'First Light' and the Universe's early years

[DaveC426913]

I've just returned from a University Cosmology lecture that introduced a phenomenon called 'First Light'. It appears to be coming from Hubble observations over the last 5-10 years (so, very recent). I have never heard of such a theory.

The theory says that the Big Bang created all the H and He in the universe in the first three minutes, which then floated around in gaseous form for hundreds of thousands of years.

Now, apparently, gaseous hydrogen does not clump into masses on galactic scales, which means the galxies could not have been formed from this initial state. In other words, we could not get here from there.

The only way hydrogen can clump on that scale is in a plasmic state (protons stripped of their electrons). When a plasma, H clumps nicely at that scale.

So, something happened, somewhere in the first billion years of the universe's life. Some form of energy swept across the universe, converting all the H from gas to plasma. This also turned the universe opaque, since plasma transmits light poorly. This is corroborated by the very deep space observance of some sort of opaque shell at the 12.5Gy distance.

In this plasmic state, the H was able to clump on galactic scales, subsequently converting back to gaseous state again, and leaving a universe the way we see it now.


Has anyone heard of such a thing?

 

[Turbot]

Who was the lecturer? Was it one of these folks?

http://www.physics.uci.edu/Cosmology/

 

[Garth]

Dave,
I think you are just a little confused.

First light refers to the epoch of first stars that form in the universe.

After the initial brilliance of the Big Bang the universe would have gradually cooled off and become dark, even at the surface of last scattering (of the CMB) the universe would have only been glowing dimly in the deep red end of the spectrum. The wavelength of peak emission would have been about 10,000 Angstroms in the infra-red. This period is called the 'Dark Ages'.

We infer that there must have been an initial population of probably very massive stars at an early period 20<z<10 called Population III stars. There was a lot of early re-ionisation in the cosmic medium and a lot of early high metallicity only produced in stars. The appearance of such PopIII stars is called 'First Light'.

There is a problem explaining how galaxies form, after the epoch of last scattering of the CMB as the Jean's mass is about 10⁶M_Solar possibly the mass of a large PopIII but not a galaxy, but before that epoch the Jean's mass would have been 10¹⁸M_Solar, the size of a galactic cluster.

Here non-interacting Dark Matter is brought into rescue the situation, it can begin to collapse before the epoch of last scattering, when the cosmic medium was still ionised and form gravitational wells into which the ordinary matter can fall. The process is modeled numerically and can be seen here amongst other web sites.

I hope this helps.

Garth

 

[DaveC426913]

Dave, I think you are just a little confused.

No, I am not confused. This was the lecture.

He did talk about very massive popIII stars, and speculated that their exotic novae might have been the cause of this wave of energy, but pointed out that they simply do not know what caused it.

 

[SpaceTiger]

He did talk about very massive popIII stars, and speculated that their exotic novae might have been the cause of this wave of energy, but pointed out that they simply do not know what caused it.

Yeah, it's not certain that Pop III stars are the dominant cause of reionization. The other potential contributor that gets a lot of attention is quasars, since we expect them to have been forming very rapidly during that epoch.

There's actually a bit of confusion in the astro community about the issue of reionization (this wave of energy), because we have two separate observations telling us that it should have occurred at different times. Analysis of WMAP data implies a very high redshift for reionization (~15), while observations of quasars in SDSS indicate a lot of neutral gas at z ~ 6. This may not actually be a conflict, since there's nothing that says reionization can't happen twice, but it certainly lends itself to less elegant theories.

 

[Garth]

There's actually a bit of confusion in the astro community about the issue of reionization (this wave of energy), because we have two separate observations telling us that it should have occurred at different times. Analysis of WMAP data implies a very high redshift for reionization (~15), while observations of quasars in SDSS indicate a lot of neutral gas at z ~ 6. This may not actually be a conflict, since there's nothing that says reionization can't happen twice, but it certainly lends itself to less elegant theories.

Perhaps two separate events? i.e. PopIII stars were the first objects to form, and being massive had very short lives, going 'hyper-nova' at z ~ 15, and then quasars forming from the BHs left behind finally firing up prior to z ~ 6?

Just a suggestion.

Garth

 

[SpaceTiger]

Perhaps two separate events? i.e. PopIII stars were the first objects to form, and being massive had very short lives, going 'hyper-nova' at z ~ 15, and then quasars forming from the BHs left behind finally firing up prior to z ~ 6?

