Sat. Mar 2nd, 2024
Galaxies: a partially solved mystery – part 1

After a typical Canadian winter, we look forward to the spring season and the changes that come with it: the fresh fragrance of flora, the lushness of the natural forest, and the tranquility of flowing water.

Spring also marks the beginning of a new landscape of interesting objects visible in the night skies: galaxies.

Why is spring a good time to observe galaxies?

While galaxies can be seen all year round, spring night skies are the best time of year to see the diversity and multitude of amazing galaxies.


This galactic assembly occurs because we look toward large galaxy clusters that are relatively close during the spring months.

In addition to the proximity of galactic clusters, the dust that exists within our own galaxy thins a bit in the direction of the skies that are best seen in both the spring and fall seasons.

To the races

Hundreds of years ago, with the invention of the telescope, many astronomers scanned the heavens for what they perceived to be cosmic interlopers: comets.

To them, these comets looked like blurry, cloudy, or nebulous patches of light, difficult to detect with their primitive telescopes, and even more difficult, if not impossible, to see without a telescope.

At that time, the discoverer of a comet was rewarded by having his name associated with that comet forever. So he began the race to be the first to find a new comet.

False alarm

There was only one problem with this race: the false alarm created by the appearance of other blurry, hazy spots in the sky that do not move and are therefore not comets.Map of the Orion Nebula.

Astronomers, such as Charles Messier, began producing lists of these pesky specks of light to help them avoid accidental false alarms in their quest for comet discovery fame and posterity.

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Thus began the list of some of the most fascinating discovered objects: cosmic nebulae.

The cosmic debate

Over time, and with increasing quality of telescopes, observers realized that these cosmic “nebulae” actually had different compositions.

Some seemed to contain hundreds, thousands, or hundreds of thousands of stars. Today we call them clusters. Some retain their ghostly appearance and retained the name “nebula” (see last month’s issue for the Orion Nebula).

Orion Nebula.

And then there was a group that was still in confusion until about a hundred years ago: the “galactic nebulae.”

Two camps emerged: one believed that these objects were inside our galaxy and another believed that they were their own galaxies of stars that were much further away.

The debate was only answered after the discovery of the expanding universe by Edwin Hubble just over 90 years ago.

Where life and death occur.

Galaxies are now recognized as a large collection of stars, dust and gas, and were formed from ripples in the universe at the time of the Big Bang.

Galaxies are also enveloped in dark matter, the name we give to a huge amount of something that cannot be easily seen, but whose gravitational force can be observed.

They are dynamic places with the birth and death of stars and collisions of clouds of dust and gas. It’s also very likely that they are full of life (although we haven’t discovered anything beyond Earth yet).

They can also interact with other galaxies, as seen in the photo at the top of today’s post.

When the stars collide

The remnant of a recent interaction is seen in this beautiful view of a starburst galaxy: M82. This spiral galaxy, seen almost edge-on, had a recent close encounter with its neighbor (M81).

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Galaxy, edited photo.We have removed the stars from this photo to provide a more realistic view of the galaxy as it would appear in space. Since there are virtually no stars between galaxies, if one were to travel far from our own galaxy, one would see the image above.

The result of the interaction has caused a huge collision of gas clouds that, as we learned about the Orion Nebula, serves as the main mechanism for star birth (note the reddish area around the central bulge of the galaxy).

When we see images of galaxies with stars (like the first image at the top), we are seeing all those stars in forehead from that distant galaxy. Those stars are more than 1,000 times closer to us than the galaxy itself!

A supermassive black hole

We have discovered some truly massive galaxies.

Photo: NASA and the Hubble Heritage Team (STScI/AURA)

One of them, called M87, is an elliptical galaxy (a galaxy that does not appear to have dust lines) and has up to ten times more stars than our own galaxy, the Milky Way.

Observed for some time, M87 appears to have a huge jet of highly focused plasma (charge particles) moving at extreme speeds.

Given its unusual size and structure, astronomers studied M87 and concluded that a supermassive black hole on the order of a billion times more massive than our Sun must lurk at its center (for comparison, the supermassive black hole in the center of our galaxy is approximately 250 times less massive).

Event Horizon Telescope Collaboration

Astronomers believe that supermassive black holes play an important role in the shape and structure of many galaxies, and we are just beginning our journey of discovering these fascinating and strange objects.

Only by continuing to study supermassive black holes in other galaxies can we learn more about their importance and the role they play. This, in turn, helps provide better context for the study of our own galaxy, our cosmic home.

Come back next month for “Galaxies – part 2”

We will discuss the appearance of our own Milky Way, both from inside and outside.