Thu. Feb 29th, 2024
Galaxies: a partially solved mystery – part 2

In our previous discussion of galaxies, we briefly described how we came to understand galaxies as unique oases of stars in the middle of the vast cosmic desert.

Now, we will embark on a journey to discover the origin and composition of galaxies and their diversity, as well as to better understand our own galaxy – the “Milky Way”.

The Big Bang and the origins of galaxies

Astronomers believe that more than 13.7 billion years ago, all the mass and energy in our universe condensed into an infinitely small point that spontaneously exploded and expanded.

The explanation for this eruption, which we commonly refer to as “the Big Bang,” is beyond the scope of our discussion. Suffice it to say, however, that it has taken us quite some time to achieve even this understanding of our cosmic origins.

About 380,000 years after the Big Bang, the temperature of the universe cooled enough to allow photons of light to flow through, creating a “light echo,” a snapshot of the universe at that time.

The image below, obtained by the European Space Agency’s Plank satellite, shows an image of this light echo that we call Cosmic Microwave Background Radiation.

Copyright ESA and the Planck collaboration

Redder regions indicate a greater density of material within that early universe, and bluer regions indicate spaces where relatively little material existed.

As the universe continued to expand, it also continued to cool, producing the first atoms that later became the first stars.

Those regions with the highest concentrations of mass produced the greatest number of stars that eventually formed galaxies.

But if the universe has areas of higher concentrations and areas of significantly less material, then we should see evidence of this today by looking at galaxy clusters and voids where few or no galaxies exist.

In the following illustration we see precisely that.

Copyright CC BY-SA 4.0 Andrew Z. Colvin

When looking at the universe today, we see areas of high concentration of galaxies that we call “clusters” or “superclusters,” and sparse areas of material that we call “voids.”

Galaxies come in all shapes and sizes.

While they are all visibly made up of stars, gas and dust, the way the material is structured can be quite different (note: galaxies also contain massive amounts of dark matter that is not visible in nature).

In the spiral galaxy image below, notice the strong spiral arms that are made up of concentrations of stars, dotted with dark, jagged lanes of dust running through them. But in the elliptical galaxy image, all evidence of those features has disappeared.

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Galaxy collage.Top left: Spiral. Top right: Elliptical. Bottom left: Barred spiral. Bottom right: Irregular

Galaxy evolution, as well as collisions with neighboring galaxies, can change the morphology of a spiral galaxy to an elliptical galaxy in millions or billions of years.

Galaxies are oriented in all possible directions in space.

This means that we can see galaxies from different perspectives and learn from these different observations.

The view below is of a frequently observed spiral galaxy, known as Needle Galaxy or NGC 4565. What makes this spiral galaxy so interesting is that we observe it almost edge-on. So instead of seeing it from above and looking at the beautiful spiral structure (like in the M101 image above), we see it from the side.

Image of NGC 4565 taken through the 10” telescope at the Waasa Debaabing Observatory (view away) in the Killarney Provincial Park Observatory Complex

A close view of the same galaxy taken by the Hubble Space Telescope reveals the incredible amount of dust obscuring much of the background stars, as well as the halo surrounding the galaxy’s core.

In this image, we see the structure of the galaxy seen from the outside.

Interestingly, the view above may be familiar to some readers, as it is relatively similar to another image of the Milky Way, as seen from Earth looking outward. Learn more about our galaxy, the Milky Way.

Credit: ESO/S. brunier

So what does our Milky Way look like from the outside?

Just as the average person is interested in seeing their neighborhood from above, astronomers have long longed for the ability to see what our galaxy looks like from the outside in.

The challenges of surveying the neighborhood involve careful measurement of distances and heights and often use prominent landmarks. Similarly, mapping the structure of our own Milky Way from within uses distance measurements at different electromagnetic wavelengths and prominent landmarks: bright stars, globular clusters, and other unique features.

As far as we know, we believe our Milky Way is a barred spiral galaxy that looks like the image below left.

NASA imagesLeft: image of our Milky Way. Credit: NASA/Adler/U. Chicago/Wesleyan/JPL-Caltech. Right: image of our UGC 12158. Credit: NASA, STScI and ESA

Our galaxy is estimated to be between 150,000 and 200,000 light years in diameter (up from previous estimates of 100,000 light years in diameter) and about 2,000 light years thick.

On the right, we see an image of a different galaxy known as UGC 12158, which appears to be a very close imitation of our own galaxy. So maybe we have a cosmic twin born in a different region of the universe, which is no less fascinating to study!

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Where do we go from here?

We have learned that galaxies tend to congregate in clusters.

We are part of one such congregation of galaxies, known as the “Local Group” consisting of the Milky Way, the Andromeda Galaxy (M31), the Triangle Galaxy (M33), and about 20 smaller galaxies.

We now believe that the Milky Way and the Andromeda Galaxy are quite similar in size and mass and, in about 3.75 billion years, these two galaxies may collide.

In the video below, you can see the Milky Way, joined by the Andromeda galaxy and the much smaller Triangle galaxy.

The collision is unlikely to directly affect our solar system, since the distance between the stars, even during a collision, is so great that they would likely pass side by side.

However, over time, the two galaxies will most likely merge into a single galaxy that looks more like an elliptical galaxy.

Our cosmic origins

Our understanding of galaxies, in turn, has led to a dramatic revolution and evolution in the way we think about our place in the universe.

Thousands of years ago, the best minds of the time determined, based on their extremely limited observations, that humanity was at the center of the solar system. That notion was put aside with the ideas of Kepler and Galileo.

Hundreds of years ago, scientists believed we were at the center of our galaxy. But that belief was also cast aside in favor of ideas based on even better observations and theories to support those observations.

Today, in 2021, we feel that we have come a long way and, in fact, our understanding of the universe has made enormous strides, even in the last 40 years!

But believing that the age of discovery is coming to an end is shrouded in as much ignorance as the ancients who believed with certainty that the planets and sun revolved around the Earth and, similarly, believed that there was nothing left to discover.

Observatory with telescopic platforms under the starry sky.The Killarney Observatory Complex

Venturing at night into our glorious provincial parks gives us the opportunity to reconnect with the stars at night and, with our greater understanding, reflect even further on the nature of the universe.

We owe it to our children and our children’s children to protect these natural environments that give us truly dark views of the stars so that they, too, can reflect on the universe and, perhaps, grow and make new discoveries that change perceptions of humanity. forever.

Ontario Park’s three dark sky reserves:

We are counting on everyone to do their part to stop the spread of COVID-19 by following the advice of public health officials. Only visit provincial parks or conservation reserves close to your home for day use and do not travel outside your area.