Dark matter, dark energy

[Larry Turner]

I'm wondering if the universe has different sized black holes, and that there may exist a multitude of very small black holes. The black holes we've discovered in the center of galaxies indicate the existance of black holes. Perhaps there are black holes of a smaller size spread through the universe that we have not been able to detect. They would be very difficult to observe. They could be the source of the dark matter, and possibly dark energy, that we have been unable to identify.

[makc]

but then there would be some process that pushes normal matter into collapse, and tiny fraction of what remains visible should also collapse pretty soon?

[Nereid]

It's an interesting idea, and has (I think) been investigated by various astronomers.

However, black holes (BH) won't do as a possible candidate for dark energy (DE), because they'd behave the wrong way, in a GR sense - 'dark energy' is a shorthand for the observed acceleration of expansion; BHs would be a form of matter, and so would produce a deceleration.

There are several bounds one can put on any distribution of small (or not so small) cosmic BHs, and makc has pointed to one.

Others include:

* if there were lots of small ones, early in the history of the universe, then many of them would be evaporating in bursts of gammas about now; such a signature would be quite distinctive, that we don't see such, in the gamma-ray sky, means there can be rather few such BHs (and far too few to account for dark matter (DM)).

* if there were enough big ones (super-massive BHs - SMBH), they'd've made their presence felt though accretion of (ordinary) matter, and we'd see lots of quasars and mini-quasars throughout rich clusters of galaxies and in the halos of (most) normal galaxies. We don't, so there can't be enough of those kinds of SMBH to make up DM.

* if they were stellar-mass BHs, of even Jupiter-mass BHs, they'd have been detected by one or more of the local gravitational lensing surveys, such as MACHO or OGLE. They weren't, so there aren't enough of them ... this is the same technique that was used to show that there can't be enough rogue Jupiters, or dead stars, floating around in the Milky Way halo, to account for the DM in that halo.

This still leaves so-called IMBH (intermediate BH), with masses of a few thousand sols, or some highly contrived mass distribution of BHs ...

[Superdoc]

Recent observation of Supernova explosions, if they had observed thru telescope, they would've known if the explosion transformed to either blackhole or Neutron star which shows if the star is visible as neutron star if not does that mean it has transformed into a blackhole which is not visible from huge telescopes?

[Nereid]

Recent observation of Supernova explosions, if they had observed thru telescope, they would've known if the explosion transformed to either blackhole or Neutron star which shows if the star is visible as neutron star if not does that mean it has transformed into a blackhole which is not visible from huge telescopes?

Yes, and no.

Supernovae which are of the 'core collapse' kind - a massive star whose central fusion fires are no longer able to keep going (and support the star against gravitational collapse) - will result in either a neutron star (thought to be much more likely) or a black hole. If the star which went supernova was not in a binary, then it is unlikely that anything will be seen afterwards*, except if we are in line with the beams of any neutron star (isolated neutron stars that we do not see as pulsars are almost invisible, even if they are quite close to us).

If the core collapse supernova was one star of a binary, then the remaining neutron star or black hole would (likely) leave a very clear signature for astronomers ... a high-mass x-ray binary, for example.

The other kind of supernova (Type Ia) is where a white dwarf acquires enough mass (hydrogen), from its companion, to detonate; there is neither a neutron star nor a black hole left ... all that's left of the star is an expanding shell of (mostly) 'unburned' oxygen and the heavier products of the carbon and oxygen fusion that 'blew' the star up.

*other than the expanding shell of very hot gas/plasma, some of which are among the most beautiful images displayed in APOD, the Veil Nebula, for example.

[harry]

Hello All

Supernova

Neried said

Supernovae which are of the 'core collapse' kind - a massive star whose central fusion fires are no longer able to keep going (and support the star against gravitational collapse) - will result in either a neutron star (thought to be much more likely) or a black hole. If the star which went supernova was not in a binary, then it is unlikely that anything will be seen afterwards*, except if we are in line with the beams of any neutron star (isolated neutron stars that we do not see as pulsars are almost invisible, even if they are quite close to us).

Its not as simple as you say

The process is a bit more complicated.

The star at this phase has its solar envelope enlarged.

The Fe build up that has taken Gyrs to form is broken down by fission chain reactions to He and than H. This triggers fusion chain reactions tranfoming H to Neutrons that rejuvinate the core. The chain reactions release the energy required to explode the solar envelope leaving behind a rejuvinated Neutron core. The size of the Neutron core will determine the extent of the EM/G fields creating an event horizon preventing EMR from escaping.

