Things you didn’t know about the Milky Way

The name Milky Way is very old and we have to go back long before the arrival of electric lights to society, in which all human beings had a beautiful unobstructed view of the night sky. The huge milky band of stars across the sky was impossible to miss. The ancient peoples had different names to the cloud-like structure of our galaxy, but our modern version derives from the Greeks, specifically from the myth that the infant Hercules was brought before the goddess Hera, who took care of him while she was asleep. When she woke up and pulled away, her breast milk spilled through the sky, hence the name Milky Way. Its use is so old that there are many people who do not know this classic origin.

Even the terraplanists will welcome this curiosity. Our galaxy is, on average, a hundred thousand light-years wide but only a thousand light-years thick. Inside this flattened disk (though somewhat twisted), the sun and its planets are embedded in a curved arm of gas and dust, placing the solar system about 26,000 light-years away from the galaxy’s turbulent core.

There’s no way of knowing who discovered it in the first place, but we do know that Galileo recognized the light band of our galaxy as individual stars in 1610. It was the first real test when the astronomer pointed his first rudimentary telescope to the sky and could see that the Milky Way was made up of countless stars.

It would have to wait until the 1920s, when the famous astronomer Edwin Hubble provided conclusive evidence that the spiral nebulae in the sky were in fact entire galaxies. This helped astronomers to understand the true nature and shape of the Milky Way, and also to discover the true size and scale of the universe around us.

We’re not exactly sure how many stars there are in the Milky Way. And counting stars is a pretty tedious job. Even astronomers argue about the best way to do it. Their telescopes only see the brightest stars in our galaxy, and many are hidden behind gas and dust. One technique for estimating the stellar population of the Milky Way is to observe how fast the stars orbit within it, giving an indication of the gravitational pull, and therefore of the mass, of the galaxy. We divide the galactic mass by the average size of a star and we will have the answer. But of course, these are approximations because the stars vary a lot in size. The European Space Agency’s Gaia satellite has mapped the location of a billion stars in our galaxy, and its scientists believe that this represents 1% of the total, so maybe the Milky Way contains about 100 billion stars.

What is a galactic year or a cosmic year? It’s basically the period of time it takes the solar system to orbit around the center of our galaxy, the Milky Way. Thus, a galactic year would be equivalent to approximately 225 million years. Within these numbers, the Earth would have about 20 galactic years and the galaxy would have about 54 galactic years.

We know that when we speak of terms related to galaxies, we use the term galactic, but where does this word come from? The word galaxy comes from the Greek galaktos, which came to us through the late Latin galaxy, which refers to celestial bodies, with the same meaning as the kyklos galaxies or the milky circle’ used by the Greeks to refer to the Milky Way.

We have already commented that the Milky Way is a fairly typical galaxy. Spiral galaxies in general tend to be larger than other types of galaxies, but the Milky Way is not only very large, but the most important thing about it is that it managed to sustain life. At the moment, the only place in the universe where we’ve found life.

Several studies have indicated that the Milky Way and its neighbors are living in the prosperity of the cosmos. From afar, the large-scale structure of the universe looks like a colossal cosmic web, with string-like filaments connecting dense regions separated by huge, mostly empty, gaps. The emphasis in that last sentence must be on "almost empty", as our own galactic abode seems to be an inhabitant of the Keenan Void, Barger and Cowie (KBC), named after three astronomers who identified him in a 2013 study in The Astrophysical Journal.

Called Sagittarius A, the supermassive black hole at the center of the galaxy weighs more than four million times the mass of the Sun. We’ve never seen this object directly, it’s hidden behind thick clouds of dust and gas, but astronomers have been able to follow the orbits of stars and clouds of gas near the galactic center, which allowed them to infer the mass of the cosmic heavyweight hidden behind that curtain. Supermassive black holes are believed to be found in the cores of most galaxies, and that some feed on nearby matter so eagerly that they shoot jets of powerful visible radiation from millions of light-years away.

