Starship Asterisk*

TheOtherBruce wrote: ↑Sat Sep 07, 2019 2:18 am
How sure are we that the filamenty look is due to an actual stringy filament structure,
as opposed to perspective effects of seeing shocked dollops of high-v gas edge-on?

https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instability wrote:

RT instability fingers evident in the 965 year old Crab Nebula

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<<The Rayleigh–Taylor instability, or RT instability (after Lord Rayleigh and G. I. Taylor), is an instability of an interface between two fluids of different densities which occurs when the lighter fluid is pushing the heavier fluid. Examples include the behavior of water suspended above oil in the gravity of Earth, mushroom clouds like those from volcanic eruptions and atmospheric nuclear explosions, supernova explosions in which expanding core gas is accelerated into denser shell gas, instabilities in plasma fusion reactors and inertial confinement fusion.

Water suspended atop oil is an everyday example of Rayleigh–Taylor instability, and it may be modeled by two completely plane-parallel layers of immiscible fluid, the more dense on top of the less dense one and both subject to the Earth's gravity. The equilibrium here is unstable to any perturbations or disturbances of the interface: if a parcel of heavier fluid is displaced downward with an equal volume of lighter fluid displaced upwards, the potential energy of the configuration is lower than the initial state. Thus the disturbance will grow and lead to a further release of potential energy, as the more dense material moves down under the (effective) gravitational field, and the less dense material is further displaced upwards. This was the set-up as studied by Lord Rayleigh. The important insight by G. I. Taylor was his realisation that this situation is equivalent to the situation when the fluids are accelerated, with the less dense fluid accelerating into the more dense fluid. This occurs deep underwater on the surface of an expanding bubble and in a nuclear explosion.

As the RT instability develops, the initial perturbations progress from a linear growth phase into a non-linear growth phase, eventually developing "plumes" flowing upwards (in the gravitational buoyancy sense) and "spikes" falling downwards. In the linear phase, equations can be linearized and the amplitude of perturbations is growing exponentially with time. In the non-linear phase, perturbation amplitude is too large for the non-linear terms to be neglected. In general, the density disparity between the fluids determines the structure of the subsequent non-linear RT instability flows (assuming other variables such as surface tension and viscosity are negligible here). The difference in the fluid densities divided by their sum is defined as the Atwood number, A. For A close to 0, RT instability flows take the form of symmetric "fingers" of fluid; for A close to 1, the much lighter fluid "below" the heavier fluid takes the form of larger bubble-like plumes.

This process is evident not only in many terrestrial examples, from salt domes to weather inversions, but also in astrophysics and electrohydrodynamics. RT instability structure is also evident in the Crab Nebula, in which the expanding pulsar wind nebula powered by the Crab pulsar is sweeping up ejected material from the supernova explosion 1000 years ago. The RT instability has also recently been discovered in the Sun's outer atmosphere, or solar corona, when a relatively dense solar prominence overlies a less dense plasma bubble.] This latter case is a clear example of the magnetically modulated RT instability.>>

TheOtherBruce wrote: ↑Sat Sep 07, 2019 2:18 am
This also makes me curious about the SN1987A remnant, considering it's a bit further away, but much more recent. Would we see it like this eventually, or is it just too far away to see such a fine-grained structure? Come to think of it, when did anyone last publish a 1987A image? The last one I remember seeing was when the "double ring" light echo was discovered.

https://en.wikipedia.org/wiki/SN_1987A wrote:

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Sequence of HST images from 1994 to 2009, showing the collision of the expanding remnant with a ring of material ejected by the progenitor 20,000 years before the supernova

<<The three bright rings around SN 1987A that were visible after a few months in images by the Hubble Space Telescope are material from the stellar wind of the progenitor. These rings were ionized by the ultraviolet flash from the supernova explosion, and consequently began emitting in various emission lines. These rings did not "turn on" until several months after the supernova. The rings are large enough that their angular size can be measured accurately: the inner ring is 0.808 arcseconds in radius. The time light traveled to light up the inner ring gives its radius of 0.66 (ly) light years. Using this as the base of a right angle triangle and the angular size as seen from the Earth for the local angle, one can use basic trigonometry to calculate the distance to SN 1987A, which is about 168,000 light-years. The material from the explosion is catching up with the material expelled during both its red and blue supergiant phases and heating it, so we observe ring structures about the star.

