First Observations Of Merging Neutron Stars Mark A New Era In Astronomy

After LIGO detected gravitational waves from the merger of two neutron stars, the race was on to detect a visible counterpart, because unlike the colliding black holes responsible for LIGO’s four previous detections, this event was expected to produce an explosion of visible light. A small team led by UCSC was the first to find the source of the gravitational waves, capturing the first images of the event with the Swope Telescope in Chile.

Two months ago, the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) notified astronomers around the world of the possible detection of gravitational waves from the merger of two neutron stars. From that moment on August 17, the race was on to detect a visible counterpart, because unlike the colliding black holes responsible for LIGO’s four previous detections of gravitational waves, this event was expected to produce a brilliant explosion of visible light and other types of radiation.

A small team led by Ryan Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz, was the first to find the source of the gravitational waves, located in a galaxy 130 million light-years away called NGC 4993. Foley’s team captured the first images of the event with the 1-meter Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile.

“This is a huge discovery,” Foley said. “We’re finally connecting these two different ways of looking at the universe, observing the same thing in light and gravitational waves, and for that alone this is a landmark event. It’s like being able to see and hear something at the same time.”

Theoretical astrophysicist Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and a member of Foley’s team, said the observations have opened a new window into understanding the physics of neutron star mergers. Among other things, the results could resolve a hotly debated question about the origins of gold and other heavy elements in the universe, which Ramirez-Ruiz has been studying for years.

“I think this can prove our idea that most of these elements are made in neutron star mergers,” he said. “We are seeing the heavy elements like gold and platinum being made in real time.”

Foley’s team is publishing four papers October 16 in Science based on their observations and analysis, as well as three papers in Astrophysical Journal Letters, and they are coauthors of several more papers in Nature and other journals, including two major papers led by the LIGO collaboration. The key Science papers include one presenting the discovery of the first optical counterpart to a gravitational wave source, led by UCSC graduate student David Coulter, and another, led by postdoctoral fellow Charles Kilpatrick, presenting a state-of-the-art comparison of the observations with theoretical models to confirm that it was a neutron-star merger. Two other Science papers were led by Foley’s collaborators at the Carnegie Institution for Science.

By coincidence, the LIGO detection came on the final day of a scientific workshop on “Astrophysics with gravitational wave detections,” which Ramirez-Ruiz had organized at the Niels Bohr Institute in Copenhagen and where Foley had just given a talk. “I wish we had filmed Ryan’s talk, because he was so gloomy about our chances to observe a neutron star merger,” Ramirez-Ruiz said. “But then he went on to outline his strategy, and it was that strategy that enabled his team to find it before anyone else.”

Foley’s strategy involved prioritizing the galaxies within the search field indicated by the LIGO team, targeting those most likely to harbor binary pairs of neutron stars, and getting as many of those galaxies as possible into each field of view. Other teams covered the search field more methodically, “like mowing the lawn,” Foley said. His team found the source in the ninth field they observed, after waiting 10 hours for the sun to set in Chile.

“As soon as the sun went down, we started looking,” Foley said. “By finding it as quickly as we did, we were able to build up a really nice data set.”

He noted that the source was bright enough to have been seen by amateur astronomers, and it likely would have been visible from Africa hours before it was visible in Chile. Gamma rays emitted by the neutron star merger were detected by the Fermi Gamma-ray Space Telescope at nearly the same time as the gravitational waves, but the Fermi data gave no better information about the location of the source than LIGO did.

Foley’s team took the first image of the optical source 11 hours after the LIGO detection and, after confirming their discovery, announced it to the astronomy community an hour later. Dozens of other teams quickly followed up with observations from other telescopes. Foley’s team also obtained the first spectra of the source with the Magellan Telescopes at Carnegie’s Las Campanas Observatory.

The gravitational wave source was named GW170817, and the optical source was named Swope Supernova Survey 2017a (SSS17a). By about seven days later, the source had faded and could no longer be detected in visible light. While it was visible, however, astronomers were able to gather a treasure trove of data on this extraordinary astrophysical phenomenon.

“It’s such a rich data set, the amount of science to come from this one thing is incredible,” Ramirez-Ruiz said.

Neutron stars are among the most exotic forms of matter in the universe, consisting almost entirely of neutrons and so dense that a sugar cube of neutron star material would weigh about a billion tons. The violent merger of two neutron stars ejects a huge amount of this neutron-rich material, powering the synthesis of heavy elements in a process called rapid neutron capture, or the “r-process.”

