Category: Astronomy

The Grand Scale: An Introduction to Cosmology and Nongalactic Astrophysics

Welcome back to the webref.org blog. We have peered into the hearts of stars and navigated the swirling disks of galaxies. Today, we zoom out to the ultimate “wide-angle” view. We are entering the realm of Cosmology and Nongalactic Astrophysics—the study of the universe as a whole and the vast, mysterious spaces that exist between the island universes of galaxies.

If galaxies are the cities of the universe, cosmology is the study of the entire planet, its history, its shape, and its eventual destiny.

What is Cosmology?

Cosmology is the branch of astrophysics that deals with the origin, evolution, and ultimate fate of the universe. It moves beyond individual objects to look at the large-scale structure of the cosmos.

Modern cosmology is built on two major pillars: Albert Einstein’s General Relativity and the Big Bang Theory. It seeks to answer the biggest questions humanity has ever asked: Where did everything come from? How is it changing? And how will it end?

The Beginning: The Big Bang and the CMB

The prevailing model for the origin of the universe is the Big Bang. Around 13.8 billion years ago, the universe began as an incredibly hot, dense point (a singularity) and has been expanding ever since.

One of the most important pieces of evidence for this is the Cosmic Microwave Background (CMB). This is the “afterglow” of the Big Bang—faint radiation that fills all of space, representing the moment the universe became transparent to light about 380,000 years after its birth.

The Invisible Majority: Dark Matter and Dark Energy

Perhaps the most shocking discovery in nongalactic astrophysics is that everything we can see—stars, planets, gas, and people—makes up only about 5% of the universe. The rest is invisible and mysterious.

  • Dark Matter (~27%): As we discussed in our galaxy blog, this acts as a gravitational “glue.” In the context of cosmology, dark matter formed the “scaffolding” upon which the first galaxies were built.

  • Dark Energy (~68%): While gravity pulls things together, dark energy acts as a repulsive force that is pushing the universe apart. Discovered in the late 1990s, dark energy is causing the expansion of the universe to accelerate.

Nongalactic Astrophysics: The Intergalactic Medium (IGM)

Space is not empty. The vast voids between galaxies are filled with the Intergalactic Medium (IGM). This is a sparse, ionized gas (mostly hydrogen) that contains more matter than all the stars and galaxies combined.

Astrophysicists study the IGM by looking at Quasar Absorption Lines. As light from a distant, bright quasar travels toward Earth, it passes through clouds of intergalactic gas, which leave “shadows” or absorption lines in the light spectrum. This allows us to map the “Cosmic Web.”

The Large-Scale Structure: The Cosmic Web

Galaxies are not scattered randomly. On the largest scales, they are organized into a vast, 3D network called the Cosmic Web.

  • Filaments: Long, thin threads of dark matter and gas where most galaxies reside.

  • Nodes: Points where filaments cross, hosting massive clusters of thousands of galaxies.

  • Voids: Enormous, nearly empty bubbles between the filaments that can be hundreds of millions of light-years across.

The Fate of the Universe

How does the story end? Cosmologists use the “Density Parameter” to predict the final chapter. Based on current observations of dark energy, the most likely scenario is the Big Freeze. The universe will continue to expand forever, galaxies will move so far apart they become invisible to each other, stars will burn out, and the universe will eventually reach a state of maximum entropy—cold, dark, and silent.

Why Cosmology Matters

Cosmology represents the peak of human curiosity. It forces us to develop new physics and pushes our technology to its absolute limit. By understanding the birth of the atoms in our bodies and the expansion of the space we inhabit, we gain a profound sense of perspective on our place in the infinite.

The Great Island Universes: The Astrophysics of Galaxies

Welcome back to the webref.org blog. In our previous look at Astronomy, we explored the objects within our cosmic neighborhood. Today, we scale up significantly. We are moving beyond individual stars to study Galaxies—the massive, gravitationally bound systems that serve as the fundamental building blocks of our universe.

The study of the astrophysics of galaxies (often called Extragalactic Astronomy) seeks to understand how these “island universes” form, how they evolve over billions of years, and the invisible forces that hold them together.

What Makes a Galaxy?

A galaxy is more than just a collection of stars. It is a complex ecosystem consisting of:

  • Stars and Stellar Remnants: Millions to trillions of them.

  • Interstellar Medium (ISM): Vast clouds of gas and dust that provide the raw material for new stars.

  • Dark Matter: An invisible substance that provides the gravitational “glue” for the galaxy.

  • A Supermassive Black Hole: Residing at the center of almost every large galaxy.

The Morphology of Galaxies: Hubble’s Tuning Fork

Galaxies are not all shaped the same. In the 1920s, Edwin Hubble developed a classification scheme that we still use as a foundational reference today.

