Home:     Window on the World
Text Size:

# Window on the World

## Our Milky Way Galaxy and Beyond

Our Latest Post: 26 December 2021

## An Overview with a Touch of Philosophy

A galaxy is a group of many individual stars. Each galaxy is composed of many millions or billions, even trillions of stars. Our Milky Way Galaxy contains on the order of 300 billion stars. Several super-giant galaxies contain trillions of starss.

Despite the immense size of even the smallest galaxies, most galaxies in the heavens are not visible to the naked eye. As optical-light (visible to humans) telescopes became more and more powerful, more and more galaxies and stars became visible. In the present era, high-definition images are created at electromagnetic wavelengths that are far shorter and far longer than the wavelength band of human vision; thus, opening our field of view to an extraordinarily wide window of observation. Explore electromagnetic wavelengths at "What Our Eyes Cannot See"

As time marches on, formation of colonies on the Moon and Mars will be routine events. On a negative note, however, visiting other solar sys­tems in our own galaxy represents a major chal­lenge, the constricting factor being the maximum speed of light: 190,000 miles per second (300,000 kilometers per second). Our nearest star could be reached in four million years, traveling at the speed of light. Visiting planets in other galaxies is, thus, a bit whimsical; for now!

##### Note:
The symbol " ~ " (tilde), as used by this author, is shorthand for " approximately" or "about." The tilda has other meanings in languages other than English.

Our nearest neighboring star (Proxima Centauri), is ~4.2 light years from our place in the Universe; earthly humans will need many years to travel to other planets outside of our Solar System. At half the speed of light, a one-way journey to Proxima Centauri would require more than eight years, and at one-tenth the speed of light, the same journey would take more than 40 years.

Just a Speculation: Our future journeys into outer space will necessarily be via self-contained, closed-loop habitat vehicles that self-produce food, textiles, building materials, and electricity. Solar energy would not be available for most of a trip, because of the great distances between the spaceship and nearby stars; brightness diminishes by the distance squared ($y = 1/x2$; i.e. brightness is inversely pro­portional to the distance squared.

Because of the immense distance traveled from Earth, a journey of this nature must also include plans for the next generation that must proceed from the first generation of travelers. A one-way trip to our nearest star would require the implementation of, for example, social and legal structures and rules for civility and procreation. In other words, new civilizations would evolve.

The foregoing issues might seem in­surmountable. If the history of the past 100 years or so is an example of what can be revolutionary application of old and new technologies, we should have faith that new technologies and human ingenuity will arise as needed. The most needed new technology is the unlimited production of energy. Although, we can see the future of energy production by gazing into the sky, the Sun and stars have continued to leave us with many gaps in our understanding of their energy-producing miracle; perhaps we can baptise this miracle, "energy of the gods".

Before the late 19th century, the heavens were viewed only in visible-light wavelengths. In the 20th century, silver-halide (stan­dard photography) sur­rendered to solid-state semi-­conductor sensors and other masterpieces of exotic engineering that dramatically extended our view at wavelengths well-beyond our human vision. Nowadays, astronomers view distant objects in a very wide range of electromagnetic wavelengths, which leads to new discoveries and better understanding of Nature.

Another example of advancements in inaging is seen in the photo­graphs of Andromeda (M31) taken in 1898 by Isaac Roberts that began to establish M31 as a galaxy, rather than a star. M31 (is also cataloged as NGC 224.)

NASA's space-based Hubble telescope revealed an immense amount of image detail shown in this zoomed-in view of one tiny area of the original Andromeda image. Extreme (4k imagery) mag­nification uncovers innumerable stars.

At a distance from Earth of ~2.5-million light years (ly), Andromeda is among the closest galaxies in our galactic neighborhood, but closeness is relative:  Compare Andromeda's ~2.5 million ly with a mere ~4.2 ly from Earth to Proxima Centauri, our Solar System's nearest star. Proxima Centauri is gravitationally bound to the alpha- and beta-Centauri stars (Proxima Centauri: Skatebiker, via Wikimedia Commons CC BY-SA 3.0).

To carry this idea of relative distance a bit further, our Sun is only ~8-light minutes from Earth and our Moon is ~1.3 light seconds from Earth.

One may have wondered why there is a noticeable gap of silence when two people are talking to each other via satellite. The speed of light explains the phenomenon. Because all electromagnetic radiation travels at or near the speed of light, a synchronous (always in th e same place in the sky) Earth-orbiting satellite is about a quarter of a light second from Earth's surface; a two-way conversation, therefore, is usually delayed by at least a quarter of a second each way; normally, however, more delay (latency) is added by terrestrial- and ocean-based cables and Internet routers (machines that direct Internet traffic).

