Afterglow sheds light on the nature, origin of neutron star collisions

Afterglow sheds light on the nature, origin of neutron star collisions
An artistic rendering of two neutron stars merging. Credit: NSF/LIGO/Sonoma State/A. Simonnet

The final chapter of the historic detection of the powerful merger of two neutron stars in 2017 officially has been written. After the extremely bright burst finally faded to black, an international team led by Northwestern University painstakingly constructed its afterglow—the last bit of the famed event's life cycle.

Not only is the resulting image the deepest picture of the neutron star collision's afterglow to date, it also reveals secrets about the origins of the , the jet it created and the nature of shorter gamma ray bursts.

"This is the deepest exposure we have ever taken of this event in ," said Northwestern's Wen-fai Fong, who led the research. "The deeper the image, the more information we can obtain."

The study will be published this month in The Astrophysical Journal Letters. Fong is an assistant professor of physics and astronomy in Northwestern's Weinberg College of Arts and Sciences and a member of CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics), an endowed research center at Northwestern focused on advancing studies with an emphasis on interdisciplinary connections.

Many scientists consider the 2017 neutron-star merger, dubbed GW170817, as LIGO's (Laser Interferometer Gravitational-Wave Observatory) most important discovery to date. It was the first time that astrophysicists captured two neutron stars colliding. Detected in both gravitational waves and electromagnetic , it also was the first-ever multi-messenger observation between these two forms of radiation.

The light from GW170817 was detected, partly, because it was nearby, making it very bright and relatively easy to find. When the collided, they emitted a kilonova—light 1,000 times brighter than a classical nova, resulting from the formation of heavy elements after the merger. But it was exactly this brightness that made its afterglow—formed from a jet travelling near light-speed, pummeling the surrounding environment—so difficult to measure.

"For us to see the afterglow, the kilonova had to move out of the way," Fong said. "Surely enough, about 100 days after the merger, the kilonova had faded into oblivion, and the afterglow took over. The afterglow was so faint, however, leaving it to the most sensitive telescopes to capture it."

Hubble to the rescue

Starting in December 2017, NASA's Hubble Space Telescope detected the visible light afterglow from the merger and revisited the merger's location 10 more times over the course of a year and a half.

The box indicates where the now-faded afterglow was located.

At the end of March 2019, Fong's team used the Hubble to obtain the and the deepest observation to date. Over the course of seven-and-a-half hours, the telescope recorded an image of the sky from where the neutron-star collision occurred. The resulting image showed—584 days after the neutron-star merger—that the visible light emanating from the merger was finally gone.

Next, Fong's team needed to remove the brightness of the surrounding galaxy, in order to isolate the event's extremely faint afterglow.

"To accurately measure the light from the afterglow, you have to take all the other light away," said Peter Blanchard, a postdoctoral fellow in CIERA and the study's second author. "The biggest culprit is light contamination from the galaxy, which is extremely complicated in structure."

Fong, Blanchard and their collaborators approached the challenge by using all 10 images, in which the kilonova was gone and the afterglow remained as well as the final, deep Hubble image without traces of the collision. The team overlaid their deep Hubble image on each of the 10 afterglow images. Then, using an algorithm, they meticulously subtracted—pixel by pixel—all light from the Hubble image from the earlier afterglow images.

The result: a final time-series of images, showing the faint afterglow without light contamination from the background galaxy. Completely aligned with model predictions, it is the most accurate imaging time-series of GW170817's visible-light produced to date.

"The brightness evolution perfectly matches our theoretical models of jets," Fong said. "It also agrees perfectly with what the radio and X-rays are telling us."

Illuminating information

With the Hubble's deep space image, Fong and her collaborators gleaned new insights about GW170817's home galaxy. Perhaps most striking, they noticed that the area around the merger was not densely populated with star clusters.

"Previous studies have suggested that neutron star pairs can form and merge within the dense environment of a globular cluster," Fong said. "Our observations show that's definitely not the case for this neutron star merger."

According to the new image, Fong also believes that distant, cosmic explosions known as short gamma ray bursts are actually neutron star mergers—just viewed from a different angle. Both produce relativistic jets, which are like a fire hose of material that travels near the speed of light. Astrophysicists typically see jets from gamma ray bursts when they are aimed directly, like staring directly into the fire hose. But GW170817 was viewed from a 30-degree angle, which had never before been done in the optical wavelength.

