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The Expanding Debris Cloud From the Kilonova Tells the Story of What Happens When Neutron Stars Collide – Universe Today

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When two neutron stars collide, it creates a kilonova. The event causes both gravitational waves and emissions of electromagnetic energy. In 2017 the LIGO-Virgo gravitational-wave observatories detected a merger of two neutron stars about 130 million light-years away in the galaxy NGC 4993. The merger is called GW170817, and it remains the only cosmic event observed in both gravitational waves and electromagnetic radiation.

Astronomers have watched the expanding debris cloud from the kilonova for years. A clearer picture of what happens in the aftermath is emerging.

A team of researchers have pieced together the story of GW170917 in a paper titled “The emergence of a new source of X-rays from the binary neutron star merger GW170817.” The lead author is Aprajita Hajela, a graduate student in the Department of Physics & Astronomy at Northwestern University. The paper is published in The Astrophysical Journal Letters.

Over the years, astronomers have trained a whole suite of scientific eyes on the expanding cloud, uncovering more and more detail about these cosmic calamities. GW170817 is an unprecedented opportunity to study the kilonova phenomena because astronomers observed gravitational waves and electromagnetic radiation from the merger. The gravitational waves (GW) tell researchers about pre-merger activity, and the electromagnetic observations tell them about the post-merger physical properties.

When two neutron stars merge, it produces a cloud of debris and a burst of light called a kilonova. A pair of astronomers introduced the model for neutron star mergers in 1998. They said that the mergers synthesized radioactive nuclei that provide a long-term heat source for the expanding debris envelope. The optical and infrared light in the kilonova comes from the decay of elements like platinum and gold created during the merger. When LIGO and Virgo detected GWs from GW170817, other telescopes detected the optical and infrared light hours later.

This is the first optical image ever to show an event initially detected as a Gravitational Wave (GW), designated GW170817, pictured left. Afterglow, designated as SSS17a, is left over from the explosion of two neutron stars that collided in galaxy NGC 4993 (shown centre). Only 10.9 hours after triggering the largest astronomical search in history, the Swope 1-m telescope at the Las Campanas Observatory in Chile discovered GW170817’s afterglow. Four days later, the image on the right shows afterglow dimming in brightness and changing from blue to red. CREDIT: Las Campanas Observatory, Carnegie Institution of Washington (Swope + Magellan)

The Chandra X-ray Observatory was also watching. Chandra saw nothing at first, which was unusual. Scientists expect kilonovae to produce x-rays in jets of high-energy particles. Now scientists think there was a jet, but it wasn’t pointed at Earth. Chandra eventually detected x-rays when the jets impacted the surrounding gas and dust, causing them to widen and slow down. Then later in 2018, the x-ray emissions declined again.

The x-rays have remained stable since the end of 2020. The inset x-ray image in the top picture is from Chandra data from December 2020 and January 2021. The x-rays come from both GW170917 and the host galaxy.

Scientists think there could be two explanations for the steadying of x-ray emissions.

On 17 August 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Interferometer detected gravitational waves from the collision between two neutron stars. Within 12 hours, observatories identified the event’s source within the lenticular galaxy NGC 4993, shown in this image gathered with the NASA/ESA Hubble Space Telescope. The associated stellar flare, a kilonova, is visible in the Hubble observations. This is the first time astronomers have observed the optical counterpart of a gravitational wave event. Hubble observed the kilonova gradually fading over six days, as shown in these observations taken between 22 and 28 August (insets). Image Credit: Hubble/NASA/ESA

The first explanation is that a kind of shock is involved, akin to a sonic boom. When the cloud of debris from the kilonova slams into gas around GW170817, the material is heated. The temperature is enough to produce x-rays and can account for the steady kilonova afterglow Chandra detected.

The artist’s illustration depicts this. The blue in the image is the debris responsible for the glow. The orange and red show the shock. The jets have faded over time, and the blue arcs in the image show where the jets struck surrounding material.

The second explanation is entirely different. It says that the neutron star merger collapsed into a remnant black hole. In this scenario, material falling into the black hole is heated enough to emit x-rays, a known phenomenon around black holes.

The team of researchers behind the new paper says that only one of the two explanations can spell out what’s happening. It would be an improbable coincidence for both sources to be producing x-rays simultaneously in the same place. They also point out that scientists have never observed a kilonova afterglow nor accretion-powered emissions like this before.

Further observations should determine the cause of the x-ray afterglow. Astronomers will continue to observe GW170817 in both x-rays and radio waves. If the glow comes from the kilonova, the radio emissions should brighten in the coming months and years. But if the glow comes from material falling into a black hole, then the x-rays should stay steady or decline rapidly, but there’ll be no radio emissions over time.