The radiation this emits looks nothing like an ordinary supernova or exploding star. Astrophysicists like Ramirez-Ruiz have developed numerical models to predict what such an event, called a kilonova, would look like, but this is the first time one has actually been observed in such detail. Kilpatrick said the data fit remarkably well with the predictions of theoretical models.

“It doesn’t look like anything we’ve ever seen before,” he said. “It got very bright very quickly, then started fading rapidly, changing from blue to red as it cooled down. It’s completely unprecedented.”

A theoretical synthesis of data from across the spectrum, from radio waves to gamma rays, was led by Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, and published in Astrophysical Journal Letters, providing a coherent theoretical framework for understanding the full range of observations. Their analysis indicates, for example, that the merger triggered a relativistic jet (material moving at near the speed of light) that generated the gamma-ray burst, while matter torn from the merger system and ejected at lower speeds drove the r-process and the kilonova emissions at ultraviolet, optical, and infrared wavelengths.

Ramirez-Ruiz has calculated that a single neutron-star merger can generate an amount of gold equal to the mass of Jupiter. The team’s calculations of heavy element production by SSS17a suggest that neutron star mergers can account for about half of all the elements heavier than iron in the universe.

The detection came just one week before the end of LIGO’s second observing run, which had begun in November 2016. Foley was in Copenhagen, taking advantage of his one afternoon off to visit Tivoli Gardens with his partner, when he got a text from Coulter alerting him to the LIGO detection. At first, he thought it was a joke, but soon he was pedaling his bicycle madly back to the University of Copenhagen to begin working with his team on a detailed search plan.

“It was crazy. We barely got it done, but our team was incredible and it all came together,” Foley said. “We got lucky, but luck favors the prepared, and we were ready.”

Foley’s team at UC Santa Cruz includes Ramirez-Ruiz, Coulter, Kilpatrick, Murguia-Berthier, professor of astronomy and astrophysics J. Xavier Prochaska, postdoctoral researcher Yen-Chen Pan, and graduate students Matthew Siebert, Cesar Rojas-Bravo and Enia Xhakaj. Other team members include Maria Drout, Ben Shappee, and Tony Piro at the Observatories of the Carnegie Institution for Science; UC Berkeley astronomer Daniel Kasen; and Armin Rest at the Space Telescope Science Institute.

Their team is called the One-Meter, Two-Hemisphere (1M2H) Collaboration because they use two one-meter telescopes, one in each hemisphere: the Nickel Telescope at UC’s Lick Observatory and Carnegie’s Swope Telescope in Chile. The UCSC group is supported in part by the National Science Foundation, Gordon and Betty Moore Foundation, Heising-Simons Foundation, and Kavli Foundation; fellowships for Foley and Ramirez-Ruiz from the David and Lucile Packard Foundation and for Foley from the Alfred P. Sloan Foundation; a Niels Bohr Professorship for Ramirez-Ruiz from the Danish National Research Foundation; and the UC Institute for Mexico and the United States (UC MEXUS).

Astronomers Strike Cosmic Gold, Confirm Origin Of Precious Metals In Neutron Star Mergers

The first detection of gravitational waves from the cataclysmic merger of two neutron stars, and the observation of visible light in the aftermath of that merger, finally answer a long-standing question in astrophysics: Where do the heaviest elements, ranging from silver and other precious metals to uranium, come from?

Based on the brightness and color of the light emitted following the merger, which closely match theoretical predictions by University of California, Berkeley and Lawrence Berkeley National Laboratory physicists, astronomers can now say that the gold or platinum in your wedding ring was in all likelihood forged during the brief but violent merger of two orbiting neutron stars somewhere in the universe.

This is the first detection of a neutron star merger by the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the United States, whose leaders were awarded the Nobel Prize in Physics two weeks ago, and the Virgo detector in Italy. LIGO had previously detected gravitational waves from four black hole mergers, and Virgo one, but such events should be completely dark. This is the first time that light associated with a source of gravitational waves has been detected.

“We have been working for years to predict what the light from a neutron merger would look like,” said Daniel Kasen, an associate professor of physics and of astronomy at UC Berkeley and a scientist at Berkeley Lab. “Now that theoretical speculation has suddenly come to life.”

The neutron star merger, dubbed GW170817, was detected on August 17 and immediately telegraphed to observers around the world, who turned their small and large telescopes on the region of the sky from which it came. The ripples in spacetime that LIGO/Virgo measured suggested a neutron star merger, since each star of the binary weighed between 1 and 2 times the mass of our sun. Apart from black holes, neutron stars are the densest objects known in the universe. They are created when a massive star exhausts its fuel and collapses onto itself, compressing a mass comparable to that of the sun into a sphere only 10 miles across.

