Galaxy Formation - Science topic

Here are the answers to the questions related to galaxy evolution, stellar formation, and the cosmological constant:

### Answers on Galaxy Evolution

1. **What are the key processes that drive the evolution of galaxies over cosmic time?**

- Galaxy evolution is driven by a combination of processes including gravitational interactions, mergers, gas inflow and outflow, star formation, and feedback from supernovae and active galactic nuclei (AGN). These factors influence the structure, composition, and star formation rates of galaxies over time.

2. **How do mergers between galaxies influence their structure and star formation rates?**

- Galaxy mergers can trigger bursts of star formation due to the gravitational interactions that compress gas and dust. They often disrupt the existing structure of the galaxies, leading to the formation of elliptical galaxies from spiral galaxies and altering their overall dynamics.

3. **What role does dark matter play in the formation and evolution of galaxies?**

- Dark matter provides the gravitational scaffolding necessary for galaxy formation. It influences the rotation curves of galaxies, helps in the clustering of matter, and affects the dynamics of galaxy mergers and interactions, ultimately shaping the structure of galaxies.

4. **How do environmental factors, such as galaxy clusters, affect the evolution of individual galaxies?**

- In dense environments like galaxy clusters, galaxies experience interactions that can strip away gas (ram-pressure stripping), affect star formation rates, and lead to morphological transformations. Galaxies in clusters often evolve differently than those in isolated environments, typically becoming more passive over time.

5. **What are the observed differences in evolution between spiral and elliptical galaxies?**

- Spiral galaxies are characterized by ongoing star formation, a well-defined disk, and prominent spiral arms. In contrast, elliptical galaxies are generally older, with little to no new star formation, and exhibit a more spherical shape. Their differences result from their formation histories and environments.

6. **How does the metallicity of a galaxy influence its evolutionary path?**

- Metallicity affects star formation efficiency and the types of stars formed. High metallicity can lead to the formation of more stars with shorter lifespans, while lower metallicity environments tend to produce massive stars and more primitive stellar populations, influencing a galaxy's evolutionary trajectory.

7. **What mechanisms regulate star formation within galaxies at different evolutionary stages?**

- Star formation is regulated by factors like molecular gas density, temperature, turbulence, and feedback from existing stars (e.g., radiation pressure, supernovae). In early galaxies, gas accretion drives star formation, while in more evolved galaxies, feedback processes can suppress it.

8. **How do feedback processes from supernovae and active galactic nuclei impact galaxy evolution?**

- Feedback from supernovae can expel gas and regulate star formation, preventing overproduction of stars. AGN feedback can heat surrounding gas, preventing it from cooling and forming new stars. Together, these processes can shape the evolution of galaxies by influencing their star formation rates and gas content.

### Answers on Stellar Formation

1. **What are the primary conditions necessary for the formation of massive stars?**

- Massive stars form in dense regions of molecular clouds where conditions like high gas density, low temperatures, and sufficient mass are present to initiate gravitational collapse.

2. **How do variations in the interstellar medium (ISM) affect the efficiency of star formation?**

- The ISM's density, temperature, and composition determine how effectively gas can cool and collapse. High-density regions with low temperatures favor efficient star formation, while lower density or hotter regions may inhibit it.

3. **What role do magnetic fields play in the formation and evolution of stars?**

- Magnetic fields can influence the collapse of gas clouds by providing support against gravitational collapse. They also affect angular momentum transfer and outflows, which are critical for regulating star formation.

4. **How does competitive accretion contribute to the growth of stars in dense clusters?**

- In dense clusters, stars can compete for material from the surrounding gas. Stars that form in the center of a cluster can gather more material due to their stronger gravitational pull, leading to higher mass stars compared to those formed in less dense regions.

5. **What are the implications of stellar winds on the mass limits of forming stars?**

- Stellar winds can remove material from forming stars, limiting their maximum mass. For high-mass stars, strong winds can prevent further accretion once they reach certain mass thresholds.

