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This paper, http://arxiv.org/abs/1507.06282, The Duhem-Quine thesis and the dark matter problem, may be of interest to those curious about how and why dark matter has gained general acceptance by cosmologists
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betzalel said:After more than 50 years the direct search for dark matter has been negative which would make sense if dark matter does not exist.
If you convinced about that then you will have to publish a theory which can explain the data better than existing models can.betzalel said:... The point is it time to relook at the entire cosmological problem as it is a fact that there are more and more anomalies concerning every aspect of the standard cosmological theory components due to multi spectrum data at all redshifts.
betzalel said:1) Direct dark matter detection, negative after 50 years search.
2) Solar system area search for dark matter, negative for dark matter.
3) Local universe search for dark matter, negative for dark matter.
4) Observed spiral galaxy central form, does not agree with simulations for galaxy formation/evolution with dark matter. Cusp problem.
5) Satellite galaxy crisis
The finding that a plane of satellite galaxies based on observations appears to be ubiquitous for all spiral galaxies, (>7σ confidence), published in Nature, is a big deal. i.e. Galaxy growth by mergers should produce a sphere of satellite galaxies not a narrow plane of satellite galaxies.
ohwilleke said:The terminology that I like to use is to say that it is beyond dispute and definitively established that dark matter phenomena exist. Galactic rotation curves, lensing, the success of the lamdaCDM model in describing the observed universe with respect to the parameters it describes, etc. all overwhelmingly support the existence of something causing dark matter phenomena other than GR as currently formulated and applied, and other than the SM forces and particles.
It is also true that we haven't solved the problem of what causes dark matter phenomena. There are several sub-types of dark matter particle based theories and a few modified gravity theories that make a good go of it, but there is no precise consensus solution that has been definitively established to solve all of the dark matter phenomena and to out perform all of the other approaches. There are at least several dozen other dark matter particle and modified gravity approaches that were considered seriously at one point or another and have been more or less definitively ruled out at this point.
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Heirarchical galaxy formation (betzalel, with dark matter or with modified gravity) simply does not fit the constraints set by the correlation structure in the Equatorial Survey.
Galaxies appear simpler than expected
Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment, and feedback from supernova explosions and supermassive black holes1. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter2,3,4. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular-momentum, baryon-fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free of optical selection effects5, shows five independent correlations among six independent observables, despite having a ...
... This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our dataset. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter paradigm in cosmology6.
...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..
What makes you think this?betzalel said:... there must be some mechanism that stops/inhibits the merger of spiral galaxies.
betzalel said:Dark matter or changes to general relativity do not explain the correlated structure of spiral galaxy parameters which is a paradox. The dark matter papers ignore the correlated structure paradox. Clouds of dark matter particles will not cause Goldlock's increases of spiral galaxy rotational (not too much or not too little) in direct proportion to the spiral galaxy's mass.
rootone said:What makes you think this?
It''s generally accepted our that our galaxy will merge with Andromeda galaxy in the very long run.
BULGELESS GIANT GALAXIES CHALLENGE OUR PICTURE OF GALAXY FORMATION
BY HIERARCHICAL CLUSTERING
We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with Vcirc > 150 km s-1, including M101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge.
We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories.
Recognition of pseudo bulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges?
.THE EDGE-ON PERSPECTIVE OF BULGELESS, SIMPLE DISK GALAXIES
However, other studies claim that neither different kinds of feedback (D’Onghia & Burkert 2004; D’Onghia et al. 2006) nor increased numerical resolution (K¨ockert & Steinmetz 2007; Piontek & Steinmetz 2009a) can resolve the angular momentum problem completely. Therefore, the formation of simple disk galaxies in a cosmological framework is not yet well understood (Burkert 2008; Mayer et al. 2008), and a detailed understanding of this topic is just at the beginning
ohwilleke said:This is simply inaccurate. The correlated one dimensional structure of spiral galaxy parameters, first described with as the Tully-Fischer relation, historically, was the primary motivation for the original modified gravity theory, MOND, and essentially all subsequent modified gravity theories address this issue.
Dark matter models address this problem as well, although with not quite such a tight fit to the galactic mass as modified gravity models. Mostly this arises because dark matter halos are less capable of maintaining distinct form than ordinary matter due to their lack of non-gravitational interactions. In dark matter models, the distribution of ordinary matter in galaxies is homogenized by the powerful role that dark matter halos (which tend to be fairly homogeneous at any given size) exert on the formation of galaxies and the distribution of ordinary matter within them. There is also gravitational feed back in the other direction from the baryonic matter to the dark matter halo, in which the disk-like distribution of baryonic matter's tugs the shape of the dark matter halo away from a sphere towards a rugby ball shape.
