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Fraser
2005-Jul-13, 05:15 PM
SUMMARY: An international team of astronomers have discovered a hidden neutron star using three different space observatories: Integral, Swift and Rossi. The object, called IGR J16283-4838, is part of a binary system which is shrouded in thick layers of dust that obscure our view from Earth. Astronomers were able to detect it because it released a blast of gamma and X-rays that penetrated this shroud of dust. It took all three observatories to pin down the source of this blast of radiation as a neutron star.

View full article (http://www.universetoday.com/am/publish/3_satellites_shy_star.html)

What do you think about this story? Post your comments below.

wstevenbrown
2005-Jul-13, 06:34 PM
Neutron stars such as IGR J16283-4838 are often part of binary systems, orbiting a normal star.

It used to be thought that neutron stars were necessarily solitary objects, because the precursor object had to be so massive that no other star could form near it.

Perceptions, evolutionary models, and population synthesis models are changing at a dizzying rate. Common-envelope rapid evolution is no longer a four-letter word. :lol: S

lswinford
2005-Jul-13, 07:32 PM
So when that dust settles it explodes to send the dust back out again?

What makes densely packed neutron stars explosive? Is it because the uncollapsed material therefore also collapses, releasing energy and some particles? I thought the issue on neutron stars was the gravitational collapse and particle change metamorphosis released all its energy, leaving the star comparatively cool, which is what allows all those neutrons to stay so close together--high gravity and low energy. This is the subatomic kind of condensation that first builds clouds, precipitates rain, and in this way diminishes the cloud as the water condenses and falls in the heat exchange with air. If neutron stars have blown out their energy then the only reactive thing remaining is if the settling dust also is forced to collapse--but that would make neutron stars like black holes in this short step above matter annihilation, with quark stars an even shorter stage in between.

Gasp! :blink: We better not find matter reaccreting on the neutron star :unsure:

eburacum45
2005-Jul-13, 07:59 PM
I thought the issue on neutron stars was the gravitational collapse and particle change metamorphosis released all its energy, leaving the star comparatively cool

Not cool by any standard I am aware of; if current theories are correct a neutron star has a surface temperature of a million degrees after 100,000 years.

om@umr.edu
2005-Jul-13, 08:20 PM
Originally posted by wstevenbrown@Jul 13 2005, 06:34 PM
It used to be thought that neutron stars were necessarily solitary objects, because the precursor object had to be so massive that no other star could form near it.

Perceptions, evolutionary models, and population synthesis models are changing at a dizzying rate. Common-envelope rapid evolution is no longer a four-letter word. :lol: S
Yes, indeed. Perceptions are changing.

And this discovery is an important step in the right direction.

With kind regards,

Oliver
http://www.umr.edu/~om

PS - Is there any evidence of hydrogen coming from this neutron star?

lswinford
2005-Jul-13, 08:56 PM
eburacum45, thanks.

So with then, returning to a water vapor analogy, when the material falls on the star its like water on a hot skillet. Yep, that would be explosive and yep that would provide momentum to keep the surrounding dust cloud in suspense.

Thanks again.

Still, its kind of hard to imagine all that energy being present and still thwarted by the still larger gravity. For an electron, for instance, to give up energy, it drops an orbit. For neutrons to coexist so compactly inherently sounds like they gave up energy, which I've been told was the energy of the supernova that happened when the neutron star formed.

I love the mental exercises that come with this place.

aesetab
2005-Jul-13, 09:05 PM
Not being an astronomer, the thought crossed my mind that with the discovery of this neuron star is it not a possibility that 'dark mater' does not exist, merely, the 'missing matter' is other undiscovered matter, like this star?

Guest
2005-Jul-13, 09:17 PM
Originally posted by lswinford@Jul 13 2005, 08:56 PM
So with then, returning to a water vapor analogy, when the material falls on the star its like water on a hot skillet.
Could this be related to the news report in 2000 of an isolated neutron star releasing more energy than could be explained by accretion?

ESO News Report (http://www.eso.org/outreach/press-rel/pr-2000/pr-19-00.html)

The surface temperature of that neutron star was estimated to be 700,000 K.

Let's hope the new finding will improve our understanding of the energy locked in neutron stars.

