APOD: Recycling Cassiopeia A (2019 Sep 06)

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APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by APOD Robot » Fri Sep 06, 2019 4:11 am

Image Recycling Cassiopeia A

Explanation: Massive stars in our Milky Way Galaxy live spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation can begin anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant would have been first seen in planet Earth's sky about 350 years ago, although it took that light about 11,000 years to reach us. This false-color image, composed of X-ray and optical image data from the Chandra X-ray Observatory and Hubble Space Telescope, shows the still hot filaments and knots in the remnant. It spans about 30 light-years at the estimated distance of Cassiopeia A. High-energy X-ray emission from specific elements has been color coded, silicon in red, sulfur in yellow, calcium in green and iron in purple, to help astronomers explore the recycling of our galaxy's star stuff. Still expanding, the outer blast wave is seen in blue hues. The bright speck near the center is a neutron star, the incredibly dense, collapsed remains of the massive stellar core.

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by bystander » Fri Sep 06, 2019 4:40 am

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by BDanielMayfield » 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.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by RocketRon » 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) ?

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Ann » Fri Sep 06, 2019 6:07 am

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.
Which is why most gas in the Universe isn't recycled, because supernovas are rare.

Consider the picture at right of young bright cluster NGC 602 in nebula N90 in the Small Magellanic Cloud. It is immediately obvious that cluster NGC 602 (slightly below and right of center) contains some ~10 bright massive stars and a number of smaller stars. Yes, the number of massive stars may certainly be higher, but that's not the point. The point is that the burst of star formation that formed NGC 602 created very many more small non-supernova-worthy stars than big massive ones.

Or to put it differently: Most of the gas that went into creating cluster NGC 602 ended up inside small lightweight stars, not inside big massive stars.

A star like the Sun will give back perhaps half of its mass to the Universe when it dies. During its lifetime the Sun will cast off some 50% of its mass (or more) through the Solar wind, which will become particularly strong during the Sun's red giant phase.

But most stars in the Universe are smaller and less massive than the Sun, let alone smaller than stars massive enough to eventually go supernova, and they are the Uncle Scrooges of the Universe. Unlike Scrooge, they don't make more money or more mass as they age, but they jealously guard whatever they were born with, and the smallest ones live to be trillions of years old.

(If the Universe itself lasts that long, that is. Why am I thinking of the song "In the year 2525, 2525"?)

The lifeblood of the Universe, the "free gas", gets locked up inside the miserly little red dwarfs.
No wonder the Universe as we know it can't live forever.

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Boomer12k » Fri Sep 06, 2019 9:20 am

Awesome and very CRISP view...

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by orin stepanek » Fri Sep 06, 2019 10:29 am

Chandrafirstlight_0_1024.jpg
Today's APOD very beautiful; 8-)
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Earliest known sighting of Uranus by an asstronomer

Post by neufer » Fri Sep 06, 2019 11:57 am

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

<<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.>>
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by neufer » Fri Sep 06, 2019 12:19 pm

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 (νe) 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→nνe. 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.>>
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Whiskybreath » 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?

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by neufer » Fri Sep 06, 2019 12:48 pm

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?
Probably...but blown inside out due to the most intense explosion being at the center.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by neufer » Fri Sep 06, 2019 12:48 pm

Click to play embedded YouTube video.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by BDanielMayfield » Fri Sep 06, 2019 1:18 pm

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

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by neufer » Fri Sep 06, 2019 2:28 pm

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.
I'm guessing that a supernova would have to, at least, reside in the Local Group of galaxies to be detected gravitationally.
https://en.wikipedia.org/wiki/LIGO#/media/File:LIGO_detector_sensitivity_curve.png wrote:

:arrow: 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.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by TheZuke! » Fri Sep 06, 2019 2:34 pm

Thanks neufer for those posts, informative!

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by BDanielMayfield » 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.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Chris Peterson » 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.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by neufer » 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
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.
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).

See the diagram above: http://asterisk.apod.com/viewtopic.php? ... 71#p295014
https://en.wikipedia.org/wiki/GW170817 wrote: 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.>>
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Chris Peterson » 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
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).
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.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Ann » 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
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.
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.

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Chris Peterson » 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
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.
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.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by Ann » 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
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.
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.

Not sure about the accreting white dwarf supernovas, though.

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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by neufer » Fri Sep 06, 2019 9:48 pm

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.
Quadrupole radiation characteristic strain scales as: f2L2M where
  • f= (twice) orbital frequency
    L = orbital separation
    M = mass of two equal orbiting bodies
Kepler's 3rd law states that f2 scales as density = M/L3

hence: Quadrupole radiation characteristic strain scales as: M2/L
  • Mn of neutron stars ~ 2 Md of white dwarfs
    Ln of neutron stars ~ Ld/800 of white dwarfs
Quadrupole radiation characteristic strain of merging neutron stars ~ 3200 times that of merging white dwarfs.
Frequency (M/L3)0.5 of the radiation of merging neutron stars ~ 32,000 times that of merging white dwarfs.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by TheOtherBruce » Sat Sep 07, 2019 2:18 am

A spectacular image.

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?

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.
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Re: APOD: Recycling Cassiopeia A (2019 Sep 06)

Post by neufer » Sat Sep 07, 2019 12:35 pm

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.
SN 1987A is just 15 times farther away than Cassiopeia A and about an order of magnitude younger;
so the expanding SN 1987A central nebula is sort of beginning to look like Cassiopeia A...maybe :?: :?
https://en.wikipedia.org/wiki/SN_1987A wrote:

:arrow: 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.>>
Art Neuendorffer