“Measuring the time of the peak of the kilonova afterglow, which probed the ejecta dynamics independent of shock microphysics, would offer a unique opportunity to do calorimetry of the kilonova’s fastest ejecta,” they write. This is important because it relates to whether or not the merger left a remnant black hole. If there’s a high-velocity tail in the ejecta, it can create excessive x-ray emissions that “… argues against the prompt collapse of the merger remnant into a black hole.”

Astrophysicists know that black holes emit electromagnetic radiation in x-ray wavelengths. The Chandra X-ray Observatory has imaged many of them. This Chandra image shows Centaurus A, which is not part of this study but is the site of a supermassive black hole, shining brightly. Credit: X-ray: NASA/CXC/U.Birmingham/M.Burke et al.

On the other hand, that same ejecta might emit “… a constant (or declining) source of X-ray emission in the next thousands of days that is not accompanied by bright radio emission.” If that’s the case, the authors say, it shows that the merger collapsed into a black hole. That represents another scientific opportunity because it “… will unveil how accretion processes work on a compact-object remnant of a BNS merger a few years after its birth.”

When LIGO detected the first gravitational waves in 2016, they opened a new window into the Universe. One hundred years before their detection, Einstein predicted them in his general theory of relativity. Three researchers who played a central role in detecting GWs received the 2017 Nobel Prize in physics.

Since the first detection, LIGO and Virgo have detected many more black holes and neutron star mergers. The combination of GW detections and quick and enduring follow-up electromagnetic observations have confirmed some theoretical work, including discovering that kilonovae produce heavy elements.

This paper, along with other articles published on the kilonova, has confirmed theoretical predictions about these events. Astrophysicists predicted that kilonovae are a significant source of heavy elements in the Universe. The type of emissions and their flux both support that. “The spectrum and flux evolution of the kilonova emission from GW170817 was in agreement with theoretical predictions, demonstrating that mergers of neutron stars are one of the major sources of heavy elements in our Universe,” the paper says.

In 2019 a team of European researchers, using data from the X-shooter instrument on ESO’s Very Large Telescope, found signatures of strontium formed in the GW170817 neutron-star merger. This artist’s impression shows two tiny but dense neutron stars when they merge and explode as a kilonova. In the foreground, we see a representation of freshly created strontium. Image Credit: ESO/L. Calçada/M. Kornmesser

Scientists have learned a lot about neutron star mergers and kilonovae since the 1998 paper outlining how they work. We know they can create either a single massive neutron star or collapse into a black hole. We know the merger can create an extraordinarily powerful magnetic field that’s trillions of times more potent than Earth’s puny magnetic field and that they can make that field in milliseconds. Astrophysicists know they can produce gamma-ray bursts and that kilonovae can synthesize heavy elements like strontium.

But scientists are excited about the future. “Observations of GW170817 are mapping an uncharted territory of the BNS (binary neutron star) merger phenomenology and have far-reaching theoretical implications,” the authors write in their paper.

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Here’s how Helene and other storms dumped a whopping 40 trillion gallons of rain on the South

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More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.

That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.

“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”

The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.

Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.

Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.

Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.

Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.

Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.

“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”

The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.

North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.

Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”

Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.

Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.

For Dello, the “fingerprints of climate change” were clear.

“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”

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Follow AP’s climate coverage at https://apnews.com/hub/climate

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Follow Seth Borenstein on Twitter at @borenbears

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Associated Press climate and environmental coverage receives support from several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.

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‘Big Sam’: Paleontologists unearth giant skull of Pachyrhinosaurus in Alberta

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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.

On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.

They call it “Big Sam.”

The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.

It didn’t die alone.

“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.

She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”

“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.

The head alone, she said, is about the size of a baby elephant.

The discovery was a long time coming.

The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.

“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.

When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”

“It contains about 100 to 300 bones per square metre,” she said.

Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.

About a year ago, they found the second adult: Big Sam.

Bamforth said both dinosaurs are believed to have been the elders in the herd.

“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.

“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”

The genders of the two adults are unknown.

Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.

The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.

She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.

“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.

“It’s pretty exciting.”

This report by The Canadian Press was first published Sept. 25, 2024.

The Canadian Press. All rights reserved.

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The ancient jar smashed by a 4-year-old is back on display at an Israeli museum after repair

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TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.

Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.

Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.

The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.

The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.

It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.

Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.

Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.

Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.

Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.

Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.

The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”

The Canadian Press. All rights reserved.

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