Starship Asterisk*

MargaritaMc wrote:I'll add this article from Physics, the APS journal.
Viewpoint: Neutron Star Merger Seen and Heard
Maura McLaughlin, 
https://physics.aps.org/articles/v10/114
which I found to be a particularly succinct and informative summary

bystander wrote: The intro to the special issue at ApJL was good.

• (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.

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

Bruce

MargaritaMc wrote:

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

Bruce

That's very nice, Bruce. Thank you!

MargaritaMc wrote:

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

Bruce

That's very nice, Bruce. Thank you!

BDanielMayfield wrote:

MargaritaMc wrote:

BDanielMayfield wrote: Alchemy is easy, if you have enough time and material.
Bruce

That's very nice, Bruce. Thank you!

Your very welcome. And all four steps are automatic, due to universal law.

[i]The upper and lower series of pictures each show a simulation of a neutron star merger. In the scenario shown in the upper panels the star collapses after the merger and forms a black hole, whereas the scenario displayed in the lower row leads to an at least temporarily stable star. [b](Image: Andreas Bauswein, HITS)[/b][/i]

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Neutron stars are the densest objects in the Universe; however, their exact characteristics remain unknown. Using simulations based on recent observations, a team of scientists including HITS researcher Dr. Andreas Bauswein has managed to narrow down the size of these stars.

When a very massive star dies, its core contracts. In a supernova explosion, the star’s outer layers are expelled, leaving behind an ultra-compact neutron star. For the first time, the LIGO and Virgo Observatories have recently been able to observe the merger of two neutron stars and measure the mass of the merging stars. Together, the neutron stars had a mass of 2.74 solar masses. Based on these observational data, an international team of scientists from Germany, Greece, and Japan including HITS astrophysicist Dr. Andreas Bauswein has managed to narrow down the size of neutron stars with the aid of computer simulations. The calculations suggest that the neutron star radius must be at least 10.7 km. The international research team’s results have been published in “Astrophysical Journal Letters.”

In neutron star collisions, two neutron stars orbit around each other, eventually merging to form a star with approximately twice the mass of the individual stars. In this cosmic event, gravitational waves – oscillations of spacetime – whose signal characteristics are related to the mass of the stars, are emitted. This event resembles what happens when a stone is thrown into water and waves form on the water’s surface. The heavier the stone, the higher the waves. ...

• Astrophysical Journal Letters 850(2):L34 (2017 Dec 01) DOI: 10.3847/2041-8213/aa9994
  arXiv.org > astro-ph > arXiv:1710.06843 > 18 Oct 2017 (v1), 09 Nov 2017 (v3)

Observations of neutron star collision challenge some existing theories

Click to play embedded YouTube video.

Last Dance of Neutron Star Pair
Credit: W. Kastaun/T. Kawamura/B. Giacomazzo/R. Ciolfi/A. Endrizzi

---

When scientists recorded a rippling in space-time, followed within two seconds by an associated burst of light observed by dozens of telescopes around the globe, they had witnessed, for the first time, the explosive collision and merger of two neutron stars.

The intense cosmological event observed on Aug. 17 also had other reverberations here on Earth: It ruled out a class of dark energy theories that modify gravity, and challenged a large class of theories.

Dark energy, which is driving the accelerating expansion of the universe, is one of the biggest mysteries in physics. It makes up about 68 percent of the total mass and energy of the universe and functions as a sort of antigravity, but we don’t yet have a good explanation for it. Simply put, dark energy acts to push matter away from each other, while gravity acts to pull matter together.

The neutron star merger created gravitational waves – a squiggly distortion in the fabric of space and time, like a tossed stone sending ripples across a pond – that traveled about 130 million light-years through space, and arrived at Earth at almost the same instant as the high-energy light that jetted out from this merger.

The gravity waves signature was detected by a network of Earth-based detectors called LIGO and Virgo, and the first intense burst of light was observed by the Fermi Gamma-ray Space Telescope.

That nearly simultaneous arrival time is a very important test for theories about dark energy and gravity. ...

• Physical Review Letters 119(25):1304 (18 Dec 2017) DOI: 10.1103/PhysRevLett.119.251304
  arXiv.org > astro-ph > arXiv:1710.05901 > 16 Oct 2017 (v1), 21 Nov 2017 (v2)

A 100-year-old “cosmological constant” theory introduced by Albert Einstein in relation to his work on general relativity and some other theories derived from this model remain as viable contenders because they propose that dark energy is a constant in both space and time: Gravitational waves and light waves are affected in the same way by dark energy, and thus travel at the same rate through space.

“The favorite explanation is this cosmological constant,” he said. “That’s as simple as it’s going to get.”

There are some complicated and exotic theories that also hold up to the test presented by the star-merger measurements. Massive gravity, for example – a theory of gravity that assigns a mass to a hypothetical elementary particle called a graviton – still holds a sliver of possibility if the graviton has a very slight mass.