With kind regards,

Oliver
http://www.umr.edu/~om

antoniseb
2005-Jul-13, 10:36 PM
Originally posted by om@umr.edu@Jul 13 2005, 08:20 PM
this discovery is an important step in the right direction.
Do you think there are discoveries that are steps in the wrong direction?

om@umr.edu
2005-Jul-13, 11:37 PM
Originally posted by antoniseb@Jul 13 2005, 10:36 PM
Do you think there are discoveries that are steps in the wrong direction?
Yes, indeed! There are many.

For example, here are a few in my own area of research:

1. The discovery of many different types of Neon in the solar system - Ne-A, Ne-B, Ne-C, De-D, Ne-E, etc. - all of which could be explained by simple mass-dependent fractionation. See: "The Neon Alphabet Game" (http://web.umr.edu/~om/abstracts2005/Neon_alphabet_game.pdf)

2. The discovery of fission products from superheavy elements in meteorites. See: "Strange Xenon, Extinct Superheavy Elements, and the Solar Neutrino Puzzle" (http://web.umr.edu/~om/archive/StrangeXenon.pdf)

3. The discovery in meteorites of "interstellar grains" that had been magically shielded from cosmic rays during their imagined interstellar journey through space. Etc.

There are, of course examples, that have wrecked havoc on mankind, e.g.,

1. The "discovery" that the Aryan race is superior to all others, etc.

With kind regards,

Oliver
http://www.umr.edu/~om

Josh
2005-Jul-14, 01:46 AM
The latter wasn't a discovery, it was an assertion. One we all know to be false. It lacked any real supporting proof or evidence. The only proof brought forward was misinterpretations and misrepresentations of truths. That's a common tool used to pulbicise and gain support for lies and propaganda (especially of the racist kind).

Take the second part of the"Strange Xenon, Extinct Superheavy Elements, and the Solar Neutrino Puzzle" document as an example. You make assertions which are completely refuted by the people whose data your findings are based upon. Among other rejections of your claims, they go as far as saying "incidentally, Manuel and Sabu misrepresent our views...". So, it seems that your theories and the theory of Aryan superiority have a lot in common.

om@umr.edu
2005-Jul-14, 02:13 AM
Josh,

The debate in Science was whether excess Xe-136 in meteorites was:

a.) a fission product of superheavy elements, or
b.) a product of stellar nucleosynthesis.

The debate was settled about 7 years later, with an admission that the correct answer is b.)

Getting back to topic, a neutron star is expected in the neighborhood from the supernova that produced the excess Xe-136 seen in meteorites and in Jupiter.

With kind regards,

Oliver
http://www.umr.edu/~om

Svemir
2005-Jul-14, 05:39 AM
Not being an astronomer, the thought crossed my mind that with the discovery of this neuron star is it not a possibility that 'dark mater' does not exist, merely, the 'missing matter' is other undiscovered matter, like this star?
I am not an astronomer either, but I think that it is the case.


Do you think there are discoveries that are steps in the wrong direction?
Discovery of atomic bomb comes to my mind.


PS - Is there any evidence of hydrogen coming from this neutron star?

I don't know if this particular NS has Hydrogen coming out, but so far NS showed up with planets, hydrogen atmosphere,enormous magnetic fields (how do you get it from neutrons?), etc.
I wonder if our picture of Neutron Stars is correct ( I mean, do they deserve to be called Neutron Stars?)

antoniseb
2005-Jul-14, 12:56 PM
Originally posted by Svemir@Jul 14 2005, 05:39 AM
I wonder if our picture of Neutron Stars is correct ( I mean, do they deserve to be called Neutron Stars?)
When they were first imagined, some of the subtleties of their structure were not thought through, but even so, the vast majority of their mass seems to be in the form of neutrons (as opposed to atoms). If you think there is a better name, please feel free to try and create one. Sometimes the term 'Compact Object' is used to refer to either a neutron star or a black hole. 'Stellar Cinder' is used in the same capacity by some. At the moment, we understand them to have complexities, but we understand what the term means.

lswinford
2005-Jul-14, 01:22 PM
Yes, indeed. Perceptions are changing.

