APOD: Simeis 147: Supernova Remnant (2009 Jan 31)

[neufer]

Simeis 147: Pigs in Space

http://apod.nasa.gov/apod/ap090131.html

You are my lucky star
I saw you from afar
Two lovely eyes at me

They where gleaming
Beaming
I was starstruck

http://au.youtube.com/watch?v=cFvZtROeJrE

[Tara_Li]

In the full-sized image, there's an object located at about 8 o'clock to the main image showing an extent. I'm curious as to what it is (obviously, it's probably a planetary nebula), and I'm used to stars in Hubble images showing some coloration - so I'm wondering why the stars in this one don't, and why that planetary nebula doesn't show at least some colors. Is this composited with one of the earth-based star surveys?

[astrolabe]

Hello All,

http://antwrp.gsfc.nasa.gov/apod/ap090131.html

"The remarkable narrow-band composite image in the Hubble color palette includes emission from hydrogen, sulfur, and oxygen atoms tracing regions of shocked, glowing gas."

Does this mean that the hydrogen, sulfur, and oxygen emissions are they themselves the shocked, glowing gas?

[Chris Peterson]

In the full-sized image, there's an object located at about 8 o'clock to the main image showing an extent. I'm curious as to what it is (obviously, it's probably a planetary nebula), and I'm used to stars in Hubble images showing some coloration - so I'm wondering why the stars in this one don't, and why that planetary nebula doesn't show at least some colors. Is this composited with one of the earth-based star surveys?

It's a diffuse nebula, not a planetary. It is cataloged as LBN 826, or Sharpless 2-242.

[Chris Peterson]

Does this mean that the hydrogen, sulfur, and oxygen emissions are they themselves the shocked, glowing gas?

Not quite sure what you're asking. Presumably, the entire remnant contains a tenuous mix of gases. Shocked regions are heated up enough to ionize these gases and produce light. So in the image, only the hot (shocked) regions are visible. The brightness in each of the color bands must tell something about the temperature and concentration for each of the three elements targeted.

[astrolabe]

Hello Chris,

A temperature gradient possibly related to light intensity would be an advantagious correlation indeed I would assume. Also areas of the different emissions (with allowances for overlap) seem to be pretty well defined- could this indicate temperature differences as well if each element emits only at certain temperatures- not soley dependent on the heat of the shocked ionized gasses? in other words, is there any indications that the hydrogen, sulfur, and oxygen are homogenous throughout the nebula or are we limited to only the areas of emission as the element locators?

I may not be making my question any clearer of course so I hope you can follow my thought.

[neufer]

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A supernova remnant (SNR) passes through the following stages as it expands:

Denial: 1. Free expansion of the ejecta, until they sweep up their own weight in circumstellar or interstellar medium. This can last tens to a few hundred years depending on the density of the surrounding gas.

Anger: 2. Sweeping up of a shell of shocked circumstellar and interstellar gas. This begins the Sedov-Taylor phase, which can be well modeled by a self-similar analytic solution. Strong X-ray emission traces the strong shock waves and hot shocked gas.

Bargaining: 3. Cooling of the shell, to form a thin (< 1 pc), dense (1-100 million atoms per cubic metre) shell surrounding the hot (few million kelvin) interior. This is the pressure-driven snowplow phase. The shell can be clearly seen in optical emission from recombining ionized hydrogen and ionized oxygen atoms.

Depression: 4. Cooling of the interior. The dense shell continues to expand from its own momentum, in a momentum-driven snowplow. This stage is best seen in the radio emission from neutral hydrogen atoms.

Acceptance: 5. Merging with the surrounding interstellar medium. When the supernova remnant slows to the speed of the random velocities in the surrounding medium, after roughly a million years, it will merge into the general turbulent flow, contributing its remaining kinetic energy to the turbulence.
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http://en.wikipedia.org/wiki/Supernova_remnant
.....................................
<<A supernova remnant (SNR) is the structure resulting from the gigantic explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way. Supernova explosions expel much or all of the stellar material with velocities as much as 1% the speed of light, some 3,000 km/s. When this material collides with the surrounding circumstellar or interstellar gas, it forms a shock wave that can heat the gas up to temperatures as high as 10 million K, forming a plasma.

