APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

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APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by APOD Robot » Wed Dec 18, 2019 5:05 am

Image A Hotspot Map of Neutron Star J0030's Surface

Explanation: What do neutron stars look like? Previously these city-sized stars were too small and too far away to resolve. Recently, however, the first maps of the locations and sizes of hotspots on a neutron star's surface have been made by carefully modeling how the rapid spin makes the star's X-ray brightness rise and fall. Based on a leading model, an illustrative map of pulsar J0030+0451's hotspots is pictured, with the rest of the star's surface filled in with a false patchy blue. J0030 spins once every 0.0049 seconds and is located about 1000 light years away. The map was computed from data taken by NASA's Neutron star Interior Composition ExploreR (NICER) X-ray telescope attached to the International Space Station. The computed locations of these hotspots is surprising and not well understood. Because the gravitational lensing effect of neutron stars is so strong, J0300 displays more than half of its surface toward the Earth. Studying the appearance of pulsars like J0030 allows accurate estimates of the neutron star's mass, radius, and the internal physics that keeps the star from imploding into a black hole.

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by bystander » Wed Dec 18, 2019 6:01 am

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by Boomer12k » Wed Dec 18, 2019 10:37 am

From a search, "A neutron star is formed during a supernova, an explosion of a star that is at least 8 solar masses. The maximum mass of a neutron star is 3 solar masses. If it gets more massive than that, then it will collapse into a quark star, and then into a black hole."

Sooo...um... if it has less than 3 solar masses... as I understand it, it can't implode further into a black hole...at 1.4 solar masses, this is not going to happen with J0030.
So... I logically submit, Captain, with J0030, it is NOT "internal physics" keeping it from imploding... it is simply its lack of mass.

With two poles in the same hemisphere... the shock seems to have really rent it asunder. Like taking Magnetic North and putting it in Australia, and the Magenetic South, in Tierra del Fruego...

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by JohnD » Wed Dec 18, 2019 10:53 am

We get discussions here about the way that colours are interpreted in astronomical photos, and it often seems to be either an aesthetic argument, or one of interpretation, using false colours to make the image clearer. But here, there is a clear misinterpretation, if not an aim to mislead the viewer.

in the small print we read, "the rest of the star's surface filled in with a false patchy blue". If the rest of the disc had been a plain, unmarked colour, that would be a true picture of this remarkable acheivement in imaging. To insert apparent markings is incorrect, with no evidence to substantiate it.

John

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by orin stepanek » Wed Dec 18, 2019 12:06 pm

Do we know if Neutron Stars have any sort of lifespan? :shock:
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by Boomer12k » Wed Dec 18, 2019 1:07 pm

orin stepanek wrote:
Wed Dec 18, 2019 12:06 pm
Do we know if Neutron Stars have any sort of lifespan? :shock:
This may give some insight...https://astronomy.stackexchange.com/que ... star-cools

Hope that helps...

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by BDanielMayfield » Wed Dec 18, 2019 1:41 pm

JohnD wrote:
Wed Dec 18, 2019 10:53 am
We get discussions here about the way that colours are interpreted in astronomical photos, and it often seems to be either an aesthetic argument, or one of interpretation, using false colours to make the image clearer. But here, there is a clear misinterpretation, if not an aim to mislead the viewer.

in the small print we read, "the rest of the star's surface filled in with a false patchy blue". If the rest of the disc had been a plain, unmarked colour, that would be a true picture of this remarkable acheivement in imaging. To insert apparent markings is incorrect, with no evidence to substantiate it.

John
Valid point John. But at least the patchy blue was explained as being false. Leaving that out of "the small print" would have made this image very misleading.
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by grisham41@gmail.com » Wed Dec 18, 2019 2:32 pm

Just wanted to let the Staff of Astronomy , that i always enjoy your pictures and information.
Thanks./12/18/19 The day Columbus Landed at Plymouth Rock in the 1620 .That would have
been something to see !
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by Chris Peterson » Wed Dec 18, 2019 2:36 pm

Boomer12k wrote:
Wed Dec 18, 2019 10:37 am
From a search, "A neutron star is formed during a supernova, an explosion of a star that is at least 8 solar masses. The maximum mass of a neutron star is 3 solar masses. If it gets more massive than that, then it will collapse into a quark star, and then into a black hole."