Only 1.7 seconds after the gravitational waves were recorded, the Fermi space telescope detected a short burst of gamma rays from the same region, evidence that concentrated jets of energy are produced during the merger of neutron stars. Less than 11 hours later, observers caught their first glimpse of visible light from the source. It was localized to a known galaxy, NGC 4993, situated about 130 million light years from Earth in the direction of the constellation Hydra.

The detection of a neutron star merger was surprising, because neutron stars are much smaller than black holes and their mergers produce much weaker gravitational waves than do black hole mergers. According to Berkeley professor of astronomy and physics Eliot Quataert, “We were anticipating LIGO finding a neutron star merger in the coming years but to see it so nearby — for astronomers — and so bright in normal light has exceeded all of our wildest expectations. And, even more amazingly, it turns out that most of our predictions of what neutron star mergers would look like as seen by normal telescopes were right!”

The LIGO/Virgo observations of gravitational waves and the detection of their optical counterpart will be discussed at a 10 a.m. EDT press conference on Monday, Oct. 16, at the National Press Club in Washington, D.C. Simultaneously, several dozen papers discussing the observations will be published online by Nature, Science and the Astrophysical Journal Letters.

Genesis of the elements

While hydrogen and helium were formed in the Big Bang 13.8 billion years ago, heavier elements like carbon and oxygen were formed later in the cores of stars through nuclear fusion of hydrogen and helium. But this process can only build elements up to iron. Making the heaviest elements requires a special environment in which atoms are repeatedly bombarded by free neutrons. As neutrons stick to the atomic nuclei, elements higher up the periodic table are built.

Where and how this process of heavy element production occurs has been one of the longest-standing questions in astrophysics. Recent attention has turned to neutron star mergers, where the collision of the two stars flings out clouds of neutron-rich matter into space, where they could assemble into heavy elements.

Speculation that astronomers might see light from such heavy elements traces back to the 1990s, but the idea had mostly been gathering dust until 2010, when Brian Metzger, then a freshly minted graduate student at UC Berkeley, now a professor of astrophysics at Columbia University, co-authored a paper with Quataert and Kasen in which they calculated the radioactivity of the neutron star debris and estimated its brightness for the first time.

“As the debris cloud expands into space,” Metzger said, “the decay of radioactive elements keeps it hot, causing it to glow.”

Metzger, Quataert, Kasen and collaborators showed that this light from neutron star mergers was roughly one thousand times brighter than normal nova explosions in our galaxy, motivating them to name these exotic flashes “kilonovae.”

Still, basic questions remained as to what a kilonova would actually look like.

“Neutron star merger debris is weird stuff — a mixture of precious metals and radioactive waste,” Kasen said.

Astronomers know of no comparable phenomena, so Kasen and collaborators had to turn to fundamental physics and solve mathematical equations describing how the quantum structure of heavy atoms determines how they emit and absorb light.

Jennifer Barnes, an Einstein postdoctoral fellow at Columbia, worked as a Berkeley graduate student with Kasen to make some of the first detailed predictions of what a kilonova should look like.

“When we calculated the opacities of the elements formed in a neutron star merger, we found a lot of variation. The lighter elements were optically similar to elements found in supernovae, but the heavier atoms were more than a hundred times more opaque than what we’re used to seeing in astrophysical explosions,” said Barnes. “If heavy elements are present in the debris from the merger, their high opacity should give kilonovae a reddish hue.”

“I think we bummed out the entire astrophysics community when we first announced that,” Kasen said. “We were predicting that a kilonova should be relatively faint and redder than red, meaning it would be an incredibly difficult thing to find. On the plus side, we had defined a smoking-gun — you can tell that you are seeing freshly produced heavy elements by their distinctive red color.”

That is just what astronomers observed.

A ‘treacherous prediction’

The August LIGO/Virgo discovery of a neutron star merger meant that “judgment day for the theorists would come sooner than expected,” Kasen said.

“For years the idea of a kilonova had existed only in our theoretical imagination and our computer models,” he said. “Given the complex physics involved, and the fact that we had essentially zero observational input to guide us, it was an insanely treacherous prediction — the theorists were really sticking their necks out.”

But as the data trickled in, one night after the next, the images began to assemble into a surprisingly familiar picture.

On the first couple nights of observations, the color of the merger event was relatively blue with a brightness that matched the predictions of kilonova models strikingly well if the outer layers of the merger debris are made of light precious elements such as silver. However, over the ensuing days the emission became increasingly red, a signature that the inner layers of the debris cloud also contain the heaviest elements, such as platinum, gold and uranium.

