Research shows short gamma-ray bursts do follow binary neutron star mergers

June 13, 2018 by Steve Lundeberg, Oregon State University
Short gamma-ray burst. Credit: Oregon State University

Researchers at Oregon State University have confirmed that last fall's union of two neutron stars did in fact cause a short gamma-ray burst.

The findings, published today in Physical Review Letters, represent a key step forward in astrophysicists' understanding of the relationship between binary neutron star mergers, and short .

Commonly abbreviated as GRBs, gamma-ray bursts are narrow beams of electromagnetic waves of the shortest wavelengths in the electromagnetic spectrum. GRBs are the universe's most powerful electromagnetic events, occurring billions of light years from Earth and able to release as much energy in a few seconds as the sun will in its lifetime.

GRBs fall into two categories, long duration and short duration. Long GRBs are associated with the death of a massive star as its core becomes a black hole and can last from a couple of seconds to several minutes.

Short GRBs had been suspected to originate from the merger of two , which also results in a new black hole—a place where the pull of gravity from super-dense matter is so strong that not even light can escape. Up to 2 seconds is the time frame of a short GRB.

The term neutron star refers to the gravitationally collapsed core of a large star; neutron are the smallest, densest stars known. According to NASA, neutron stars' matter is packed so tightly that a sugar-cube-sized amount of it weighs in excess of a billion tons.

In November 2017, scientists from U.S. and European collaborations announced they had detected an X-ray/gamma-ray flash that coincided with a blast of gravitational waves, followed by visible light from a new cosmic explosion called a kilonova.

Gravitational waves, a ripple in the fabric of time-space, were first detected in September 2015, a red-letter event in physics and astronomy that confirmed one of the main predictions of Albert Einstein's 1915 general theory of relativity.

"A simultaneous detection of gamma rays and gravitational waves from the same place in the sky was a major milestone in our understanding of the universe," said Davide Lazzati, a theoretical astrophysicist in the OSU College of Science. "The gamma rays allowed for a precise localization of where the gravitational waves were coming from, and the combined information from gravitational and electromagnetic radiation allows scientists to probe the binary neutron star system that's responsible in unprecedented ways."

Prior to Lazzati's latest research, however, it had been an open question as to whether the detected were "a short gamma-ray burst, or just a short burst of gamma rays—the latter being a different, weaker phenomenon.

In summer 2017, Lazzati's team of theorists had published a paper predicting that, contrary to earlier estimates by the astrophysics community, short gamma-ray bursts associated with the gravitational emission of binary neutron star coalescence could be observed even if the gamma-ray burst was not pointing directly at Earth.

"X- and gamma rays are collimated, like the light of a lighthouse, and can be easily detected only if the beam points toward Earth," Lazzati said. "Gravitational waves, on the other hand, are almost isotropic and can always be detected."

Isotropic refers to being evenly transmitted in all directions.

"We argued that the interaction of the short gamma-ray burst jet with its surroundings creates a secondary source of emission called the cocoon," Lazzati said. "The cocoon is much weaker than the main beam and is undetectable if the main beam points toward our instruments. However, it could be detected for nearby bursts whose beam points away from us."

In the months following the November 2017 , astronomers continued to observe the location from which the gravitational waves came.

"More radiation came after the burst of : radio waves and X-rays," Lazzati said. "It was different from the typical short GRB afterglow. Usually there's a short burst, a bright pulse, bright X-ray radiation, then it decays with time. This one had a weak gamma-ray pulse, and the afterglow was faint, brightened very quickly, kept brightening, then turned off."

"But that behavior is expected when you're seeing it from an off-axis observation point, when you're not staring down the barrel of the jet," he said. "The observation is exactly the behavior we predicted. We haven't seen the murder weapon, we don't have a confession, but the circumstantial evidence is overwhelming. This is doing exactly what we expected an off-axis jet would do and is convincing proof that binary star mergers and short gamma-ray bursts are indeed related to each other."

Explore further: Gamma-ray burst detection just what OSU researchers exclusively predicted

More information: Late Time Afterglow Observations Reveal a Collimated Relativistic Jet in the Ejecta of the Binary Neutron Star Merger GW170817 , Physical Review Letters (2018). journals.aps.org/prl/abstract/ … ysRevLett.120.241103

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12 comments

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Parsec
5 / 5 (3) Jun 13, 2018
Convincing evidence yes. Proof? No.
rossim22
1.7 / 5 (6) Jun 13, 2018
Convincing evidence yes. Proof? No.


I agree. Researcher's bias riding the curtails of all this gravitational wave lunacy.

#itsnotatheoryifitcantbefalsified
jonesdave
3.9 / 5 (7) Jun 13, 2018
Convincing evidence yes. Proof? No.


I agree. Researcher's bias riding the curtails of all this gravitational wave lunacy.