1. Spiral Galaxies

Characterized by a central bulge surrounded by a flat, rotating disk with spiral arms. These are sites of active star formation. Our own Milky Way is a barred spiral galaxy.

2. Elliptical Galaxies

These range from nearly spherical to elongated shapes. They contain mostly older, redder stars and have very little gas or dust, meaning their “star-making” days are largely over.

3. Irregular Galaxies

These lack a distinct shape or structure. They are often the result of gravitational interactions or collisions between other galaxies.

The Engines of Growth: Active Galactic Nuclei (AGN)

At the heart of many galaxies lies a Supermassive Black Hole. When this black hole is actively “feeding” on surrounding gas and stars, it creates an Active Galactic Nucleus (AGN). These are some of the most luminous and energetic objects in the universe, sometimes outshining the entire galaxy that hosts them. Quasars are a well-known, high-energy type of AGN found in the distant, early universe.

The Dark Matter Mystery

One of the most profound discoveries in astrophysics occurred when scientists measured the rotation speeds of galaxies. They found that the outer stars were moving much faster than the visible matter should allow.

To explain this, astrophysicists proposed the existence of Dark Matter—a form of matter that does not emit light but exerts a massive gravitational pull. We now believe that galaxies exist inside giant “halos” of dark matter, which account for about 85% of the total matter in the universe.

Galactic Evolution and Mergers

Galaxies are not static; they are dynamic and “cannibalistic.” Over billions of years, smaller galaxies are pulled into larger ones.

  • The Local Group: Our Milky Way is part of a small cluster called the Local Group.

  • The Great Collision: In about 4 billion years, the Milky Way and the neighboring Andromeda Galaxy will collide and eventually merge into a single, massive elliptical galaxy.

Why Galactic Astrophysics Matters

Understanding galaxies is essential for understanding the history of the universe itself:

  1. Cosmic Chronometers: Because light takes time to travel, looking at distant galaxies is like looking back in time, allowing us to see the universe as it was shortly after the Big Bang.

  2. Chemical Evolution: Galaxies are the “factories” that cook up the heavy elements (like carbon and oxygen) necessary for life, distributing them through supernovae.

  3. Expansion of Space: By observing how galaxies move away from us (Redshift), we can measure the rate at which the universe is expanding.

Voyagers of the Void: An Introduction to Astronomy

Welcome back to the webref.org blog. We’ve spent time looking at the microscopic structures of cells and the invisible logic of computer code. Today, we cast our eyes upward. It is time to explore Astronomy, the oldest of the natural sciences and the study of everything beyond Earth’s atmosphere.

Astronomy is the scientific study of celestial objects—such as stars, planets, comets, and galaxies—and the phenomena that originate outside our planet. It is a field that combines physics, chemistry, and mathematics to explain the origin, evolution, and eventual fate of our universe.

The Two Lenses of Astronomy

To understand the cosmos, astronomers generally divide their work into two distinct but overlapping approaches:

1. Observational Astronomy

This is the data-gathering side of the science. It involves using telescopes and sensors to record the light, radio waves, and radiation coming from space. Whether it is a backyard telescope or the James Webb Space Telescope orbiting the sun, this branch is about seeing what is out there.

2. Theoretical Astrophysics

While the observers gather data, the theorists create the “manual.” They use mathematical models and computer simulations to explain why things happen. They tackle the big questions: How does a star die? What happens at the center of a black hole? How did the Big Bang unfold?

The Scale of the Universe

One of the biggest hurdles in astronomy is grasping the sheer scale of space. To manage these distances, astronomers use specific units:

  • Astronomical Unit (AU): The average distance from the Earth to the Sun (approx. 93 million miles). This is mostly used for measuring things within our solar system.

  • Light-Year: The distance light travels in one year (approx. 5.88 trillion miles). When you look at a star that is 50 light-years away, you are actually looking back in time 50 years.

Our Cosmic Neighborhood

Astronomy begins at home. Our Solar System consists of a central star (the Sun) and everything bound to it by gravity.

  • The Terrestrial Planets: Mercury, Venus, Earth, and Mars. These are small, rocky worlds.

  • The Gas and Ice Giants: Jupiter, Saturn, Uranus, and Neptune. These massive worlds are composed mostly of hydrogen, helium, and ices.

  • The Kuiper Belt and Oort Cloud: The icy “junkyards” at the edge of our system where comets originate.

Beyond the Solar System: The Life of Stars

Stars are the engines of the universe. They aren’t permanent; they have birth cycles and death rattles. A star’s life is a constant battle between gravity (pulling inward) and nuclear fusion (pushing outward).

    • Nebulae: Huge clouds of gas and dust where stars are born.

    • Main Sequence: The “adult” stage of a star where it burns hydrogen (like our Sun).