6. **How does the initial mass function (IMF) relate to the processes of stellar formation?**

- The IMF describes the distribution of stellar masses in a population. It reflects the conditions and processes during star formation, with most stars forming at lower masses and fewer forming at higher masses, influenced by factors like gas density and temperature.

7. **What is the significance of Population III stars in the context of early galaxy formation?**

- Population III stars are the first stars formed in the universe, composed almost entirely of hydrogen and helium. Their formation and subsequent supernovae enriched the universe with heavier elements, influencing the formation of later stars and galaxies.

8. **How do simulations of star formation compare with observational data from young star clusters?**

- Simulations aim to replicate the conditions and processes of star formation, often matching observed data from young clusters. Discrepancies can arise due to simplifications in models, but advancements in simulations are improving their predictive power and alignment with observations.

### Answers on the Cosmological Constant

1. **What is the cosmological constant, and how does it relate to the expansion of the universe?**

- The cosmological constant (Λ) is a term in Einstein's field equations representing a constant energy density that fills space homogeneously. It accounts for the accelerated expansion of the universe, acting as a form of dark energy.

2. **How does the cosmological constant influence the evolution of large-scale structures in the universe?**

- The cosmological constant affects the rate of expansion, influencing the formation and growth of structures like galaxies and galaxy clusters. It alters the balance between gravitational attraction and repulsive expansion, shaping the large-scale structure of the universe.

3. **What evidence supports the existence of the cosmological constant in contemporary cosmology?**

- Evidence from observations of distant supernovae, the cosmic microwave background radiation, and large-scale structure surveys all indicate an accelerated expansion of the universe, consistent with a positive cosmological constant.

4. **How does the cosmological constant affect theories of dark energy and the fate of the universe?**

- The cosmological constant is often associated with dark energy, contributing to our understanding of the universe's fate. It suggests that the universe will continue to expand indefinitely, potentially leading to scenarios like the "Big Freeze."

5. **What are the implications of a varying cosmological constant for galaxy formation and evolution?**

- A varying cosmological constant could alter the rate of expansion and the dynamics of structure formation, leading to different rates of galaxy formation and evolution compared to a constant cosmological constant.

6. **How do different models of the cosmological constant compare with observations of cosmic microwave background radiation?**

- Models that include the cosmological constant align well with observations of the cosmic microwave background, which show fluctuations consistent with the density and expansion history predicted by ΛCDM (Lambda Cold Dark Matter) models.

7. **What challenges exist in reconciling the cosmological constant with quantum field theories?**

- The observed value of the cosmological constant is much smaller than theoretical predictions from quantum field theories, leading to the "cosmological constant problem." This discrepancy raises questions about the nature of vacuum energy and its influence on cosmic expansion.

8. **How does the cosmological constant factor into current debates about the accelerating expansion of the universe?**

- The cosmological constant is central to understanding the observed acceleration of the universe's expansion. Ongoing debates focus on whether this acceleration is due to a true constant or if alternative models of dark energy might better explain the observations.

Extraterrestrial life is hypothetical life which may occur outside Earth and which did not originate on Earth. Such life might range from simple prokaryotes (or comparable life forms) to intelligent beings and even sapient beings, possibly bringing forth civilizations which might be far more advanced than humanity. The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life in all its forms is known as astrobiology. https://en.m.wikipedia.org/wiki/Extraterrestrial_life

In fact, when searching for life in other planets, scientists follow the principle (follow the water), in order to reduce and limit the search process, not necessarily liquid surface water, but even the water in the ground because even the water under the surface of the earth can contain life, and indeed, because not only higher or sophisticated organisms need it, but even microorganisms, in our study there is what is called the water activity. Every microorganism needs this percentage when it is less than that, it cannot continue its life activities... So in order to be water exists, there must be an atmosphere that pushes it to the surface, as well as there is sufficient heat in the interior of the planet to keep water liquid underground. In addition, the existence of life is also related to the distance of the planet from the sun. In our solar system, the possibility of life was limited to an earlier time only on Mars because of the evidence of the presence of liquid water on its surface for long periods, and there may also be water under the surface due to its volcanic activity... In fact, research and studies are still ongoing to determine the harshest conditions in which a living creature can live in space, So scientists send water bears and they are the toughest creatures in terms of endurance on earth to explore that... On the other hand, what the creatures on the surface of the earth need may be different from others, this is very possible, because the organisms usually adapt to their surroundings and this is what we find with the microorganisms there whoever kills them is salt, and there are organisms that halophiles, the same is true of acid and heat, even there are organisms that live in volcanoes, did we ask ourselves why?? (my supervisor always said in the sense that they agreed to live in a very harsh atmosphere in order not to die). So from this, we conclude that it is possible to find forms of life in the harshest conditions in which we cannot expect them to exist... My sincere gratitude to everyone.

