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Hubble's new image reveals unprecedented details of the neutral-star collision

In March, astronomers directed the Hubble Space Telescope to a point distant from the space where two neutron stars were struck. With the help of Hubble's giant eye, they watched this distant place for 7 hours, 28 minutes and 32 seconds during six orbits of the telescope around the Earth. It was the longest exposure ever to the collision site, what astronomers call the "deepest" image. But their fire, made more than 19 months after the light of the collision reached the Earth, did not recover any remains of the neutron star fusion. And that's good news.

This story began with a flicker on August 17, 2017. A gravitational wave, having traveled 130 million light-years in space, jostled the lasers of the interferometer observatory to gravitational laser (LIGO), gravitational wave detector globe. This signal followed a pattern, which told the researchers that it was the result of the fusion of two neutron stars – the very first neutron-star fusion ever detected. Gravitational wave detectors can not tell which direction a wave is coming from, but as soon as the signal arrived, astronomers from around the world went into action, searching the night sky for the source of the explosion. . They soon found it: a point on the periphery of a galaxy known as NGC4993 was lit with the "kilonova" of the collision – a massive explosion that projected a rapidly decaying radioactive material into a bright burst.

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A few weeks later, NGC4993 passed behind the sun and appeared again only about a hundred days after the first sign of the collision. At that time, the kilonova was dimmed, revealing the "remnant" of the neutron star fusion – a weaker but more lasting phenomenon. Between December 2017 and December 2018, astronomers used the Hubble to observe the remanence 10 times as it gradually faded. This last image, however, showing no visible trail or any other sign of collision, could be the most important to date.

"We were able to create a very accurate image, which helped us look at the previous 10 images and establish a very accurate time series," said Wen-fai Fong, astronomer at Northwestern University, who led this latest effort d & # 39; imaging.

This "time series" represents 10 clear shots of remanence evolving over time. The last image in the series, showing this point of space without any glow, allowed them to return to previous images and subtract light from all surrounding stars. With all this stellar light removed, the researchers found themselves with unprecedented and extremely detailed images of the shape and evolution of remanence over time.

This is what the ten previous pictures look like, subtracting Fong's.

(Image credit: Wen-fai Fong et al, Hubble Space Telescope / NASA)

The resulting picture is nothing like what we would see if we looked up into the night sky, Fong told Live Science.

"When two neutron stars merge, they form a heavy object – a massive neutron star or a clear black hole – and they spin very fast, and the materials are ejected along the poles," she said.

This material takes off at a blazing speed in two columns, one from the South Pole and the other from the North, she said. Moving away from the collision site, it collides with dust and other interstellar space debris, transferring some of its kinetic energy and giving a glow to this interstellar material. The energies involved are intense, said Fong. If it happened in our solar system, it would far surpass our sun.

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Much of this was already known from previous theoretical studies and observations of remanence, but the true importance of Fong's work for astronomers is that it reveals the context in which the collision occurred. Origin is produced.

"It's a good job." It shows what we suspected in our work based on Hubble's earlier observations, "said Joseph Lyman, an astronomer at the University of Warwick in England, who had conducted a previous study on persistence. "The binary neutron star did not fuse inside a globular cluster."

Globular clusters are regions of dense spaces in stars, said Lyman, who did not participate in the new effort, told Live Science. Neutron stars are rare, and neutron star binaries, or pairs of neutron stars in orbit, are even rarer. From the beginning, astronomers had suspected that the fusion of neutron star binaries would be more likely to occur in areas of space where the stars were closely grouped and swayed wildly around each other. Lyman and his colleagues, analyzing Hubble's earlier data, have highlighted some evidence that may not be the case. Fong's image showed that there was no globular group to find, which seems to confirm that, at least in this case, a neutron star collision does not need a dense group of stars to train.

According to Fong, an important reason for studying these remanences is that it could help us understand short gamma-ray bursts – mysterious gamma-ray explosions that astronomers occasionally detect in space.

"We think these explosions could be the fusion of two neutron stars," she said.

The difference in these cases (above astronomers not detecting any gravitational wave that would confirm their nature) lies in the angle of fusions to the Earth.

The Earth had a side view of the merger of this merger, Fong said. We have seen the light rise and fade over time.

But when brief bursts of gamma rays occur, she says, "It's like you're looking in the cannon of the fire hose."

One of the streams of material that escapes in these cases, she said, is directed to the Earth. So we first see the light of the fastest particles that move, moving at the speed of the TK light, in the form of a brief flash of gamma rays. Then, the light will slowly disappear as the slow-moving particles reach the Earth and become visible. (However, no one has yet compared a short occurrence of gamma rays to the signature of a gravitational wave from a neutron star fusion, however.)

This new article, which will be published in Astrophysical Journal Letters, does not confirm this theory. But it offers researchers more resources than they have ever had before to study the persistence of a neutron star-fusion.

"This is a good advertisement for Hubble's importance in understanding these extremely weak systems," said Lyman, "and gives clues to the additional possibilities offered by [the James Webb Space Telescope], "Hubble's massive successor that should be deployed in 2021.

Originally published on Science live.

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