Starship Asterisk*

Afterglow from cosmic smash-up continues to brighten, confounding expectations

Credit: NASA/CXC/McGill/J.Ruan et al. (2018 ApJL)[/i][/b]

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The afterglow from the distant neutron-star merger detected last August has continued to brighten – much to the surprise of astrophysicists studying the aftermath of the massive collision that took place about 138 million light years away and sent gravitational waves rippling through the universe.

New observations from NASA's orbiting Chandra X-ray Observatory, reported in Astrophysical Journal Letters, indicate that the gamma ray burst unleashed by the collision is more complex than scientists initially imagined.

"Usually when we see a short gamma-ray burst, the jet emission generated gets bright for a short time as it smashes into the surrounding medium – then fades as the system stops injecting energy into the outflow," says McGill University astrophysicist Daryl Haggard, whose research group led the new study. "This one is different; it's definitely not a simple, plain-Jane narrow jet." ...

• Astrophysical Journal Letters 853(1):L4 (2018 Jan 20) DOI: 10.3847/2041-8213/aaa4f3
  arXiv.org > astro-ph > arXiv:1712.02809 > 07 Dec 2017 (v1), 27 Dec 2017 (v3)

Credit: NASA/CXC/Trinity University/D. Pooley et al. Illustration: NASA/CXC/M.Weiss

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The spectacular merger of two neutron stars that generated gravitational waves announced last fall likely did something else: birthed a black hole. This newly spawned black hole would be the lowest mass black hole ever found, as described in our latest press release.

After two separate stars underwent supernova explosions, two ultra-dense cores (that is, neutron stars) were left behind. These two neutron stars were so close that gravitational wave radiation pulled them together until they merged and collapsed into a black hole. The artist's illustration shows a key part of the process that created this new black hole, as the two neutron stars spin around each other while merging. The purple material depicts debris from the merger. An additional illustration shows the black hole that resulted from the merger, along with a disk of infalling matter and a jet of high-energy particles.

A new study analyzed data from NASA's Chandra X-ray Observatory taken in the days, weeks, and months after the detection of gravitational waves by the Laser Interferometer Gravitational Wave Observatory (LIGO) and gamma rays by NASA's Fermi mission on August 17, 2017.

X-rays from Chandra are critical for understanding what happened after the two neutron stars collided. The question is: did the merged neutron star form a larger, heavier neutron star or a black hole? ...

• Astrophysical Journal Letters 859(2):L23 (2018 Jun 01) DOI: 10.3847/2041-8213/aac3d6
  arXiv.org > astro-ph > arXiv:1712.03240 > 08 Dec 2017 (v1), 14 May 2018 (v2)

https://en.wikipedia.org/wiki/Rotating_black_hole wrote:

The boundaries of a Kerr (rotating) black hole.

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<<A rotating black hole is a black hole that possesses angular momentum. In particular, it rotates about one of its axes of symmetry. Rotating black holes are formed in the gravitational collapse of a massive spinning star or from the collapse of a collection of stars or gas with a total non-zero angular momentum. As most stars rotate it is expected that most black holes in nature are rotating black holes.

In late 2006, astronomers reported estimates of the spin rates of black holes in The Astrophysical Journal. A black hole in the Milky Way, GRS 1915+105, may rotate 1,150 times per second (i.e., C# : two octives above middle C), approaching the theoretical upper limit.

The formation of a rotating black hole by a collapsar is thought to be observed as the emission of gamma ray bursts.

A rotating black hole can produce large amounts of energy at the expense of its rotational energy. This happens through the Penrose process in the black hole's ergosphere, an area just outside its event horizon. In that case a rotating black hole gradually reduces to a Schwarzschild black hole, the minimum configuration from which no further energy can be extracted.>>

BDanielMayfield wrote: ↑Thu Oct 19, 2017 3:28 pm This was and is a great confirmation of expectations as to the site of heavy element production in the universe.

Recipe for making gold, uranium, etc.:

• (1) Condense two close orbiting massive stars out of interstellar medium.
  (2) Allow cores of two stars to cook light elements up to iron.
  (3) Return excess gas and light elements back to interstellar medium via core collapse supernovae, producing binary neutron star pair.
  (4) Allow orbital decay to bring two neutron stars into contact, producing kilonova.

Alchemy is easy, if you have enough time and material.