"GW170817 is the first time we have been able to see the jet 'off-axis,'" Fong said. "The new time-series indicates that the main difference between GW170817 and distant short gamma-ray bursts is the viewing angle."


Explore further

Researchers see beam of light from first confirmed neutron star merger emerge from behind sun

More information: "The Optical Afterglow of GW170817: An Off-Axis Structured Jet and Deep Constraints on a Globular Cluster Origin," Wen-fai Fong et al., 2019, to appear in the Astrophysical Journal Letters: arxiv.org/abs/1908.08046
Journal information: Astrophysical Journal Letters

Citation: Afterglow sheds light on the nature, origin of neutron star collisions (2019, September 9) retrieved 18 September 2019 from https://phys.org/news/2019-09-afterglow-nature-neutron-star-collisions.html
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Sep 09, 2019
This Event in Visible Light

This is the deepest exposure
We have ever taken
Of this event in visible light
Said Northwestern's Wen-fai Fong
Who led the research
The deeper the image
The more information we can obtain

As much as we dream of
An artistic rendering of two neutron stars merging

Artistic rendering, is no replacement, for deep sky telescopic imagery

Sep 09, 2019
Models that are described as being perfectly fit by the authors (and reported here through a Northwestern University bias, the institution involved in this image synthesis) are so numerous and ad hoc that there is almost no relationship anymore to statistics derived from the LIGO signal, which already were back-fitted from extreme luminosity distance and redshift error, the choice of NGC 4993 merely a first selection bias. It has not been explained why initial kilonova models have been rejected and how no truly simultaneous observations of the NGC 4993-associated object were ever made, despite its importance. GRB170817A was a mild photon count enhancement ~1.3x above an energetic magnetospheric background during solar wind coupled magnetospheric proton flares. Fermi, INTEGRAL, and Swift detect sub-300 keV transients (like GRB170817A) ~10^2-10^3 times daily. LIGO detects dozens of template-fitting GW chirp candidates daily. GW170817 was first rejected due to low SNR, excessive noise.

Sep 09, 2019
^^^^^^ Gibberish.

Sep 10, 2019
GW170817 and foreground interplanetary magnetic storm shocks affecting LIGO-Virgo-Fermi-INTEGRAL:
https://fulguriti...bar.html

NGC4993 and the back-evolution of a hypothesis:
https://fulguriti...993.html

Magnetosphere-ground coupling drives global coherent-synchronized CG lightning burst behavior around all LIGO-Virgo signals:
https://fulguriti...ung.html

LIGO confirmation bias is systematic:
https://fulguriti...for.html
Having no empirical methodology by which to resolve identity for gravitational waves invites pure bias into model selection: no true distinction exits for gravitational waves and myriads of log-normal terrestrial/interplanetary field transients (~1 every 100 seconds) into the LIGO-Virgo network, their magnetometers generally inoperative.

Sep 10, 2019
A processed composite fits anything that mismatched models dictate.

AT2017gfo transient was fit to GRB170817A at assumed NGC 4993 luminosity distance (still the subject of much uncertainty) of ~40 Mpc (130,500,000 ly); LIGO signal, from original low SNR signal (published spectrograms are reconstructed from wavelets after glitch removal) supported initial luminosity error >50% of 40 Mpc. X-ray flux/optical luminosity increased after months; at 1 year no signif. decline. Light curves >2 orders of mag. dimmer than off axis models. Prior threshold object found in pre-GW170817 images; AT2017gfo indistinguishable from MW X-ray var. stars. Manual transparencies used for sky area search, with first novel object located selected (optical wavelengths after ~11 hrs; X-ray >9 days).

GRB trig (>10^2 GRB alerts to LIGO/day) ~1.3 over mean background counts, only found in 10-300 keV bins, rescaled to DL estimate derived from post hoc LIGO template given ~20 Mpc DL error in a 28 deg2 search area.

Sep 10, 2019
^^^^^^More gibberish.

Sep 10, 2019
Amazing how all the cranks end up here! I'd love to see some of these clowns actually post on a real physics forum, where they would be torn a new one. Too chicken I suppose. 'Let's head off to Phys.org, so I can pose, and feel better about myself.' Sad buggers.