Some other theories, though, which held that the arrival of gravitational waves would be separated in time from the arriving light signature of the star merger by far longer periods – stretching up to millions of years – don’t explain what was seen, and must be modified or scrapped.

The study notes that a class of theories known as scalar-tensor theories is particularly challenged by the neutron-star merger observations, including Einstein-Aether, MOND-like (relating to modified Newtonian dynamics), Galileon, and Horndeski theories, to name a few.

BDanielMayfield wrote:That article caught my attention bystander. Had to read more, wondering what this event might have to say re MOND theories. Note this excerpt:

A 100-year-old “cosmological constant” theory introduced by Albert Einstein in relation to his work on general relativity and some other theories derived from this model remain as viable contenders because they propose that dark energy is a constant in both space and time: Gravitational waves and light waves are affected in the same way by dark energy, and thus travel at the same rate through space.

“The favorite explanation is this cosmological constant,” he said. “That’s as simple as it’s going to get.”

There are some complicated and exotic theories that also hold up to the test presented by the star-merger measurements. Massive gravity, for example – a theory of gravity that assigns a mass to a hypothetical elementary particle called a graviton – still holds a sliver of possibility if the graviton has a very slight mass.

Some other theories, though, which held that the arrival of gravitational waves would be separated in time from the arriving light signature of the star merger by far longer periods – stretching up to millions of years – don’t explain what was seen, and must be modified or scrapped.

The study notes that a class of theories known as scalar-tensor theories is particularly challenged by the neutron-star merger observations, including Einstein-Aether, MOND-like (relating to modified Newtonian dynamics), Galileon, and Horndeski theories, to name a few.

So there goes MOND down the drain, and Einstein's "biggest mistake" gets even bigger.

Bruce

Ann wrote:

BDanielMayfield wrote:
So there goes MOND down the drain, and Einstein's "biggest mistake" gets even bigger.

Perhaps not. Einstein's "biggest mistake", as he saw it, was introducing the cosmological constant "to keep the cosmos constant" and prevent it from either expanding or contracting. But what is said in the article above is that a cosmological constant may be the best explanation for the dark energy in the Universe. So Einstein may have been absolutely right in seeing the need of introducing the cosmological constant. He was just dead wrong about what the cosmological constant would do.

Radio observations are illuminating what happened during recent gravitational-wave event

On August 17, 2017, observatories around the world witnessed the collision of
two neutron stars. At first, many scientists thought a narrow high-speed jet,
directed away from our line of sight, or off-axis, was produced (diagram at
left). But observations made at radio wavelengths now indicate the jet hit
surrounding material, producing a slower-moving, wide-angle outflow, dubbed
a cocoon (pink structure at right). Credit: NRAO/AUI/NSF/D. Berry

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Millions of years ago, a pair of extremely dense stars, called neutron stars, collided in a violent smash-up that shook space and time. On August 17, 2017, both gravitational waves—ripples in space and time—and light waves emitted during that neutron star merger finally reached Earth. The gravitational waves came first and were detected by the twin detectors of the National Science Foundation (NSF)-funded Laser Interferometry Gravitational-wave Observatory (LIGO), aided by the European Virgo observatory. The light waves were observed seconds, days, and months later by dozens of telescopes on the ground and in space.

Now, scientists from Caltech and several other institutions are reporting that light with radio wavelengths continues to brighten more than 100 days after the August 17 event. These radio observations indicate that a jet, launched from the two neutron stars as they collided, is slamming into surrounding material and creating a slower-moving, billowy cocoon. ...

On August 17, NASA's Fermi Gamma-ray Space Telescope and the European INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) missions detected gamma rays just seconds after the neutron stars merged. The gamma rays were much weaker than what is expected for sGRBS, so the researchers reasoned that a fast and narrowly focused jet was produced but must have been pointed slightly askew from the direction of Earth, or off-axis.

The radio emission—originally detected 16 days after the August 17 event and still measurable and increasing in strength as of December 2—tells a different story. If the jet had been fast and beam-like, the radio light would have weakened with time as the jet lost energy. The fact that the brightness of the radio light is increasing instead suggests the presence of a cocoon that is choking the jet. The reason for this is complex, but it has to do with the fact that the slower-moving, wider-angle material of the cocoon gives off more radio light than the faster-moving, sharply focused jet material. ...

• Nature (online 20 Dec 2017) DOI: 10.1038/nature25452

neufer wrote:

Ann wrote:

BDanielMayfield wrote:
So there goes MOND down the drain, and Einstein's "biggest mistake" gets even bigger.

Perhaps not. Einstein's "biggest mistake", as he saw it, was introducing the cosmological constant "to keep the cosmos constant" and prevent it from either expanding or contracting. But what is said in the article above is that a cosmological constant may be the best explanation for the dark energy in the Universe. So Einstein may have been absolutely right in seeing the need of introducing the cosmological constant. He was just dead wrong about what the cosmological constant would do.

Einstein produced a general equation that couldn't rule out the existence of a cosmological constant.

Einstein was unhappy in not knowing a prior the value of that constant.

