Impact of Dark Matter Halos on the Formation of Galaxies

When I was growing up, kids were going gaga over Ben 10, it was a cartoon TV show which followed the story of a boy named Ben Tennyson.

He could transform into any type of alien with a turn of his watch which I don’t remember the name of now. It was quite the craze, though. I remember never really liking the show since it dealt with topics related to outer space.

But who would have thought that I would one day write an article on the impact of dark matter halos on the formation of galaxies?

See, the thing is the universe and its workings have always terrified me. The thought of something so vast exists that it makes our existence seem so inconsequential, it is so gratifying yet frightening.

However, all of this changed when one fine day a friend of mine made me watch the movie Interstellar. To tell you that my whole being was in rapture with that film would be an understatement. Since then, the universe is no longer a symbol of terror but of hope. 

So let us take one step at a time and learn about its different constituents that we have wasted so much time being ignorant of.

1. Throwing Light on Dark Matter Halos

Before interweaving a long thread of connection between dark matter halos and the galaxies, we must know what exactly they are.

After all, you can’t skip the number system and jump straight to trigonometry. Though if you are a prodigy, then, I will mind my business. 

Anyway, what I am trying to say is let us first get familiar with the basics of these entities then get to the more complex stuff.

1.1 What is Dark Matter?

It is believed that dark matter is a type of hypothetical matter which accounts for 85% of the matter in the universe. The term “dark” has been attributed to it because it does not interact with electromagnetic fields. It does not reflect, absorb or emit any kind of electromagnetic radiation.

Scientists also suggest that dark matter is present in abundance throughout the universe, it also has a hand in galaxy formation and its movements.

1.2 Dark Matter Halo: The Hacker Group

The internet is such a bizarre place sometimes (most of the time). Why did I need to know that there exists a hacker group with the name Dark Matter Halo? By the way, they are also known as the Cozy Bear.

Moving on, the basic unit of a cosmological structure is a dark matter halo. Like hypothetical matter, it is a hypothetical region decoupled by cosmic expansion, it consists of matter that is gravitationally bound matter. 

A dark matter halo can also contain clusters of dark matter bound together by gravity which are known as subhalos. Many cosmological models indicate that many dark matter halos may contain galaxies.

2. A Spiral of Galaxies 

You are aware that the sun has planets revolving around it. The planets have their moons doing so for them.

Did you know that individual galaxies also have satellite galaxies? These satellite galaxies also have smaller satellite galaxies of their own. Isn’t it kind of wholesome though?

Every entity in our universe has one or many (looking right at you Jupiter) entities following them. No one is ever lonely.

Now, it is understood that each of these galaxies and their satellite galaxies are formed within a dark matter halo. The growth and development of the galaxies over time are interdependent.

They depend on the growth of the dark matter halos that they are formed in. Firstly, we will understand the formation of these galaxies within the dark matter halo. Then, we will understand how these dark matter halos are formed.

3. The DNA of these Dark Matter Halos

The formation of dark matter halos played a very essential role in the formation of galaxies. Remember how in Interstellar when the protagonist was sucked up in a dark matter halo? He was transported into a whole new universe, a new galaxy.

Maybe the genius brain of Christopher Nolan already knew about this correlation between galaxies and a dark matter halo.

When the galaxies were being formed initially, the temperature of the baryonic matter would have been too much for it to form gravitationally self-bound objects.

Therefore, there was a need for an already-formed dark matter structure for the addition of extra gravitational interactions, the present hypothesis of this is based on cold dark matter (CDM).

3.1 What Constitutes this Dark Matter Halo?

Dark matter halos, along with the galaxies that live within their intricate structure, are ignited by the small sparks started by the process that sets the embryonic pattern of overdensities and under-duties in every component that makes up the Universe. 

The overdensities embark on this venture as minute perturbations on the apex of the smooth density.

Their growth depends upon the influence of gravity and different other physical processes which eventually act as an aid in developing them into gigantic structures that form the bound, virialized objects known to mankind as dark matter halos. 

4. Galaxies and their Structure

We have already established the fact above that almost all galaxies known to us have satellite galaxies of their own. And to make matters more complex these satellite galaxies also come with their own family of satellite galaxies.

The Large Magellanic Cloud (LMC) is a satellite galaxy of our very own Milky Way galaxy and can be seen from the Southern Hemisphere. It is thought that when it first came into contact with the Milky Way galaxy, it was already accompanied by at least six of its satellite galaxies. 

Astrophysicists firmly believe that much of that structure is courtesy of dark matter.

4.1. Hints Towards Structure and Size of Galaxies

All of this has led to the gathering of more hints towards the presumed connection between the dark matter halos and the structure and size of the galaxies that they surround. 

