Our Galaxy: Everything We Know About the Milky Way

Look up on a clear, dark night, and you might see a hazy band of light stretching across the sky. Early cultures compared this shimmering ribbon to spilled milk, and this gave our Milky Way its name. What appears to be a faint smear is actually the edge-on view of a vast galactic disk containing about 200 billion stars. Our solar system is embedded within this disk, and every twinkling star you can see with the naked eye belongs to this galaxy. In this video, we'll journey through the Milky Way structure, explore its history and its future, and highlight the most incredible parts of our cosmic home. By the end, you may have a new appreciation for the galaxy that cradles it. Galactic archaeology suggests that the Milky Way began forming about 13.6 billion years ago, only a few hundred million years after the Big Bang. Early clouds of gas collapsed under gravity to form the first generation of stars and globular clusters in the halo. As more gas accrued, a flat disk formed, giving rise to the spiral structure that we see today. Over billions of years, the Milky Way grew by merging with smaller galaxies, leaving behind streams of stars that still orbit in the halo. Evidence suggests our galaxy experienced several of these mergers. Some of those collisions likely trigger periods of intense star formation and may have even helped shape the spiral arm. Speaking of spirals, astronomers describe the Milky Way as a barred spiral galaxy. From above, it would look like a pinwheel, a bright central bulge with a thin bar of stars stretching across it and graceful spiral arms winding outward. The galactic disk is roughly 100,000 light-years wide and only about 1,000 light-years thick. If the galaxy was scaled down to the size of a pizza, the disk would be even thinner than a sheet of paper. Surrounding the disk is a peanut-shaped bulge about 10,000 light-years across that contains around 10 billion old red giant stars. Outside the visible structures lies an even larger halo of stars and globular clusters enveloped by an invisible halo of dark matter which comprises up to 90% of the galaxy's mass. Within the disk, four main spiral arms—Perseus, Scutum Centaurus, Sagittarius, and a smaller, local Orion arm—wind out from the center. These arms are like cosmic traffic jams. As gas and stars crowd together, the material is compressed and triggers star formation. And this is why the arms make a brilliant cluster of young blue stars. Counting stars from inside a galaxy can be quite challenging, but current estimates put the Milky Way's star population at around 200 billion. However, stars account for only about 10% of the galaxy's mass. The rest is gas, dust, and the elusive dark matter that we can't see but infer from its gravitational effects. Strongers measure the Milky Way's total mass, including this dark matter, at roughly 1.5 trillion times the mass of the Sun. The visible matter is distributed among stars, their planets, and vast clouds of gas and dust. If most stars have planets, as surveys suggest, the Milky Way likely hosts hundreds of billions of planets, possibly even trillions. As of 2025, more than 3,900 X of planets have been confirmed, and many are rocky worlds within their star's habitable zones. With so many planetary systems, the probability of life existing elsewhere in the galaxy is definitely cantiwizing. Where exactly do we sit in this cosmic pinwheel? Our solar system resides within the loculum, which is sometimes called the Orion Spur, between the larger Perseus and Centaurius Carinae arms. It lies about 2,600 light-years from the Milky Way's center, roughly halfway from the core to the outer edge. Our solar system completes one galactic year in around 230 to 250 million years. So the last time Earth was in this part of the galaxy, dinosaurs were just emerging. Today we travel inside of the local bubble, a 1,000 light-year wide cavity with a density much lower than the average interstellar medium. This bubble was carved out roughly 14 million years ago when up to 1,000 supernovae exploded near each. The combined shockwaves from this swept surrounding gas into a dense shell where new stars now form. Our sun entered the local bubble about 5 million years ago, and we will remain inside this cavity for another couple million years as we continue our voyage around the Milky Way. At the heart of the Milky Way lies Sanitarius A, a supermassive black hole with a mass around 4 million suns. Despite its mass, Sanitarius A is relatively quiet compared with active galactic nuclei. In May 2022, astronomers using the Event Horizon Telescope produced the first direct image of this black