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Mysterious X-rays could be kilonova “afterglow” from 2017 neutron star merger – Ars Technica

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Enlarge / Artist’s representation of the merger of two neutron stars to form a black hole (hidden within bright bulge at center of image). The merger generates opposing, high-energy jets of material (blue) that heat up material around the stars, making it emit X-rays (reddish clouds).
NASA/CXC/M. Weiss

Back in 2017, astronomers detected a phenomenon known as a “kilonova“: the merger of two neutron stars accompanied by powerful gamma-ray bursts. Three and a half years later, astrophysicists spotted mysterious X-rays they believe could be the very first detection of a kilonova “afterglow,” according to a new paper published in The Astrophysical Journal Letters. Alternatively, what the astrophysicists saw could be the first observation of matter falling into the black hole that formed after the merger.

As we’ve reported previously, LIGO detects gravitational waves via laser interferometry. This method uses high-powered lasers to measure tiny changes in the distance between two objects positioned kilometers apart. (LIGO has detectors in Hanford, Washington, and in Livingston, Louisiana. A third detector in Italy, known as Advanced VIRGO, came online in 2016.) Having three detectors means scientists can triangulate and better pinpoint where in the night sky any telltale chirps are coming from.

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In addition to seven more binary black hole mergers, LIGO’s second run, from November 30, 2016, to August 25, 2017, detected a binary neutron-star merger with a simultaneous gamma-ray burst and signals in the rest of the electromagnetic spectrum. The event is now known as GW170817. These signals included the telltale signatures of heavy elements—notably gold, platinum and uranium—created by the collision. Most lighter elements are forged in the death-throe explosions of massive stars known as supernovas, but astronomers have long theorized that the heavier elements might originate in kilonovas produced when two neutron stars collide.

The 2017 detection of the kilonova provided evidence that those astronomers were right. Recording this kind of celestial event was unprecedented, and it officially marked the dawn of a new era in so-called “multi-messenger astronomy.”

Ever since, astronomers have been looking for a corresponding optical signature whenever LIGO/VIRGO picks up a gravitational wave signal for neutron star mergers or possible neutron star-black hole mergers. The assumption had been that black hole-black hole mergers would not produce any optical signature, so there was no point even looking for one—until 2020. That’s when astronomers found the first evidence of just such a phenomenon. The astronomers made the discovery by combining gravitational wave data with data collected during a robotic sky survey.

But the 2017 kilonova remains unique, according to Aprajita Hajela, the lead author of the new paper and a graduate student at Northwestern University. Hajela calls the kilonova “the only event of its kind” and “a treasure chest of several first observations our field.” Along with other astronomers at Northwestern and the University of California, Berkeley, she has been monitoring the evolution of GW170817 since LIGO/Virgo first detected it by using the space-based Chandra X-ray Observatory.

Illustration of the space-based Chandra X-ray Observatory, the most sensitive X-ray telescope ever built.
Enlarge / Illustration of the space-based Chandra X-ray Observatory, the most sensitive X-ray telescope ever built.
NASA/CXC/NGST (Public domain)

Chandra first detected X-ray and radio emissions from GW170817 a couple of weeks after the merger, which persisted for 900 days. But those initial X-rays, powered by a jet resulting from the merger moving close to the speed of light, started to fade in early 2018. However, from March 2020 through the end of that year, the steep decline in brightness stopped, and the X-ray emission became fairly constant in terms of brightness.

To help resolve the mystery, Hajela and her team collected additional observational data with both Chandra and the Very Large Array (VLA) in December 2020, 3.5 years after the merger. It was Hajela who was awakened at 4 am by a notification of surprisingly strong and bright X-ray emissions—four times higher than would be expected at this point if the emission were powered solely by the jet. (The VLA didn’t pick up any radio emissions.) These new emissions have remained at a constant level for 700 days.