This is one option and there are many variations to it.

[makc]

ha ha, harry, you are asking for it...

[Nereid]

Hello All

Supernova

Neried said

Supernovae which are of the 'core collapse' kind - a massive star whose central fusion fires are no longer able to keep going (and support the star against gravitational collapse) - will result in either a neutron star (thought to be much more likely) or a black hole. If the star which went supernova was not in a binary, then it is unlikely that anything will be seen afterwards*, except if we are in line with the beams of any neutron star (isolated neutron stars that we do not see as pulsars are almost invisible, even if they are quite close to us).

Its not as simple as you say

The process is a bit more complicated.

The star at this phase has its solar envelope enlarged.

The Fe build up that has taken Gyrs to form is broken down by fission chain reactions to He and than H. This triggers fusion chain reactions tranfoming H to Neutrons that rejuvinate the core. The chain reactions release the energy required to explode the solar envelope leaving behind a rejuvinated Neutron core. The size of the Neutron core will determine the extent of the EM/G fields creating an event horizon preventing EMR from escaping.

This is one option and there are many variations to it.

harry, would you mind letting us all know where you got this summary from? I imagine it's several different sources, because it seems to me to contain a mixture of pretty standard stuff, mis-statements (or simple mis-understandings, like "The Fe build up that has taken Gyrs to form"), and wild nonsense (or pseudo-science).

I'm particularly interested to see what papers this can be traced to: "the extent of the EM/G fields creating an event horizon preventing EMR from escaping"

[harry]

Hello Neried

What I posted is quite general info.

I can just google for th info.

A person of your ability should be able to look it up.

Its nothing new.

I'm very surprised at the lack of info some of you have.

Neried I have given you one option.

In your statement you have a core collapse. Please explain. How does a core colapse into a Neutron Core.


Hello MakC

Laterly you have been sitting on the fence. Why?

[makc]

Hello MakC

Laterly you have been sitting on the fence. Why?

I guess the answer Nereid would give you is my lack of knowledge I am very simple guy, my profile is computer science (which is math, but neither physics nor astronomy). My current understanding of relativity (thing I posted above you probably refer to) is limited, since I had no time to explore the meaning behind some complex math constructions they use. But there are basics that I like to think I do understand, it will suffice to say I can derive things like SR speed addition law from the scratch or explain, or actually draw space curvature in case of accelerated particle (I even started some flash tutorial on that subject once, but never finished it). So I cannot really say that I have an understanding strong enough to debate things like space inflation (which doesn't stop me from doing so, but ) BUT the way some people try to paint this thing conceptually does NOT make sense to me right away, given very basic things I know.....

To sum up, since Nereid admins this board and expects anyone who does not agree to whatever she says on subject, to PROVE THEMSELVES WITH MATH, I try to keep quitet and obey the law, but sometimes my alter ego makes its way out.

[Dutchman]

I'm wondering if the universe has different sized black holes, and that there may exist a multitude of very small black holes. The black holes we've discovered in the center of galaxies indicate the existance of black holes. Perhaps there are black holes of a smaller size spread through the universe that we have not been able to detect. They would be very difficult to observe. They could be the source of the dark matter, and possibly dark energy, that we have been unable to identify.

Basically yes there are many different sizes for black holes out there. These are generally differentitated between by what created the black hole. Most black holes are measured in size by the number of solar masses (mass of our own local star the Sun) that they seem to posses as measured by their gravitational pull. The general consensus up until the last that I heard is that black holes are "usually" formed by stars, that if I remember correctly are at least 1.5 times the solar mass, collapsing and producing a supernova. Black holes as of yet are divided in categories based on their mass, or gravitational effect that they produce on neighboring objects. There are also the supermassive black holes that have been found to exist at the center of a good number of galaxies out there. Last I hear they haven't pinned down a specific method of formation, but there are some theories out there that I'll leave to you to find.

As far as tiny black holes, there was some speculation a few years ago that miniature black holes are being formed all the time on the out skirts of our atmosphere as a result of collisions between our atmosphere and cosmic rays (high speed atomic nuclei emitted from the Sun). This remains just a theory since these black holes have extremely small mass and are of a particular interest to the field of quantum mechanics.

