APOD: Cooling Neutron Star (2017 May 01)

[APOD Robot]

Cooling Neutron Star

Explanation: The bright source near the center is a neutron star, the incredibly dense, collapsed remains of a massive stellar core. Surrounding it is supernova remnant Cassiopeia A (Cas A), a comfortable 11,000 light-years away. Light from the Cas A supernova, the death explosion of a massive star, first reached Earth about 350 years ago. The expanding debris cloud spans about 15 light-years in this composite X-ray/optical image. Still hot enough to emit X-rays, Cas A's neutron star is cooling. In fact, years of observations with the orbiting Chandra X-ray Observatory find that the neutron star is cooling rapidly -- so rapidly that researchers suspect a large part of the neutron star's core is forming a frictionless neutron superfluid. The Chandra results represent the first observational evidence for this bizarre state of neutron matter.

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[Ann]

And to think that we can see both the expanding shell and the cooling neutron star, but when the actual star exploded some 300 years ago, no one noticed. Well, with the possible exception of John Flamsteed.

Wikipedia wrote:
Cassiopeia A (Cas A) is a supernova remnant (SNR) in the constellation Cassiopeia and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. The supernova occurred approximately 11,000 light-years (3.4 kpc) away within the Milky Way.[2][3] The expanding cloud of material left over from the supernova now appears approximately 10 light-years (3 pc) across from Earth's perspective. In wavelengths of visible light, it has been seen with amateur telescopes down to 234mm (9.25 in) with filters.[4]

It is believed that first light from the stellar explosion reached Earth approximately 300 years ago but there are no historical records of any sightings of the supernova that created the remnant, probably due to interstellar dust absorbing optical wavelength radiation before it reached Earth (although it is possible that it was recorded as a sixth magnitude star 3 Cassiopeiae by John Flamsteed on August 16, 1680[5]). Possible explanations lean toward the idea that the source star was unusually massive and had previously ejected much of its outer layers. These outer layers would have cloaked the star and re-absorbed much of the light released as the inner star collapsed.

Ann

[Boomer12k]

Beautiful...AND Fascinating...

Got out 8" Meade light switch scope and took some pics of Jupiter, Sunday night.
Warmer this week, really nice Wednesday, hope is a clear night, get the Moon too....
:---[===] *

[JohnD]

Gosh, in my ignorance it's not often I can correct Ann, but surely that star exploded 11300 years ago? (11K LY away, first seen, noticed or not on Earth, 300 years ago)

And I also thought, how can "the expanding debris cloud spans about 15 light-years" be right when we in our terms it's only had 300 years to expand. Is the Wiki correct then, in that there must have been prior explosive/ejection events?

John

[De58te]

Yes, John, the perplexing conundrum of the finite speed of light in a vacuum. The star did supernova 11,300 years ago. But since it is (or was) 11,000 light years away from Earth, an observer on Earth couldn't see the explosion happen until 300 years ago. ( If Flamsteed did see the explosion in 1680, then it happened 337 years ago as seen from Earth.)
As for the 15 ly in diameter, If we assume the physical debris from the explosion traveled out equally in a perfect sphere, then the outer rim is some 7.5 light years away from the central star. That means over the 300 years, it would have traveled 1 light year in 40 years. (Assuming the speeds remain the same and that it doesn't slow down over time. Newton's laws of motion.)

[Ann]

Gosh, in my ignorance it's not often I can correct Ann, but surely that star exploded 11300 years ago? (11K LY away, first seen, noticed or not on Earth, 300 years ago)

That's a good point, John, and it is certainly correct as far as it goes. In a way we could argue that when it comes to the Milky Way, we should be more careful in determining when supernova explosions "really" happened. Indeed the massive star that became the supernova remnant of Cas A would have exploded some 11,000 years ago, but its light only reached the Earth about 300 years ago. And the fact that the supernova explosion wasn't actually observed on the Earth at the time when it would have been possible to see it here is further argument that we should talk about the supernova as being 11,000 years old, not 300 years old.

Click to view full size image

Tycho Brahe's Supernova of 1572. Or should it be the supernova of 7,428 B.C.?
Illustration: Camille Flammarion.