That means a completely different source of X-rays must be powering them. One likely explanation is that expanding debris from the merger generated a shock wave, akin to a sonic boom, in addition to the jets. In that case, the merged neutron stars could not have immediately collapsed into a black hole. Instead, the stars spun down rapidly for a second. That rapid spin would have briefly counteracted the gravitational collapse just long enough to produce a fast tail of heavy kilonova ejecta, which drove the shock wave. As that heavy ejecta decelerated over time, its kinetic energy was converted into heat by the shocks.

“It would just fall in. Done.”

“If the merged neutron stars were to collapse directly to a black hole with no intermediate stage, it would be very hard to explain this X-ray excess that we see right now, because there would be no hard surface for stuff to bounce off and fly out at high velocities to create this afterglow,” said co-author Raffaella Margutti of the UC Berkeley. “It would just fall in. Done. The true reason why I’m excited scientifically is the possibility that we are seeing something more than the jet. We might finally get some information about the new compact object.”

Brian Metzger of Columbia University proposed an alternative scenario: the X-ray emission could be powered by matter falling into the back hole that was formed during the merger. This is also a scientific first, according to Hajela, since this kind of long-term accretion has never been observed before.

There are more observations planned going forward, and that data will help resolve the issue. If the X-rays and radio emissions brighten over the next few months or years, this would confirm the kilonova afterglow scenario. If the X-ray emissions decline steeply or remain steady, with no accompanying radio emission, that would confirm the accreting black hole scenario.

Regardless, “This would either be the first time we’ve seen a kilonova afterglow or the first time we’ve seen material falling onto a black hole after a neutron star merger,” said co-author Joe Bright, postdoc at UC Berkeley. “Either outcome would be extremely exciting.”

DOI: Astrophysical Journal Letters, 2022. 10.48550/arXiv.2104.02070  (About DOIs).

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Marine plankton could act as alert in mass extinction event: UVic researcher – Langley Advance Times

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A University of Victoria micropaleontologist found that marine plankton may act as an early alert system before a mass extinction occurs.

With help from collaborators at the University of Bristol and Harvard, Andy Fraass’ newest paper in the Nature journal shows that after an analysis of fossil records showed that plankton community structures change before a mass extinction event.

“One of the major findings of the paper was how communities respond to climate events in the past depends on the previous climate,” Fraass said in a news release. “That means that we need to spend a lot more effort understanding recent communities, prior to industrialization. We need to work out what community structure looked like before human-caused climate change, and what has happened since, to do a better job at predicting what will happen in the future.”

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According to the release, the fossil record is the most complete and extensive archive of biological changes available to science and by applying advanced computational analyses to the archive, researchers were able to detail the global community structure of the oceans dating back millions of years.

A key finding of the study was that during the “early eocene climatic optimum,” a geological era with sustained high global temperatures equivalent to today’s worst case global warming scenarios, marine plankton communities moved to higher latitudes and only the most specialized plankton remained near the equator, suggesting that the tropical temperatures prevented higher amounts of biodiversity.

“Considering that three billion people live in the tropics, the lack of biodiversity at higher temperatures is not great news,” paper co-leader Adam Woodhouse said in the release.

Next, the team plans to apply similar research methods to other marine plankton groups.

Read More: Global study, UVic researcher analyze how mammals responded during pandemic

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Scientists Say They Have Found New Evidence Of An Unknown Planet… – 2oceansvibe News

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In the new work, scientists looked at a set of trans-Neptunian objects, or TNOs, which is the technical term for those objects that sit out at the edge of the solar system, beyond Neptune

The new work looked at those objects that have their movement made unstable because they interact with the orbit of Neptune. That instability meant they were harder to understand, so typically astronomers looking at a possible Planet Nine have avoided using them in their analysis.

Researchers instead looked towards those objects and tried to understand their movements. And, Dr Bogytin claimed, the best explanation is that they result from another, undiscovered planet.

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The team carried out a host of simulations to understand how those objects’ orbits were affected by a variety of things, including the giant planets around them such as Neptune, the “Galactic tide” that comes from the Milky Way, and passing stars.

The best explanation was from the model that included Planet 9, however, Dr Bogytin said. They noted that there were other explanations for the behaviour of those objects – including the suggestion that other planets once influenced their orbit, but have since been removed – but claim that the theory of Planet 9 remains the best explanation.