Perhaps the most famous and best-observed young SNR was formed by SN 1987A, a supernova in the Large Magellanic Cloud that was discovered in 1987. Other well-known, older, supernova remnants include Tycho (SN 1572), a remnant named after Tycho Brahe, who recorded the brightness of its original explosion (AD 1572) and Kepler (SN 1604), named after Johannes Kepler. The most recent remnant in our galaxy is G1.9+0.3, discovered in the galactic center and estimated to have gone supernova 140 years ago.
---------------------------------------
Types of supernova remnant

There are three types of supernova remnant:

* Shell-like, such as Cassiopeia A.

* Composite, in which a shell contains a central pulsar wind nebula, such as G11.2-0.3 or G21.5-0.9.

* Mixed-morphology (also called "thermal composite") remnants, in which central thermal X-ray emission is seen, enclosed by a radio shell. The thermal X-rays are primarily from swept-up interstellar material, rather than supernova ejecta. Examples of this class include the SNRs W28 and W44. (Confusingly, W44 additionally contains a pulsar and pulsar wind nebula; so it is simultaneously both a "classic" composite and a thermal composite.)
---------------------------------------
. Origin of cosmic rays

Supernova remnants are considered the major source of Galactic cosmic rays. The connection between cosmic rays and supernovas was first suggested by Walter Baade and Fritz Zwicky in 1934. Vitaly Ginzburg and Sergei Syrovatskii in 1964 remarked that if the efficiency of cosmic ray acceleration in supernova remnants is about 10 percent, the cosmic ray losses of the Milky Way are compensated. This hypothesis is supported by a specific mechanism called "shock wave acceleration" based on Enrico Fermi's ideas, which is still under development. Indeed, Enrico Fermi proposed in 1949 a model for the acceleration of cosmic rays through particle collisions with magnetic clouds in the interstellar medium. This process, known as the "Second Order Fermi Mechanism", increases particle energy during head-on collisions, resulting in a steady gain in energy. A later model to produce Fermi Acceleration was generated by a powerful shock front moving through space. Particles that repeatedly cross the front of the shock can gain significant increases in energy. This became known as the "First Order Fermi Mechanism".

Supernova remnants can provide the energetic shock fronts required to generate ultra-high energy cosmic rays. Observation of the SN 1006 remnant in the X-ray has shown synchrotron emission consistent with it being a source of cosmic rays. However, for energies higher than about 10^15 eV a different mechanism is required as supernova remnants cannot provide sufficient energy.>>
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[aristarchusinexile]

Remarkably similar to computer simulations of void bubble expansion.

[neufer]

Remarkably similar to computer simulations of void bubble expansion.

Is that any way to talk about our beloved Link Hogthrob?

[Chris Peterson]

A temperature gradient possibly related to light intensity would be an advantagious correlation indeed I would assume. Also areas of the different emissions (with allowances for overlap) seem to be pretty well defined- could this indicate temperature differences as well if each element emits only at certain temperatures- not soley dependent on the heat of the shocked ionized gasses? in other words, is there any indications that the hydrogen, sulfur, and oxygen are homogenous throughout the nebula or are we limited to only the areas of emission as the element locators?

I don't know. It's a complicated question. Intensity is all we have to work with in the image, and that is determined by two variables, density and temperature. Somebody studying this area closely could use spectroscopy to look at the widths of the emission lines, which (due to Doppler broadening) could be used to deduce the temperatures in different areas.

Also, the ionization energies are different for the three elements, so just because an area looks like a single color, that doesn't necessarily mean it consists of only the one element. And there's some continuum energy diluting things as well.

Finally, I suspect the elements are not homogeneous at all. When a star explodes, it has an internal shell structure consisting of different elemental zones. You'd think some of that structure would be preserved in the remnant- although it might be so chaotic that you couldn't work backwards to learn anything about the progenitor.