hole's shadow, an orange rain created by glowing gas swirling around the Event Horizon. The central bar and bolts are packed with old stars and measure about 10,000 light-years across. Because dust obscures our direct view of the galactic center at optical wavelength, astronomers math its structure using radio and infrared observations and by tracking star motion. Evidence suggests that the bar is modest compared with other galaxies, but its presence affects the orbits of stars in the inner disk and may drive gas towards the center, feeding star formation and thus Sanitarius A. Now for a couple of the mysteries of our galaxy. Above and below the galactic plane, the Ferny Gamma-ray Space Telescope discovered two enormous lobes of high-energy radiation known as the Fermi bubbles. These bubbles stretched 2,500 light-years north and south of the galaxy's center and likely formed a few million years ago. Scientists have debated their origin. One possibility is a past outburst from Sanitarius A. Another is an intense episode of star formation in the center. Whatever caused them injected tremendous energy into the galactic halo. The existence of such structures reminds us that galaxies are dynamic and evolving, shaped by both internal processes and external interaction. We will continue to monitor these and hopefully learn more. Dark matter is one of the biggest mysteries in modern astrophysics. Observations show that stars near the edge of the Milky Way disk orbit almost as fast as those near the center, which can only be explained in a visible form of mass and velocity galaxy. This dark matter doesn't emit light, but instead exerts gravity, and it makes up around 90% of the Milky Way's total mass. Understanding the nature of dark matter is one of the great quests of physics because it dominates the mass budget of not just our galaxy, but also the universe. Now, the Milky Way is not just floating alone in space. It belongs to a neighborhood of more than 50 galaxies called the local. Gravity binds the group together, and the local group itself is located on the outskirts of the Virgo Cluster, embedded within the vast Laniakea Supercluster. Even this supercluster is just one branch of the cosmic web stretching across billions of light years. Our nearest major neighbor, the Andromeda Galaxy, sits about 2.5 million light years away. It's actually on a collision course with the Milky Way, approaching at about 250,000 miles per hour. The expected merger will occur in around 4 billion years, so we do have some time to prepare a good watch party. When the galaxies collide, their stars are unlikely to smash into each other because the space between the stars is so enormous. Instead, the gravitational dance will distort the spiral arms, funnel gas into bursts of star formation, and eventually create a new, more massive elliptical galaxy. Our solar system should remain intact, but we may be flung into a completely different orbit around the remnant's center. So one of the most intriguing questions about our galaxy, and likely the one that you have been waiting for, is whether or not our galaxy can harbor other life. With potentially hundreds of billions of planets in the Milky Way, including many Earth-sized worlds in a habitable zone, the Milky Way seems ripe with possibilities. We just haven't found any yet. Life as we know it requires liquid water. The right chemistry and stability over long timescales, millions of exoplanet systems could offer such condition. Moreover, the galaxy's star formation rate of several stars per year suggests that new potential habitats are continually emerging. Nevertheless, interstellar distances are vast, even within our own galaxy. Even signals traveling at life speed take tens of thousands to cross the galaxy, so contact is rare and extremely difficult. Up until now, it's been impossible. Still, missions like the James Webb Space Telescope and the upcoming Extremely Large Telescopes, aimed to study exoplanet atmospheres for biosignatures, bring us closer to answering the age-old question, are we alone? The Milky Way will continue evolving long after humanity's time. Understanding our galaxy not only satisfies our curiosity, but it also helps contextualize our place in the cosmos, reminding us that Earth is part of an intricate and ever-changing universe. Next time you see that Milky Band, remember the vast story that it represents. The countless stars, planets, and mysteries still waiting to be found. Thank you very much for watching. If you enjoyed this video and want to see more like it, please like and subscribe to Stellar Quest for more videos just like this every week. We look forward to seeing you around.