Around 2001, the expanding (>7000 km/s) supernova ejecta collided with the inner ring. This caused its heating and the generation of x-rays—the x-ray flux from the ring increased by a factor of three between 2001 and 2009. A part of the x-ray radiation, which is absorbed by the dense ejecta close to the center, is responsible for a comparable increase in the optical flux from the supernova remnant in 2001–2009. This increase of the brightness of the remnant reversed the trend observed before 2001, when the optical flux was decreasing due to the decaying of ⁴⁴Ti isotope.

A study reported in June 2015, using images from the Hubble Space Telescope and the Very Large Telescope taken between 1994 and 2014, shows that the emissions from the clumps of matter making up the rings are fading as the clumps are destroyed by the shock wave. It is predicted the ring will fade away between 2020 and 2030. These findings are also supported by the results of a three-dimensional hydrodynamic model which describes the interaction of the blast wave with the circumstellar nebula. The model also shows that X-ray emission from ejecta heated up by the shock will be dominant very soon, after the ring will fade away. As the shock wave passes the circumstellar ring it will trace the history of mass loss of the supernova's progenitor and provide useful information for discriminating among various models for the progenitor of SN 1987A.

In 2018, radio observations from the interaction between the circumstellar ring of dust and the shockwave has confirmed the shockwave has now left the circumstellar material. It also shows that the speed of the shockwave, which slowed down to 2,300 km/s while interacting with the dust in the ring, has now re-accelerated to 3,600 km/s.>>

Ann wrote: ↑Fri Sep 06, 2019 6:56 pm

Chris Peterson wrote: ↑Fri Sep 06, 2019 6:39 pm

Ann wrote: ↑Fri Sep 06, 2019 6:32 pm
Out of curiosity, Chris, why would type Ia supernovas create stronger gravitational waves than core collapse supernovas? I was under the impression that the total energy released by core collapse supernovas was greater than that of type Ia supernovas.

Not sure... I was just looking at the energy spectrum for gravitational wave sources. I might speculate, however, that it's because a Type 1a supernova is preceded by an inspiral event (as with merging neutron stars or black holes), which represents a particularly strong source of gravitational radiation.

Yes, the type Ia supernovas that arise from two colliding white dwarfs should generate gravitational waves because of the collision, and then there is the supernova explosion on top of that. I can see that the merging white dwarfs scenario might generate stronger gravitational waves than the core collapse supernova.

• f= (twice) orbital frequency
  L = orbital separation
  M = mass of two equal orbiting bodies

• M_n of neutron stars ~ 2 M_d of white dwarfs
  L_n of neutron stars ~ L_d/800 of white dwarfs

Chris Peterson wrote: ↑Fri Sep 06, 2019 6:39 pm

Ann wrote: ↑Fri Sep 06, 2019 6:32 pm

Chris Peterson wrote: ↑Fri Sep 06, 2019 5:44 pm

That's only core collapse supernovas. Type 1a supernovas should create much stronger gravitational waves, and therefore be detectable at a greater distance. But at a frequency that is probably too low for LIGO.

Out of curiosity, Chris, why would type Ia supernovas create stronger gravitational waves than core collapse supernovas? I was under the impression that the total energy released by core collapse supernovas was greater than that of type Ia supernovas.

Not sure... I was just looking at the energy spectrum for gravitational wave sources. I might speculate, however, that it's because a Type 1a supernova is preceded by an inspiral event (as with merging neutron stars or black holes), which represents a particularly strong source of gravitational radiation.

Ann wrote: ↑Fri Sep 06, 2019 6:32 pm

Chris Peterson wrote: ↑Fri Sep 06, 2019 5:44 pm

neufer wrote: ↑Fri Sep 06, 2019 5:33 pm

They are likely to be at somewhat higher (100 to 800 Hz) frequencies
than our current ground-based detectors are most sensitive;
(and to last for only about a second).

That's only core collapse supernovas. Type 1a supernovas should create much stronger gravitational waves, and therefore be detectable at a greater distance. But at a frequency that is probably too low for LIGO.