Could black holes be the source behind dark energy and dark matter? I'll have to agree with most of the others that have already posted here, no. There is still a lot to be learned of black holes, but one thing that I can tell you is that black holes generally are composed of matter, not dark matter. Dark matter is thought to be a form of matter that was created during the big bang. The interesting thing about dark matter is that it is spread out fairly uniformly throught most galaxies, but not through the universe. The part that is interesting about dark matter in galaxies is that it has not followed the tendencies of the rest of the matter in the galaxy to form up into large packets under the influence of gravity. However, dark matter has been indirectly observed through it's lensing effects from the gravity that it produces. This means that there are large chunks of uniformly distributed dark matter out there that produces a gravitational effect, but does not experience a gravitational pull as regular matter does. By and large dark matter plays a fairly relaxed role in our universe. It does not even react stronly with electromagnetic waves, which is why it can only be observed indirectly as of yet. That said, up until the time that a black hole begins breaking down or "evaporating" its only output is Hawking radiation which consists of matter and antimatter that has formed along the outskirts of the black hole's event horizon, which is not a form of dark matter. As for dark energy, it has the effect of repeling objects with mass whereas black holes are largely governed by gravity which attracts objects which posses mass, and also light.

Hope that lengthy answer provides some clarification.

[goredsox]

Okay, at the risk of inflaming everyone's passions, I need to ask a very simple question about dark energy. I will make a series of statements, to the best of my ability, followed by a question.

1. Immediately following BB, space inflated rapidly, causing the universe to have dimensions of billions of light years in a fraction of a second.
2. This was possible because matter did not accelerate beyond the speed of light, space between matter inflated.
3. The universe has been expanding ever since this rapid inflationary epoch, albeit more slowly.
4. Multiple independent observations confirm that the rate of expansion is accelerating.
5. The fact of this acceleration has been used to deduce the existence of dark energy, which presumed to act somewhat like the opposite of gravity, i.e. to repel objects with mass from each other, and cause actual acceleration of masses.
6. Carefully note that in the above summary I have drawn a distintion between inflation, in which space inflated without the acceleration of objects with mass, and expansion, in which objects with mass are actually accelerating.

Here comes the question. Lads and Lasses -- please answer in all sincerity. How do we know that space is currently EXPANDING and not INFLATING? Because if it is inflating there is no acceleration of mass, and hence no need for dark energy?

<<<I will now duck to avoid the coming slings, arrows, and tomatoes>>>

[harry]

Hello goresox

you said

Here comes the question. Lads and Lasses -- please answer in all sincerity. How do we know that space is currently EXPANDING and not INFLATING? Because if it is inflating there is no acceleration of mass, and hence no need for dark energy?

Space itself does not expand or contract.

Parts within the universe do undo go expansion and contraction depending of their evolutionary phase.

Stars show this process.

Galaxies show this process as they evolve. Elliptical to spiral and spiral to elliptical a process depandent of the size and activity of the neucleon.

As for the universe expanding and contraction at the same time, i cannot see it as probable.

You need to look at the obseravtions, deep field and close images to observe the movements and actual grouping together of galaxies.

[GOD]

I'm wondering if the universe has different sized black holes, and that there may exist a multitude of very small black holes. The black holes we've discovered in the center of galaxies indicate the existance of black holes. Perhaps there are black holes of a smaller size spread through the universe that we have not been able to detect. They would be very difficult to observe. They could be the source of the dark matter, and possibly dark energy, that we have been unable to identify.

Your guess about what dark matter being tiny is correct, however it's not tiny black holes. It's simply matter that's smaller and vibrating faster than we can currently detect.

[Nereid]

I'm wondering if the universe has different sized black holes, and that there may exist a multitude of very small black holes. The black holes we've discovered in the center of galaxies indicate the existance of black holes. Perhaps there are black holes of a smaller size spread through the universe that we have not been able to detect. They would be very difficult to observe. They could be the source of the dark matter, and possibly dark energy, that we have been unable to identify.

Your guess about what dark matter being tiny is correct, however it's not tiny black holes. It's simply matter that's smaller and vibrating faster than we can currently detect.

I haven't heard of such an idea, nor read of any such in the literature; do you have a paper you can cite where we can read more?

[makc]

god is not bound by peer reviewed papers

[Nereid]

god is not bound by peer reviewed papers

That may be so.

However, us mere mortals are limited wrt scientific insights to just such (or stuff that can be traced back to such), at least on this forum.

[makc]

mmm it's just you were talking to GOD so I thought I would point that out....

[Nereid]

mmm it's just you were talking to GOD so I thought I would point that out....

Which one?