Let me put this another way. Dark matter models became popular because in crude simulations they crudely reproduced what we observed, with some very simple starting assumptions. They do work. Particular versions of them may not perfectly fit the data, but the extent to which a very simple version of them can come reasonably close to reality with relatively arbitrarily chosen parameters shows why these models are promising, even if there is more fine tuning of the model that is necessary to fit the better resolved data matched to better simulations, than one would have initially hoped.
...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..
BULGELESS GIANT GALAXIES CHALLENGE OUR PICTURE OF GALAXY FORMATION BY HIERARCHICAL CLUSTERING
We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with Vcirc > 150 km s-1, including M101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge.
We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories.
Recognition of pseudo bulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges?
The dark matter crisis: falsification of the current standard model of cosmology
The current standard model of cosmology (SMoC) requires The Dual Dwarf Galaxy Theorem to be true according to which two types of dwarf galaxies must exist: primordial dark-matter (DM) dominated (type A) dwarf galaxies, and tidal-dwarf and ram-pressure-dwarf (type B) galaxies void of DM. Type A dwarfs surround the host approximately spherically, while type B dwarfs are typically correlated in phase-space. Type B dwarfs must exist in any cosmological theory in which galaxies interact. Only one type of dwarf galaxy is observed to exist on the baryonic Tully-Fisher plot and in the radius-mass plane. TheMilkyWay satellite system forms a vast phase-space-correlated structure that includes globular clusters and stellar and gaseous streams. Other galaxies also have phase-space correlated satellite systems. Therefore, The Dual Dwarf Galaxy Theorem is falsified by observation and dynamically relevant cold or warm DM cannot exist.
Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey
12-8 Conservation of Angular Momentum
If the net external torque acting on a system is zero, the angular momentum L of the system remains the same, no matter what changes take place within the system.
If any component of the net external torque on a system is zero, then that component of the angular momentum of the system along that axis cannot change, no matter what changes take place within the system.
...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..
My understanding is that galaxies can and do merge and that spirals are no exception.betzalel said:there must be some mechanism that stops/inhibits the merger of spiral galaxies.
Yes, it appears that what was been interpreted to be a merger may not be a merger.rootone said:My understanding is that galaxies can and do merge and that spirals are no exception.
Also that we have accumulated a significant amount of astro photography which actually shows galaxies in different stages of merger.
In the case of spirals of roughly equal size merging, the result apparently is what might be expected, - that both systems become heavily structurally disrupted and their contents eventually settle into an elliptical galaxy carrying the sum of angular momentum of the original galaxies.
(Well not quite all of it, since it's expected that some star systems will end up being ejected altogether.)
That's the ordinary matter of course, but I suppose that dark matter content behaves similarly since the interaction is gravitational.
In the case of the future collision of the Milky way and Andromeda, a merger of this sort seems to be inevitable, though no one can predict the form of exact final result
If this merger cannot happen then what is going to intervene which will prevent it?, and why do we have the astro photography showing merges in progress?
Are you saying that these images are being misinterpreted as merging galaxies when really something different is happening?
http://arxiv.org/ftp/arxiv/papers/0811/0811.1554.pdfTHE MILKY WAY: AN EXCEPTIONALLY QUIET GALAXY; IMPLICATIONS FOR THE FORMATION OF SPIRAL GALAXIES
Disk galaxies constitute the majority of the galaxy population observed in the local universe. They represent 70% of intermediate mass galaxies (stellar masses ranging from 3× 10^10 to 3 × 10^11 M⊙), which themselves include at least two-third of the present-day stellar mass (e.g., Hammer et al. 2005).However, there are several outstanding difficulties with this standard scenario. One such difficulty is the so-called angular momentum problem. That is, simulated galaxies cannot reproduce the large angular momentum observed in nearby spiral galaxies (e.g., Steinmetz & Navarro 1999). Another is the assumed absence of collisions during and after the gas condensation process. Indeed, the hierarchical nature of CDM cosmology predicts that galaxies have assembled a significant fraction of their masses through collisions with other galaxies. It is likely that such collisions would easily destroy galactic disks (e.g., Toth & Ostriker 1992). Although the accretion of satellites may preserve the disk, it is also true that major collisions would certainly affect it dramatically.
