up to the unfortunate name. According to a new study by researchers at the University of Oxford and other institutions, published in the journal Nature Astronomy, the upper layer of Uranus's atmosphere consists largely of hydrogen sulfide—the same compound that gives farts their putrid stench.

Scientists have long suspected that the clouds floating over Uranus contained hydrogen sulfide, but the compound's presence wasn't confirmed until recently. Certain gases absorb infrared light from the Sun. By analyzing the infrared light patterns in the images they captured using the Gemini North telescope in Hawaii, astronomers were able to get a clearer picture of Uranus's atmospheric composition.

On top of making farts smelly, hydrogen sulfide is also responsible for giving sewers and rotten eggs their signature stink. But the gas's presence on Uranus has value beyond making scientists giggle: It could unlock secrets about the formation of the solar system. Unlike Uranus (and most likely its fellow ice giant Neptune), the gas giants Saturn and Jupiter show no evidence of hydrogen sulfide in their upper atmospheres. Instead they contain ammonia, the same toxic compound used in some heavy-duty cleaners.

"During our solar system's formation, the balance between nitrogen and sulfur (and hence ammonia and Uranus’s newly detected hydrogen sulfide) was determined by the temperature and location of planet’s formation," research team member Leigh Fletcher, of the University of Leicester, said in a press statement. In other words, the gases in Uranus's atmosphere may be able to tell us where in the solar system the planet formed before it migrated to its current spot.

From far away, Uranus's hydrogen sulfide content marks an exciting discovery, but up close it's a silent but deadly killer. In large enough concentrations, the compound is lethal to humans. But if someone were to walk on Uranus without a spacesuit, that would be the least of their problems: The -300°F temperatures and hydrogen, helium, and methane gases at ground level would be instantly fatal.

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Scott Butner, Flickr // CC BY-NC-ND 2.0
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Space
Look Up! The Lyrid Meteor Shower Arrives Saturday Night
Scott Butner, Flickr // CC BY-NC-ND 2.0
Scott Butner, Flickr // CC BY-NC-ND 2.0

There is a thin line between Saturday night and Sunday morning, but this weekend, look up and you might see several of them. Between 11:59 p.m. on April 21 and dawn on Sunday, April 22, the Lyrid meteor shower will peak over the Northern Hemisphere. Make some time for the celestial show and you'll see a shooting star streaking across the night sky every few minutes. Here is everything you need to know.

WHAT IS THE LYRID METEOR SHOWER?

Every 415.5 years, the comet Thatcher circles the Sun in a highly eccentric orbit shaped almost like a cat's eye. At its farthest from the Sun, it's billions of miles from Pluto; at its nearest, it swings between the Earth and Mars. (The last time it was near the Earth was in 1861, and it won't be that close again until 2280.) That's quite a journey, and more pressingly, quite a variation in temperature. The closer it gets to the Sun, the more debris it sheds. That debris is what you're seeing when you see a meteor shower: dust-sized particles slamming into the Earth's atmosphere at tens of thousands of miles per hour. In a competition between the two, the Earth is going to win, and "shooting stars" are the result of energy released as the particles are vaporized.

The comet was spotted on April 4, 1861 by A.E. Thatcher, an amateur skywatcher in New York City, earning him kudos from the noted astronomer Sir John Herschel. Clues to the comet's discovery are in its astronomical designation, C/1861 G1. The "C" means it's a long-period comet with an orbit of more than 200 years; "G" stands for the first half of April, and the "1" indicates it was the first comet discovered in that timeframe.

Sightings of the Lyrid meteor shower—named after Lyra, the constellation it appears to originate from—are much older; the first record dates to 7th-century BCE China.

HOW CAN I SEE IT?

Saturday night marks a first quarter Moon (visually half the Moon), which by midnight will have set below the horizon, so it won't wash out the night sky. That's great news—you can expect to see 20 meteors per hour. You're going to need to get away from local light pollution and find truly dark skies, and to completely avoid smartphones, flashlights, car headlights, or dome lights. The goal is to let your eyes adjust totally to the darkness: Find your viewing area, lay out your blanket, lay down, look up, and wait. In an hour, you'll be able to see the night sky with great—and if you've never done this before, surprising—clarity. Don't touch the smartphone or you'll undo all your hard ocular work.

Where is the nearest dark sky to where you live? You can find out on the Dark Site Finder map. And because the shower peaks on a Saturday night, your local astronomy club is very likely going to have an event to celebrate the Lyrids. Looking for a local club? Sky & Telescope has you covered.

WHAT ELSE IS GOING ON UP THERE?

You don't need a telescope to see a meteor shower, but if you bring one, aim it south to find Jupiter. It's the bright, unblinking spot in the sky. With a telescope, you should be able to make out its stripes. Those five stars surrounding it are the constellation Libra. You'll notice also four tiny points of light nearby. Those are the Galilean moons: Io, Europa, Ganymede, and Callisto. When Galileo discovered those moons in 1610, he was able to prove the Copernican model of heliocentricity: that the Earth goes around the Sun.

THERE'S BAD WEATHER HERE! WHAT DO I DO?

First: Don't panic. The shower peaks on the early morning of the 22nd. But it doesn't end that day. You can try again on the 23rd and 24th, though the numbers of meteors will likely diminish. The Lyrids will be back next year, and the year after, and so on. But if you are eager for another show, on May 6, the Eta Aquariids will be at their strongest. The night sky always delivers.

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