This is what I meant by:

This may not actually be a conflict, since there's nothing that says reionization can't happen twice

 

[Garth]

This is what I meant by:

I'm glad we agree - so the task in hand is to determine the distribution and Initial Mass Function of the Pop III stars that will deliver the observed distribution of early high metallicity and re-ionization?

How does the total baryon density and initial metallicity required to produce this IMF compare with that determined from the cosmological model?

Garth

 

[SpaceTiger]

I'm glad we agree - so the task in hand is to determine the distribution and Initial Mass Function of the Pop III stars that will deliver the observed distribution of early high metallicity and re-ionization?

How does the total baryon density and initial metallicity required to produce this IMF compare with that determined from the cosmological model?

Models of Pop III stars are too crude to make this comparison as of yet. Aside from the IMF (which is extremely difficult to predict, even locally), one also has to consider star formation efficiency and feedback effects. There's a lot of research going on in this area right now, but we're a long way from constraining cosmology with it.

 

[Garth]

Thank you ST.

What are the problems in the formation of stars with zero metallicity? Is it that they require rotation as well as very large masses?

Garth

 

[Intuitive]

I've just returned from a University Cosmology lecture that introduced a phenomenon called 'First Light'. It appears to be coming from Hubble observations over the last 5-10 years (so, very recent). I have never heard of such a theory.
The theory says that the Big Bang created all the H and He in the universe in the first three minutes, which then floated around in gaseous form for hundreds of thousands of years.
Now, apparently, gaseous hydrogen does not clump into masses on galactic scales, which means the galxies could not have been formed from this initial state. In other words, we could not get here from there.
The only way hydrogen can clump on that scale is in a plasmic state (protons stripped of their electrons). When a plasma, H clumps nicely at that scale.
So, something happened, somewhere in the first billion years of the universe's life. Some form of energy swept across the universe, converting all the H from gas to plasma. This also turned the universe opaque, since plasma transmits light poorly. This is corroborated by the very deep space observance of some sort of opaque shell at the 12.5Gy distance.
In this plasmic state, the H was able to clump on galactic scales, subsequently converting back to gaseous state again, and leaving a universe the way we see it now.
Has anyone heard of such a thing?

First off, I don't think an absolute (Void) (Edge) of space has ever been detected by Astronomers, Star systems are being found no matter how far we look out into the Universe, The better our telescopes become the more we find. (Deep Star Fields)

It's quite possible that the Universe always existed changing from one state to another eternally.

Maybe one day, When Telescopes become powerful enough we will find another Universe far far away from our own. But it would be incredably far away and very very dim, current Telescopes would not be powerful enough to detect a second Universe trillions and trillions of light years away.

But for now it is the (known) Universe that sets the limits to it size and edge.

We need better eyes in the sky.

Maybe when we link array some telescopes on the Moon with Earth base Telescopes we can collect enough light to prove the Universe has no real edge. It may even take a linked Telescope array the size of our Solar System.

I hoped that I helped.

 

[Turbot]

First off, I don't think an absolute (Void) (Edge) of space has ever been detected by Astronomers, Star systems are being found no matter how far we look out into the Universe, The better our telescopes become the more we find. (Deep Star Fields)

Yes, and the farther back we look, the more galaxies and quasars we find, generally with super-solar metallicities and masses equivalent to or often larger than that of the galaxies in our own neighborhood.

It's quite possible that the Universe always existed changing from one state to another eternally.

Indeed, although if you wish to explore an infinite steady state universe, the adherents of the Standard Model will scoff and call you names. If you dare to explore the possibility that the universe did not begin 13.7Gy ago in a Big Bang, you will find yourself in a rather lonely endeavor.

Maybe one day, When Telescopes become powerful enough we will find another Universe far far away from our own. But it would be incredably far away and very very dim, current Telescopes would not be powerful enough to detect a second Universe trillions and trillions of light years away.

By definition, our universe contains all that exists, and our visible universe contains all that we can possibly observe from our vantage point. There is a limit to how much we can see. That limit may be shown to us as we observe more and more distant objects that are redshifted into the infrared and ultimately into the CMB. Olber's Paradox does not seem to be much of a problem if EM from distant objects are redshifted into lower and lower frequencies. If you look at the night sky at the appropriate frequencies, the sky is brightly and pretty uniformly illuminated.

 

[SpaceTiger]

What are the problems in the formation of stars with zero metallicity? Is it that they require rotation as well as very large masses?