Sooo...um... if it has less than 3 solar masses... as I understand it, it can't implode further into a black hole...at 1.4 solar masses, this is not going to happen with J0030.
So... I logically submit, Captain, with J0030, it is NOT "internal physics" keeping it from imploding... it is simply its lack of mass.
It is neutron degeneracy pressure- quantum physics internal to the neutron star- that is preventing collapse.
Chris

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by Chris Peterson » Wed Dec 18, 2019 2:42 pm

JohnD wrote:
Wed Dec 18, 2019 10:53 am
We get discussions here about the way that colours are interpreted in astronomical photos, and it often seems to be either an aesthetic argument, or one of interpretation, using false colours to make the image clearer. But here, there is a clear misinterpretation, if not an aim to mislead the viewer.

in the small print we read, "the rest of the star's surface filled in with a false patchy blue". If the rest of the disc had been a plain, unmarked colour, that would be a true picture of this remarkable acheivement in imaging. To insert apparent markings is incorrect, with no evidence to substantiate it.
If you look at the published papers, they show the star in wireframe with the hotspots overlain. But the video really requires a structured background in order to see how the model handles rotation. They could have used something like a fine checkerboard, but that might have been distracting. So a low contrast, low spatial frequency map consistent with small temperature variations that are almost certainly present seems like a reasonable choice, along with a clear statement that this background is synthesized, not derived from the data. To me that's the very opposite of misleading.
Chris

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by TheOtherBruce » Wed Dec 18, 2019 3:21 pm

orin stepanek wrote:
Wed Dec 18, 2019 12:06 pm
Do we know if Neutron Stars have any sort of lifespan? :shock:
A lot depends on circumstances. A solo neutron star, not part of a binary system or any surviving planets, will just get steadily cooler and rotate slower over a very, very, very long timescale (the very first neutron stars formed are probably all still out there somewhere, they just can't be detected any more at astronomical distances). Neutron stars that are part of a binary system have a good chance of eventually colliding or merging with their partner, which might or might not be a neutron star itself, resulting in either complete disruption in a massive kaboom or a black hole. The wikipedia page on neutron stars goes into the gory mathematical details; they're all a bit over my head.
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by Chris Peterson » Wed Dec 18, 2019 3:44 pm

orin stepanek wrote:
Wed Dec 18, 2019 12:06 pm
Do we know if Neutron Stars have any sort of lifespan? :shock:
A neutron star is essentially just a huge atomic nucleus, containing only neutrons. These are degenerate neutrons, in their lowest possible energy state. So they can't decay. They are stable. In other words, absent external influences (like accreting material from the surrounding medium, or a collision with another star), a neutron star will exist forever, just getting cooler as it asymptotically approaches the temperature of the Universe (which itself is getting cooler).
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by Ralphbolt » Wed Dec 18, 2019 3:59 pm

12,000 RPM!! Amazing. Where did the energy to spin them up come from?

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by neufer » Wed Dec 18, 2019 4:03 pm

Chris Peterson wrote:
Wed Dec 18, 2019 3:44 pm
orin stepanek wrote:
Wed Dec 18, 2019 12:06 pm

Do we know if Neutron Stars have any sort of lifespan? :shock:
A neutron star is essentially just a huge atomic nucleus, containing only neutrons. These are degenerate neutrons, in their lowest possible energy state. So they can't decay. They are stable. In other words, absent external influences (like accreting material from the surrounding medium, or a collision with another star), a neutron star will exist forever, just getting cooler as it asymptotically approaches the temperature of the Universe (which itself is getting cooler).
  • Getting cooler & spinning slower:
https://en.wikipedia.org/wiki/Neutron_star#Spin_down wrote:
<<Over time, neutron stars slow, as their rotating magnetic fields in effect radiate energy associated with the rotation; older neutron stars may take several seconds for each revolution. This is called spin down. The rate at which a neutron star slows its rotation is usually constant and very small.