Sep 10, 2019
Here's the paper:
https://arxiv.org...8046.pdf
The images:
https://photos.ap...76qLwK57
"afterglow"
https://photos.ap...Z6qiAQZ8
Abuse of hyperbole and reliance on endless cumulative assumptions in this propaganda-laced article are apparent once the paper is actually given a thorough read. Its arguments rely on equivocation between viewing angle and models from multiple assumptions invoking viewing angle error to explain prevalent equivocation of models in prior papers, models that are not comparable with those assumed from prior short GRB observations. In other words, LIGO is buying time and saving face. Collectively, most astronomers had abandoned the continued observation of the sky area due to difficultly in locating the source, which can not be confirmed to be outside our own galaxy, hence long gaps in observation and a near total lack of extended observation spanning many epochs. For a project this significant, there is no excuse.

Sep 10, 2019
^^^^^^Gibberish. Go write it up like a real scientist would. Nobody cares what cranks think.

Sep 10, 2019
^^^^^^Gibberish. Go write it up like a real scientist would. Nobody cares what cranks think.

I think his comments are way more scientific and appropriate for the forum than yours. He is at least trying to make some conversation on the topic, not just calling other people with names.

"Real" scientist has also written criticism on the measurements so it's funny you call them cranks.

Sep 10, 2019
I think his comments are way more scientific and appropriate for the forum than yours. He is at least trying to make some conversation on the topic, not just calling other people with names.

"Real" scientist has also written criticism on the measurements so it's funny you call them cranks.


Oooooh, who pulled your chain? Lol. The guy is a clown. How many times has this been explained to the hard of thinking? Three separate facilities detected the GW. Take note of the number 3, because we are now going to talk about triangulation. How many sides do triangles have? So, a simple exercise in triangulation tells us where to look in the sky for the event. Lo and behold, there is a coincident EM event, just where it should be! And just when it should be! And guess what? These dumb scientist types had predicted what the signal would look like, including r-process nucleosynthesis. What did they see? I'll leave you to ponder that by reading the bloody papers. Now butt out.

Sep 10, 2019
Fong misrepresents AT2017gfo observation, since after ~3 weeks the putative GW170817 source (AT2017gfo/NGC 4993) was occluded by the Sun for ~3 months https://arxiv.org...712.028:

"For us to see the afterglow, the kilonova had to move out of the way," Fong said. "Surely enough, about 100 days after the merger, the kilonova had faded into oblivion, and the afterglow took over. The afterglow was so faint, however, leaving it to the most sensitive telescopes to capture it."

Any determinable transition between prompt kilonova emission and afterglow was not possible.

Castrogiovanni is a bot that has posted thousands of disparaging comments since joining ScienceX/Phys.org in March, 2019 https://photos.ap...ZWbnuz8. Several bots are active in comments sections. Obviously, the bot is not considering that there exist several well-regarded critics of the LIGO-Virgo project, nor of the status quo of open science, which LIGO-Virgo claims to also practice.


Sep 10, 2019
^^^^^^Gibberish.

Sep 10, 2019
Fong misrepresents AT2017gfo observation...................


Oh, and a coward too! You are accusing somebody who is certainly going to be more acquainted with the subject than you, of misrepresentation. Where is Fong's work published for all to see and reply to? And where is your drivel?
Just another physics crank. Yawn.

Sep 10, 2019
So, what does this clown say above?

Fong misrepresents AT2017gfo observation, since after ~3 weeks the putative GW170817 source (AT2017gfo/NGC 4993) was occluded by the Sun for ~3 months https://arxiv.org...712.028:
So, here is another link;
https://arxiv.org...2669.pdf

They say;

For the Hubble Space Telescope (HST), the end of Sun constraint for GW170817 was on ***6 December 2017*** (∼110 rest-frame days post-merger), and we immediately obtained deep observations in the optical and infrared.....


Now, what does Fong say?

The observations comprise ten epochs spanning ***2017 Dec 6*** to 2018 Aug 14 UT,.......


Now sod off you lying poser.


Sep 10, 2019
Fong misrepresents AT2017gfo observation....