Note: Light travels down a fiber-optic cable (very thin sttrands of glass) near the maximum speed of light; electrons travel down a copper wire also at, or nearly at, the speed of light.

Communicating here on Earth, however, does not have a noticeable delay, because the maximum distance between any two points anywhere on the surface of the Earth is about ~20,000 km (~11,000 miles); at a speed of 300,000 kilometers per second (186,000 miles per second), the minimum travel time between two points anywhere on the surface of the Earth is slightly faster than the blink of an eye (~4 milliseconds):  i.e.~4/1000 of a second; therefore, no one notices a delay.

Many of the stars that appear to us on Earth at this time in history will no longer be alive in the future and, conversely, many new stars will have replaced old stars that are in our view now. Millions of years from now, the sky will be different; our own Milky Way galaxy will be different. Ancient Asian and Latin philosophers observed that "everything changes."

To put these ideas into some semblance of comprehension, realize that our Earth is 4.5 billion years old. About 4-billion years from now, the Andromeda Galaxy and our Milky Way galaxy will have begun the process of colliding with each other, dramatically changing the geography of this part of the Universe. Galactic collisions are a common occurrence in our Universe.

Will our Universe die?, at the end of "Creation", or will our Universe not die? Is our Universe forever, perhaps? How might new discoveries and the magic of "quantum physics" shape space, time, and reality? No one knows, yet!

## Categorizing Galaxies

A galaxy is a group of stars. Some galaxies are composed of many millions (x,000,000) of stars while other galaxies contain a trillion (x,000,000,000) or more stars. As a reference point, our Milky Way Galaxy is home to about 30 billion stars. The largest known galaxies each have a trillion or more stars. Our Universe is indeed quite immense.

• ☀ Dwarf Galaxies Contains youngest stars
• ☀ SpiralMilky Way Galaxy
• ☀ EllipticalSombrero Galaxy
• ☀ Globular ClustersMessier 2
• ☀ IrregulerMagellanic Clouds
• ☀ Super GiantContains oldest stars

Galaxies are classified by their shape. The more common galactic shapes are described below. The galaxy in which our Earth resides is called the Milky Way Galaxy, which is classified as a "Spiral" galaxy. Spiral galaxies resemble earthly hurricanes, having spiral arms that appear to rotate around a central bulge.

### Dwarf Galaxies

Dwarf galaxies are the nurseries of the Universe. Dwarf galaxies, or nebulae (foggy clouds), contain young stars and tend to not have a well-formed structure, which is why many dwarf galaxies are referred to as "nebulae". As these dwarfs create new stars, these galaxies typically increase in size and they eventually form spiral galaxies, which in turn, evolve into elliptical galaxies.

### Spiral Galaxies

Our Sun and Solar System are whirling around in one arm of our "Milky Way Galaxy". The spiral arms contain dust, gas clouds, and stars, that appear as a "milky" haze that stretches across the evening sky. Most stars in the spherical center, or bulge, of a spiral galaxy are older stars, while younger stars inhabit the outer areas of a spiral galaxy.

The spacing of the spirals in a spiral galaxy follows an intriguing phenomenon throughout Nature, the Fibonacci Series, named after the Italian mathe­matician Leonardo Fibonacci (~1170–1240 CE). The first few numbers in the Fibonacci Series are:
$0 1 1 2 3 5 8 13 21…$ The spacing of planetary distances from the Sun closely correlates with the same ratio of $1.6:1$ as the ratio represented in each pair of Fibonacci numbers.

The ratio between each pair of Fibonacci numbers are not only observed in the cosmos, but also observed in geology, biology, and zoology here on Earth. For example, spirally shaped snail shells, hurricane swirls, and the layout of seeds in a plant pod are all arranged according to the Fibonacci Series. This phenomenon is also referred to as the Golden Ratio, which equals $1.6:1$ [or $16:10$]; high-definition television receivers commonly use $16:9$ as the ratio of width to height.

The Whirlpool Galaxy  is in reality two galaxies inter­acting with each other. The streaks of red in the image indicate hydrogen, which indicates regions where stars are born.

### Elliptical Galaxies

Elliptical Galaxies are usually shaped like an ellipse. In visible light, they appear smooth, revealing no features, such as individual stars or dust-laden gaseous clouds. Structural detail, however, is uncovered when these galaxies are viewed in ultraviolet and infrared light or in other wavelengths of electromagnetic radiation, such as x-rays or gamma-rays. Stars found inside elliptical galaxies are very much older than stars found in spiral galaxies.