A better understanding of the existence or not of Planet 9 will come when the Vera C Rubin Observatory is turned on, the authors note. The observatory is currently being built in Chile, and when it is turned on it will be able to scan the sky to understand the behaviour of those distant objects.

Planet Nine is theorised to have a mass about 10 times that of Earth and orbit about 20 times farther from the Sun on average than Neptune. It may take between 10,000 and 20,000 Earth years to make one full orbit around the Sun.

You may be tempted to ask how an entire planet could ‘hide’ in our solar system when we have zooming capabilities such as the new iPhone 15 has, but consider this: If Earth was the size of a marble, the edge of our solar system would be 11 kilometres away. That’s a lot of space to hide a planet.

[source:independent]

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Dragonfly: NASA Just Confirmed The Most Exciting Space Mission Of Your Lifetime – Forbes

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NASA has confirmed that its exciting Dragonfly mission, which will fly a drone-like craft around Saturn’s largest moon, Titan, will cost $3.35 billion and launch in July 2028.

Titan is the only other world in the solar system other than Earth that has weather and liquid on the surface. It has an atmosphere, rain, lakes, oceans, shorelines, valleys, mountain ridges, mesas and dunes—and possibly the building blocks of life itself. It’s been described as both a utopia and as deranged because of its weird chemistry.

Set to reach Titan in 2034, the Dragonfly mission will last for two years once its lander arrives on the surface. During the mission, a rotorcraft will fly to a new location every Titan day (16 Earth days) to take samples of the giant moon’s prebiotic chemistry. Here’s what else it will do:

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  • Search for chemical biosignatures, past or present, from water-based life to that which might use liquid hydrocarbons.
  • Investigate the moon’s active methane cycle.
  • Explore the prebiotic chemistry in the atmosphere and on the surface.

Spectacular Mission

“Dragonfly is a spectacular science mission with broad community interest, and we are excited to take the next steps on this mission,” said Nicky Fox, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington. “Exploring Titan will push the boundaries of what we can do with rotorcraft outside of Earth.”

It comes in the wake of the Mars Helicopter, nicknamed Ingenuity, which flew 72 times between April 2021 and its final flight in January 2023 despite only being expected to make up to five experimental test flights over 30 days. It just made its final downlink of data this week.

Dense Atmosphere

However, Titan is a completely different environment to Mars. Titan has a dense atmosphere on Titan, which will make buoyancy simple. Gravity on Titan is just 14% of the Earth’s. It sees just 1% of the sunlight received by Earth.

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The atmosphere is 98% nitrogen and 2% methane. Its seas and lakes are not water but liquid ethane and methane. The latter is gas in Titan’s atmosphere, but on its surface, it exists as a liquid in rain, snow, lakes, and ice on its surface.

COVID-Affected

Dragonfly was a victim of the pandemic. Slated to cost $1 billion when it was selected in 2019, it was meant to launch in 2026 and arrive in 2034 after an eight-year cruise phase. However, after delays due to COVID, NASA decided to compensate for the inevitable delayed launch by funding a heavy-lift launch vehicle to massively shorten the mission’s cruise phase.

The end result is that Dragonfly will take off two years later but arrive on schedule.

Previous Visit

Dragonfly won’t be the first time a robotic probe has visited Titan. As part of NASA’s landmark Cassini mission to Saturn between 2004 and 2017, a small probe called Huygens was despatched into Titan’s clouds on January 14, 2005. The resulting timelapse movie of its 2.5 hours descent—which heralded humanity’s first-ever (and only) views of Titan’s surface—is a must-see for space fans. It landed in an area of rounded blocks of ice, but on the way down, it saw ancient dry shorelines reminiscent of Earth as well as rivers of methane.

The announcement by NASA makes July 2028 a month worth circling for space fans, with a long-duration total solar eclipse set for July 22, 2028, in Australia and New Zealand.

Wishing you clear skies and wide eyes.

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