Starship Asterisk*

SimonASK wrote:Just watched the double news conference, however they didn't say much about what was the result of the neutron star merger. At one point it was hinted that this is as yet unknown, elsewhere it was suggested that it was the smallest black hole known. Can anyone offer any further knowledge or insights?

dstarrman wrote:Apparently, the gamma rays from this event traveled faster than light, or the light from the event traveled at less than light speed. Which is it and how?

dstarrman wrote:Apparently, the gamma rays from this event traveled faster than light, or the light from the event traveled at less than light speed. Which is it and how?

De58te wrote:

dstarrman wrote:Apparently, the gamma rays from this event traveled faster than light, or the light from the event traveled at less than light speed. Which is it and how?

If I may submit a layman's armchair science theory.

Spif wrote:
As I recall from school, neutron stars are in fact not composed of pure neutrons. There is expected to be some complexity in their structure. Some ratio of protons are typically mixed in with the degenerate neutron matter and to balance the charge there is also a soup of electrons typically flowing in a loop of current. Some divergence of these flowing and spinning charges are what create the magnetic field? And around the surface is an outer blanket or shell of non-degenerate or normal atomic matter of some relatively small depth.

I wonder then, when a merge event like this happens, does any fraction of the expelled matter come from the degenerate cores of the two stars or does nearly all of the remnant cloud come only from the two outer shells of atomic matter?

Also, I wonder if there is any confidence regarding what the typical composition of the outer shell of a neutron star is? I imagine that since these shells were formed from gravitationally collapsing and fusing matter at the bottom layers of a supernova, they are probably made (to a fair degree) out of atoms heavier than iron?

• ~16,000 Earth masses (= ~2% of the star masses) got ejected
  (predominantly from fastest moving outer equatorial regions).

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

[b][color=#0000FF]Cross-section of neutron star. Densities are in terms of ρ[sub]0[/sub] the saturation nuclear matter density, where nucleons begin to touch.[/color][/b]

---

<<Current models indicate that matter at the surface of a neutron star is composed of ordinary atomic nuclei crushed into a solid lattice with a sea of electrons flowing through the gaps between them. It is possible that the nuclei at the surface are iron, due to iron's high binding energy per nucleon. It is also possible that heavy elements, such as iron, simply sink beneath the surface, leaving only light nuclei like helium and hydrogen. If the surface temperature exceeds 10⁶ kelvin (as in the case of a young pulsar), the surface should be fluid instead of the solid phase that might exist in cooler neutron stars.

The "atmosphere" of a neutron star is hypothesized to be at most several micrometers thick, and its dynamics are fully controlled by the neutron star's magnetic field. Below the atmosphere one encounters a solid "crust". This crust is extremely hard and very smooth (with maximum surface irregularities of ~5 mm), due to the extreme gravitational field. The expected hierarchy of phases of nuclear matter in the inner crust has been characterized as nuclear pasta.

Proceeding inward, one encounters nuclei with ever-increasing numbers of neutrons; such nuclei would decay quickly on Earth, but are kept stable by tremendous pressures. As this process continues at increasing depths, the neutron drip becomes overwhelming, and the concentration of free neutrons increases rapidly. In that region, there are nuclei, free electrons, and free neutrons. The nuclei become increasingly small (gravity and pressure overwhelming the strong force) until the core is reached, by definition the point where mostly neutrons exist.

The composition of the superdense matter in the core remains uncertain. One model describes the core as superfluid neutron-degenerate matter (mostly neutrons, with some protons and electrons). More exotic forms of matter are possible, including degenerate strange matter (containing strange quarks in addition to up and down quarks), matter containing high-energy pions and kaons in addition to neutrons, or ultra-dense quark-degenerate matter.>>

Uncle Jeff wrote:
Any word yet on spectral analysis of the visible light? Do we see the heavy elements (Gold, Thorium and Uranium) in the ejecta? Are there spikes in the gamma spectrum corresponding to known decays of actinides (or even transactinides)?

APOD Robot wrote:

The video depicts hot neutron stars as they spiral in toward each other and emit gravitational radiation. As they merge, a powerful jet extends that drives the short-duration gamma-ray burst, followed by clouds of ejecta and, over time, an optical supernova-type episode called a kilonova.

EricP wrote:
The APOD for August 16 says that "The explosive episode was seen on August 17". Was a temporal anomaly caused by the event?

Ann wrote:

APOD Robot wrote:

The video depicts hot neutron stars as they spiral in toward each other and emit gravitational radiation. As they merge, a powerful jet extends that drives the short-duration gamma-ray burst, followed by clouds of ejecta and, over time, an optical supernova-type episode called a kilonova.

Why would this event lead to an optical supernova over time?

neufer wrote:

EricP wrote: read October as August?

Ann wrote:

APOD Robot wrote:

The video depicts hot neutron stars as they spiral in toward each other and emit gravitational radiation. As they merge, a powerful jet extends that drives the short-duration gamma-ray burst, followed by clouds of ejecta and, over time, an optical supernova-type episode called a kilonova.

...

Did we see a supernova here?

Ann