Out of curiosity, Chris, why would type Ia supernovas create stronger gravitational waves than core collapse supernovas? I was under the impression that the total energy released by core collapse supernovas was greater than that of type Ia supernovas.

Chris Peterson wrote: ↑Fri Sep 06, 2019 5:44 pm

neufer wrote: ↑Fri Sep 06, 2019 5:33 pm

Chris Peterson wrote: ↑Fri Sep 06, 2019 3:38 pm

Theory suggests that some supernovas should produce strong enough gravitational wave signals to be fairly easily detected. However, they are likely to be at somewhat lower frequencies than our current ground-based detectors are sensitive. Somewhat nearby core collapse supernovas may be detectable by LIGO and cousins, however.

They are likely to be at somewhat higher (100 to 800 Hz) frequencies
than our current ground-based detectors are most sensitive;
(and to last for only about a second).

That's only core collapse supernovas. Type 1a supernovas should create much stronger gravitational waves, and therefore be detectable at a greater distance. But at a frequency that is probably too low for LIGO.

neufer wrote: ↑Fri Sep 06, 2019 5:33 pm

Chris Peterson wrote: ↑Fri Sep 06, 2019 3:38 pm

BDanielMayfield wrote: ↑Fri Sep 06, 2019 2:42 pm
Yeah, the distance would need to be cosmologically short.

Looking at this Cas A SN remnant, it looks fairly well symmetrical. Thus it seems to me that a g wave SN would be a very tough detection.

Theory suggests that some supernovas should produce strong enough gravitational wave signals to be fairly easily detected. However, they are likely to be at somewhat lower frequencies than our current ground-based detectors are sensitive. Somewhat nearby core collapse supernovas may be detectable by LIGO and cousins, however.

They are likely to be at somewhat higher (100 to 800 Hz) frequencies
than our current ground-based detectors are most sensitive;
(and to last for only about a second).

Chris Peterson wrote: ↑Fri Sep 06, 2019 3:38 pm

BDanielMayfield wrote: ↑Fri Sep 06, 2019 2:42 pm

neufer wrote: ↑Fri Sep 06, 2019 2:28 pm
I'm guessing that supernova would have to, at least, reside in the Local Group of galaxies to be detected gravitationally.

Yeah, the distance would need to be cosmologically short.

Looking at this Cas A SN remnant, it looks fairly well symmetrical. Thus it seems to me that a g wave SN would be a very tough detection.

Theory suggests that some supernovas should produce strong enough gravitational wave signals to be fairly easily detected. However, they are likely to be at somewhat lower frequencies than our current ground-based detectors are sensitive. Somewhat nearby core collapse supernovas may be detectable by LIGO and cousins, however.

https://en.wikipedia.org/wiki/GW170817 wrote:

The inspiral of two neutron stars

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GW 170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy NGC 4993. The GW was produced by the last minutes of two neutron stars spiraling closer to each other and finally merging, and is the first GW observation which has been confirmed by non-gravitational means.

The gravitational wave signal, designated GW 170817, had a duration of approximately 100 seconds, and shows the characteristics in intensity and frequency expected of the inspiral of two neutron stars. Analysis of the slight variation in arrival time of the GW at the three detector locations (two LIGO and one Virgo) yielded an approximate angular direction to the source. Independently, a short (~2 seconds' duration) gamma-ray burst, designated GRB 170817A, was detected by the Fermi and INTEGRAL spacecraft beginning 1.7 seconds after the GW merger signal.

The gravitational wave signal lasted for approximately 100 seconds starting from a frequency of 24 hertz. It covered approximately 3,000 cycles, increasing in amplitude and frequency to a few hundred hertz in the typical inspiral chirp pattern.

An automatic computer search of the LIGO-Hanford datastream triggered an alert to the LIGO team about 6 minutes after the event. The gamma-ray alert had already been issued at this point (16 seconds post-event), so the timing near-coincidence was automatically flagged. The absence of a clear detection by the Virgo system implied that the source was in one of Virgo's blind spots; this absence of signal in Virgo data contributed to considerably reduce the source containment area.>>

BDanielMayfield wrote: ↑Fri Sep 06, 2019 2:42 pm

neufer wrote: ↑Fri Sep 06, 2019 2:28 pm I'm guessing that supernova would have to, at least, reside in the Local Group of galaxies to be detected gravitationally.

