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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.

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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Blood moon, big city: Skywatcher captures total lunar eclipse over New York (photos) – Space.com

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The eclipsed moon burns red high above the bright lights of New York City in gorgeous photos captured by amateur astronomer Alexander Krivenyshev.

Krivenyshev, the president of WorldTimeZone.com, snapped images of the total lunar eclipse on Sunday night (May 15) from Guttenberg, New Jersey, which is across the Hudson River from the Big Apple. 

He persevered through cloudy conditions, Krivenyshev told Space.com via email, to get shots of the blood-red moon shining like a beacon in a light-polluted sky.

Related: Amazing photos of the Super Flower Blood Moon of 2022

A closeup of the eclipsed moon on May 15, 2022, as photographed by Alexander Krivenyshev. (Image credit: Alexander Krivenyshev, WorldTimeZone.com)

The eclipse began at 9:32 p.m EDT on Sunday (0132 GMT on May 16) when the moon nosed into the light part of Earth’s shadow, known as the penumbra, and ended five hours later. The total eclipse phase, in which the moon was completely darkened by Earth’s heavier umbral shadow, lasted 85 minutes, the longest of any lunar eclipse in 33 years.

Earth’s nearest neighbor temporarily turns a coppery red during total lunar eclipses. This “blood moon” effect is caused by Earth’s atmosphere, which bends some red light onto the lunar surface while scattering away shorter-wavelength light. (No sunlight is hitting the moon directly at this point, of course; Earth is blocking the sun from the moon’s perspective.)

Another series of shots of the total lunar eclipse over New York City, photographed by Alexander Krivenyshev on May 15, 2022.  (Image credit: Alexander Krivenyshev, WorldTimeZone.com)

Related stories:

Last weekend’s sky show was best observed from the Americas and parts of Western Europe and West Africa. It was the first total lunar eclipse of the year, but it won’t be the last; another one will occur on Nov. 8. The Nov. 8 lunar eclipse will be best observed from Australia, eastern Asia and the western United States. 

If you’re hoping to photograph the moon, or want to prepare for the next total lunar eclipse, check out our best cameras for astrophotography and best lenses for astrophotography. Our guides on how to photograph a lunar eclipse, and how to photograph the moon with a camera, also have some helpful tips to plan out your lunar photo session.

Editor’s Note: If you snap an amazing lunar eclipse photo (or your own eclipse webcast) and would like to share it with Space.com’s readers, send your photo(s), comments, and your name and location to spacephotos@space.com.

Mike Wall is the author of “Out There” (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook.  

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NASA's Mars InSight mission coming to an end as dust covers solar panels – CBC News

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A NASA spacecraft on Mars is headed for a dusty demise.

The Insight lander is losing power because of all the dust on its solar panels. NASA said Tuesday it will keep using the spacecraft’s seismometer to register marsquakes until the power peters out, likely in July. Then flight controllers will monitor InSight until the end of this year, before calling everything off.

“There really hasn’t been too much doom and gloom on the team. We’re really still focused on operating the spacecraft,” said Jet Propulsion Laboratory’s Bruce Banerdt, the principal scientist.

Since landing on Mars in 2018, InSight has detected more than 1,300 marsquakes; the biggest one, a magnitude 5, occurred two weeks ago.

It will be NASA’s second Mars lander lost to dust: A global dust storm took out Opportunity in 2018. In InSight’s case, it’s been a gradual gathering of dust, especially over the past year.

WATCH | NASA scientists discuss InSight’s goals on Mars: [embedded content]

Rethinking solar power

NASA’s two other functioning spacecraft on the Martian surface — rovers Curiosity and Perseverance — are still going strong thanks to nuclear power.

The space agency may rethink solar power in the future for Mars, said planetary science director Lori Glaze, or at least experiment with new panel-clearing tech or aim for the less-stormy seasons.

InSight currently is generating one-tenth of the power from the sun that it did upon arrival.

Deputy project manager Kathya Zamora Garcia said the lander initially had enough power to run an electric oven for one hour and 40 minutes; now it’s down to 10 minutes max.

The InSight team anticipated this much dust buildup, but hoped a gust of wind or a dust devil might clean off the solar panels. That has yet to happen, despite several thousand whirlwinds coming close.

“None of them have quite hit us dead-on yet enough to blow the dust off the panels,” Banerdt told reporters.

Another science instrument, dubbed the mole, was supposed to burrow five metres underground to measure the internal temperature of Mars. But the German digger never got deeper than a half-metre because of the unexpected composition of the red dirt, and it finally was declared dead at the beginning of last year.

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See Astronaut's Sublime Shot of Total Lunar Eclipse Snapped From the ISS – CNET

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Earthlings on Earth weren’t the only ones who got to witness the lovely blushing of the “flower blood moon” total lunar eclipse on Sunday night and Monday morning. Residents of the International Space Station had a great view of the spectacular celestial event.

European Space Agency astronaut Samantha Cristoforetti shared a beautiful series of photos of the eclipse as seen from orbit. “A partially eclipsed moon playing hide-and-seek with our solar panel,” Cristoforetti tweeted on Monday.

The photos show the eclipse in progress, with the moon peeking under the station’s solar panels. One stunning view also shows Earth below, clouds visible against an expanse of blue. The images highlight the subtle shading of the moon as our planet threw its shadow across it.

Cristoforetti shared another look with just the eclipsed moon peeking over the curve of Earth.

Cristoforetti is an accomplished space photographer, having snapped plenty of gorgeous images during her last stay on the ISS in 2014 and 2015. Her most recent stint started in late April as part of NASA’s Crew-4 mission launched by SpaceX. 

I watched the eclipse last night from New Mexico. As the shadow moved across the moon, the ISS flew over, a bright bead of light crossing against the starry sky. So as I was seeing the ISS, Cristoforetti was likely tracking the eclipse, too. It doesn’t matter whether you’re on the ground or up in orbit, an eclipse is worth witnessing.

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