The problems that I'm aware of include the fragmentation of the initial molecular cloud (important for determining the IMF), mass loss due to stellar winds/rotation and, of course, the subsequent supernovae. Note that it also depends on the environment in which the stars are forming. A strong UV flux can ionize the gas in protogalaxies and prevent star formation, while a strong X-ray flux can increase the rate of molecular hydrogen formation and actually induce star formation. There's much literature on the subject and I'm most certainly not doing it justice. If I get the time, I'll try to find a nice review paper and put it in the Classic Papers sticky.

 

[SpaceTiger]

First off, I don't think an absolute (Void) (Edge) of space has ever been detected by Astronomers,

He's referring to the fact that we observe an extremely high column density of neutral hydrogen gas at redshifts ~6. Neutral hydrogen has a nasty habit of absorbing the light we use to observe galaxies and quasars, so effectively blocks off the very distant universe from our view.

Star systems are being found no matter how far we look out into the Universe, The better our telescopes become the more we find. (Deep Star Fields)

Our telescopes are limited by brightness, not distance, so it's not necessarily true that star systems are being observed as far as we're theoretically capable of observing. The brightness you would expect at a certain distance depends on your cosmological model. There is certainly a maximum redshift at which stars/galaxies have been observed so far (~6.5), but it's still unclear as to whether that will become a long-term boundary.

It's quite possible that the Universe always existed changing from one state to another eternally.

I don't think we could ever rule out the possibility that the universe simply shifted from one state to another at some point in the past. It's more of a philosophical point than a scientific one.

Maybe one day, When Telescopes become powerful enough we will find another Universe far far away from our own. But it would be incredably far away and very very dim, current Telescopes would not be powerful enough to detect a second Universe trillions and trillions of light years away.

Not really, the universe is only of order 10 billion years old, so we can't see light from objects more distant than about 10 billion light years. There are some caveats to this, but none of them involve observations of stars or galaxies at the distances you're describing.

 

[Garth]

The problems that I'm aware of include the fragmentation of the initial molecular cloud (important for determining the IMF), mass loss due to stellar winds/rotation and, of course, the subsequent supernovae. Note that it also depends on the environment in which the stars are forming. A strong UV flux can ionize the gas in protogalaxies and prevent star formation, while a strong X-ray flux can increase the rate of molecular hydrogen formation and actually induce star formation. There's much literature on the subject and I'm most certainly not doing it justice. If I get the time, I'll try to find a nice review paper and put it in the Classic Papers sticky.

Thank you ST. I'll look forward to that.

At the recent monthly meeting of the Royal Astronomical Society we had a lecture by Dr Danny Lennon -The Magellanic Clouds: Laboratories for understanding Massive Stars. He made the point in passing that it was very difficult to understand how very massive stars - referring to Pop III - could form without rotation.

I would like to understand how that worked as it seemed counter-intuitive.

Garth

 

[rtharbaugh1]

what do we mean when we say the Universe has an age?

the universe is only of order 10 billion years old, so we can't see light from objects more distant than about 10 billion light years

I have been wondering about the idea that the universe has an age. Given the space-time deformations of special and general relativity, isn't it true that the universe, whatever that is, must have different ages for different observers? Since there is no preferred referance frame, shouldn't we be careful to state what reference frame we are using? But then I suppose we could just assume we are talking about the reference frame common to observers here on Earth in the 21st century.

And yet, we are talking after all about cosmological events at the horizon of our powers of observation, regions where acceleration is significant. Even closer to home, in the black hole now thought to be at the center of our own galaxy, regions near the event horizon must experience time quite differently from the rate we consider ordinary.

I am sure participants in this forum have considered these things. Is there an unspoken consensus?

Thanks,

Richard

 

[SpaceTiger]

I have been wondering about the idea that the universe has an age. Given the space-time deformations of special and general relativity, isn't it true that the universe, whatever that is, must have different ages for different observers?

It is indeed possible for that to be the case, but when homogeneity and isotropy are assumed (and/or observed), then the universe can be defined to have a single age.

Since there is no preferred referance frame, shouldn't we be careful to state what reference frame we are using? But then I suppose we could just assume we are talking about the reference frame common to observers here on Earth in the 21st century.

I'm implicitly referring to a reference frame stationary relative to the microwave background and yes, you're right that such a specification needs to be made for the age to be well defined. The Earth is not, actually, stationary relative to this frame.