[neufer]

---------------------------------
You Tube videos: Cassiopeia A Supernova - Expanding

3D Fly-Through of the Supernova Remnant, Cassiopeia A
---------------------------------
Cassiopeia A and Supernova 1680 or 1667
Supernova 1680 or 1667 (3 Cassiopeiae ?) and Supernova Remnant G111.7-2.1 (Cassiopeia A, 3C 461) in Cassiopeia

Right Ascension: 23 : 23.4 (h:m)
[Numbers 23:23] What hath God wrought!

Declination: +58 : 50 (deg:m)
Distance: 11,000 (ly)
Visual brightness: 6? (mag)
Apparent Dimension: 5 (arc min)

<<This is the [next] youngest known supernova remnant in our Milky Way Galaxy, and the strongest extrasolar radio source in the sky. Calculating its expansion back, astronomers have found that the supernova must have blown up around the year 1667. Strangely, it was not widely noticed by that epoch's astronomers. However, as astronomy historian William Ashworth found out in 1980, it was perhaps observed by John Flamsteed on August 16, 1680, who cataloged a star near its position as "3 Cassiopeiae". However, he did not recognize it as a supernova, or "New Star", or anything particular else, and simply cataloged it as ordinary star. As this star was not noticed elsewhere, it cannot have been much brighter than 6th magnitude.

Later astronomers didn't find any sufficiently bright star near Flamsteed's position, and classified his catalog entry as erroneous.

As the supernova was rather close, its observed maximum brightness was extremely faint for a supernova, only about 250,000 solar luminosities, fainter than the brighter "normal" stars. This indicates that it was heavily obscured by interstellar matter.

The supernova remnant was found among the earliest discrete radio sources, in 1947 by radio astronomers from Cambridge, England, and is the strongest radio source in the sky beyond the solar system. This radio source was first named Cassiopeia A and later cataloged 3C 461. Its optical counterpart coudn't be found until a more precise position was obtained, by radio interferometry in 1950. Consequently, David Dewhirst of Cambridge obtained first deep optical photos of this region in the sky and discovered a strange faint nebula, which was then investigated by Walter Baade and Rudolph Minkowski with the then-new Palomar 5-meter telescope (Baade & Minkowski, 1954). Spectroscopic observations soon confirmed its nature as the rapidly expanding shell of a supernova remnant, also cataloged as G111.7-2.1. Within two years, American astronomers were able to determine its angular expansion rate, and calculated back that the expansion must have started around the year AD 1667, as mentioned above. Nevertheless, until Ashworth' publication of 1980, it was thought that the supernova had not been observed because of heavy obstruction. Even now there are some doubts, as the position of "3 Cassipeiae" does not exactly co-incide with that of Cassiopeia A, and some historians think Flamsteed may simply have cataloged an erroneous position of another star.

Cassiopeia A was the first target to be photographed by Nasa's new Chandra X-ray Observatory (CXO), also known as AXAF. It was always one of the preferred targets of X-ray astronomers, in particular with the Chandra orbital observatory.>>

[Zigomer Trubahin]

Just one observation, the text says "This supernova remnant has an estimated age of about 40,000 years - meaning light from the massive stellar explosion first reached Earth 40,000 years ago." I don't see the logical correlation between the two parts of the sentence. Light from a thing the age of about 40,000 years can reach the Earth any time (any time later than 40,000 years ago), depending on the distance. It could reach us today, or tomorrow. As this cloud is 3,000 ly away, the time its light first reached the Earth should have been about 37,000 years ago. Not that it matters much.

[Chris Peterson]

Just one observation, the text says "This supernova remnant has an estimated age of about 40,000 years - meaning light from the massive stellar explosion first reached Earth 40,000 years ago." I don't see the logical correlation between the two parts of the sentence. Light from a thing the age of about 40,000 years can reach the Earth any time (any time later than 40,000 years ago), depending on the distance. It could reach us today, or tomorrow. As this cloud is 3,000 ly away, the time its light first reached the Earth should have been about 37,000 years ago. Not that it matters much.:)

It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.