“Perhaps the biggest surprise was how well-behaved the visual signal acted compared to our theoretical expectations,” Metzger noted. “No one had ever seen a neutron star merger up close before. Putting together the complete picture of such an event involves a wide range of physics — general relativity, hydrodynamics, nuclear physics, atomic physics. To combine all that and come up with a prediction that matches the reality of nature is a real triumph for theoretical astrophysics.”

Kasen, who was also a member of observational teams that discovered and conducted follow-up observations of the source, recalled the excitement of the moment: “I was staying up past 3 a.m. night after night, comparing our models to the latest data, and thinking, ‘I can’t believe this is happening; I’m looking at something never before seen on Earth, and I think I actually understand what I am seeing.'”

Kasen and his colleagues have presented updated kilonova models and theoretical interpretations of the observations in a paper released Oct. 16 in advance of publication in Nature. Their models are also being used to analyze a wide-ranging set of data presented in seven additional papers appearing in Nature, Science and the Astrophysical Journal.

Not only did the observations confirm the theoretical predictions, but the modeling allowed Kasen and his colleagues to calculate the amount and chemical makeup of the material produced. The scientists inferred that around 6 percent of a solar mass of heavy elements were made. The yield of gold alone was around 200 Earth masses, and that of platinum nearly 500 Earth masses.

Initially, astrophysicists thought ordinary supernovae might account for the heavy elements, but there have always been problems with that theory, said co-author Enrico Ramirez-Ruiz, a professor of astronomy and astrophysics at UC Santa Cruz. According to Ramirez-Ruiz, the new observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.

“Most of the time in science you are working to gradually advance an established subject,” Kasen said. “It is rare to be around for the birth of an entirely new field of astrophysics. I think we are all very lucky to have had the chance to play a role.”

Kasen’s work is supported by the U.S. Department of Energy, and simulations were made possible by resources from the National Energy Research Scientific Computing Center (NERSC). Kasen’s and Quataert’s work is supported by the Gordon and Betty Moore Foundation. Quataert is also supported by the Simons Foundation.

NASA Finds Newly formed Tropical Storm lan Over Open Waters

NASA-NOAA’s Suomi NPP satellite provided a visible picture of newly formed Tropical Storm Lan in the Northwestern Pacific Ocean.

Tropical Storm Lan developed on Oct. 15 and has been moving to the west-northwest over open ocean.

On Oct. 16 at 12 a.m. EDT (0400 UTC) the VIIRS instrument aboard NASA-NOAA’s Suomi NPP satellite provided a visible image of the storm. The image showed the bulk of clouds were on the eastern and southeastern sides of the storm indicating the storm was being affected by vertical wind shear.

At 11 a.m. EDT (1500 UTC) Tropical storm Lan was centered near 10.8 degrees north latitude and 133.1 degrees east longitude, about 214 nautical miles north-northwest of Koror, Palau. It was moving to the west 12 knots (13.8 mph/22.2 kph) and had maximum sustained winds near 35 knots (40 mph/62 kph).

The Joint Typhoon Warning Center noted that Lan is intensifying and is expected to become a typhoon over the open waters of the western Pacific.

A Rare Hurricane Near Europe Turned The Sun Red

At least two people have died after former Hurricane Ophelia hit Ireland’s west coast this morning (Oct. 16) as a post-tropical storm that turned the Sun red as it rose over the UK.

Ophelia made landfall on the southwest Irish coast in the counties of Cork and Kerry with wind gusts as high as 120 mph, the equivalent of category-3 storm. (It was not technically a hurricane because it formed in the Bay of Biscay rather than tropical waters.)

Ophelia’s size, bigger than the island itself, shows the sheer potential for destruction:

Ophelia could still bring hurricane-force winds across Ireland and Britain.

Ophelia tears into Ireland

Ophelia is the most powerful storm ever recorded in the northeastern Atlantic and the worst storm to hit Ireland since Hurricane Debbie in 1961, which killed 15 .

Met Éireann, the Irish weather office, issued a red-wind warning, the highest level available, for the entire country today (Oct. 16), cautioning “There is a danger to life and property.” Schools throughout the country closed.
The Met Office in the UK issued an amber weather warning for Northern Ireland into parts of Wales and Scotland, with gusts up to 80 mph expected.

“Bear in mind that while in some parts of the country the storm is not yet that bad, it is coming your way,” Ireland’s prime minister Leo Varadkar said at a news conference. “This is a national red alert. It applies to all cities, all counties and all areas.”