Bruce

MarkBour wrote:And what element is the neutron star itself? Atomic number 0, apparently. This element has many stable isotopes, ranging from

^1E+57₀Z . . . to . . . ^4E+57₀Z . . .

Last year, the first detection of gravitational waves linked to a gamma-ray burst triggered a vast follow-up campaign with ground and space telescopes to study the aftermath of the neutron star merger that gave rise to the explosion. ESA's XMM-Newton observations, obtained a few months after the discovery, caught the moment when its X-ray emission stopped increasing, opening new questions about the nature of this peculiar source.

• Astronomy & Astrophysics 613:L1 (2018 May) DOI: 10.1051/0004-6361/201832664
  arXiv.org > astro-ph > arXiv:1801.06164 > 18 Jan 2018 (v1), 24 Apr 2018 (v2)

BDanielMayfield wrote: ↑Tue Jun 05, 2018 2:12 pm

MarkBour wrote:
And what element is the neutron star itself? Atomic number 0, apparently. This element has many stable isotopes, ranging from

^1E+57₀Z . . . to . . . ^4E+57₀Z . . .

Neutronium, of course. But only stable under the extreme conditions inside neutron stars. If the entire star was nothing but neutrons they couldn't be so magnetic.

https://en.wikipedia.org/wiki/Neutronium wrote:

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<<Neutronium [Nu] is a hypothetical substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the discovery of the neutron) for the conjectured "element of atomic number zero" that he placed at the head of the periodic table. It was subsequently placed in the middle of several spiral representations of the periodic system for classifying the chemical elements, such as those of Charles Janet (1928), E. I. Emerson (1944), John D. Clark (1950) and in Philip Stewart's Chemical Galaxy (2005). However, the meaning of the term has changed over time, and from the last half of the 20th century onward it has been also used to refer to extremely dense substances resembling the neutron-degenerate matter theorized to exist in the cores of neutron stars; hereinafter "degenerate neutronium" will refer to this. The term "neutronium" has been popular in science fiction since at least the middle of the 20th century. It typically refers to an extremely dense, incredibly strong form of matter. While presumably inspired by the concept of neutron-degenerate matter in the cores of neutron stars, the material used in fiction bears at most only a superficial resemblance, usually depicted as an extremely strong solid under Earth-like conditions, or possessing exotic properties such as the ability to manipulate time and space. In contrast, all proposed forms of neutron star core material are fluids and are extremely unstable at pressures lower than that found in stellar cores. According to one analysis, a neutron star with a mass below about 0.2 solar masses would explode.

Although the term is not used in the scientific literature either for a condensed form of matter, or as an element, there have been reports that, besides the free neutron, there may exist two bound forms of neutrons without protons. If neutronium were considered to be an element, then these neutron clusters could be considered to be the isotopes of that element. However, these reports have not been further substantiated.

• Mononeutron: An isolated neutron undergoes beta decay with a mean lifetime of approximately 15 minutes (half-life of approximately 10 minutes), becoming a proton (the nucleus of hydrogen), an electron and an antineutrino.
  
  Dineutron: The dineutron, containing two neutrons was unambiguously observed in the decay of beryllium-16, in 2012 by researchers at Michigan State University. It is not a bound particle, but had been proposed as an extremely short-lived state produced by nuclear reactions involving tritium. It has been suggested to have a transitory existence in nuclear reactions produced by helions (helium 3 nuclei, completely ionised)that result in the formation of a proton and a nucleus having the same atomic number as the target nucleus but a mass number two units greater. The dineutron hypothesis had been used in nuclear reactions with exotic nuclei for a long time. Several applications of the dineutron in nuclear reactions can be found in review papers. Its existence has been proven to be relevant for nuclear structure of exotic nuclei. A system made up of only two neutrons is not bound, though the attraction between them is very nearly enough to make them so. This has some consequences on nucleosynthesis and the abundance of the chemical elements.
  
  Tetraneutron: A tetraneutron is a hypothetical particle consisting of four bound neutrons. Reports of its existence have not been replicated.

Although not called "neutronium", the National Nuclear Data Center's Nuclear Wallet Cards lists as its first "isotope" an "element" with the symbol n and atomic number Z = 0 and mass number A = 1. This isotope is described as decaying to element H with a half life of 10.24±0.02 min. Due to the beta (β−) decay of mononeutron and extreme instability of aforementioned heavier "isotopes", neutron matter is not expected to be stable under ordinary pressures.>>

MarkBour wrote: ↑Tue Jun 05, 2018 3:48 pm
What are the odds that a neutron star collision produces a neutron star, as opposed to a black hole? Is it close to 50% ?