Dear Preston,

Intriguin view, thanks for sharing Vera Lima

We are speaking of the same hypersphere.

Why wouldn't time be essential? Why do you posit that it has to be created?

I chose to use The Simplest Model where time is always there and it times metric and dimensionality fluctuations that yield Universes. Fluctuations are governed by the Heisenberg Principle, which is supported by observations. So, that explains what was before and what will be after and that model is just fine with observations.

There is no need to create time with energy. That is a convoluted model which has no observational support of any kind and shouldn't be pursued.

To state that the intrinsic energy of a body in an Universe traveling at the speed of light is mc^2, is trivial, given that that energy was impacted in an impulse. That is no insight.

Insight is to understand that Gravitation is perpendicular to the direction of expansion and thus cannot have any work done or have any effect upon the expansion. That is what I concluded and that is what is consistent with observations.

I have to confess ignorance of your derivation. That said, it it that relevant since I agreed upon your conclusion E=mc^2 by considering that the Universe was accelerate to c impulsively. That is a very, very, very small part of the argument I created.

That is the problem I am trying to explain to you. Since all forces, include gravitation have no influence on the expansion and the expansion is timed by a Cosmological Time. So the hypersphere is a circle also on the 4D spacetime and it does not care upon the Universe content.

What you use in the current spacetime curvature has to do with the twisting of the local time. Just look at the double cross-sections, representing the Current Universe.

This is all irrelevant since the constant expansion means that Einstein's equations are fundamentally incorrect.

I derived a velocity and epoch dependent law of gravitation that is Quantum Mechanical, Relativistic.

I also provided a new model for matter, which is used to derive the Natural Laws. I also corrected Newtonian Dynamics with the introduction of the Hypergeometrical Force and corrected Newton Laws of Dynamics with the introduction of the Fundamental Dilator and the Quantum Lagrangian Principle.

Don't use a metric at all. The refutal of Einstein's Equations by the my discovery using the SDSS data shows that the geodesics paradigm is not to be used.

If you have an Algebraic Addiction, you might need help..:)

Please, read this:

Run the scripts here:

to convince yourself that you cannot use, ever, the geodesics model. It is just wrong. Einstein's interpretations of Time are also incorrect, etc, etc.

The presence of multiple Main Sequence and Red Giant branches in old globular star clusters are due to abundance differences. Here are a few references reporting observations, and modeling by self-enrichment:

Milone et al. https://arxiv.org/abs/1110.1077

Dotter et al. https://arxiv.org/abs/1410.4570

Han et al. http://iopscience.iop.org/article/10.1088/0004-637X/707/2/L190/meta

Roh et al. http://adsabs.harvard.edu/abs/2011ApJ...733L..45R

Carretta et al. https://arxiv.org/abs/1307.4085

Take \omega_0=vmax/(2*\pi*c), where vmax is the flattened or maximum tangential velocity, use this for ellipticals, barred spirals and spirals:

v(r)= vmax * \frac{omega_0 * r}{sqrt(1+omega_0^2 *r^2)}

for the rotation profile. r is of course in light years.

For the spiral shape of these galaxies use:

r=\frac{2*\pi}{vmax/c} * \theta

where r is in ly, and \theta is in radians. The constant 2*/pi is in ly per radian. It just works out that way.

Cheers.