Oh, and a coward too! You are accusing somebody who is certainly going to be more acquainted with the subject than you, of misrepresentation. Where is Fong's work published for all to see and reply to? And where is your drivel?
Just another physics crank. Yawn.
.........yawnnnn, and you Castrov, just another foul mouthed name calling crank who has been unable to comprehend that the lifetime beta particle decay rate of a free unbound neutron is 14.7 minutes, thus negating any possibility that neutron stars actually exist in reality.

Yeah, I know, you will launch yet another fusillade mis-applying the 1/2 life radioactive decay rate to a sub-atomic particle (neutron) that is not a radio-active atomic isotope, you don't know the difference so you just continue stumbling around here in this chatroom impressing yourself with the bot quantity of nothing but name calling rants you like to impress yourself with.

Sep 10, 2019
Yeah, I know, you will launch yet another fusillade mis-applying the 1/2 life radioactive decay rate to a sub-atomic particle (neutron) that is not a radio-active atomic isotope, you don't know the difference so you just continue stumbling around here in this chatroom impressing yourself with the bot quantity of nothing but name calling rants you like to impress yourself with.


Lol. What a moron! You have been given links to numerous scientific papers and articles from respected scientists and institutions, showing that you are a clueless loon. Free neutron decay has a half-life, you utter clown. No why don't you join Thaddeus, and sod off as well?

Sep 10, 2019
I'll just tidy up a previous post, as editing one letter in it caused mayhem with a link, and I didn't have time to fix it properly;

So, our lying physics crank accused Fong of misrepresentation in a cowardly way. He said;

Fong misrepresents AT2017gfo observation, since after ~3 weeks the putative GW170817 source (AT2017gfo/NGC 4993) was occluded by the Sun for ~3 months


And linked to paper, but the link is broken. So, let's look at another paper;

The optical afterglow of the short gamma-ray burst associated with GW170817
Lyman, R. D. et al.
https://arxiv.org...2669.pdf

They say;

For the Hubble Space Telescope (HST), the end of Sun constraint for GW170817 was on ***6 December 2017*** (∼110 rest-frame days post-merger), and we immediately obtained deep observations in the optical and infrared....


Now, what does Fong say?

The observations comprise ten epochs spanning ***2017 Dec 6*** to 2018 Aug 14 UT,.......


So, who is lying? Bye physics crank!


Sep 10, 2019
@Cortezz,

I think his comments are way more scientific and appropriate for the forum than yours. He is at least trying to make some conversation on the topic, not just calling other people with names.

"Real" scientist has also written criticism on the measurements so it's funny you call them cranks.


Happy now? :)

Sep 10, 2019
Fong misrepresents AT2017gfo observation....


Oh, and a coward too!
.........yawnnnn, and you Castrov, just another foul mouthed name calling crank who has been unable to comprehend that the lifetime beta particle decay rate of a free unbound neutron is 14.7 minutes, thus negating any possibility that neutron stars actually exist in reality. ...nothing but name calling rants you like to impress yourself with.


Sigh, the neutrons in a neutron star are not in an unbound state, they are all in gluon range of each other and are just as stable as neutrons in a helium atom.
Sigh again, a little knowledge is a dangerous thing.

Sep 11, 2019
Oooooh, who pulled your chain? Lol. The guy is a clown. How many times has this been explained to the hard of thinking? Three separate facilities detected the GW. Take note of the number 3, because we are now going to talk about triangulation. How many sides do triangles have? So, a simple exercise in triangulation tells us where to look in the sky for the event. Lo and behold, there is a coincident EM event, just where it should be! And just when it should be! And guess what? These dumb scientist types had predicted what the signal would look like, including r-process nucleosynthesis.

You pulled my chain with your constant idiotic off-topic comments. You could just stfu if you have nothing else to comment but "gibberish" or some fancy way saying "this poster is a idiot".

Then the fact that magazines like New scientist have had large features on the criticism towards the measurement. But you're a "one opinion" guy, everything against you're opinion is just wrong.

Sep 11, 2019
If you posted pure non-sense like many here, you would be on ignore but often enough you make completely rational comments. I would not want to ignore you so I'm just saying you could make better comments. Even if the other poster was a complete idiot racist retard, it does not make you or your post any better calling him with those names. Better chill and handle things professionally like any rational being should.

I'm happier with the better posts, yes.

Sep 11, 2019
I'm happier with the better posts, yes.


