Astronomers detect terrible glow even after years of neutron star collision


It has now been over three years since history was traced to the colliding of neutron stars. From 130 million light-years away, astronomers saw a brilliant glow of gamma-radiation, rippling gravitational waves, caused by two dead stars coming together.

Since then, astronomers have carefully monitored the corner of space in which the collision occurred, to see what happens after such a violent event. And, unsurprisingly, they found that it still continued to shine in the X-ray spectrum until the model would eliminate such brightness.

“We are entering a new phase in our understanding of neutron stars,” said astronomer Elonora Troja of the University of Maryland.

“We don’t really know what to expect from this point forward, because all of our models were predicting X-rays and we were surprised to see them 1,000 days after the collision event was detected. Many have found answers to this. It may take years. Which is going on, but our research opens up many possibilities. ”

A collision event named GW170817 was first detected as gravitational waves emanating from a section of the sky in the constellations of Hydra on 17 August 2017, thanks to LIGO-Virgo gravity wave inspectors.

Then, just 1.7 seconds later, two space-based observatories, NASA’s Firm Gamma-Ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory, picked up an intense gamma-ray burst – the brightest and most energetic event in the universe – at the same Area of ​​sky from.

Nine days later, astronomers raised a glow, extending the electromagnetic spectrum from radio waves to X-rays. It was something new, never seen after the gamma-ray burst. Previously, all gamma-ray bursts had completely faded in a few minutes, while this glare spoiled our understanding of gamma-ray bursts.

This new afterglow emission was interpreted as the result of a relativistic jet – that is, a jet that operates at a significant percentage of the speed of light – from the Kilonova explosion. As this jet expands into space, it creates its own shockwave, which emits light from the spectrum, from radio waves to X-rays.

Afterglow continued to grow in brightness, peaking at 160 days and then rapidly fading – but X-radiation became sluggish. It was last detected in March of this year from the Chandra X-ray Observatory, two and a half years after the first identification of the collision; In later observations in May using the Australian Telescope Compact Array, the brightness was below the detection limit.

(E. Troja)

Troja and his team have mapped X-ray brightness, and found that long-term emission still corresponds to a relative jet, but it is not certain what is capable of continuing it long after the collision.

Given that GW170817 is the first event of its kind that we are able to observe, it is likely that there are things that we do not understand how gamma-ray bursts and neutron star collisions occur.

“We have a collision that shows that it opens a window throughout the process, which we hardly have access to,” said Troja. “It may be that there are physical processes that we have not included in our models because they are not relevant in earlier stages that we are more familiar with when jets are formed.”

It is also possible that it is not the jet itself that caused the extended emission, but an extended cloud of gas from the Kilonova running behind it, creating its own shockway. If multiple shocks occur at different times and behave differently, this difference may explain how different wavelengths have faded.

Or X-rays could be kept for a long time in what researchers called “continuous energy injection by a long-lived central engine” – the one that was left behind by the collision continued to emit X-radiation. .

We currently do not have much data as to which of these scenarios caused continuous glare, but some things are clear. First, we do not fully understand neutron star mergers. Something is missing from our model, and only constant observations and analysis will help to find out what is what.

Secondly, since this luminosity has only been identified in relation to the collision of a neutron star, it may be a signature that we can use to identify other neutron star collisions that we may have missed. It can be used to look for similar emissions in X-ray data archives to highlight these miss events.

More observations of the GW170817 patch of the sky will begin in December of this year, and astronomers are unsure what they are going to find. Either way, it will help constrain our understanding of the phenomenon.

“It may be the last breath of a historical source or the beginning of a new story, in which the sign shines again in the future and may appear for decades or centuries,” Troja said. “Whatever happens, this phenomenon is changing what we know to merge neutron stars and rewrite our model.”

Research is due to appear in Monthly notice of the Royal Astronomical Society, And available on arXiv.

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