And yet, we are talking after all about cosmological events at the horizon of our powers of observation, regions where acceleration is significant. Even closer to home, in the black hole now thought to be at the center of our own galaxy, regions near the event horizon must experience time quite differently from the rate we consider ordinary. I am sure participants in this forum have considered these things. Is there an unspoken consensus?

The consensus is as I gave above, but it really is just a matter of convention. This particular convention is by far the most convenient for doing cosmology, but you could consider an infinite number of reference frames in calculating the age of the universe for a particular observer. The reason we don't bother is that such frames tell us nothing more about cosmology, they only rescale what we already know...and in a messier way, because they will be observer-specific.

 

[turbo]

I have been wondering about the idea that the universe has an age. Given the space-time deformations of special and general relativity, isn't it true that the universe, whatever that is, must have different ages for different observers? Since there is no preferred referance frame, shouldn't we be careful to state what reference frame we are using? But then I suppose we could just assume we are talking about the reference frame common to observers here on Earth in the 21st century.

Even that has to be taken as a bit of a generalization. Every observer has his or her own "present" and resides at a time cusp such that wherever we look we are receiving information from the past. For instance, as we look out into space, we see farther and farther back in time in every direction. This is because our observations of distant objects is limited by the time observational information (in EM) takes to get from there to here. This effect is not limited to astronomical observations. If you could build a high enough tower in Minnesota and I could build one in Maine (to see each other around the curvature of the Earth), and I waved "hi" you would not see me waving in your present, but as I appeared 1/186 of a second in your past. This is because it's about 1000 miles (OOM guess here) between us and the visual information takes a finite amount of time to get from me to you. If you could wave back as soon as you saw me wave (REALLY good reflexes), I wouldn't see your acknowledging wave until 1/93 sec after I waved. That's close enough to "simultaneous" for practical purposes, but it should demonstrate that we each reside at our own personal "present".

 

[rtharbaugh1]

Thanks for the answers.
R

 

[Chronos]

Previous posts pretty much answer the question. Every observer has a personal clock that measures the 'age' of the universe. If you run the movie 'observable universe' in reverse, it 'shrinks' to zero size after a finite amount of time. However, not many few theorists believe it physically reaches such a state, just that existing theories fall apart right around the time the size of the universe appoaches the Planck scale. You have a similar situation when black holes form. They collapse until they almost, but not quite, become singularities... at least by our clock.

 

[rtharbaugh1]

Ah yes, the observable universe. That is something, isn't it. Deep field looks amazingly like near field, doesn't it? No edges in sight. We presume that an observer at the end of our visble universe would also find the same conditions, no end in sight from there either.

So, one must assume, the beginning also. Not a singularity after all, not a point, but only a little dot, small, but of some measurable size. Discrete. How discomforting, that maths should go where we cannot. No attainable zero point. A little door at the bottom of the rabbit hole, too small to pass through. One must always wonder. But perhaps it is best this way. We must keep our heads. Caution doesn't permit us to dive through the sphagetti strainer. There were the wars, and the black ships burning on the shelving shores. Many of us will never go home again.

But about that idea of the age of the universe relative to the CMBE, Space Tiger, I was wondering. Microwaves travel at light speed, where time is collapsed to, well, maybe just the Planck time anyway. I should think, relative to CMBE, the universe has hardly aged a bit, but is still brand spanking new. You travel close to the speed of light, and time, for you, hardly passes at all, isn't that it? In all our ages, the universe of microwaves has never changed.

Be well,

Richard

 

[SpaceTiger]

But about that idea of the age of the universe relative to the CMBE, Space Tiger, I was wondering. Microwaves travel at light speed, where time is collapsed to, well, maybe just the Planck time anyway. I should think, relative to CMBE, the universe has hardly aged a bit, but is still brand spanking new. You travel close to the speed of light, and time, for you, hardly passes at all, isn't that it? In all our ages, the universe of microwaves has never changed.

An individual photon does not experience time, this is true. In fact, it would be impossible to define a special frame in relation to the motion of this one photon because that photon has no "preferred" energy. Another way of saying this is that we can never achieve the speed of light so as to become stationary relative to this photon.