But it took me all of a couple of minutes to show why that guy was a poser. Everybody (i thought) could access the material on the neutron star merger and see that for themselves. And it has been pointed out here often enough. Particularly re r-process nucleosynthesis, triangulation, predictions et al. The lie about Fong is easily seen by reading his paper and checking the dates!
Now, perhaps I needed to point these things out. Again, in most cases. However, I suspect I'm hardly the only one here who knows that the NS merger killed pretty much any doubts about LIGO/VIRGO. Perhaps I credit others with knowledge they simply don't have. So, instead of continually pointing it out, I call the poster's ramblings gibberish. Which they were. Not to mention the obvious lie about Fong.
I have no time for posers, and less time for people who lie to make their nonsense seem legit.
Perhaps you have a high tolerance for such things. I get sick of it.

Sep 11, 2019
If you have no time for posers and bs, simply ignore them and don't give them your time. If you have time, give them a proper answer without going into insults. Simple as that and no forum space filled with nonsense.

Sep 11, 2019
@cortezz, you already screwed up on identifying a climate liar denier who has now 'fessed up and is busily trolling the climate threads because of you.

You are blocked for me; I don't see any point in what you're doing, because it's been tried before over and over and over and over again and never works. You are dead to me.

Sep 11, 2019
I'm Happier with the Better Posts: By Castrogiovanni

But it took me
all of a couple of minutes
to show why that guy was a poser
Everybody
i thought
could access the material
on the neutron star merger
and see that for themselves
And it has been pointed out
there often enough
Particularly
re r-process nucleosynthesis
triangulation
predictions et al
The lie about Fong
is easily seen
by reading his paper and checking the dates
Now
perhaps I needed to point these things out Again
in most cases
However
I suspect I'm hardly the only one here
who knows that the NS merger
killed pretty much any doubts
about LIGO
VIRGO
Perhaps I credit other
with knowledge
they simply don't have
So
instead of continually pointing it out
I call the poster's ramblings gibberish
Which they were
Not to mention the obvious lie about Fong
I have no time for posers
and less time for people
who lie to make their nonsense seem legit
Perhaps you have a high tolerance for such things
I get sick of it

Thank you, Castro

Sep 11, 2019
Sigh, the neutrons in a neutron star are not in an unbound state, they are all in gluon range of each other and are just as stable as neutrons in a helium atom.
Sigh again, a little knowledge is a dangerous thing.
.......well, you're abut to do a lot more sighing, there is no evidence such conditions allowing unbound neutrons to exist beyond 14.7 minutes exist.

All neutrons that make up a so-called neutron star are unbound because that's where the definition of a neutron star comes from:

"Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons."

https://en.wikipe...ron_star

Maybe you can come up with a better Pop-Cosmology psycho-babble explanation as to what constitutes a free unbound neutron condition whereby the 14.7 minute lifetime decay rate does not apply?

Sep 11, 2019
.......well, you're abut to do a lot more sighing, there is no evidence such conditions allowing unbound neutrons to exist beyond 14.7 minutes exist.


Wrong.

All neutrons that make up a so-called neutron star are unbound because that's where the definition of a neutron star comes from:


Wrong.

Maybe you can come up with a better Pop-Cosmology psycho-babble explanation as to what constitutes a free unbound neutron condition whereby the 14.7 minute lifetime decay rate does not apply?


Degeneracy, you clown. You should know what degeneracy is, as it appears that what counts for your brain is currently undergoing it.

Sep 11, 2019
Fong misrepresents AT2017gfo observation....


......yawnnnn, and you Castrov, just another foul mouthed name calling crank who has been unable to comprehend that the lifetime beta particle decay rate of a free unbound neutron is 14.7 minutes, thus negating any possibility that neutron stars actually exist in reality.

Yeah, I know, you will launch yet another fusillade mis-applying the 1/2 life radioactive decay rate to a sub-atomic particle (neutron) that is not a radio-active atomic isotope, you don't know the difference so you just continue stumbling around here in this chatroom impressing yourself with the bot quantity of nothing but name calling rants you like to impress yourself with.
says Benni

This is why Castrovagina alias jonesdave failed to become a working scientist and has ended up trying to impress the future scientists who come to physorg to learn Physics/Astronomy, with his pseudoscience from Wiki and Arxiv articles. He hates competition.

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