[astrolabe]

Hello Chris,

I don't know. It's a complicated question. Intensity is all we have to work with in the image, and that is determined by two variables, density and temperature. Somebody studying this area closely could use spectroscopy to look at the widths of the emission lines, which (due to Doppler broadening) could be used to deduce the temperatures in different areas.

Also, the ionization energies are different for the three elements, so just because an area looks like a single color, that doesn't necessarily mean it consists of only the one element. And there's some continuum energy diluting things as well.

Finally, I suspect the elements are not homogeneous at all. When a star explodes, it has an internal shell structure consisting of different elemental zones. You'd think some of that structure would be preserved in the remnant- although it might be so chaotic that you couldn't work backwards to learn anything about the progenitor.

Thank you for sticking with me on this and for your astute appraisal of my question. I'm glad I persisted for it resulted in a very abundant and informative answer that I can understand. Good thought order too!

[neufer]

Just one observation, the text says "This supernova remnant has an estimated age of about 40,000 years - meaning light from the massive stellar explosion first reached Earth 40,000 years ago." I don't see the logical correlation between the two parts of the sentence. Light from a thing the age of about 40,000 years can reach the Earth any time (any time later than 40,000 years ago), depending on the distance. It could reach us today, or tomorrow. As this cloud is 3,000 ly away, the time its light first reached the Earth should have been about 37,000 years ago. Not that it matters much.

It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.

The important thing is not so much when a prehistoric supernova "happens"
but rather how old the SNR is that we observe now.

The Simeis 147 SNR that we observe now is apparently about 40,000 years old.

The weird thing is that 3 years ago Simeis 147 was apparently about 100,000 years old!

Explanation: It's easy to get lost following the intricate filaments in this detailed image of faint supernova remnant Simeis 147. Seen towards the constellation Taurus it covers nearly 3 degrees (6 full moons) on the sky corresponding to a width of 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. The above image is a color composite of 66 blue and red color band images from the National Geographic Palomar Observatory Sky Survey taken with the wide field Samuel Oschin 48-inch Telescope. The area of the sky shown covers over 70 times the area of the full Moon. This supernova remnant has an apparent age of about 100,000 years - meaning light from the massive stellar explosion first reached Earth 100,000 years ago - but this expanding remnant is not the only aftermath. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the original star's core.

Simeis 147 is the Benjamin Button of supernova remnants!

Benjamin Button: Some people, were born to sit by a river. Some get struck by lightning. Some have an ear for music. Some are artists. Some swim. Some know buttons. Some know Shakespeare. Some are mothers. And some people, dance.

[Chris Peterson]

It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.

The important thing is not so much when a prehistoric supernova "happens"
but rather how old the SNR is that we observe now.

The Simeis 147 SNR that we observe now is apparently about 40,000 years old.

Is there a difference? It "happened" 40,000 years ago, because that's when it was observed from Earth. Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).

[astrolabe]

Hello All,

Just an afterthought: 3,000 ly away is still fairly close to us regardless isn't it? I mean after all we are in a galaxy roughly 100,000 ly across.

[neufer]

It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.

The important thing is not so much when a prehistoric supernova "happens"
but rather how old the SNR is that we observe now.

The Simeis 147 SNR that we observe now is apparently about 40,000 years old.

Is there a difference? It "happened" 40,000 years ago, because that's when it was observed from Earth.

Who exactly observed it from Earth? ...Or as the old saying goes:
"If Helen Keller fell down in the woods, would she make a sound?"

Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).

So you agree that it "really" happened 40,000 years + distance in light years ago.

[Chris Peterson]

Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).

So you agree that it "really" happened 40,000 years + distance in light years ago.

I put "really" in quotes to reflect the very difficult to define meaning of the word. I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here. But as I said, that usage isn't generally very useful, which is why you don't usually see it used except in explanations for a lay audience. Nothing wrong with that, of course.

[neufer]

Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).

So you agree that it "really" happened 40,000 years + distance in light years ago.

I put "really" in quotes to reflect the very difficult to define meaning of the word. I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here. But as I said, that usage isn't generally very useful, which is why you don't usually see it used except in explanations for a lay audience. Nothing wrong with that, of course.

