Galaxies, part 2: Crash Course Astronomy #39
TLDRThis video delves into the fascinating world of active galaxies, powered by supermassive black holes at their cores. It explores how galaxies cluster together, forming groups, clusters, and even larger superclusters, with our Milky Way destined to collide with Andromeda in a few billion years. The script reveals the staggering number of galaxies in the universe, estimated at a hundred billion, as seen in the iconic Hubble Deep Field image. The video celebrates our curiosity and thirst for knowledge about the vast cosmos, underscoring the significance of our quest to understand the universe's immense scale and structure.
Takeaways
- 🌌 Active galaxies are powered by supermassive black holes at their centers, which heat up the matter falling into them, causing it to emit intense radiation across the electromagnetic spectrum.
- 🔭 Our Milky Way galaxy will eventually collide and merge with the Andromeda Galaxy, potentially turning the resulting 'Milkomeda' galaxy into an active galaxy due to the merger of their supermassive black holes.
- 🌉 Galaxies are not isolated, but tend to exist in groups, clusters, and even larger superclusters, with the largest known structures in the Universe being the vast filaments and voids that make up the cosmic web.
- 🔢 The Hubble Deep Field observations revealed that even in a tiny portion of the sky, there are thousands of galaxies, leading to an estimate of around 100 billion galaxies in the observable Universe.
- 🌀 Supermassive black holes, with millions or billions of times the mass of our Sun, are found at the centers of most large galaxies and are thought to have formed at the same time as their host galaxies.
- 🔘 Active galaxies can exhibit different characteristics, such as jets and varying spectra, depending on the viewing angle of their accretion disks relative to Earth.
- 🔄 Galactic collisions and mergers can provide fresh material for supermassive black holes to feed on, potentially turning quiescent galaxies into active ones.
- 🧩 The cosmic large-scale structure, including the distribution of galaxies, clusters, and superclusters, holds clues to understanding the composition, origin, and fate of the Universe.
- ✨ The immense size and complexity of the Universe does not diminish our significance, but rather highlights the remarkable human capacity for curiosity and the pursuit of knowledge.
- 🔬 Studying active galaxies, galaxy clusters, and the cosmic web can help answer some of the biggest questions in astronomy, such as the nature of dark matter and the evolution of the Universe.
Q & A
What are active galaxies, and what powers them?
-Active galaxies are galaxies that emit an immense amount of energy across the electromagnetic spectrum, including X-rays and gamma rays. They are powered by supermassive black holes at their centers, which heat up matter falling into them, causing it to radiate energy.
How are different types of active galaxies classified?
-Active galaxies are classified into various subcategories depending on how they emit their light and the characteristics of their spectra. The viewing angle also plays a role, as the accretion disk and jets can appear differently from different perspectives.
Does our Milky Way galaxy have a supermassive black hole?
-Yes, the Milky Way has a supermassive black hole in its center with a mass of over 4 million times the Sun's mass. However, it is currently quiescent and not actively feeding, so the Milky Way is not an active galaxy.
What is the Local Group, and what galaxies are part of it?
-The Local Group is a small group of galaxies that includes the Milky Way and the Andromeda Galaxy as the two largest members, along with a few dozen smaller galaxies. It's a relatively isolated group of galaxies.
What will happen when the Milky Way and Andromeda galaxies collide?
-The collision between the Milky Way and Andromeda, which is expected to happen in a few billion years, will result in the formation of a new, larger elliptical galaxy nicknamed 'Milkomeda.' The merger may also trigger the supermassive black holes to become active and create an active galaxy.
What are galaxy clusters and superclusters?
-Galaxy clusters are groups of hundreds or thousands of galaxies bound together by gravity. Superclusters are even larger structures, containing many galaxy clusters and spanning hundreds of millions of light-years across.
How many galaxies are estimated to exist in the observable universe?
-Based on observations from the Hubble Space Telescope and deep field images, astronomers estimate that there are around 100 billion galaxies in the observable universe.
What is the significance of the Hubble Deep Field image?
-The Hubble Deep Field image, which captures an incredibly small portion of the sky, revealed thousands of galaxies in that tiny area, highlighting the vast number of galaxies in the universe and the scale of the cosmos.
What role do galactic collisions play in the formation of active galaxies?
