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Secrets of the Milky Way- From Spiral Arms to Galactic Bulges

When you were a child, didn’t you find yourself fascinated by the beautiful sky and wondered what it contained? Because I always was awe-struck by this. The galaxy in which we live is termed the Milky Way. It’s not only the part that we can easily see with our naked eyes; it’s much more than that.

I remember a general catalog was published in 1888. It designated numbers for different galaxies, nebulae, and star clusters. These catalog numbers contain far more useful information for astronomers.

Catalog numbers were eventually assigned to the galaxy with descriptive labels as well. Nevertheless, no galaxy index includes our galaxy. Thus, it required a name that astronomers could use to identify it. Astronomers refer to G as the galaxy when not using the name, and all other galaxies are lowercase.

Let Me Tell You More About Milky and Its Composition

Milky way
– Source: Pixabay

 The sky full of stars you always see at night is also in the Milky Way Galaxy. A common comparison is linked to two fried eggs pressed together side by side. The enormous globe of stars at the corner of the galaxy that extends both above and below the galaxy’s plane is known as the Giant bulge or the yoke of the egg.

No one believes that the Milky Way is made up of four spiral arms that radiate outward from its center, resembling the arms of a Catherine wheel.

However, the center does not need these arms to truly converge. Astronomers found out a few years ago that the Milky Way is a Barrett spiral galaxy. This indicates that its spiral arms extend from either and, and a “bar” of stars crosses its center. In the universe, barred spiral galaxies are not rare. However, we are still unsure of how that central bar forms.

Aren’t You Curious about Its Size?

American astronomer Harlow Shapley took the first precise measurements of the Galaxy’s size. Initially, he determined the geographical dispersion of the global clusters before calculating their size. Shapley found that the Galaxy is huge, as opposed to being a relatively tiny system, with the sun being closer to its edge than its core.

Assuming that the global clusters form the Galaxy’s shape, he claimed that the diameter of the Galaxy is about 100,000 light years, and from the center, the location of the sun is nearly 30,000 light years. And you know what! His beliefs have proven their importance over time. The star disk of the Milky Way system is nearly as large as Shapley’s model anticipated, depending in part on the particular element under consideration.

The bulb of dark matter or unobservable stuff may be considerably bigger than previously thought, while neutral hydrogen is spread more evenly. From the galactic center, the distance of the sun is said to be about 25000 light-years, while for the stars and the gas clouds, which are extremely far away, their distance can be measured accurately, which is 100,000 light-years away.

In fact, planets make up just a small fraction of a Milky Way Galaxy’s overall mass and range from 890 billion to 1.54 trillion times that of the Sun (8.91011 to 1.541012 solar masses).

Various methods and data sets are used to determine the Milky Way’s mass. The estimated range’s low end is 5.81011 solar masses (M), which is just a little bit less massive than the Andromeda Galaxy. Stars near the edge of the Milky Way have been observed moving at speeds as high as 254 km/s (570,000 mph) in 2009, according to observations made with the Very Long Baseline Array.

Now Let’s Talk about Stars and Clusters

Milky way
– Source: Pixabay

Upon examining a cluster of stars, we discover two distinct populations based on their age, each with a unique appearance and distinct spatial distributions throughout our galaxy. Open clusters are groups of about 100 to 1000 stars with a range of younger ages (typically a few million to several 100 million years) that are concentrated in the Milky Way’s plane.

Cepheid variables and RR Lyrae variables are two examples of these classes of periodic variables. For these stars, there is a relationship between period and luminosity that makes it possible to calculate a star’s luminosity (or absolute magnitude) from its period. (Physically, this is because larger, more luminous stars “pulse” more slowly.)

“Variable stars” are giant and supergiant stars that are unstable and have fluctuating luminosities. Stars in a specific area of the H-R diagram will pulse like a heartbeat, and as they modify their internal balance between gravitational contraction and energy production, this variation in luminosity will occur repeatedly.

We can determine a variable star’s distance by comparing its measured apparent brightness with either an RR Lyrae or a Cepheid variable star. Cepheid variables are luminous giant stars that can be used to measure distances within and even between other galaxies and the Milky Way Galaxy.

Structural Features of the Milky Way

The structure of the Milky Way galaxy is like a massive spiral system.

Milky way
– Source: Pixabay

The structure can be divided into six components:

  • A thick and thin disk
  • A central bulge
  • A nucleus
  • Spiral arms
  • A spherical component
  • A massive halo

Some of the elements have similar characteristics.

A black hole surrounded by an accretion disc of temperature gas lies at the very center of the Galaxy. Because of the thick screen of intervening dust in the Milky Way, neither the central object nor any of the material immediately surrounding it can be observed at optical wavelengths.

Radio astronomers have named the object Sagittarius A* because it is easily detectable at radio wavelengths. The galactic nucleus, which is similar to the centers of the active galaxies but on a smaller scale, is the site of a wide range of activity that appears to be powered by the black hole. The region emits infrared and x-ray radiation, and rapidly moving gas clouds can be seen.

An extended, nearly spherical mass of stars, mostly composed of population II stars despite their relative abundance of heavy elements, surrounds the nucleus.