Astronomers attempted to photograph the black hole monster in the center of the Milky Way. This hungry giant has a weight of 4 million suns. In recent years, astronomers have been combining observations from multiple radio telescopes to try to glimpse the environment around the black hole, which is filled with gas and dust that revolves around the jaws of the black hole. The project, called Event Horizon, expects to have preliminary images of the black hole’s edge in the coming months. On April 10th, 2019 the Event Horizon Telescope (EHT) published the first ever picture of a blackhole.

Such dust blocks our light, our vision of the most distant parts of the Milky Way", so there are areas of the galaxy that are relatively hidden from view because they’re behind huge dust columns that we can’t see through the optical wavelengths that our eyes work on. To improve this problem, astronomers sometimes work at longer wavelengths, such as radio or infrared, that decrease the effects of dust.

Our galaxy lies within a group of dark matter that is much larger and more massive than the galaxy itself. In the late 1960s, the astronomer Vera Rubin inferred the presence of these invisible halos around the galaxies when he observed that the stars near the edge of Andromeda were lashing at the centre of the galaxy at speeds that should send them flying into space. And yet it didn’t happen, which meant there was some kind of cosmic glue that kept it all together. That glue is dark matter.

There are countless spaceships and telescopes that study the Milky Way. The most famous is the Hubble Space Telescope, while other space telescopes such as Chandra, Spitzer and Kepler are also collecting data to help astronomers discover the mysteries of our star swirl. The next historic telescope under development is NASA’s James Webb Space Telescope. Meanwhile, projects as ambitious as APOGEE are solving the structure and evolution of our spiral house by doing "galactic archaeology". APOGEE is spectroscopy study of the Milky Way, which measures in great detail the chemical compositions of hundreds of thousands of stars across the galaxy. The properties of the stars around us are fossil evidence of their formation, which, combined with their ages, helps astronomers understand the timeline and evolution of the galaxy we call home.

The oily organic molecules known as aliphatic carbon compounds are produced in certain types of stars and then filtered into interstellar space. A recent study found that these fat-like substances could account for between a quarter and half of the Milky Way’s interstellar carbon, five times what was previously thought. Although strange, the findings are a cause for joy, because carbon is an essential component of living things, finding it in abundance across the galaxy could suggest that other star systems can host life.

The Magellanic Clouds, Large and Small are complementary objects of our galaxy. They are separate systems located more than 100,000 light-years away. There are more small objects in the vicinity of our galaxy, such as the dwarf Sagittarius, a galaxy that is in free fall into the Milky Way after being captured by our clearly more powerful gravity. There are also objects such as Draco, Carina, Sextans, Sculptor, Fornax... and other even weaker objects.

Galaxies in the universe sometimes exchange stars. Researchers recently searched for hypervelocity stars, which launch at incredible speeds from the Milky Way after interacting with the giant black hole at its centre. What they found was even stranger: instead of flying away from our galaxy, most of the fast stars were heading towards us. " These could be stars from another galaxy, passing through the Milky Way," said Tommaso Marchetti, an astronomer at the University of Leiden in the Netherlands, in his study published in the Monthly Notices of the Royal Astronomical Society. Have these stars originated in the Great Magellanic Cloud or further away?

A team of scientists discovered in 2010 gigantic structures, never seen before, stretching for 25,000 light-years above and below the galaxy. Called "Fermi bubbles" in honor of the telescope that found them, these gamma-ray emitting objects have defied astronomers' explanations ever since. For now, the evidence suggests that the bubbles are the consequence of an energy event of 6-9 million years ago, when the supermassive black hole in the galactic center swallowed a lot of gas and dust.

For the past decade, astronomers continue to detect strange flashes of light from the distant cosmos. Known as rapid radio bursts, these mysterious signals have no agreed explanation. Although they have been known for more than 10 years, researchers have managed to capture only about 30 examples of these signals. Although they do not yet know the origin of the flashes, a recent study has been able to determine that light had traveled through several billion light-years of gas and dust, suggesting that they have come a long way.

The Milky Way collision with another galaxy will be sooner than expected. According to a new study, the collision between our galaxy and the Large Magellanic Cloud (located 163,000 light-years from the Milky Way) will occur before the collision with the Andromeda Galaxy. This first mortal encounter will occur in 2 billion years, while the collision with the Andromeda Galaxy will take place in 8 billion years.