-Galactic collisions can trigger an influx of gas and dust into the supermassive black holes at the centers of galaxies, fueling their activity and potentially turning them into active galaxies.
How does the structure of the universe on large scales provide clues about its origin and evolution?
-The distribution of matter on large scales, including the filamentary structures of superclusters and the vast voids between them, holds important information about the composition of the universe, its initial conditions, and its eventual fate.
Outlines
🌌 Active Galaxies and Supermassive Black Holes
This paragraph introduces the concept of active galaxies, which are immensely powerful and luminous objects in the Universe. It explains how these galaxies were first discovered, like 3C273, and how they emit tremendous amounts of energy across the electromagnetic spectrum, including X-rays and gamma rays. The paragraph then delves into the explanation that active galaxies are powered by supermassive black holes at their centers, which accrete matter from their surroundings and heat it up to millions of degrees, causing it to radiate across the spectrum. It also discusses features like accretion disks and jets associated with active galaxies.
🌎 The Milky Way and the Future Collision with Andromeda
This paragraph discusses the Local Group, a small collection of galaxies that includes our Milky Way and the Andromeda Galaxy. It explains that the Andromeda Galaxy is approaching the Milky Way at a speed of about 100 km/s, and the two galaxies will eventually collide and merge in a few billion years, forming a new, larger galaxy called "Milkomeda." The paragraph also mentions that both the Milky Way and Andromeda have supermassive black holes at their centers, which may interact during the merger and potentially create a new active galaxy. Additionally, it touches on the possibility that the collision could affect the Earth's orbit within the new galaxy.
🌍 Galaxy Clusters, Superclusters, and the Large-Scale Structure
This paragraph expands the scope to discuss the large-scale structure of the Universe. It explains that galaxies are not randomly distributed but tend to cluster together in groups, clusters, and even larger superclusters. The paragraph provides details on galaxy clusters, which can contain thousands of galaxies bound together by their mutual gravity, and superclusters, which are even larger structures composed of many galaxy clusters. It also mentions the Virgo Cluster and the Virgo Supercluster, which are part of the larger Laniakea Supercluster. The paragraph further describes the filamentary and foamy structure of the Universe on the largest scales, with galaxies and clusters distributed along filaments and separated by vast, empty voids.
Mindmap
Keywords
💡Galaxies
💡Active Galaxies
💡Supermassive Black Holes
💡Accretion Disks
💡Galactic Collisions
💡Local Group
💡Galaxy Clusters
💡Superclusters
💡Cosmic Large-Scale Structure
💡Hubble Deep Field
Highlights
Galaxies can be classified based on their shape (spiral, elliptical, irregular, or peculiar) and behavior (active or non-active).
Active galaxies are extremely luminous and powerful, emitting energy across the electromagnetic spectrum, including radio waves, X-rays, and gamma rays.
The energy source powering active galaxies is matter being accreted onto supermassive black holes at the center of these galaxies.
The accretion disk around a supermassive black hole heats up due to friction, emitting intense radiation, and can also produce powerful jets of matter and energy.
The viewing angle of the accretion disk determines the type of radiation we observe from active galaxies.
The Milky Way has a supermassive black hole, but it is currently quiescent (not actively feeding).
Galactic collisions can trigger active galactic nuclei by funneling gas and dust into the central supermassive black holes.
The Andromeda Galaxy is on a collision course with the Milky Way, and their eventual merger in a few billion years could trigger an active galactic nucleus in the resulting 'Milkomeda' galaxy.
Galaxies are not randomly distributed but tend to cluster together, forming groups, clusters, and superclusters, with vast voids in between.
The large-scale structure of the Universe holds clues to understanding its composition, origin, and fate.
The Hubble Deep Field revealed thousands of galaxies in a tiny portion of the sky, indicating the Universe contains hundreds of billions of galaxies.
The vastness of the Universe and our ability to study and comprehend it make humanity significant and expansive, not insignificant.
Active galaxies pour out energy due to their central supermassive black holes accreting matter.
Galaxies exist in groups, clusters, and superclusters, with the Milky Way part of the Local Group, which will eventually merge with the Andromeda Galaxy.
There are hundreds of billions of galaxies in the Universe, revealed by deep field observations like the Hubble Deep Field.
Transcripts
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