This used to be a more straightforward question 20 years ago. But observations have shown considerable mass influx into the milky way via small mergers and satellite infall thus allowing the stellar mass to grow slightly on scales of billion of years.

The average star formation rate in the Milky Way is about 10 solar masses per year.

A currently unknown astrophysical question is when did our Galaxy (and others)

reach their 1/2 mass point as defined by stellar mass (not dynamical mass) -

that probably took 5-7 billion years, but the question is not well constrained either by local data or by observations of galaxies at high redshift (when they were younger)

Manuel and Indranil: I wasn't guessing my answer. I provided a factual statement about relativistic cosmography. Allow me to elaborate. Please see also this stackexchange discussion: http://physics.stackexchange.com/questions/57402/size-of-the-observable-universe

Light that took 13.7 billion years to reach us traveled exactly 13.7 billion light years from its point of origin. This is not a measurement of coordinate distance, however, since we are comparing the location of two points in spacetime (ours and the light emitting object's) at different times. (light emitted at t=t1, r=13.7 Gly, and observerd at t=t2, r=0.)

Consider a coordinate system in which we (the observers) sit at the origin, at rest. That means that our spatial coordinates do not change; we were also at the origin 13.7 billion years ago. Therefore, the coordinate distance between us and the light emitting object was 13.7 billion light years at the time the light ray was emitted. (The coordinate distance between events marked by t=t1, r=0 and t=t1, r=13.7 Gly.)

What this distance is today (i.e., the radial coordinate of the object at t=t2) depends on the rate of expansion. Without repeating what can be read elsewhere, stuff that was 13.7 billion light years from us when it emitted light that reaches us today would be about 46 billion light years from us today.

Manuel: in your answer you say, "if those galaxies are 14 billion ly from us now"... but that's not what we infer from the redshift. We observe that it took 14 billion years for their light to reach us, i.e., that they were 14 billion light years from us back when the light was emitted, not their present-day distance from us.

Indranil: In your answer you mention acceleration. It is indeed true that acceleration can result in a distant source that was once able to send us a signal to be no longer able to do so. But the reason is simply that these sources will be traveling faster than the speed of light relative to us and thus, would no longer form part of the observable universe.

Not sure the word "huge" is needed but the basic question of interest is whether or not most of the baryons in the Universe are inside or outside of gravitational potentials (e.g. galaxies).

Agreed that understanding how the first generation of stars formed inside galaxy halos remains largely unknown.

Michael,

The Big Bang theory says little about the geometry of space a Long Time after the initial expansion. Thanks to Dark Energy (aka, something we don't understand except that it's a neat name for a poorly understood pressure), it appears that the Universe may well have a negatively curvature - ie, it never recollapses and nor is it flat.

When I was a lad there was a fervent hope that the average mass-energy density would be found to be sufficient to close the Universe, alas that conceptually neat solution appears not to be the case.

Hey ho.

Farzad,

All theories attempt to explain known observations and make testable predictions.

I am not sure what 'truth' is in this regard.

The Big Bang hypothesis fits many of the known observed properties of the universe (red shifts, background radiation, etc.). It's not perfect, and may need alteration. I am unsure as to what the 'bouncing theory' is. Care to point to a peer-reviewed summary?

Examples are the reflection nebulae around the stars of the Pleiades.

We set the initial conditions of formation of our galaxy by observing distant ( probably a redshift greater than 7 wherein we can observe the star formation process) similar galaxies and correlating their information with respect to our own galaxy. There is or are certain theories stating that all stars might have been a part of binary star system or a cluster. But regarding the observation of singular stars, they may have formed in the outer edges of a giant molecular cloud where the density of hydrogen may have increased just about enough to form only a single star. Finally, concurring to current observations, the formation of giant galaxies such as our galaxy is the result of a bottom-up process. Thus the Milky Way may not have been "embedded" in a multiple system, but may have formed as a result of merger of many smaller galaxies. The density waves may have started at sometime after the merger thus giving our galaxy a spiral structure.

No because v=cz does not hold at velocities near c. It is a low velocity approximation.