However, imagine instead that you have many, many photons moving around in space. How might one define a special frame that was "stationary" relative to this bath of photons? One possibility is to look for a frame in which their three-momenta are isotropically distributed. Such a frame does exist for the CMB and it turns out that the photon energy distribution in this frame is very close to a perfect blackbody. This is what I mean by "stationary" relative to the CMB. I'm not saying that one should move to a frame in which they're stationary relative to any or all of the particular photons contained within. That would be impossible.

 

[rtharbaugh1]

An individual photon does not experience time, this is true. In fact, it would be impossible to define a special frame in relation to the motion of this one photon because that photon has no "preferred" energy. Another way of saying this is that we can never achieve the speed of light so as to become stationary relative to this photon.

However, imagine instead that you have many, many photons moving around in space. How might one define a special frame that was "stationary" relative to this bath of photons? One possibility is to look for a frame in which their three-momenta are isotropically distributed. Such a frame does exist for the CMB and it turns out that the photon energy distribution in this frame is very close to a perfect blackbody. This is what I mean by "stationary" relative to the CMB. I'm not saying that one should move to a frame in which they're stationary relative to any or all of the particular photons contained within. That would be impossible.

Ah, I am delighted. However I am now having trouble imagining such a frame as special. Seems to me any old frame would do for the purpose you mention. Is there some evidence I have missed that local motion affects our view of CMBE?

Thanks,

Richard

 

[Garth]

Seems to me any old frame would do for the purpose you mention. Is there some evidence I have missed that local motion affects our view of CMBE?
Thanks,
Richard

Hi Richard! Our local motion does affect the CMB, it produces a dipole of strength around 10^-3 in the Planck spectrum.

One part of the sky looks (1 + 2x10^-3) times hotter than the diametrically opposite part of the sky.

We are moving towards the hotter part and away from the cooler part measured w.r.t. the surface of last scattering (SLS).

This dipole itself may be distorted by being lensed by a 'local' mass moving relative to us, in which case it would produce a quadrupole and octopole signal on the CMB at the 10^-5 level. This is at the level of the primordial anisotropies in the CMB being examined in the WMAP data. Indeed these large angle quadrupole and octopole signals are there and aligned orthogonal to our motion against the SLS. However the standard theory wishes they were not! - They should be arranged completely randomly across the sky.

A mystery to be solved that lies within your question!

You too Be Well!

Garth

 

[hellfire]

Regarding the sources of reionization as well as the question about an extended or a fast reionization, there are high expectations with the Square Kilomater Array and the Low Frequency Array. These are great engineering projects which should make it possible to detect very faint radio signals from the reionization epoch. The main observation (IIRC made by Rees some years ago) is that there should be a 21-cm line “radio background” which should contain the signature of the reionization sources. The basic mechanism is as follows. The spin temperature T_s (the fraction of atoms in the ground state and the excited state of the hyperfine levels of the neutral hydrogen) of the neutral intergalactic medium is coupled to the CMB due to absorption of CMB photons, which drive T_s towards T_CMB. However, it is also coupled to the kinetic energy of the IGM due to Lyman-α photon scattering and atomic collissions.

During the dark age and before the first reionization sources appear, the adiabatic expansion of space decreases the kinetic energy of the IGM, whereas the spin temperature is kept close to the CMB temperature due to the first coulping mechanism. As soon as the first reionization sources appear, the second coupling becomes dominant and drives the spin temperature towards the kinetic temperature of the IGM which was less than T_CMB. This causes a 21-cm absorption line. As the reionization sources evolve, the IGM is heated (by photoionization or shocks and collapse). The kinetic temperature of the gas increases and therefore also the spin temperatures increases and becomes T_s > T_CMB. This should make the 21-cm signal observable in emission. The line disappears when reionization is completed.

It seams that contamination by other radio sources makes it very difficult to observe the absorption line from earth, but it should be possible to observe the emission line with the SKA and the LOFAR. As the ionized bubbles grow and overlap, the 21-cm line should from a background with redshift anisotropies (due to its evolution during reionization) and angular anisotropies (regions near to the reionization sources). This is a very fascinating aspect of the current reseach in cosmology. LOFAR and SKA are very interesting projects (I highly recommed a visit to their websites) and we may be soon at the beginning of a new era of radio observations. What I do not exactly know is the difference in the signature of the first stars and the quasars in the 21-cm line, but I remember have read that these observations may shed light on that.

 

[Garth]

Thank you hellfire, that sounds very promising.
Of course the 21 cm lines from these different epochs will be red shifted considerably by different amounts and will be differentiated from one another.

Garth