The key questions are then: Do major collisions always destroy disks? Can major collisions lead to the formation of new disks? Do these rebuilt or altered disks have properties consistent with those of local galaxies?
Combining the pair fraction and characteristic time scale estimates suggests that for a present-day galaxy with a stellar mass larger than 3 × 1010 M⊙, the chance it has experienced a major merger since z=1 is 50±17%, 75±25% and 70% according to Lotz et al. (2006), Hammer et al. (2005), and Bell et al. (2006), respectively1. Although less certain, integrating the merger rate to higher redshift implies that a typical bright galaxy may have experienced up to four to five major merging events since z=3 (Conselice et al. 2003).
The high frequency of major mergers may be a real problem for the standard theory of disk formation. Assuming that protogalactic disks lie in the distant universe, how can this be reconciled with an absence of major collisions? How can we explain the large fraction of local disks if major mergers (with mass ratio ranging from 1:1 to 1:3) unavoidably lead to the formation of an elliptical? Even at z less than 1 the observations are challenging for the standard scenario
.
...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..
ohwilleke said:Kroupa explains why modified gravity can produce the observed spectrum while WDM and CDM cannot. http://arxiv.org/pdf/1204.2546.pdf See especially, pages 28-36 and also here http://arxiv.org/pdf/1006.1647.pdf
Another proposal is cold neutrino dark matter. http://iopscience.iop.org/0295-5075/86/5/59001/fulltext/epl_86_5_59001.html de Vega argues that WDM can manage to reproduce what we see http://arxiv.org/pdf/1004.1908.pdf Kesselman offers a self-interacting DM scenario that purports to rise to the challenge. http://arxiv.org/pdf/0912.4177.pdf
Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment, and feedback from supernova explosions and supermassive black holes1. The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter2,3,4. The properties of an individual galaxy should be controlled by six independent parameters including mass, angular-momentum, baryon-fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free of optical selection effects5, shows five independent correlations among six independent observables, despite having a ...
... This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our dataset. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter paradigm in cosmology6.
...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey..
The high frequency of major mergers may be a real problem for the standard theory of disk formation. Assuming that protogalactic disks lie in the distant universe, how can this be reconciled with an absence of major collisions? How can we explain the large fraction of local disks if major mergers (with mass ratio ranging from 1:1 to 1:3) unavoidably lead to the formation of an elliptical? Even at z less than 1 the observations are challenging for the standard scenarioTHE MILKY WAY: AN EXCEPTIONALLY QUIET GALAXY; IMPLICATIONS FOR THE FORMATION OF SPIRAL GALAXIES
Disk galaxies constitute the majority of the galaxy population observed in the local universe. They represent 70% of intermediate mass galaxies (stellar masses ranging from 3× 10^10 to 3 × 10^11 M⊙), which themselves include at least two-third of the present-day stellar mass (e.g., Hammer et al. 2005).
However, there are several outstanding difficulties with this standard scenario. One such difficulty is the so-called angular momentum problem. That is, simulated galaxies cannot reproduce the large angular momentum observed in nearby spiral galaxies (e.g., Steinmetz & Navarro 1999). Another is the assumed absence of collisions during and after the gas condensation process. Indeed, the hierarchical nature of CDM cosmology predicts that galaxies have assembled a significant fraction of their masses through collisions with other galaxies. It is likely that such collisions would easily destroy galactic disks (e.g., Toth & Ostriker 1992). Although the accretion of satellites may preserve the disk, it is also true that major collisions would certainly affect it dramatically.
The key questions are then: Do major collisions always destroy disks? Can major collisions lead to the formation of new disks? Do these rebuilt or altered disks have properties consistent with those of local galaxies?Combining the pair fraction and characteristic time scale estimates suggests that for a present-day galaxy with a stellar mass larger than 3 × 1010 M⊙, the chance it has experienced a major merger since z=1 is 50±17%, 75±25% and 70% according to Lotz et al. (2006), Hammer et al. (2005), and Bell et al. (2006), respectively1. Although less certain, integrating the merger rate to higher redshift implies that a typical bright galaxy may have experienced up to four to five major merging events since z=3 (Conselice et al. 2003).
12-8 Conservation of Angular Momentum
If the net external torque acting on a system is zero, the angular momentum L of the system remains the same, no matter what changes take place within the system.