However, in the cases when we know when the light from the supernova reached the Earth, it is usually a very bad idea to ignore the "detection date" in favor of the "actual explosion date". Consider "Tycho Brahe's supernova" that was discovered in 1572. It was not Tycho himself that detected it, but it has been named after him because he was able to show that the object was a "new star", farther away than the then-known planets of the solar system. We still don't know exactly how far the remnant of this supernova is - according to Wikipedia, the distance to it is believed to be between 8,000 and 9,800 light-years - and therefore we can't say how many years the light echo of the supernova had to travel before it reached the Earth in 1572.

Similarly, what about supernova 1987A in the Large Magellanic Cloud? According to Wikipedia, the actual supernova explosion took place in the large Magellanic Cloud approximately 168,000 light-years away, and if we consider that distance to be quite exact, then the light from the supernova traveled for 168,000 years to reach the Earth, and it actually exploded in 166,013 B.C. But surely it is our 1987 detection of it that is important to us here on the Earth, not its ~166,000 B.C. explosion date?

However, Cas A is a special case, since the actual explosion was never observed on the Earth. So I'll be fine with you calling it the 9,300 B.C. supernova, John!

And I also thought, how can "the expanding debris cloud spans about 15 light-years" be right when we in our terms it's only had 300 years to expand. Is the Wiki correct then, in that there must have been prior explosive/ejection events?

It is a known fact that many supernova progenitors undergo (major) ejection events before they go supernova. This could certainly have happened to the progenitor of Cas A.

Ann

[JohnD]

Thank you, Ann!

It's all in which way you're looking at it - in history - so maybe we should refer to such events' ages "as observed from Earth"?
So 300 years ago AOFE would be correct, even to us pedants!

JOhn

[BDanielMayfield]

Thank you, Ann!

It's all in which way you're looking at it - in history - so maybe we should refer to such events' ages "as observed from Earth"?
So 300 years ago AOFE would be correct, even to us pedants!

JOhn

"As observed from Earth" would be GAAP (Generally Accepted Accounting Principles) in CPA speak.

Bruce

[neufer]

Click to play embedded YouTube video.

[sillyworm]

"NASA's Chandra X-ray Observatory has discovered the first direct evidence for a superfluid, a bizarre, friction-free state of matter, at the core of a neutron star. Superfluids created in laboratories on Earth exhibit remarkable properties, such as the ability to climb upward and escape airtight containers. The finding has important implications for understanding nuclear interactions in matter at the highest known densities." A quote from Chandra X Ray & ScienceDaily Interesting! I was curious about "superfluid". Does anyone have anymore information?

[neufer]

Click to play embedded YouTube video.

Click to play embedded YouTube video.

I was curious about "superfluid". Does anyone have anymore information?

In a Liquid Helium II superfluid
everyone can hear you steam.

[Chris Peterson]

Gosh, in my ignorance it's not often I can correct Ann, but surely that star exploded 11300 years ago?

In addition to what others have said, there is the perspective offered by special relativity. As I still clearly recall from my first encounter with Taylor and Wheeler at Caltech, we can visualize the Universe as being filled with a latticework of meter sticks, with a clock at every intersection.

meter-clock-system_2.png (118.94 KiB) Viewed 6291 times

Such an arrangement fundamentally frames the idea of "now" with the way that space and time are connected. It is impossible for us to observe something earlier than a signal traveling at c can cover the distance between the event and the observer. From the standpoint of a signal traveling at c, time is not moving... every clock along the way will read the same value. In almost all ways that matter, it is most useful and most theoretically consistent to treat the time an event occurs, t=0, as the moment the event is observable. If you're interested in this, you can look up spacetime intervals, and the notions of timelike, spacelike, and lightlike.

On more practical grounds, we don't adjust the time based on distance because we don't usually know the distance with any accuracy. Astronomical distances are almost always problematic. Can you imagine the problems if every time we adjusted or refined our distance measurement to some object, we had to also adjust our timings to any events associated with that object?

[neufer]

As I still clearly recall from my first encounter with Taylor and Wheeler at Caltech, we can visualize the Universe as being filled with a latticework of meter sticks, with a clock at every intersection.

• I prefer to visualize the Universe as being filled with a loose latticework of light cones.
  Cassiopeia A (casually/causally speaking) is about 350 years ago inside our past light cone.