Officials in County Waterford said a female driver was killed when a tree fell through her windshield. A man in County Tipperary died from a chainsaw injury after trying to clear a fallen tree. About 360,000 people are without power.

The storm is expected to move into Britain late tonight or early tomorrow (Oct. 17). The US National Hurricane Center, which tracks Atlantic storms, expects Ophelia to weaken over the next day and dissipate over Norway tomorrow night.

About that Red Sun

According to BBC weather reporter Simon King, the redness was caused by the remnants of Ophelia dragging tropical air and dust from the Sahara, along with debris from forest fires in Portugal and Spain. The dust scatters the short-wavelength blue light, allowing longer-wavelength red light to shine through, making the Sun appear red.

Indonesian Volcano Spews Clouds Of Ash And Prepares To Erupt As Authorities Plan For Emergency Evacuations

A huge volcano in Indonesia erupted on Sunday, spewing hot ash into the air.

Thousands were evacuated after Mount Sinabung in Karo, Indonesia, started erupting and spewing ash half a kilometre into the air.

The volcano began erupting in 2010 after lying dormant for four centuries.

A large eruption in May 2016 killed seven people.

Meanwhile, more than 3,000km away in Bali, Mount Agung has been threatening to erupt for weeks,
Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho has Mount Agung is ‘very dangerous’ and could explode anytime.

It’s been at its highest alert level since September 22, sparking an exodus of more than 140,000 people from the area.
Mount Agung last erupted in 1963, killing more than 1,100 people.

Bali’s Mount Agung Reaches Highest Activity Since Volcano Came Back ToLife

Earthquake activity from Bali’s Mount Agung has reached its highest level since the volcano came back to life in August.

The Volcano Observatory Notice for Aviation has the volcano at its highest alert level short of an eruption.

Last weekend there was an earthquake that measured at 4.6 on the Richter scale while almost 1000 smaller tremors a day are also being recorded.

There are increases in shallow and deep tremors indicating magma is moving upwards.

All airlines are monitoring the situation closely and travellers have been urged to make sure their contact details are up to date.

Various governments have warned that travel to Bali could be severely affected by an eruption and Bali’s international airport has set up an emergency operations centre.

Travel insurance companies started imposing restrictions on policies after warnings about the potential eruption became public.

This means people who bought travel insurance after a certain date will not be covered for losses relating to the volcano.

Mt Agung’s last major eruption in 1963 killed almost 2000 people and lasted for more than a year.

That eruption was of the same explosive intensity as Mount St Helens in 1981 and Mount Pinatubo in 1991.

Last month Professor Heather Handley, an ARC Future Fellow in the Department of Earth and Planetary Sciences at Macquarie University in Sydney, said “if Mount Agung erupts and the eruption is similar to its two previous large-scale eruptions then we might expect to see lava flows reach several kilometres from the summit, in any direction and deadly pyroclastic flows travel tens of kilometres from the summit.”

“Due to the high level of sulphur dioxide in magma erupted at Agung, if this mixes with water vapour in the atmosphere it can create sulphric acid and so acid rain could be an issue”.

Bali travellers are being told to take face masks with them and stock up on bottled water once in Bali.

Hong Kong, Southern China Brace For Typhoon Khanun

BEIJING – Typhoon Khanun is likely to hit southern China early Monday with winds of up to 114 kph (70 mph), China’s meteorological agency said, as authorities in the financial hub of Hong Kong raised the third-highest weather warning.

The typhoon is expected to make landfall between Zhanjiang, in Guangdong province, and Wenchang, in Hainan province, the official Xinhua News Agency cited the National Meteorological Center as saying.

The agency has issued an orange alert, the second highest in China’s four-tier, color-coded alert system for severe weather, with red being the most severe, followed by orange, yellow and blue.

From Sunday to Monday morning, parts of Zhejiang, Guangdong, Guangxi and Hainan provinces will be drenched in heavy rain, Xinhua warned. In some areas, precipitation is expected to be up to 200 millimetres (7.8 inches), it said.

In Hong Kong, some transport services were disrupted Sunday because of strong wind. Ferries linking Hong Kong, to Macau and nearby islands, were suspended while some flights to Taiwan and mainland China were canceled, transport authorities said.

The storm comes about two months after Typhoon Hato, a maximum category 10 storm, caused havoc in Hong Kong and deaths in nearby Macau, with extensive flooding and disruption to transport.

Xinhua said in Hainan, high-speed train services were suspended from early Sunday, while ferries on the Qiongzhou Strait, which connects the island province with Guangdong on the mainland, were suspended on Saturday, Xinhua said.