Many star clusters, known as globular clusters, are mixed in with the stars. Both the stars and the cluster orbit the nucleus almost radially. Optical observation of the bulging stars is possible where they protrude above the galactic plane’s obscuring dust.

Milky way
– Source: by Pixabay

The disk, which stretches out from the galaxy’s nucleus for about 75,000 light-years, is the most noticeable feature from a distance. The Galaxy has a bright, flat distribution of stars and gas clouds that is outlined by a spiral structure, making it similar to other spiral systems.

And think of the disk as the superposed arms on top of the underlying body of stars. The thickness of this body is approximately one-fifth of its diameter; however, the characteristic thickness of its various components varies.

The youngest stars and dust and gas comprise the thinnest component, often referred to as the “thin disk,” while slightly older stars are found in the thicker component, sometimes referred to as a “thick disk.”

It was not until 1953 that the distances to stellar associations could be reliably determined that astronomers discovered the galaxy’s spiral structure. It is extremely difficult to detect optically due to the interstellar dust that obscures it and the solar system’s inner location.

Since both molecular clouds and neutral hydrogen can be detected through the dust, it is easier to identify this structure from radio maps of either one.

To estimate the distance to the detected neutral hydrogen atoms, measured velocities must be utilized in combination with a rotation curve for the Galaxy, which may be generated from observations made at different Galactic longitudes.

How Did the Milky Way Get Its Spiral?

Theoretical understanding of the Galaxy’s spiral arms has progressed greatly since the 1950s, but there is still more to learn about the relative importance of the several effects thought to affect the formation of the arms.

Almost certainly, a general dynamical effect called a density-wave pattern is responsible for the overall pattern. Any large-scale disruption of the star density distribution in a Galactic desk will naturally result in a spiral-shaped galaxy, as demonstrated by American astronomers Frank H. Shu and Chia-Chiao Lin.

Calculating the interaction between the stars reveals that the resulting density distribution adopts a spiral pattern that revolves around the nucleus more slowly than it does with stars.

Here Are Some Interesting Theories about the Galaxy

The first law is the Hubble Law. The relationship between the speed at which a Galaxy is moving away from us and its distance is one of the most important laws in astronomy, and it makes use of the Doppler effect, which is relatively easy to measure. Hubble discovered that the farther away a Galaxy is, the faster it is moving away from us, based on studies of galaxies with known distances.

So velocity = Hubble constant (HO) multiplied by distance, where velocity = speed of light multiplied by redshift (at low redshift). The distance and redshift are the observational quantities. In the Hubble connection, the Hubble constant serves as the proportionality constant. The Hubble constant is currently around 75 km/sec/mpc.

The second theory is the Big Bang Theory. Other evidence is also there that claims that the Big Bang theory is correct, aside from the Hubble Law expansion of the universe. As the theory states, there was an original hot ‘fireball’ when the universe was very small.

Another fact that supports this model is that we have detected remnant radiation from a time when the universe was extremely hot. Cosmic microwave background radiation. First discovered by chance in the early 1960s, it had been predicted; we believe it is relic radiation from a hotter universe that has since expanded, shifting to longer and longer wavelengths.

The COBE (Cosmic Microwave Background Explorer) satellite recently measured what was predicted to be thermal (black body) radiation. The wavelength of the black body curve’s peak yields a temperature (via Wien’s Law) of 2.7 kelvin—close to absolute zero now but evidence of a much hotter past. The sky’s microwave background radiation is visible in all directions, as would be expected.

Origins of the Universe 101 | National Geographic

Finally, the third major piece of evidence for the Big Bang is that it would solve a puzzle like a cosmic abundance of light elements (heavy elements are made in massive stars), namely that the universal abundance of helium is observed to be about 24% everywhere. This is puzzling because ordinary hydrogen burning in main sequence stars produces helium, but not nearly enough of it; about 10% of hydrogen is converted to helium.

To get around this, assume that most of the helium was created during the first 3 minutes of the Big Bang when the entire universe was hot enough to fuse hydrogen.

Milky Way’s New Discoveries

Astronomers just discovered another important finding a few years ago. The Milky Way is shaped more like an extended S than a flat disk of stars. The disc was warped for some reason.

Right now, the Sagittarius door galaxy’s proximity to the Earth is the source of the gravitational pull. Like moths around a flame, it is one of about 20 small galaxies that orbit the Milky Way. The wrap is the result of the Sagittarius Galaxy’s gravitational pull on our Galaxy’s stars as it slowly revolves around us.

Other objects are connected to the Milky Way as well. Globular Clusters form a ring around our galaxy. Globular clusters are star clusters that have the appearance of fuzzy golf balls. They are home to a million or so extremely old stars.

Milky way
– Source: Pixabay

 The Milky Way galaxy is still being discovered. Research into their nature and origins is advancing as new astronomical instruments, like the orbiting Gaia observatory from the European Space Agency, become accessible. Gaia is creating an exquisite, unprecedented three-dimensional map of our Galaxy’s stars.

Last Updated on May 16, 2024 by Pragya


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