[b][color=#0000FF]Light cones near a black hole resulting from a collapsing star. The purple (dashed) line shows the path of a photon emitted from the surface of a collapsing star. The green (dot-dash) line shows the path of another photon shining at the singularity.[/color][/b]

---

<<In flat spacetime, the future light cone of an event is the boundary of its causal future and its past light cone is the boundary of its causal past.

In a curved spacetime, assuming spacetime is globally hyperbolic, it is still true that the future light cone of an event includes the boundary of its causal future (and similarly for the past). However gravitational lensing can cause part of the light cone to fold in on itself, in such a way that part of the cone is strictly inside the causal future (or past), and not on the boundary.

Light cones also cannot all be tilted so that they are 'parallel'; this reflects the fact that the spacetime is curved and is essentially different from Minkowski space. In vacuum regions (those points of spacetime free of matter), this inability to tilt all the light cones so that they are all parallel is reflected in the non-vanishing of the Weyl tensor.>>

[Chris Peterson]

As I still clearly recall from my first encounter with Taylor and Wheeler at Caltech, we can visualize the Universe as being filled with a latticework of meter sticks, with a clock at every intersection.

I prefer to visualize the Universe as being filled with a loose latticework of light cones.

Also reasonable. Indeed, it's just a different visualization of the same basic model. I think the clocks and meter stick lattice is a simpler visualization, however.

[BDanielMayfield]

... we can visualize the Universe as being filled with a latticework of meter sticks, with a clock at every intersection.

I prefer to visualize the Universe as being filled with a loose latticework of light cones.

We can depend on Art to add complexity, especially when simplicity will do.

[rstevenson]

We can depend on Art to add complexity, especially when simplicity will do.

That's what makes it Art.

Rob

[neufer]

... we can visualize the Universe as being filled with a latticework of meter sticks, with a clock at every intersection.

I prefer to visualize the Universe as being filled with a loose latticework of light cones.

We can depend on Art to add complexity, especially when simplicity will do.

• I received my Diploma/Pied-loma from Howard Johnson 50 years ago in 1967:

<<Howard Wesley Johnson (July 2, 1922 – December 12, 2009) served as president of MIT between 1966 and 1971.>>

[b][color=#FF8000][size=135]The Howard Johnson's trademark Simple Simon & the Pieman logo was created by artist John Alcott in the 1930s[/size][/color][/b]

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<<In 1925, Howard Deering Johnson (February 2, 1897 – June 20, 1972) borrowed $2,000 to buy and operate a small corner pharmacy near Quincy, Massachusetts. Johnson was surprised to find it easy to pay back the money lent to him after discovering his recently installed soda fountain had become the busiest part of his drugstore. He enhanced the quality of the ice cream by buying a recipe from a pushcart vendor for $300. It doubled the butterfat of the product and used only natural flavorings. He used hand-cranked makers in his basement and by 1928 was grossing about $240,000 from ice cream sold in the store and nearby beaches. Eventually Johnson came up with 28 flavors of ice cream. Johnson is quoted as saying, "I thought I had every flavor in the world. That '28' (flavors of ice cream) became my trademark."

Johnson convinced local bankers to lend him enough money to operate a sit-down restaurant. Negotiations were made and, toward the end of the decade, the first Howard Johnson's restaurant opened in Quincy. The first Howard Johnson's restaurant featured fried clams, baked beans, chicken pot pies, frankfurters, ice cream, and soft drinks. In 1929, Howard Johnson's company received an incredible break due to an unusual set of circumstances: The mayor of nearby Boston, Malcolm Nichols, prohibited the planned production of Eugene O'Neill's play, Strange Interlude, from performing in his city. Rather than fight the mayor, the Theatre Guild moved the production to Quincy. The five-hour play was presented in two parts with a dinner break. The first Howard Johnson's restaurant was near the theater; hundreds of influential Bostonians flocked to the restaurant. Through word of mouth, more Americans became familiar with the Howard Johnson's company.

Johnson was able to persuade an acquaintance in 1932 to open a second Howard Johnson's restaurant in Orleans, Massachusetts. The second restaurant was franchised and not company-owned. This was one of America's first franchising agreements. By the end of 1936, there were 39 more franchised restaurants, creating a total of 41 Howard Johnson's restaurants. By 1939, there were 107 Howard Johnson's restaurants along various American East Coast highways, generating revenues of $10.5 million.>>

[JohnD]

"From the standpoint of a signal traveling at c, time is not moving... every clock along the way will read the same value."