### Globular Clusters

Globular Clusters are spherically shaped concentra­tions of stars that typically reside within the central core of galaxies and typically contain the oldest stars in their respective galaxies. We might say, "a globular cluster is a galaxy within a galaxy." In 1665, the first globular cluster was discovered and was labeled M22.

### Irregular Galaxies

Oddly shaped galaxies that do not resemble any of the more common forms are listed as "irregular" galaxies. Many of these irregular galaxies are among the oldest galaxies in our Universe. Younger galaxies seem to have more describable shapes. In visible light, irregular galaxies appear smooth, revealing no features, such as individual stars or dust-laden gaseous clouds. Structural detail, however, is uncovered when these galaxies are viewed in ultraviolet and infrared light or other wavelengths of electromagnetic radiation, such as x-rays or gamma-rays. A dense region of the larger of the two Magellanic Clouds reveals much structural detail.

### Super Giant Galaxies

Among the billions upon billions of galaxies and clusters of stars flying around the Universe, the largest and brightest, thus far found, is the dying elliptical galaxy IC-1101 in the constellation Virgo. Containing ~100,000,000,000,000 (~100 trillion) stars and about ~1,000,000,000 (~one billion) light years distant from Earth. Telescopes at the time of IC-1101's discovery in 1789, could reveal very little of the structure of heavenly objects; at the time, objects in the sky appeared as smudges of light when viewed through early telescopes.

Another limiting factor for astronomers was Earth's atmosphere. When viewing the heavans from the Earth's surface, stars appear to be twinkling, though, stars do not twinkle. (Some stars, hovever, do emit pulses of light.) The launching of satellites in the 1960s opened the way to observe the heavens from high above the Earth's surface, for example, the Earth Orbiting Hubble telescope.

A profoundly limiting factor at the time was the inability to observe objects beyond the limits of human-visible light. Advances in the quality and power of modern telescopes facilitated the way to observe objects in wavelengths beyond visible light. Observing objects in infrared, ultraviolet, and x-ray wavelengths revealed much much more information about individual stars, as well as previously unseen structures within galaxies.

Modern telescopes have drastically increased our ability to see very fine structural detail and to see in many different wavelengths of electromagnetic radiation, which includes visible light that our human eyes can see. We could say that our Milky Way Galaxy, as well as the Universe itself, has revealed much information about how celestial objects shine for billions of years, how they are born, mature, and die. In the last several decades, we have seen much that was formerly invisible.

Note: Because "visible light" is a form of "electro-magnetic radiation", the two words are often used interchangeably. Human vision is only a narrow sliver of the total electro-magnetic spectrum.
An aside: many species of insects, birds, and reptiles "see" in parts of the light spectrum that are invisible to humans. A few examples: rattle snakes see in the infra­red; many insects and birds see in ultraviolet; dogs see in yellow and blue-to-ultraviolet; and raccoons and dolphins see in black-and-white.

## Black Holes

A global group of eight collaborating astro­nomic institutes in 2019 focused their astronomical multi-meter-wide dish anten­nas on the massive galaxy M87. From the radio images, dozens of scientists from around the world constructed the first-ever image of a black hole. Although theory had predicted the existence of black holes, no black hole had ever been imaged.

Note: In the modern vernacular, "imaged" replaces "photographed." Silver-hailide photography has been replaced by solid-state sensors, thus, "imaged".
Also note that the black-hole images are invisible to humans; black holes become visible when viewed at millimeter wavelengths, which is equal to a frequency of $~25 GHz / 25 GigaHertz\right)$.

Black holes are a strange and fascinating phenomenon that have been described as the "vacuum cleaners" of the cosmos. The prevailing theory is that black holes suck up anything that approaches an obserbable ring at the edge of an invisible bottomless pit; this precipice of doom is called by astro-physicists an event horizon, from which nothing escapes, not even light.

The grandest question at the present time is "what is on the other end" of a black hole or is there no end to the depths of the intense gravitational pull that drives a black hole.

The black hole image shown here focuses on the center of massive galaxy M-87 by a colaboration of Event Horizen Telescope (EHT) radio astronomers from across the planet. The imaging technique synchronizes a global array of huge multi-meter-diameter radio dish antennas. These global arrays of super-sensitive radio receivers form a gigantic virtual radio telescope the size of Earth. The end product of all these radio telescopes working together is incredible sensitivity to very faint radio signals arriving at Earth after traveling many millions and billions of light years before reaching Earth.

Routine chores for these individual arrays is tracking thousands of orbiting commmunications satellites and monitoring spacecraft journeying through our solar system and beyond. Many of these organizations participate in the search for life beyond Earth.

Returm to the beginning of this chapter, Galaxies.