The spin-down rate (P-dot) of neutron stars usually falls within the range of 10−22 to 10−9, with the shorter period (or faster rotating) observable neutron stars usually having smaller P-dot. As a neutron star ages, its rotation slows (as P increases); eventually, the rate of rotation will become too slow to power the radio-emission mechanism, and the neutron star can no longer be detected.

P and P-dot allow minimum magnetic fields of neutron stars to be estimated. P and P-dot can be also used to calculate the characteristic age of a pulsar, but gives an estimate which is somewhat larger than the true age when it is applied to young pulsars.

P and P-dot can also be plotted for neutron stars to create a P–P-dot diagram. It encodes a tremendous amount of information about the pulsar population and its properties, and has been likened to the Hertzsprung–Russell diagram in its importance for neutron stars.>>
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by Chris Peterson » Wed Dec 18, 2019 4:04 pm

Ralphbolt wrote:
Wed Dec 18, 2019 3:59 pm
12,000 RPM!! Amazing. Where did the energy to spin them up come from?
This is just the result of angular momentum being conserved. Start with a normal star with a rotation period of days, and reduce its diameter by five orders of magnitude, and the rotation rate increases. No additional energy needs to be added; it was already there in the rotational kinetic energy of the progenitor.

No different from a figure skater speeding up her rotation by tucking in her arms.
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by TheOtherBruce » Wed Dec 18, 2019 4:18 pm

Ralphbolt wrote:
Wed Dec 18, 2019 3:59 pm
12,000 RPM!! Amazing. Where did the energy to spin them up come from?
The rotational energy was already there, in the star that existed before the supernova. When the neutron star formed, this energy was concentrated, spinning the compressed core faster and faster with no limit until neutron pressure stopped the collapse. Freshly created neutron stars typically rotate at hundreds of times per second. (A neutron star was probably created in the 1987A supernova, but it hasn't been detected yet due to thick clouds of gas and dust.) They do gradually slow down, though, as the star's magnetic field is also massively compressed and "leaks" energy as it spins.
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by orin stepanek » Wed Dec 18, 2019 4:35 pm

10Q All! :D 8-)
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by neufer » Wed Dec 18, 2019 5:48 pm

TheOtherBruce wrote:
Wed Dec 18, 2019 4:18 pm
Ralphbolt wrote:
Wed Dec 18, 2019 3:59 pm

12,000 RPM!! Amazing. Where did the energy to spin them up come from?
The rotational energy was already there, in the star that existed before the supernova. When the neutron star formed, this energy was concentrated....
The rotational energy was NOT already there :!:

The neutron star rotational energy comes from the gravitational potential energy of the uncompressed star.

It is rather the angular momentum that was already there in the star before the supernova.

The spinning ice skater must use her arm muscles to provide the high spinning energy.

Until she finally edges her skates, however, she cannot influence her angular momentum
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by DL MARTIN » Wed Dec 18, 2019 6:45 pm

What is being considered took place a thousand years ago. Shouldn't this qualifier be included in the discussion?