Is there a known/expected distribution of sizes for neutron stars? And perhaps they don't get much chance to interact beyond a single pair that may have formed as a binary ... still, in a globular cluster or a galactic center, perhaps there are lots of them in proximity. Presumably if they have a combined mass of about 4 Sols, they will have enough mass that their product will form a black hole, rather than a larger neutron star. How different would that event appear to LIGO ?

https://en.wikipedia.org/wiki/GW170817 wrote:
<<GW170817 was a gravitational wave (GW) signal produced by the last minutes of two neutron stars spiralling closer to each other and finally merging. A hypermassive neutron star is believed to have formed initially and then collapsed into a black hole within milliseconds, as evidenced by:

• the large amount of ejecta (much of which would have been swallowed by an immediately forming black hole) and
  
  the lack of evidence for emissions being powered by neutron star spin-down, which would occur for longer-surviving neutron stars.>>

https://en.wikipedia.org/wiki/Neutron_star#Mass_and_temperature wrote:
<<A neutron star has a mass of at least 1.1 and perhaps up to 3 solar masses (M☉). The maximum observed mass of neutron stars is about 2.01 M_☉. But in general, compact stars of less than 1.39 M_☉ (the Chandrasekhar limit) are white dwarfs, whereas compact stars with a mass between 1.4 M_☉ and 3 M_☉ (the Tolman–Oppenheimer–Volkoff limit) should be neutron stars (though there is an interval of a few tenths of a solar mass where the masses of low-mass neutron stars and high-mass white dwarfs can overlap). Between 3 M_☉ and 5 M_☉, hypothetical intermediate-mass stars such as quark stars and electroweak stars have been proposed, but none have been shown to exist. Beyond 10 M_☉ the stellar remnant will overcome the neutron degeneracy pressure and gravitational collapse will usually occur to produce a black hole, though the smallest observed mass of a stellar black hole is about 5 M_☉.

The temperature inside a newly formed neutron star is from around 10¹¹ to 10¹² kelvin. However, the huge number of neutrinos it emits carry away so much energy that the temperature of an isolated neutron star falls within a few years to around 10⁶ kelvin. At this lower temperature, most of the light generated by a neutron star is in X-rays.>>

neufer wrote: ↑Tue Jun 05, 2018 4:16 pm

MarkBour wrote: ↑Tue Jun 05, 2018 3:48 pm
What are the odds that a neutron star collision produces a neutron star, as opposed to a black hole? Is it close to 50% ?

Is there a known/expected distribution of sizes for neutron stars? And perhaps they don't get much chance to interact beyond a single pair that may have formed as a binary ... still, in a globular cluster or a galactic center, perhaps there are lots of them in proximity. Presumably if they have a combined mass of about 4 Sols, they will have enough mass that their product will form a black hole, rather than a larger neutron star. How different would that event appear to LIGO ?

https://en.wikipedia.org/wiki/GW170817 wrote:
<<GW170817 was a gravitational wave (GW) signal produced by the last minutes of two neutron stars spiralling closer to each other and finally merging. A hypermassive neutron star is believed to have formed initially and then collapsed into a black hole within milliseconds, as evidenced by:

• the large amount of ejecta (much of which would have been swallowed by an immediately forming black hole) and
  
  the lack of evidence for emissions being powered by neutron star spin-down, which would occur for longer-surviving neutron stars.>>

A neutron star collision should produces a stable neutron star if:
the mass of the colliding neutron star minus the mass of the gravitational radiation is 3 M_☉ or less:

https://en.wikipedia.org/wiki/Neutron_star#Mass_and_temperature wrote:
<<A neutron star has a mass of at least 1.1 and perhaps up to 3 solar masses (M☉). The maximum observed mass of neutron stars is about 2.01 M_☉. But in general, compact stars of less than 1.39 M_☉ (the Chandrasekhar limit) are white dwarfs, whereas compact stars with a mass between 1.4 M_☉ and 3 M_☉ (the Tolman–Oppenheimer–Volkoff limit) should be neutron stars (though there is an interval of a few tenths of a solar mass where the masses of low-mass neutron stars and high-mass white dwarfs can overlap). Between 3 M_☉ and 5 M_☉, hypothetical intermediate-mass stars such as quark stars and electroweak stars have been proposed, but none have been shown to exist. Beyond 10 M_☉ the stellar remnant will overcome the neutron degeneracy pressure and gravitational collapse will usually occur to produce a black hole, though the smallest observed mass of a stellar black hole is about 5 M_☉.