So, by that definition, I guess:

Tycho's Supernova at ~8,000 years [= 436 years + 7,500 (light-)years] was the last known supernova to occur.

Kepler's supernova at 404 years is "the most recent stellar explosion seen to occur within our Milky Way galaxy."

And Supernova remnant G1.9+0.3 at ~140 years is the youngest known supernova remnant (SNR) in the Milky Way Galaxy.


Composite image of Supernova remnant G1.9+0.3, using a 1985 radio images (blue) and a 2008 x-ray image (orange). The difference in size revealed that the supernova remnant is still expanding rapidly, and allowed astronomers to calculate its age.

[Chris Peterson]

I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here.

So, by that definition, I guess:

Tycho's Supernova at ~8,000 years [= 436 years + 7,500 (light-)years] was the last known supernova to occur.

Kepler's supernova at 404 years is "the most recent stellar explosion seen to occur within our Milky Way galaxy."

And Supernova remnant G1.9+0.3 at ~140 years is the youngest known supernova remnant (SNR) in the Milky Way Galaxy.

I'm not following your reasoning here. If you're trying to place all these events into a common time reference, don't you need to include the distances for the latter two?

[neufer]

I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here.

So, by that definition, I guess:

Tycho's Supernova at ~8,000 years [= 436 years + 7,500 (light-)years] was the last known supernova to occur.

Kepler's supernova at 404 years is "the most recent stellar explosion seen to occur within our Milky Way galaxy."

And Supernova remnant G1.9+0.3 at ~140 years is the youngest known supernova remnant (SNR) in the Milky Way Galaxy.

I'm not following your reasoning here. If you're trying to place all these events into a common time reference, don't you need to include the distances for the latter two?

Sorry, I was NOT trying to place all these events into a common time reference.

Rather, I was trying to clarify in my mind which known supernova
actually occurred last in a Machian universe... and I got it wrong.

I now think that SN 1054 (M1: The Crab Nebula) at ~7,000 years ago
[= 954 years + 6,000 (light-)years] was the last known supernova to occur.

Tycho's Supernova & SN 1006 are tied for second at ~8,000 years ago.

I think this is sort of "illuminating" (and may even become a Jeopardy question).
-------------------------------------------------------
Also, the unobserved supernova remnant associated with 716 Hertz pulsar PSR J1748-2446ad
may well be the youngest "known" supernova remnant (SNR) in the Milky Way Galaxy.

<<The scientists discovered the pulsar, named PSR J1748-2446ad, in a globular cluster of stars called TERZAN 5, located some 28,000 light-years from Earth in the constellation Sagittarius. The newly-discovered pulsar is spinning 716 times per second, or at 716 Hertz (Hz), readily beating the previous record of 642 Hz from a pulsar discovered in 1982. The scientists say the object's fast rotation speed means that it cannot be any larger than about 20 miles across. According to Hessels, "If it were any larger, material from the surface would be flung into orbit around the star." The scientists' calculation assumed that the neutron star contains less than two times the mass of the Sun, an assumption that is consistent with the masses of all known neutron stars.>>

[Heliocracy]

What's that puffy, cloud-like object that appears near the lower left corner of the Simeis 147 photo?

[Chris Peterson]

I now think that SN 1054 (M1: The Crab Nebula) at ~7,000 years ago [= 954 years + 6,000 (light-)years] was the last known supernova to occur.

How about SN 185, at ~4800 years (1823 years ago + 3000 ly distant)?

[bystander]

What's that puffy, cloud-like object that appears near the lower left corner of the Simeis 147 photo?

In the full-sized image, there's an object located at about 8 o'clock to the main image showing an extent. I'm curious as to what it is (obviously, it's probably a planetary nebula), and I'm used to stars in Hubble images showing some coloration - so I'm wondering why the stars in this one don't, and why that planetary nebula doesn't show at least some colors. Is this composited with one of the earth-based star surveys?

It's a diffuse nebula, not a planetary. It is cataloged as LBN 826, or Sharpless 2-242.

http://asterisk.apod.com/vie ... 82#p100711