    • Supernovae: The explosive death of massive stars, which scatters heavy elements (like the iron in your blood) across the galaxy.

    • Black Holes: The remnants of the most massive stars, where gravity is so strong that even light cannot escape.

Shutterstock

Why Astronomy Matters in 2025

It is easy to think of astronomy as “looking at pretty pictures,” but it is vital for our survival and technological progress:

  1. Planetary Defense: Tracking Near-Earth Objects (NEOs) like asteroids to ensure we aren’t caught off guard by a potential impact.

  2. GPS and Satellite Tech: Our understanding of orbital mechanics and general relativity (to correct clock drift) is the only reason your phone knows where you are.

  3. The Origin Question: By studying the chemical makeup of distant planets, we are getting closer to answering whether we are alone in the universe.

  4. Inspiration and Unity: Astronomy provides a “Pale Blue Dot” perspective, reminding us that we all share a single, fragile home in a vast cosmic ocean.

Isaac Newton

Isaac Newton (1643-1727) was an English physicist, mathematician, astronomer, and natural philosopher who is widely recognized as one of the most influential scientists in history. His groundbreaking contributions to physics and mathematics laid the foundation for modern science and revolutionized our understanding of the natural world.

Key Contributions and Achievements of Isaac Newton:

  1. Laws of Motion: Newton’s laws of motion, published in his monumental work “Mathematical Principles of Natural Philosophy” (1687), established the fundamental principles governing the motion of objects. His laws describe the relationship between an object’s motion, the forces acting upon it, and the resulting acceleration. The laws are still widely used in classical mechanics today.
  2. Universal Gravitation: Newton formulated the theory of universal gravitation, which explains the force of gravity between objects. He proposed that every object in the universe attracts every other object with a force proportional to their masses and inversely proportional to the square of their distance. This theory provided a unified explanation for celestial motion and terrestrial phenomena.
  3. Calculus: Newton independently developed the mathematical framework of calculus, along with the German mathematician Gottfried Wilhelm Leibniz. Calculus is a branch of mathematics that deals with change and is fundamental to the study of motion, rates, and infinitesimal analysis. Newton’s work laid the foundation for differential and integral calculus.
  4. Optics: Newton conducted significant research in optics and made important discoveries. He studied the behavior of light, investigated the properties of lenses and prisms, and developed the theory of color. His work on optics culminated in his book “Opticks” (1704), which presented his experiments and theories on light and color.
  5. Reflecting Telescope: Newton designed and built the first practical reflecting telescope, now known as the Newtonian telescope. By using a curved mirror instead of a lens to gather and focus light, the reflecting telescope overcame many of the limitations of refracting telescopes, allowing for improved astronomical observations.
  6. Principia Mathematica: Newton’s seminal work “Philosophiæ Naturalis Principia Mathematica” (Mathematical Principles of Natural Philosophy) presented his laws of motion and the theory of universal gravitation. It is considered one of the most important scientific works ever published and had a profound impact on the scientific community.

Isaac Newton’s discoveries and theories revolutionized our understanding of physics, astronomy, and mathematics. His work laid the foundation for classical mechanics, and his scientific methodology and approach to empirical investigation influenced generations of scientists. Newton’s contributions to science, particularly in the areas of mechanics and gravitation, remain fundamental to our understanding of the physical world.

Magnetic braking during direct collapse black hole formation

Muhammad A. Latif, Dominik R. G. Schleicher

Magnetic fields are expected to be efficiently amplified during the formation of the first massive black holes via the small-scale dynamo and in the presence of strong accretion shocks occurring during gravitational collapse. Here, we analyze high-resolution cosmological magneto-hydrodynamical simulations of gravitational collapse in atomic cooling halos, exploring the dynamical role of magnetic fields, particularly concerning the effect of magnetic braking and angular momentum transport. We find that after the initial amplification, magnetic fields contribute to the transport of angular momentum and reduce it compared to pure hydrodynamical simulations. However, the magnetic and Reynolds torques do not fully compensate for the inward advection of angular momentum, which still accumulates over timescales of ∼1~Myr. A Jeans analysis further shows that magnetic pressure strongly contributes to suppressing fragmentation on scales of 0.1−10~pc. Overall, the presence of magnetic fields thus aids in the transport of angular momentum and favors the formation of massive objects.

High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

VINTERGATAN-GM: How do mergers affect the satellite populations of MW-like galaxies?