The temperature inside a newly formed neutron star is from around 10¹¹ to 10¹² kelvin. However, the huge number of neutrinos it emits carry away so much energy that the temperature of an isolated neutron star falls within a few years to around 10⁶ kelvin. At this lower temperature, most of the light generated by a neutron star is in X-rays.>>

A research team led by astronomers at the University of Warwick had to wait over 100 days for the sight of the first of confirmed neutron star merger to re-emerge from behind the glare of the sun.

Artist’s impression of jets of material from first confirmed neutron star merger. Copyright 2018 Mark Garlick/University of Warwick

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They were rewarded with the first confirmed visual sighting of a jet of material that was still streaming out from merged star exactly 110 days after that initial cataclysmic merger event was first observed. Their observations confirm a key prediction about the aftermath of neutron star mergers.

The binary neutron star merger GW170817 occurred 130 million light years away in a galaxy named NGC 4993. It was detected in August 2017 by the Advanced Laser Interferometer Gravitational-Wave Observatory (Adv-LIGO), and by Gamma Ray Burst (GRB) observations, and then became the first ever neutron star merger to be observed and confirmed by visual astronomy.

After a few weeks the merged star then passed behind the glare of our sun leaving it effectively hidden from astronomers until it remerged from that glare 100 days after the merger event. It was at that point that the University of Warwick research team were able to use the Hubble Space Telescope to see the star was still generating a powerful beam of light in a direction that, while off centre to the Earth, was starting to spread out in our direction. ...

• Nature Astronomy (online 02 Jul 2018) DOI: 10.1038/s41550-018-0511-3
  arXiv.org > astro-ph > arXiv:1801.02669 > 08 Jan 2018 (v1), 19 Jan 2018 (v2)

https://en.wikipedia.org/wiki/Peekaboo wrote:
<<Peekaboo (also spelled peek-a-boo) is a form of play played with an infant. To play, one player hides their face, pops back into the view of the other, and says Peekaboo!, sometimes followed by I see you! Peekaboo is thought by developmental psychologists to demonstrate an infant's inability to understand object permanence. Object permanence is an important stage of cognitive development for infants. In early sensorimotor stages, the infant is completely unable to comprehend object permanence. Psychologist Jean Piaget conducted experiments with infants which led him to conclude that this awareness was typically achieved at eight to nine months of age. Infants before this age are too young to understand object permanence. A lack of object permanence can lead to A-not-B errors, where children reach for a thing at a place where it should not be.>>

Aftermath of the merger of two neutron stars. Ejecta from an initial explosion formed a shell around the black hole formed from the merger. A jet of material propelled from a disk surrounding the black hole first interacted with the ejecta material to form a broad 'cocoon.' Later, the jet broke through to emerge into interstellar space, where its extremely fast motion became apparent. (Credit: Sophia Dagnello, NRAO/AUI/NSF)

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Precise measurement using a continent-wide collection of National Science Foundation (NSF) radio telescopes has revealed that a narrow jet of particles moving at nearly the speed of light broke out into interstellar space after a pair of neutron stars merged in a galaxy 130 million light-years from Earth. The merger, which occurred in August of 2017, sent gravitational waves rippling through space. It was the first event ever to be detected both by gravitational waves and electromagnetic waves, including gamma rays, X-rays, visible light, and radio waves.

The aftermath of the merger, called GW170817, was observed by orbiting and ground-based telescopes around the world. Scientists watched as the characteristics of the received waves changed with time, and used the changes as clues to reveal the nature of the phenomena that followed the merger.

One question that stood out, even months after the merger, was whether or not the event had produced a narrow, fast-moving jet of material that made its way into interstellar space. That was important, because such jets are required to produce the type of gamma ray bursts that theorists had said should be caused by the merger of neutron-star pairs.

The answer came when astronomers used a combination of the NSF’s Very Long Baseline Array (VLBA), the Karl G. Jansky Very Large Array (VLA), and the Robert C. Byrd Green Bank Telescope (GBT) and discovered that a region of radio emission from the merger had moved, and the motion was so fast that only a jet could explain its speed.