If any component of the net external torque on a system is zero, then that component of the angular momentum of the system along that axis cannot change, no matter what changes take place within the system.
Kroupa notes the Disney finding that spiral galaxies are controlled by a single parameter which invalidates the assumption that spiral galaxies grow by hierarchical mergers which is a paradox. How then do they grow?ohwilleke said:Actually, all of the papers that I referenced cite Disney and engage that issue. Hierarchical formation is an idea specific to DM particle models which he attacks with arguments almost the same as the ones that you are advancing. I used list of papers citing Disney to find them. Please read more carefully. You are reading without thinking.
Also Kroupa proposes changing gravity because it fits the data better. This is a very logical reason.
...Consider spin alone, which is thought to be the result of early tidal torquing. Simulations produce spins, independent of mass, with a log-normal distribution. Higher-spin discs naturally cannot contract as far; thus, to a much greater extent than for low-spin discs, their dynamics is controlled by their dark halos, so it is unexpected to see the nearly constant dynamical-mass/luminosity ratio that we and others14 actually observe. Heirarchical galaxy formation simply does not fit the constraints set by the correlation structure in the Equatorial Survey...
...In the current cold DM ( CDM) framework of structure formation and evolution, galaxies in DM halos grow hierarchically by the absorption of smaller substructures in sub halos (Searle & Zinn 1978; White & Rees 1978; Blumenthal et al. 1984). This means that disk galaxies have always been subject to merging and interaction. Almost all galaxies with present halo mass comparable to the Milky Way (MDM 10^13solar masses to 10^11 solar masses) morphological transformations of disk galaxies. At the upper limit, a merger may cause the total destruction of the disk and the formation of a spheroidal, elliptical galaxy (e.g., Toomre 1977; Barnes 1992; Gardner 2001; Cox & Loeb 2008). Massive disks can then be rebuilt from gas deposited in a gas-rich (major) merger (Hammer et al. 2009; Robertson & Bullock 2009; Yang et al. 2009) supported by the additional accretion of cold gas (Dekel & Birnboim 2006). However, these so-called rebuilt scenarios assume that disks will be reformed around preexisting spheroidal bulges (Steinmetz 2003; Springel& Hernquist 2005). In less violent cases of major mergers, spheroidal bulges can formed by dynamically heated disk stars and accreted material (Aceves et al. 2006; Bournaud et al. 2007; Khochfar 2009). In addition, new bulge stars can be formed from disk gas that lost its angular momentum by nonaxisymmetric distortions due to galaxy-galaxy interactions (Noguchi 2001; Benson et al. 2004; Hopkins et al. 2009a; Koda et al. 2009)
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According to these model predictions, not many simple disks should have survived the cosmological evolution.
The fraction of the simple disk class Sd(f) is 16% among the disk galaxies in the Kautsch et al. (2006a) catalog. This fraction increases to 32% if the seemingly bulgeless (but less strictly defined) Scd(f) types are included.
Bulgeless galaxies are located in all environments, ranging from low to high density (Kautsch et al. 2005, 2009). The majority of these galaxies are weakly associated with galaxy clusters and can be found in more isolated environments comparable to galaxy groups and the field (Kudrya et al. 1997; Karachentsev 1999b; Kautsch et al. 2009). Because of the low relative velocities of group galaxies, merging and morphological processes that transform late-type galaxies into bulgedominated and spheroidal galaxies are common in the group environment (e.g., Barnes 1985; Kautsch et al. 2008; Tran et al. 2008). This implies that simple disks either have to be stable against morphological preprocessing or are located in this environment due to recent infall.
Field studies show that the number density of large bulgeless galaxies is constant (maybe slightly increasing) at redshifts z 0 to 1 whereas the number of galaxies with bulges decreases at larger distances (Sargent et al. 2007; Dom´ınguez-Palmero & Balcells 2009).
Simple disks are not a separate morphological class, but rather at the end of a smooth continuum without a well-defined boundary (Matthews & Gallagher 1997; Kautsch et al. 2006a).
On average, bulgeless disks rotate slower than galaxies with bulges as shown in Figure 3. .
betzalel said:In private industry when there are piles and piles of paradoxes, a group is assigned the task to relook at every assumption and to think out of the box. i.e. To ensure that every possible alternative (I repeat every possible alternative) is systematically examined.