And this discovery is an important step in the right direction.


Certainly no fan, but Richard Dawkins, the evangelist of evolution famous for the "selfish gene", recently commented that the universe may be "too queer" to really understand (http://news.bbc.co.uk/1/hi/sci/tech/4676751.stm).

I suspect that there's room for disagreement. I suspect that, if the long history of science is any indication, that we've got more than a few impossible surprises in store for us. I did like the way Dawkins described things though, that we are in a "middle world". So there's the sub-atomic world, with its quirks and oddities, and the larger world of cosmologists and we stand in the middle: "Middle world is the narrow range of reality that we judge to be normal as opposed to the queerness that we judge to be very small or very large." An interesting correlary it seems to thesis joined with antithesis equalling synthesis, which then becomes either a thesis or antithesis generating still another synthesis in a long and amazing chain of human understanding.

Oliver's ideas obviously are an antithesis for those of others here, but perhaps they help someone, at some crucial time, to make an important synthesis that moves us forward. Let him speak.

antoniseb
2005-Jul-14, 01:29 PM
Originally posted by lswinford@Jul 14 2005, 01:22 PM
perhaps they help someone, at some crucial time, to make an important synthesis that moves us forward. Let him speak.
Perhaps they impare someone at some crucial time and prevents a move forward... Let him follow our rules, and speak his deceptions on his own website.

wstevenbrown
2005-Jul-14, 03:40 PM
Almost everyone's perception of neutron stars seems to be locked into the journalistic description of a big ball of neutrons. First, in any particular case, it's not that simple. Second, there is considerable variety among NS based on progenitor mass and composition, as well as the surrounding environment.

To clarify: In the first seconds after the onset of a core-collapse Supernova, the core temperature is OOM 10 exp 10 Kelvin. The neutronization of the former nuclear matter of the star 'cools' this, on a timescale of hours, to a mere 1.5 exp 6 Kelvin, by two mechanisms. First, the reaction itself is endothermic-- it subtracts heat in order to create the neutrons. Second (and this part is really counterintuitive), the reaction produces neutrinos, which carry away heat as kinetic energy, either by escaping, or by pushing on the outer envelope of the star, which hadn't had time to collapse into the core and participate in the neutronization reaction. What is this pushing? Haven't we been taught that neutrinos are so non-reactive they can go through light-years of matter without reacting? True, at normal densities of matter. But a neutronized core is not normal. Picture an object less than 22 Km in diameter which is so dense that the mean free path (distance between collisions) of neutrinos is only thirty meters . The push of the neutrinos blows off almost all of the stellar envelope, creating the SN optical flash, as the expanding hot gas increases its surface area enough to be visible from afar.

What's left is the bag of neutrons, at a temperature OOM 1.5-2 X 10 exp 6 Kelvin, which is spinning very rapidly-- remember that the rotational momentum of the progenitor star must be conserved. It has an atmosphere of ionized normal matter, whose thickness is only a few meters.

Spinning ions make the resultant NS have a (relatively small) magnetic field. For a while, things are relatively stable, as the SN shell expands, sweeping the surrounding medium with it. After 50 KYr or less, the planetary nebula has dissipated into the interstellar medium, and gravitational capture (accretion) of normal matter can start.

Here is where you can win your Nobel Prize. During the long fall down the very steep gravitational well, the accreting matter is ionized before it can reach the surface. What happens to the separated charges under the influence of a spinning magnetic field? We dunno. What we know is that accretion disks of stalled infalling matter form, which probably have a magnetic field of their own. Apparently only about half, or a bit less, of the infalling matter is accreted-- the rest is blown off as polar (jet) winds and equatorial (disk) winds. Everything after that is model-dependent speculation.

The visible result is that older neutron stars are cooler (less than 100,000K), and rotate much more slowly. Precisely how the infalling matter converts kinetic energy into rotational slowdown (and cooling) will be under 'spirited debate' for decades to come.