Gandhali D. Joshi, Andrew Pontzen, Oscar Agertz, Martin P. Rey, Justin Read, Florent Renaud

We investigate the impact of a galaxy’s merger history on its system of satellites using the new \textsc{vintergatan-gm} suite of zoom-in hydrodynamical simulations of Milky Way-mass systems. The suite simulates five realizations of the same halo with targeted `genetic modifications’ (GMs) of a z≈2 merger, but resulting in the same halo mass at z=0. We find that differences in the satellite stellar mass functions last for 2.25-4.25 Gyr after the z≈2 merger; specifically, the haloes that have undergone smaller mergers host up to 60% more satellites than those of the larger merger scenarios. However, by z=0 these differences in the satellite stellar mass functions have been erased. The differences in satellite numbers seen soon after the mergers are driven by several factors, including the timings of major mergers, the masses and satellite populations of the central and merging systems, and the subsequent extended history of minor mergers. The results persist when measured at fixed central stellar mass rather than fixed time, implying that a host’s recent merger history can be a significant source of scatter when reconstructing its dynamical properties from its satellite population.

https://arxiv.org/abs/2307.02206

Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Astronomy

Astronomy is the scientific study of celestial objects, such as stars, planets, galaxies, and the universe as a whole. It explores their formation, evolution, composition, and behavior through observation and theoretical models. Astronomers utilize advanced instruments and techniques to observe celestial phenomena and seek to understand the fundamental principles that govern the universe.

Key Areas of Astronomy:

  1. Observational Astronomy: Observational astronomy involves the study of celestial objects and phenomena through direct observation. Astronomers use telescopes and other instruments to gather data across different wavelengths of the electromagnetic spectrum, including visible light, radio waves, X-rays, and gamma rays. They observe and analyze objects such as stars, planets, galaxies, nebulae, and black holes.
  2. Stellar Astronomy: Stellar astronomy focuses on the study of stars, their properties, and life cycles. It examines the formation of stars, their structure, composition, and classification based on factors such as temperature, luminosity, and spectral characteristics. Stellar astronomers investigate processes like stellar evolution, nucleosynthesis, and the formation of stellar remnants such as white dwarfs, neutron stars, and black holes.
  3. Planetary Astronomy: Planetary astronomy focuses on the study of planets, moons, asteroids, comets, and other objects within our solar system. It examines their physical characteristics, composition, atmospheres, orbits, and geological processes. Planetary astronomers investigate planetary formation, surface features, weather patterns, and the potential for life beyond Earth.
  4. Galactic Astronomy: Galactic astronomy explores the structure, dynamics, and properties of galaxies, which are vast systems of stars, gas, and dust. It investigates galaxy formation and evolution, the distribution and properties of different types of galaxies (such as spiral, elliptical, and irregular), as well as the presence of dark matter and the role it plays in shaping galactic structures.
  5. Cosmology: Cosmology is the study of the origin, structure, evolution, and fate of the universe as a whole. It explores the Big Bang theory, cosmic microwave background radiation, the large-scale structure of the universe, the distribution of matter and energy, and the concept of dark matter and dark energy. Cosmologists seek to understand the fundamental nature and fundamental laws that govern the universe.

Research Methods in Astronomy:

Astronomers employ various research methods and techniques to investigate the cosmos. These include:

  1. Observational Techniques: Astronomers use ground-based telescopes, space telescopes (such as the Hubble Space Telescope), and arrays of telescopes to observe celestial objects across different wavelengths. They collect data through direct imaging, spectroscopy, photometry, and other techniques to study properties such as brightness, temperature, chemical composition, and motion.
  2. Computational Modeling: Astronomers develop theoretical models and use computer simulations to study and understand complex astrophysical processes. These models incorporate physical laws, mathematical equations, and computer algorithms to simulate the behavior of celestial objects, their interactions, and evolutionary processes.
  3. Data Analysis: Astronomers analyze large datasets collected from observations, including images, spectra, and other measurements. They employ statistical analysis, data mining, and other analytical techniques to extract meaningful information, identify patterns, and draw conclusions from the data.

Applications of Astronomy:

Astronomy has practical applications and contributes to various fields:

  1. Technology Development: Astronomy drives advancements in technology, such as telescope design, imaging technologies, spectroscopy, and data analysis techniques. These technologies have broader applications in medicine, telecommunications, imaging systems, and other scientific fields.
  2. Space Exploration: Astronomy provides valuable knowledge for space missions and the exploration of celestial bodies. It contributes to understanding planetary environments, identifying potential landing sites, and assessing the habitability of other planets and moons.
  3. Education and Outreach: Astronomy inspires public interest and engagement in science. It plays a crucial role in science education, public outreach programs, and promoting scientific literacy.
  4. Fundamental Research: Astronomy contributes to our fundamental understanding of the universe, its origins, and its physical laws. It addresses profound questions about the nature of space, time, matter, and energy.

Astronomy allows us to explore the wonders of the universe, unravel its mysteries, and deepen our understanding of our place within it. By studying celestial objects and cosmic phenomena, astronomers expand our knowledge of the cosmos and inspire curiosity about the nature of our existence.