Yeah, the distance would need to be cosmologically short.

Looking at this Cas A SN remnant, it looks fairly well symmetrical. Thus it seems to me that a g wave SN would be a very tough detection.

neufer wrote: ↑Fri Sep 06, 2019 2:28 pm I'm guessing that supernova would have to, at least, reside in the Local Group of galaxies to be detected gravitationally.

BDanielMayfield wrote: ↑Fri Sep 06, 2019 1:18 pm
From a list of sources of gravitational waves:

A supernova will radiate except in the unlikely event that the explosion is perfectly symmetric.

But putting out enough gravitational waves to be detected by us would be rare, as evidenced by our not catching a SN caused g wave yet.

https://en.wikipedia.org/wiki/LIGO#/media/File:LIGO_detector_sensitivity_curve.png wrote:

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Detector noise curves for Initial and Advanced LIGO as a function of frequency. They lie above the bands for space-borne detectors like the evolved Laser Interferometer Space Antenna (eLISA) and pulsar timing arrays such as the European Pulsar Timing Array (EPTA). The characteristic strains of potential astrophysical sources are also shown. To be detectable the characteristic strain of a signal must be above the noise curve. These frequencies that aLIGO can detect are in the range of human hearing.

RocketRon wrote: ↑Fri Sep 06, 2019 5:08 am Would such an event create gravity wave(s) ?

A supernova will radiate except in the unlikely event that the explosion is perfectly symmetric.

Whiskybreath wrote: ↑Fri Sep 06, 2019 12:23 pm
Is the cause of the clear differentiation of elements based in the layering of those elements in the star at the time of the supernova, or is there a different reason?

RocketRon wrote: ↑Fri Sep 06, 2019 5:08 am
Has anyone ever calculated how much energy was released from such events ?
Truly of astronomical proportions.
And all the more beautiful a photograph for knowing...

Would such an event create gravity wave(s) ?

https://en.wikipedia.org/wiki/Supernova#Energy_output wrote:
Supernova Energy output:

• -------------------------------------------------------------------------
  Cassiopeia A Core collapse supernova:
  
  • Neutrino energy: 100 foe
    Kinetic energy: 1 foe
    Electromagnetic radiation: 0.001 – 0.01 foe
  -------------------------------------------------------------------------
  Type Ia supernova:
  
  • Neutrino energy: 0.1 foe
    Kinetic energy: 1.3-1.4 foe
    Electromagnetic radiation: 0.01 foe
  -------------------------------------------------------------------------

A foe is a unit of energy equal to 10⁴⁴ joules or 10⁵¹ ergs, used to express the large amount of energy released by a supernova. The word is an acronym derived from a part of the pronunciation "ten to the power of fifty-one ergs". It was coined by Gerald E. Brown of Stony Brook University in his work with Hans Bethe, because "it came up often enough in our work". It was coined by Steven Weinberg. This unit of measure is convenient because a supernova typically releases about one foe of observable [Kinetic] energy in a very short period (which can be measured in seconds). In comparison, if the Sun had its current luminosity throughout its entire lifetime, it would release ≈ 1.2 foe.

One solar mass has a rest mass energy of 1787 foe.

(A [better name?] bethe (B) is equivalent to one foe. The bethe (B) is named after Hans Bethe.)
------------------------------------------------------------------------------
Supernovae are potentially strong galactic sources of gravitational waves, but none have so far been detected. The only gravitational wave events so far detected are from mergers of black holes and neutron stars, probable remnants of supernovae.

https://en.wikipedia.org/wiki/SuperNova_Early_Warning_System wrote:
<<The SuperNova Early Warning System (SNEWS) is a network of neutrino detectors designed to give early warning to astronomers in the event of a supernova in the Milky Way, our home galaxy, or in a nearby galaxy such as the Large Magellanic Cloud or the Canis Major Dwarf Galaxy.