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by neufer » Wed Dec 18, 2019 6:56 pm

DL MARTIN wrote:
Wed Dec 18, 2019 6:45 pm

What is being considered took place a thousand years ago. Shouldn't this qualifier be included in the discussion?
DL MARTIN made his comment an hour ago. Shouldn't this qualifier be included in the discussion?
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by JohnD » Wed Dec 18, 2019 6:58 pm

Chris Peterson wrote:
Wed Dec 18, 2019 2:42 pm
JohnD wrote:
Wed Dec 18, 2019 10:53 am
We get discussions here about the way that colours are interpreted in astronomical photos, and it often seems to be either an aesthetic argument, or one of interpretation, using false colours to make the image clearer. But here, there is a clear misinterpretation, if not an aim to mislead the viewer.

in the small print we read, "the rest of the star's surface filled in with a false patchy blue". If the rest of the disc had been a plain, unmarked colour, that would be a true picture of this remarkable acheivement in imaging. To insert apparent markings is incorrect, with no evidence to substantiate it.
If you look at the published papers, they show the star in wireframe with the hotspots overlain. But the video really requires a structured background in order to see how the model handles rotation. They could have used something like a fine checkerboard, but that might have been distracting. So a low contrast, low spatial frequency map consistent with small temperature variations that are almost certainly present seems like a reasonable choice, along with a clear statement that this background is synthesized, not derived from the data. To me that's the very opposite of misleading.
Video?? What video!! Ah!!! Click on the link "first maps" and you get to this NASA page:
https://www.nasa.gov/feature/goddard/20 ... urface-map
that does show a video of the neutron star! The first few seconds show the image as seen on APOD, while after an excellent explanation a rotating latitide/longitude grid is used. That surely describes the work more accurately and honestly, as well as making clear the the apparent 'inflation' of the star and the movement of the hotspots. The elatter would appear preferable, in science and education terms!

John

PS Neufer and DL Martin. Why is this of significance?

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by BDanielMayfield » Wed Dec 18, 2019 7:36 pm

This statement in today's explanation was interesting:
Because the gravitational lensing effect of neutron stars is so strong, J0300 displays more than half of its surface toward the Earth.
So photon paths are bent around the normal horizon of NSs, letting us see more than half of their surfaces!

I number crunched some stats to estimate the escape velocity for NSs in the mass range of 1.1 to 2.14 Solar masses and came up with a range of .54 to .73 c.

So, what percentage of a neutron star's surface are we able to see?

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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by BDanielMayfield » Wed Dec 18, 2019 7:48 pm

neufer wrote:
Wed Dec 18, 2019 6:56 pm
DL MARTIN wrote:
Wed Dec 18, 2019 6:45 pm

What is being considered took place a thousand years ago. Shouldn't this qualifier be included in the discussion?
DL MARTIN made his comment an hour ago. Shouldn't this qualifier be included in the discussion?
Excellent point Art. And whenever we look at the Moon or the Sun, don't fail to say, 'look at how the moon looked 2 seconds [almost] ago' or 'Look at where the Sun was 8 minutes ago' and wonder where they are now. :lol2:
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by MarkBour » Wed Dec 18, 2019 8:01 pm

I like simple math. 16 mi diameter = 16*pi*1609.34m/mi = 1.65x 10^7 m/sec.
So a neutron on the rotational equator of J0030 is zipping around at about 5.5% of the speed of light.
This estimate is probably low, since the neutron star must be oblate, due to the rotation.

Wouldn't Hawking radiation apply to these bodies just as well as it would to a black hole?
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Re: APOD: A Hotspot Map of Neutron Star... (2019 Dec 18)

Post by neufer » Wed Dec 18, 2019 8:04 pm

BDanielMayfield wrote:
Wed Dec 18, 2019 7:36 pm
Because the gravitational lensing effect of neutron stars is so strong, J0300 displays more than half of its surface toward the Earth.
So photon paths are bent around the normal horizon of NSs, letting us see more than half of their surfaces!

I number crunched some stats to estimate the escape velocity for NSs in the mass range of 1.1 to 2.14 Solar masses and came up with a range of .54 to .73 c.

So, what percentage of a neutron star's surface are we able to see?
If the radius were 1.5 times its Schwarzschild radius then one would be able to see all of the neutron star's surface.

In this case the actual radius of this neutron star is ~1.8 times its Schwarzschild radius so perhaps ~10% of the neutron star's surface is unseen.
Art Neuendorffer