I wish I had time to figure this all out! Best regards-- Steve

lswinford
2005-Jul-15, 11:40 PM
And, if I remember the picture correctly, if there is a (magnetic) polar jet or hot spot to vent, and it happens to be somewhat pointed into our field of reception, we call it a pulsar, from the rhythmic radio pulses we might hear.

antoniseb
2005-Jul-16, 12:17 AM
Originally posted by lswinford@Jul 15 2005, 11:40 PM
And, if I remember the picture correctly, if there is a (magnetic) polar jet or hot spot to vent, and it happens to be somewhat pointed into our field of reception, we call it a pulsar
No, not from the polar jet. That would not sweep around every few milliseconds, but instead be a relatively constant flow. We'd call THAT a micro-quasar. We think pulsars have the Earth near their magnetic equitorial plane.

Nereid
2005-Jul-22, 05:56 PM
Originally posted by wstevenbrown@Jul 14 2005, 03:40 PM
Almost everyone's perception of neutron stars seems to be locked into the journalistic description of a big ball of neutrons. First, in any particular case, it's not that simple. Second, there is considerable variety among NS based on progenitor mass and composition, as well as the surrounding environment.

To clarify: In the first seconds after the onset of a core-collapse Supernova, the core temperature is OOM 10 exp 10 Kelvin. The neutronization of the former nuclear matter of the star 'cools' this, on a timescale of hours, to a mere 1.5 exp 6 Kelvin, by two mechanisms. First, the reaction itself is endothermic-- it subtracts heat in order to create the neutrons. Second (and this part is really counterintuitive), the reaction produces neutrinos, which carry away heat as kinetic energy, either by escaping, or by pushing on the outer envelope of the star, which hadn't had time to collapse into the core and participate in the neutronization reaction. What is this pushing? Haven't we been taught that neutrinos are so non-reactive they can go through light-years of matter without reacting? True, at normal densities of matter. But a neutronized core is not normal. Picture an object less than 22 Km in diameter which is so dense that the mean free path (distance between collisions) of neutrinos is only thirty meters . The push of the neutrinos blows off almost all of the stellar envelope, creating the SN optical flash, as the expanding hot gas increases its surface area enough to be visible from afar.

What's left is the bag of neutrons, at a temperature OOM 1.5-2 X 10 exp 6 Kelvin, which is spinning very rapidly-- remember that the rotational momentum of the progenitor star must be conserved. It has an atmosphere of ionized normal matter, whose thickness is only a few meters.

Spinning ions make the resultant NS have a (relatively small) magnetic field. For a while, things are relatively stable, as the SN shell expands, sweeping the surrounding medium with it. After 50 KYr or less, the planetary nebula has dissipated into the interstellar medium, and gravitational capture (accretion) of normal matter can start.

Here is where you can win your Nobel Prize. During the long fall down the very steep gravitational well, the accreting matter is ionized before it can reach the surface. What happens to the separated charges under the influence of a spinning magnetic field? We dunno. What we know is that accretion disks of stalled infalling matter form, which probably have a magnetic field of their own. Apparently only about half, or a bit less, of the infalling matter is accreted-- the rest is blown off as polar (jet) winds and equatorial (disk) winds. Everything after that is model-dependent speculation.

The visible result is that older neutron stars are cooler (less than 100,000K), and rotate much more slowly. Precisely how the infalling matter converts kinetic energy into rotational slowdown (and cooling) will be under 'spirited debate' for decades to come.

I wish I had time to figure this all out! Best regards-- Steve
Excellent summary steve! :D

It may indeed turn out that most NS are solitary ... unless they're young or close, we'd only come across them by pure luck (e.g. in MACHO or OGLE).

Perhaps NS in binaries are rare (except in globular clusters, where lots of NS in binaries would be expected, unless the NS were flung out!), but if an NS has an active accretion disk, it's quite likely they'll be 'seen' - all that hard EM!

Can an NS feed from a nice, fat, long-term accretion disk? With the right sort of companion, sure.

So what are accretion disks? What physics do we need to model them?

It's not hard to see why this is a 'hot' area in astrophysics - full MHD with densities, pressures, temperatures, magnetic fields, ... all spanning many OOM. And while our most powerful particle colliders may probe the sorts of more exotic regimes in such disks, our colliders are for trivial numbers of particles, and can't even begin to get us answers on large-scale behaviour of such disks.

Nick4
2005-Jul-27, 03:27 AM
That looks like a cool discovery.