Powerful bursts of electron neutrinos (ν_e) with typical energies of the order of 10 MeV and duration of the order of 10 seconds are produced in the core of a star as it collapses on itself via the "neutronization" reaction, i.e. fusion of protons and electrons into neutrons: pe⁻→nν_e. It is expected that the neutrinos are emitted well before the light from the supernova peaks, so in principle neutrino detectors could give advance warning to astronomers that a supernova has occurred and may soon be visible. The neutrino pulse from [the core collapse] supernova 1987A arrived 3 hours before the associated photons – but SNEWS was not yet active and it was not recognised as a supernova event until after the photons arrived. However, SNEWS is not able to give advance warning of a type Ia supernova, as they are not expected to produce significant numbers of neutrinos. Type Ia supernovae, caused by a runaway nuclear fusion reaction in a white dwarf star, are thought to account for roughly one-third of all supernovae.

There are currently seven neutrino detector members of SNEWS: Borexino, Daya Bay, KamLAND, HALO, IceCube, LVD, and Super-Kamiokande. SNEWS began operation prior to 2004, with three members (Super-Kamiokande, LVD, and SNO). The Sudbury Neutrino Observatory is no longer active as it is being upgraded to its successor program SNO+. The detectors send reports of a possible supernova to a computer at Brookhaven National Laboratory to identify a supernova. If the SNEWS computer identifies signals from two detectors within 10 seconds, the computer will send a supernova alert to observatories around the world to study the supernova. The SNEWS mailing list is open-subscription, and the general public is allowed to sign up; however, the SNEWS collaboration encourages amateur astronomers to instead use Sky and Telescope magazine's AstroAlert service, which is linked to SNEWS.>>

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

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<<John Flamsteed FRS (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal. Flamsteed accurately calculated the solar eclipses of 1666 and 1668. He was responsible for several of the earliest recorded sightings of the planet Uranus, which he mistook for a star and catalogued as '34 Tauri'. The first of these was in December 1690, which remains the earliest known sighting of Uranus by an astronomer.

On 16 August 1680 Flamsteed catalogued a star, 3 Cassiopeiae, that later astronomers were unable to corroborate. Three hundred years later, the American astronomical historian William Ashworth suggested that what Flamsteed may have seen was the most recent supernova in the galaxy's history, an event which would leave as its remnant the strongest radio source outside of the Solar System, known in the third Cambridge (3C) catalogue as 3C 461 and commonly called Cassiopeia A by astronomers. Because the position of "3 Cassiopeiae" does not precisely match that of Cassiopeia A, and because the expansion wave associated with the explosion has been worked backward to the year 1667 and not 1680, some historians feel that all Flamsteed may have done was incorrectly note the position of a star already known.

In 1681 Flamsteed proposed that the two great comets observed in November and December 1680 were not separate bodies, but rather a single comet travelling first towards the Sun and then away from it. Although Isaac Newton first disagreed with Flamsteed, he later came to agree with him and theorized that comets, like planets, moved around the Sun in large, closed elliptical orbits. Flamsteed later learned that Newton had gained access to his observations and data through Edmund Halley, his former assistant with whom he previously had a cordial relationship.

As Astronomer Royal, Flamsteed spent some forty years observing and making meticulous records for his star catalogue, which would eventually triple the number of entries in Tycho Brahe's sky atlas. Unwilling to risk his reputation by releasing unverified data, he kept the incomplete records under seal at Greenwich. In 1712, Isaac Newton, then President of the Royal Society, and Edmund Halley again obtained Flamsteed's data and published a pirated star catalogue. Flamsteed managed to gather three hundred of the four hundred printings and burned them. "If Sir I.N. would be sensible of it, I have done both him and Dr. Halley a great kindness," he wrote to his assistant Abraham Sharp.

In 1725 Flamsteed's own version of Historia Coelestis Britannica was published posthumously, edited by his wife, Margaret. This contained Flamsteed's observations, and included a catalogue of 2,935 stars to much greater accuracy than any prior work. It was considered the first significant contribution of the Greenwich Observatory, and the numerical Flamsteed designations for stars that were added subsequently to a French edition are still in use.>>

BDanielMayfield wrote: ↑Fri Sep 06, 2019 5:04 am The recycling of gas (H & He) in supernovas is most efficient. ALL of the leftover gas that isn't used up in making heavier elements gets blasted back into the interstellar medium.