#itsnotatheoryifitcantbefalsified


Idiot. Have you read the papers, woo boy? If so, let us hear your take on them. Or do you need to wait until geniuses like the idiot Thornhill have spoken, before you make up your mind? W*****s! Seriously, you EU loons are so thick! What did you study, Rossim? Complete sh*te? Because you are very good at it! Loon.
jonesdave
4 / 5 (4) Jun 13, 2018
Convincing evidence yes. Proof? No.


I agree. Researcher's bias riding the curtails of all this gravitational wave lunacy.

#itsnotatheoryifitcantbefalsified


OK, thicko. Let us give your sub-human IQ a minute or two in the Sun. Yes? What do you think caused those gravity waves, closely followed by the EM signature? What are your qualifications, woo child? What did you study, before you left school at 12 years old? Please,.....the whole world is waiting on your pronouncement on this matter!
Errrr, no, they aren't. Go away woo boy - you haven't got a clue. Correct?
ursiny33
3 / 5 (2) Jun 13, 2018
I doubt if black holes or gravity can consume any wave particles
ursiny33
3 / 5 (2) Jun 13, 2018
Wave particles like light have no mass weight,
tallenglish
not rated yet Jun 14, 2018
One thing I would love to know, and so far I have yet to see any theoretical or experimental evidence to show what the fabric of spacetime is - i.e. the medium that propigates the gravity waves.

We have plenty evidence I think as to the effect of them and what causes them - but not how they move at all, as gravity (or bending of spacetime) requires mass?

So could gravity waves also be proof that dark matter is real and all around us as well, dark matter being the medium that is perterbed in the wave and not interacting via E/M?
Ojorf
3.7 / 5 (3) Jun 14, 2018
So could gravity waves also be proof that dark matter is real and all around us as well, dark matter being the medium that is perterbed in the wave and not interacting via E/M?


No, absolutely not.

Explained here: https://www.physi....948973/
tallenglish
not rated yet Jun 14, 2018
No, absolutely not.

Explained here: https://www.physi....948973/


When thinking of the fabric of spacetime - this image is usually what most people think of:

https://upload.wi...arth.jpg

A 2D frame, with mass above (and what I think could well be dark matter underneath), I actually think the idea they exist in the same space (and time) is actually incorrect - if they did they would interact by one of the other forces instead of just gravity.

I.e. dark matter exists under the frame pushing up, mass on the top pushing down - the frame is the demarcation point of E/M and strong forces which they can't cross, but as gravity can bend spacetime it can do it in either direction.

This would mean dark matter is actually just mass (nothing special) - its how it is moving relative to mass that is special. So WIMPS/MACHOS are a myth.
tallenglish
not rated yet Jun 14, 2018
WIMPS/MACHOS and all other magic particles for dark matter assume it exists in the same spacetime as mass - which I think we have just about proved it doesn't or it would interact in some way with strong or E/M forces.

My main question is with the usual diagram of what gravity is - what is the stuff underneath the usual frame they draw - it can't be nothing. If it were other mass pushing up, it would naturally create a halo around mass (even reflecting it back inward towards the center of mass - which is very handy for compressing a gas into a star and dark matter would not exist where mass is as they would repel (they curve spacetime in mutually opposite ways) - that would explain to me how gravity waves propegate.

It would also explain zero point energy, as no point in space is empty, its either filled with mass or dark matter (but not both at the same time). I.e. the simple explanation using what we know for mass already.
tallenglish
not rated yet Jun 14, 2018
Also if you think of it this way - dark matter would effectively change the ground point (what we see and think of as zero E/M, strong force or gravity) greating a gravity hill - which would naturally make the spacetime we see stretch in all directions (aka to reduce the extra potential energy) - if I am not mistaken this would slow light down as it passes through these zones and give us the effect we think of as dark energy.

DM is normal mass, and if correct our universe has a top and bottom for which we assume we are on the top. No fancy particles, just standard model. Oh and this model is also symetrical, which I think everything in this universe must be. I.e. dark matter is also proof of parallel universe and specifically a mirror of our own.
Ojorf
not rated yet Jun 15, 2018
A 2D frame, with mass above (and what I think could well be dark matter underneath), I actually think the idea they exist in the same space (and time) is actually incorrect - if they did they would interact by one of the other forces instead of just gravity.

I.e. dark matter exists under the frame pushing up, mass on the top pushing down - the frame is the demarcation point of E/M and strong forces which they can't cross, but as gravity can bend spacetime it can do it in either direction.


The frame in the picture is not real, there is no underneath. The frame is a graph, superimposed on the picture, to represent the curvature of space-time (not just space) and in only a single, 2-dimentional plane. It's not real.

None of the rest of what you say makes any sense if you look at the effects of DM that have been observed and documented.

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