“We measured an apparent motion that is four times faster than light. That illusion, called superluminal motion, results when the jet is pointed nearly toward Earth and the material in the jet is moving close to the speed of light,” said Kunal Mooley, of the National Radio Astronomy Observatory (NRAO) and Caltech.

The astronomers observed the object 75 days after the merger, then again 230 days after. ...

• Nature (online 05 Sep 2018) DOI: 10.1038/s41586-018-0486-3
  arXiv.org > astro-ph > arXiv:1806.09693 > 25 Jun 2018

For the first time astronomers have detected gravitational waves from a merged, hyper-massive neutron star. ...

Graph showing data points from the LIGO gravitational wave observatory, plotting frequency against time. The GW170817 chirp in gravitational waves produced by the coalescence of two neutron stars is clearly visible as a sequence of dots in an ascending curve. (Credit: LIGO / M.H.P.M van Putten & M. Della Valle)

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The initial observations of GW170817 suggested that the two neutron stars merged into a black hole, an object with a gravitational field so powerful that not even light can travel quickly enough to escape its grasp. Van Putten and della Valle set out to check this, using a novel technique to analyse the data from LIGO and the Virgo gravitational wave detector sited in Italy.

Their detailed analysis shows the H1 and L1 detectors in LIGO, which are separated by more than 3,000 kilometres, simultaneously picked up a descending ‘chirp’ lasting around 5 seconds. Significantly, this chirp started between the end of the initial burst of gravitational waves and a subsequent burst of gamma rays. Its low frequency (less than 1 KHz, reducing to 49 Hz) suggests the merged object spun down to instead become a larger neutron star, rather than a black hole.

There are other objects like this, with their total mass matching known neutron star binary pairs. But van Putten and della Valle have now confirmed their origin. ...

• Monthly Notices of the RAS: Letters 482(1):L46 (Jan 2019) DOI: 10.1093/mnrasl/sly166
  arXiv.org > astro-ph > arXiv:1806.02165 > 03 Jun 2018 (v1), 14 Sep 2018 (v3)

The box indicates where the now-faded afterglow was located.
Credit: NASA/ESA/Hubble

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Afterglow sheds light on the nature, origin of neutron star collisions; Researchers use Hubble to capture deepest optical image of first neutron star merger; New optical images align with theoretical predictions as well as images taken with X-ray and radio instruments; Neutron star merger did not take place in dense star cluster, as previously suggested; Optical afterglow shows short gamma ray bursts are likely neutron star mergers, viewed from different angle.

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 merger, the jet it created and the nature of shorter gamma ray bursts. ...

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.

At the end of March 2019, Fong’s team used the Hubble to obtain the final image 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. ...

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. ...

• arXiv.org > astro-ph > arXiv:1908.08046 > 21 Aug 2019

A finding made using instruments at the Arecibo Observatory indicates asymmetrical double neutron star systems may be the key to understanding dead star collisions and the expansion of the universe. (Credit: Arecibo Observatory/UCF William Gonzalez)

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The National Science Foundation’s Arecibo Observatory in Puerto Rico has proven itself instrumental in another major astronomical discovery.

An international team of scientists, led by the University of East Anglia in the United Kingdom, found an asymmetrical double neutron star system using the facility’s powerful radio telescope. This type of star system is believed to be a precursor to merging double neutron star systems like the one that the LIGO/Virgo discovered in 2017. The LIGO/Virgo observation was important, because it confirmed the gravitational waves associated with merging neutron stars.

The work published by this team ... indicates these specific kinds of double neutron star systems may be the key to understanding dead star collisions and the expansion of the universe. ...

One of the unique aspects of the 2017 discovery and today’s is that the double neutron systems observed are composed of stars that have very different masses. Current theories about the 2017 discovery are based on the masses of stars being equal or very close in size. ...

The team discovered an unusual pulsar – one of deep space’s magnetized spinning neutron-star ‘lighthouses’ that emits highly focused radio waves from its magnetic poles.

The newly discovered pulsar (known as PSR J1913+1102) is part of a binary system – which means that it is locked in a fiercely tight orbit with another neutron star. ...

This asymmetric system gives scientists confidence that double neutron star mergers will provide vital clues about unsolved mysteries in astrophysics – including a more accurate determination of the expansion rate of the universe, known as the Hubble constant. ...

• Nature 583(7815):211 (09 July 2020) DOI: 10.1038/s41586-020-2439-x
• arXiv.org > astro-ph > arXiv:2007.04175 > 08 Jul 2020