It sets its hypothesis in the belief that the scientists’ models are correct and concludes that the Milky Way galaxy must have 150 or more indistinct satellite galaxies. Supposedly they are waiting to be discovered by the next generation of scientists and their projects.

Ethan Nadler, a graduate student at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) stands firm on the belief that the study by the Astrophysical Journal in 2020, is the start of a chain reaction of efforts to comprehend the mechanism of dark Halo on scales smaller than our galaxy.

5. Questions about these Satellite Galaxies Arose

In the previous paragraphs, we became aware of one of the satellite galaxies of the Milky Way galaxy. It is known as the Large Magellanic Cloud and can be seen with the naked eye in the southern hemisphere of the earth.

With this much knowledge, scientists thought that the extent of the satellite galaxies of the Milky Way would be 10-12 maximum.

Turns out they were reaching the zenith of delusion with this assumption. Courtesy of the Sloan Digital Sky Survey and a dozen different discoveries by projects like the Dark Energy Survey (DES), we now know that there are at least 60 satellite galaxies of the Milky Way galaxy.

These kinds of discoveries and data are not only thrilling to learn about but also can inform us a lot about the cosmos. 

Scientists like Risa Wechsler, Nadler, and their colleagues utilized the data on these satellite galaxies in league with computer simulations. However, they have placed much tighter constraints on the interactions of dark matter with ordinary matter.

Researchers have been conducting various searches over most of the sky in an attempt to ask the right questions.

Till now they have managed to ask questions on the amount of dark matter required to form a galaxy, the number of satellite galaxies around the Milky Way galaxy and the possibility of galaxies bringing their satellites into orbit around our Milky Way galaxy.

6. Impact of Dark Matter Halos on the Formation of Galaxies 

SLAC and Stanford University researchers in collaboration with the dark energy survey use certain types of simulations to understand the relation between dark matter and galaxy formation.

One of the simulations they utilized is a simulation of the formation of dark matter structures from the initial universe until the present day. 

The simulation showcases how gravity forces the dark matter to clump together to form dense halos, this is the place where galaxies form. After some time in this simulation, the formation of a halo identical to the one where the Milky Way galaxy resides is displayed.

Then a smaller halo is viewed to be formed, this halo falls into the first, larger halo, thus, reenacting the fall of the Large Magellanic Cloud into the Milky Way.

7. The Hierarchy Followed by Galaxies

When the DES first discovered the presence of more satellite galaxies in the surroundings of the Large Magellanic Cloud, speculations concerning a galactic hierarchy arose.

However, the observations would not have been so monumental if those satellites were randomly scattered throughout the sky. 

The observations were furthermore interesting since they hinted at the possibility of six of these satellite galaxies belonging to the Milky Way galaxy along with the LMC.

7.1 Computer Simulations

Nadler and his team used computer simulations of millions of possible universes, like the one mentioned above, to study the satellite galaxies of the LMC more appropriately. 

These simulations, run by Yao-Yuan Mao, a student at Rutgers University, are a replica of the formation of dark matter structure that penetrates the Milky Way galaxy.

It also pays attention to details like the comparatively smaller dark matter clusters within the Milky Way galaxy which are envisaged to host the satellite galaxies.

To correlate galaxy formation to dark matter, the researchers opted for a more flexible of the other cosmological models. It allowed them to rationalize the irregularities in the contemporary understanding of galaxy formation.

The relationship between the brightness of the galaxies was also rationalized by it. The mass of the dark matter clusters within which the galaxies form was also taken into account.

7.2 Cosmological Model with Varied Simulations

Keeping all of this information in mind, the team tested this model, different from the previous cosmological models, with a varied range of parameters for simulations that forced LMC-like satellite galaxies to fall into the gravitational pull of a galaxy.

When the researchers compared these cases with the galactic observations, they could draw a range of astrophysical parameters which also included the number of satellite galaxies tagging along with the LMC.

The results aligned with the previous discoveries concurring that six satellite galaxies were present in the surroundings of the LMC, moving with roughly the same velocities and in roughly the constant places as in the previous observations made by the astronomers.

These simulations also hinted at the fact that the LMC first came near the Milky Way galaxy about 2.2 billion years ago, which was unwavering with highly precise measurements of the movement of the LMC from the Hubble Space Telescope.

8. Impact of Dark Matter Halos on the Formation of Unknown Galaxies

After the successful LMC findings, the researchers put restrictions on the link between dark matter halo and galaxy structure. 

For instance, the simulations that matched the history of the Milky Way galaxy and the LMC the most accurately had the smallest galaxies. They also contained stars having a combined mass of around a hundred suns, and a million times as much dark matter.

According to a conclusion of the cosmological model, the faintest galaxies that could ever be observed by mankind could form in dark matter structures up to a hundred times less massive than that.