Paradoxes and anomalies indicate the base theory and base assumptions are incorrect. There has been sufficient information to solve the cosmological puzzle for at least a decade. It is impossible to solve a problem if the base theory and assumptions are incorrect. The solution cannot be found by guessing, by throwing theories up in the air.ohwilleke said:One mechanism that gets you quite a bit of the way there is as follows.
Assume that the gravitational field in a modified gravity theory has different strength in different directions around a spiral galaxy.
For example, it may be stronger in the plane of its disk (which also promotes satellite galaxy alignment in that disk) and promotes mergers by accretion from end to end spiral galaxies producing something like:
https://encrypted-tbn0.gstatic.com/...C7iFX8JiUwUdKMI-OMmIZB4pfcTGAyYMLWZfj0eWJ9ddm
Meanwhile gravity might be weaker in a corresponding amount on its axis. Thus, a lot of spiral galaxies on a near collision course with each other on the wrong angle of attack would just miss each other, despite the fact that if each had a spherically symmetric gravitational field around its central black hole, they would have collided to form an elliptical or bulged spiral galaxy.
Just saying that what is a clear paradox in particle based CDM models (which are discussed in the quotations above) is not necessary such a paradox in modified gravity models and that for the most part nobody has run the simulations of modified gravity models to quantify those differences.
Fundamentals of Physics Extended Fifth Edition H.R.W.Page 289The high frequency of major mergers may be a real problem for the standard theory of disk formation. Assuming that protogalactic disks lie in the distant universe, how can this be reconciled with an absence of major collisions? How can we explain the large fraction of local disks if major mergers (with mass ratio ranging from 1:1 to 1:3) unavoidably lead to the formation of an elliptical? Even at z less than 1 the observations are challenging for the standard scenario..
12-8 Conservation of Angular MomentumIf the net external torque acting on a system is zero, the angular momentum L of the system remains the same, no matter what changes take place within the system.If any component of the net external torque on a system is zero, then that component of the angular momentum of the system along that axis cannot change, no matter what changes take place within the system..
The solution is not dark matter or MOND. Dark matter and/or MOND does not produce a torque which is necessary for spiral galaxies to increase spin as they grow, does not explain how spiral galaxies grow, does not explain how spiral galaxies avoid mergers, why spiral galaxies exist.
As I noted angular momentum is conserved. The merger of two spiral galaxies is at random directions and should hence produce an elliptical like galaxy not a spiral galaxy and certainly not a bulgeless galaxy.
ohwilleke said:Angular momentum is not conserved in galaxies anyway. If it has more angular momentum than it can gravitationally constrain then it flings some of the stars on the rim off into deep space. As new objects passing through space enter a galaxy, they may be assimilated and transfer their momentum angular and otherwise to the galaxy. A galaxy is not a closed system.
An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. Unlike flat spiral galaxies with organization and structure, they are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center.
Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity, and they tend to be surrounded by large numbers of globular clusters. Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall.[3] They are preferentially found close to the centers of galaxy clusters.[4] Elliptical galaxies are (together with lenticular galaxies) also called "early-type" galaxies (ETG), due to their location in the Hubble sequence, and are found to be less common in the early Universe
Dark matter is a hypothetical form of matter that is believed to make up about 85% of the total matter in the universe. It does not interact with light and therefore cannot be seen directly, making it difficult to detect and study.
Dark matter plays a crucial role in the formation and evolution of galaxies. Its gravitational pull helps to hold galaxies together and without it, galaxies would not have formed in the first place. Understanding dark matter is essential to understanding the structure and evolution of the universe.
Scientists have observed the effects of dark matter through its gravitational influence on visible matter in galaxies. They have also studied the rotation curves of galaxies, which show that there is more mass present than can be accounted for by visible matter alone. Additionally, observations of the cosmic microwave background radiation provide evidence for the existence of dark matter.
There are several theories that attempt to explain the nature of dark matter. One popular theory is that dark matter is made up of Weakly Interacting Massive Particles (WIMPs), which are particles that interact with each other and with ordinary matter only through the weak nuclear force. Another theory is that dark matter is composed of massive astrophysical compact halo objects (MACHOs), such as black holes or brown dwarfs.
If dark matter is discovered and its properties are better understood, it could lead to a more complete understanding of the universe and its evolution. However, if dark matter is not found, it could mean that our current understanding of gravity and the laws of physics is incomplete, which would have significant implications for our understanding of the universe as a whole.