Shiva? Buddha? Yahwey? Guaranteed Overnight Delivery? Flying Spaghetti Monster?

[makc]

This one....

P.s.: I have god faq in my sig on another forum.

[Nereid]

Okay, at the risk of inflaming everyone's passions, I need to ask a very simple question about dark energy. I will make a series of statements, to the best of my ability, followed by a question.

1. Immediately following BB, space inflated rapidly, causing the universe to have dimensions of billions of light years in a fraction of a second.
2. This was possible because matter did not accelerate beyond the speed of light, space between matter inflated.
3. The universe has been expanding ever since this rapid inflationary epoch, albeit more slowly.
4. Multiple independent observations confirm that the rate of expansion is accelerating.
5. The fact of this acceleration has been used to deduce the existence of dark energy, which presumed to act somewhat like the opposite of gravity, i.e. to repel objects with mass from each other, and cause actual acceleration of masses.
6. Carefully note that in the above summary I have drawn a distintion between inflation, in which space inflated without the acceleration of objects with mass, and expansion, in which objects with mass are actually accelerating.

Here comes the question. Lads and Lasses -- please answer in all sincerity. How do we know that space is currently EXPANDING and not INFLATING? Because if it is inflating there is no acceleration of mass, and hence no need for dark energy?

<<<I will now duck to avoid the coming slings, arrows, and tomatoes>>>

Interesting question!

Here's a few words that attempt to define the scope of the question (and the preamble) a little further.

'Inflation', when used in modern cosmology, refers to a specific class of 'add on' theory to GR, involving '(an) inflaton field(s)'; the only time any such fields are postulated to have an observable effect on the universe we live in is very early on (per your point #1). Putting this another way, AFAIK, there are no postulated 'inflaton fields' for (comoving time) after the surface of last scattering (when the CMB streamed free).

'Acceleration' is a tricky thing, in GR, more tricky than mere 'expansion'. For example, your points #2, 5, and 6 are somewhat inaccurate wrt 'expansion' ('cold' matter does not move, wrt the universal expansion, other than due to 'local' causes such as a supernova explosion or tidal forces of a nearby galaxy). This can be seen, for example, in the Sachs-Wolfe effect; basically, even with (GR) non-accelerated expansion, matter just goes along for the ride.

'Dark energy' is, essentially, just a shorthand for what has been observed, in analyses of the light-curves of distant supernovae, in the CMB, and very recently, in an analysis of the gravitational lensing of distant sources by rich clusters (though this sets an upper limit, rather than estimates DE). In this sense, your point #5 is a tautology.

The really exciting questions about DE (well, some really exciting questions) concern its nature. For example, is it 'just geometry', like the rest of GR (lambda, or the cosmological constant)? Or does it vary by (co-moving) time?

And all this sprang from the work of two independent teams who were studying distant (high-z) supernovae, trying to detect a deceleration of the rate of expansion, as predicted by a straight-forward application of GR to the universe as a whole!

Cue the J.B.S. Haldane quote ...

[GOD]

I'm wondering if the universe has different sized black holes, and that there may exist a multitude of very small black holes. The black holes we've discovered in the center of galaxies indicate the existance of black holes. Perhaps there are black holes of a smaller size spread through the universe that we have not been able to detect. They would be very difficult to observe. They could be the source of the dark matter, and possibly dark energy, that we have been unable to identify.

Your guess about what dark matter being tiny is correct, however it's not tiny black holes. It's simply matter that's smaller and vibrating faster than we can currently detect.

I haven't heard of such an idea, nor read of any such in the literature; do you have a paper you can cite where we can read more?

No, literature of manner you're asking for does not exist, because this fact about dark matter hasn't been discovered yet. Like most things still to be discovered, literature currently available only exists in the form most would consider to be rantings of individuals who are out of their mind.

[Superdoc]

Nereid said

The other kind of supernova (Type Ia) is where a white dwarf acquires enough mass (hydrogen), from its companion, to detonate; there is neither a neutron star nor a black hole left ... all that's left of the star is an expanding shell of (mostly) 'unburned' oxygen and the heavier products of the carbon and oxygen fusion that 'blew' the star up.

have telescopes observed and sent evidence images of a white dwarf eating up the remains of a star after it dies or is this another dark matter?[/quote]

[harry]

Hello Superdoc

Good question

[Nereid]

mmm it's just you were talking to GOD so I thought I would point that out....

But is GOD a god? And if so, what other names does it have?