If the simulations are correct, there are more discoveries to be made. According to scientists, there exist around 100 more satellite galaxies, more than double the number already discovered, floating around the Milky Way galaxy. 

The discovery of these multiple galaxies would work as an aid in confirming the researchers’ cosmological model of the connections between dark matter halo and galaxy formation. It will place tighter restraints on the nature of dark matter particles themselves.

9. Why is Dark Matter Shown as a Halo Around a Galaxy?

A type of spherical distribution of dark matter around the visible part of a galaxy and clusters of galaxies is what we call a dark matter halo. But the question is why does dark matter form a halo around a galaxy? I mean it could have chosen any other shape, right?

Now, we can approach this matter in two ways, one straightforward while the other a little more complex.

The simple approach deals with the idea of dark matter interacting weakly with other entities but not non-interacting.

It is known that the dark matter particles when interacting gravitationally will undergo dynamical friction. In effect, a cloud formed by dark matter cools by evaporation. 

Normally when particles are interacting gravitationally a small proportion of them will eventually catch a high momentum. These are the same particles that will manage to escape the cloud thus, taking away excess momentum with them.

The more complex approach deals with the creation of primordial density differences, this is generally credited to fluctuations during inflation. The fluctuations which are measurable in the CMB comprise this mechanism.

10. Impact of Dark Matter Halos on the Formation of Galaxies and Stars

We now know that astrophysical and cosmological data suggest that baryonic matter consists of only 5% of the elements of the Universe, the rest of it is dark matter (almost 23%) and dark energy (mostly 72%). 

It is also learnt that the reason dark matter (DM) is called dark is that there is no absorption, reflection or emission of electromagnetic radiation by it. Thus, it cannot be detected easily though the gravitational force is felt by it. 

There might be different candidates for dark matter, but its true nature and origin are still a mystery greater than those written by Agatha Christie. Among these candidates, some are of non-baryonic origin while others have a baryonic one.

Apart from all of this, dark matter also has some effects on the existence of the stars. Researchers believe that dark matter might be behind the incomprehensive motions of stars within galaxies.

Dark matter might also influence the characteristics of hybrid stars which possess both normal and quark matter. They do so by changing the energy density and diminishing the minimum mass necessary for a quark core.

It might also be responsible for the formation of dark stars, they are hypothetical entities powered by the destruction of dark matter particles instead of nuclear fusion. These stars are believed to emit gamma rays, neutrinos, and antimatter.

11. The Dark Matter Halo of the Milky Way Galaxy

Now that we are brimming with knowledge regarding every aspect of dark halo and its galaxy formation efficiency, it will be only fair to learn a bit about the dark matter halo of our galaxy.

It is believed that the visible disk of the Milky Way Galaxy is embedded in a dark matter halo, the dark matter halo is a much larger, roughly spherical dark matter halo. The density of the dark matter lowers with the increasing distance from the galactic centre. 

It is also believed that the majority of the galaxy is now made up of dark matter. This does not seem to affect the rest of the matter and energy of the galaxy in any way except through the influence of gravity. 

The luminous matter makes up approximately 9×1010 solar masses. The dark matter halo includes around 6×1011 to 3×1012 solar masses of dark matter. 

12. Impact of Dark Matter Halos on Our Lives

When I was a child, I had the worst kind of love-hate relationship with power cuts at night. I detested them because no fans or ACs worked, and we had to try to sleep in that excruciating July heat.

However, I also adored them because since there was no electricity and it was hot and humid, we had to sleep on the terrace. 

Also sleeping on the terrace was a giveaway of no school the next day. You see, the whole night would just pass by in a spree of endless conversations about our parents’ childhood.

Sometimes, it also revolved around the secrets of the stars and the early universe, but somehow all topics were equally mystical.

After all, there is a reason why even poets are more fascinated with the sky at night. The twinkling of the stars, the occasional presence of the moon and the ever-shifting clouds.  

Humankind has always been attracted to the ever-expanding universe, our galaxy and the possibility of many such galaxies. Even children cannot help but skip to the universe chapter in their science books and rightfully so.

13. EndNote

The quest of intelligent minds to unravel the mystery that is our galaxy and the universe it resides in will always be on. No wonder so many science-fiction movies and books have been made and written about the same.

People are devouring the content along the lines of these topics and why wouldn’t they? All of this is a symbol of hope, of endless possibilities for them. 

Every day new research is conducted by our space agencies, they are rooting for the success of the space agencies of their countries in landing on the moon. Observations are made on the possibility of life somewhere other than the planet that has sustained us since time immemorial.

People are enamoured with all of this, and this article is just a small star in context with the knowledge of this forever-expanding universe.

Last Updated on August 2, 2024 by Sathi