But he was only wrong it was in believing that that equation had a stable solution ... which it doesn't.

BDanielMayfield wrote:

neufer wrote:

Ann wrote:
Einstein's "biggest mistake", as he saw it, was introducing the cosmological constant "to keep the cosmos constant" and prevent it from either expanding or contracting. But what is said in the article above is that a cosmological constant may be the best explanation for the dark energy in the Universe. So Einstein may have been absolutely right in seeing the need of introducing the cosmological constant. He was just dead wrong about what the cosmological constant would do.

Einstein produced a general equation that couldn't rule out the existence of a cosmological constant.

Einstein was unhappy in not knowing a prior the value of that constant.

But he was only wrong it was in believing that that equation had a stable solution ... which it doesn't.

Clarification: I was just using "Einstein's biggest mistake" as another way of saying cosmological constant.

He himself called it that, but ironically, it now seems very likely that he wasn't wrong at all,
and thus his real mistake was thinking he was wrong.

https://qz.com/113811/for-almost-a-century-people-have-been-misquoting-einsteins-biggest-mistake/ wrote:

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Einstein may never have uttered the phrase “biggest blunder.”
by Rebecca J. Rosen, The Atlantic_, August 09, 2013

<<Astrophysicist and author Mario Livio can find no documentation that puts those words [i.e., “biggest blunder”] into Einstein’s mouth (or, for that matter, his pen). Instead, all references eventually lead back to one man, physicist George Gamow, who reported Einstein’s use of the phrase in two sources: his posthumously published autobiography My World Line (1970) and a Scientific American article from September 1956.

This, for reasons Livio recounts in detail in his new book Brilliant Blunders, is some seriously thin sourcing. For one, Gamow, brilliant physicist though he might have been, had a bit of a reputation for, shall we say, antics. Once, for example, Gamow had teamed up with a student of his named Ralph Alpher to write a paper. “He then realized,” Livio told me, “that if he were to add as a co-author another known astrophysicist, whose name was Hans Bethe, then the three names would be Alpher Bethe Gamow, like alpha beta gamma, even though Hans Bethe hadnothing to do with that paper.” (His first wife, Livio writes, once remarked, “In more than twenty years together, Geo has never been happier than when perpetuating a practical joke.”)

Livio looked at almost every single paper that Einstein ever wrote, including making a trip to the Einstein archive in Jerusalem to look at the collection personally. “And nowhere did I ever find the phrase ‘biggest blunder’, ” Livio told me. “I didn’t find it—anywhere.”

So he turned his attention to the correspondence between Einstein and Gamow, and it is at this point that Gamow’s story begins to look even worse. “When might Einstein have used this expression with Gamow?” Livio writes in the book. As Gamow tells it in his autobiography, he and Einstein were quite close, with Gamow visiting the aging scientist every other Friday as the liaison between the Navy and Einstein during World War II. “He describes what good friends they were, how Einstein would greet him in one of his soft sweaters, and so on,” Livio explains.

“Well, guess what,” he continues. “I discovered a small article published in some obscure journal of the Navy by somebody named Stephen Brunauer,” a scientist who had recruited both Einstein and Gamow to the Navy. In that article, Brunauer wrote, “Gamow, in later years, gave the impression that he was the Navy’s liaison man with Einstein, that he visited every two weeks, and the professor ‘listened’ but made no contribution—all false [emphasis added]. The greatest frequency of visits was mine, and that was about every two months.” Clearly, Livio says, Gamow exaggerated his relationship with the famous physicist. The correspondence between Einstein and Gamow seems to confirm this. The letters are quite formal, not those of the sort that would pass between intimate friends. Einstein was polite but not particularly effusive. “So wait a second,” Livio says doubtfully, “Einstein never used this phrase with any more intimate colleagues, but he used it with Gamow?”

Moreover, this is not to say that Einstein was at ease with the cosmological constant. “I’m not saying he didn’t regret it,” Livio says. “He definitely regretted it. He wrote about that to a number of friends. He thought it was ugly.” But to say it was his “biggest blunder” implies a level of regret that it seems Einstein did not feel. By contrast, when he did write about the error (which, it should be noted, in more recent years, has turned out to be less clearly an error than Einstein thought, but that’s a whole other story), he did so with a dispassionate tone that conveys comfort with the notion that science would overturn some of his work. In a 1932 paper with Willem de Sitter, Einstein wrote, “Historically the term containing the ‘cosmological constant’ Λ was introduced into the field equations in order to enable us to account theoretically for the existence of a finite mean density in a static universe. It now appears that in the dynamical case this end can be reached without the introduction of Λ.” And that was that.

There was, however, one regret that stood out for Einstein, and it had nothing to do with the elegance of his calculations. After a visit with the scientist at Princeton on November 16, 1954, Linus Pauling wrote in his diary: “He said that he had made one great mistake—when he signed the letter to Pres. Roosevelt recommending that atom bombs be made; but that there was some justification—the danger that the Germans would make them.”>>