Gosh, Chris, I wish I hadn't read that, it's really confusing, when clearly time does pass while the light is travelling, or we would not measure in light years/minutes/seconds. But yes, I "know" that time slows the faster you travel, and yes, I think I read before that time does not pass for a photon, so I can't disagree.

More pretty pictures and less science please! Not.
John

[Chris Peterson]

"From the standpoint of a signal traveling at c, time is not moving... every clock along the way will read the same value."

Gosh, Chris, I wish I hadn't read that, it's really confusing, when clearly time does pass while the light is travelling, or we would not measure in light years/minutes/seconds. But yes, I "know" that time slows the faster you travel, and yes, I think I read before that time does not pass for a photon, so I can't disagree.

Well, the fact that every clock reads the same value as the photon passes them does not mean that time is not passing. What it's really saying is that there is no universal reference for time, no heartbeat of the Universe. You can't separate time from space. You can synchronize clocks in your lattice by sending a signal out from some point and allowing it to reset each clock it passes. If you were somehow outside this lattice (which isn't possible, except mathematically) you'd note that the clocks all show different values; from inside this universe they are synchronized, because from any point they all seem to show the same value.

[neufer]

You can synchronize clocks in your lattice by sending a signal out from some point and allowing it to reset each clock it passes.

Or in this case: one can synchronize clocks in the lattice by receiving signals
and reseting each space-time signal event clock to the UTC of those received signals.

[MarkBour]

I love the energy conveyed in today's image. It has the appearance of a really, really large plasma lamp!

I am wondering what the false colors represent.

I read a short article on the Chandra site (from the "supernova remnant" link) that mentions supernovas like this one ejecting matter at about 50 million km/hr. At that rate, if it were constant, in about 350 years, the debris would spread to a radius of 15 light years. I wonder if the spreading field slows down. If not, then since the ball seems to have a diameter of 15 ly, rather than a radius of 15 ly, perhaps this material was ejected more slowly, like at 25 million km/hr.

[neufer]

I read a short article on the Chandra site (from the "supernova remnant" link) that mentions supernovas like this one ejecting matter at about 50 million km/hr. At that rate, if it were constant, in about 350 years, the debris would spread to a radius of 15 light years. I wonder if the spreading field slows down. If not, then since the ball seems to have a diameter of 15 ly, rather than a radius of 15 ly, perhaps this material was ejected more slowly, like at 25 million km/hr.

One would expect the remnant expansion to slow down:

• 1) first when it encounters earlier ejecta (such as that which presumably hid the supernova back then and
  2) second when it encounters interstellar matter & magnetic fields.

[BDanielMayfield]

I read a short article on the Chandra site (from the "supernova remnant" link) that mentions supernovas like this one ejecting matter at about 50 million km/hr. At that rate, if it were constant, in about 350 years, the debris would spread to a radius of 15 light years. I wonder if the spreading field slows down. If not, then since the ball seems to have a diameter of 15 ly, rather than a radius of 15 ly, perhaps this material was ejected more slowly, like at 25 million km/hr.

One would expect the remnant expansion to slow down:

• 1) first when it encounters earlier ejecta (such as that which presumably hid the supernova back then and
  2) second when it encounters interstellar matter & magnetic fields.

• 3) plus, all along this ejecta's flight, it is being slowed down by by the gravitational attraction of the SN remnant. "What goes up must come down" or, at least, must slow down, if it was launched at greater than escape velocity, which this ejecta was.

Bruce

[neufer]

One would expect the remnant expansion to slow down:

• 1) first when it encounters earlier ejecta (such as that which presumably hid the supernova back then and
  2) second when it encounters interstellar matter & magnetic fields.

• 3) plus, all along this ejecta's flight, it is being slowed down by by the gravitational attraction of the SN remnant. "What goes up must come down" or, at least, must slow down, if it was launched at greater than escape velocity, which this ejecta was.

I would assume that the stated initial velocity had already taken into account the initial gravitational attraction of the SN remnant.

[JohnD]

Mark,
We see the remnant as 15 LY across, now, but with light emitted 11,000 years ago.
If the supernova occurred 300 years ago AOFE (!), and by your calculations then the emissions must have happened at least 300 years before that for the nebula to be where it is now.

John