The Universe: The Biggest Object in the Galaxy (S2, E16) | Full Episode | History

This paragraph introduces the concept of size in the universe, emphasizing the incomprehensible vastness of space and the gargantuan celestial bodies within it. It discusses how size matters differently in space, often with larger entities not necessarily being better. The paragraph mentions the cosmic web, an enormous structure composed of superclusters of galaxies and dark matter, as the largest known entity in the universe. Astronomers use various methods to study these massive objects, such as observing X-ray-emitting gas and gravitational lensing effects. The cosmic web is believed to have originated from the Big Bang, containing all the original matter from that event, and its size is so immense that if the Milky Way were a poppy seed, the observable universe would be equivalent to the volume of the Rose Bowl Stadium.

The second paragraph delves into the debate over whether the cosmic web is technically the largest object in the universe due to its discontinuous nature. It introduces the concept of superclusters of galaxies, which are gravitationally bound and thus considered more as single objects. The paragraph highlights the Shapley Supercluster as the current record holder for the largest supercluster, detailing its immense size and the time it would take to traverse it. It also discusses the hierarchical organization of the universe, from stars to galaxies to clusters and superclusters, and how astronomers have traced the origins of these structures back to the Big Bang. The paragraph concludes with the potential for future discoveries of even larger structures as technology advances.

This paragraph contrasts the crowded superclusters with the vast empty regions of space known as voids. It describes the Bootes void as an example, a near-empty space that is 250 million light years across. The paragraph also discusses the potential for discovering larger voids by analyzing the cosmic microwave background radiation. Additionally, it introduces Lyman-alpha blobs, giant clouds of gas that are thought to be precursors to galaxy clusters. These blobs are described as expanding due to heat and ultraviolet radiation from newly formed stars, and the largest known Lyman-alpha blob is compared in size to our Milky Way galaxy, emphasizing its massive scale.

The fourth paragraph continues the exploration of galaxy formation, touching on the challenges of defining the boundaries of galaxies and introducing Cluster Diffuse (CD) galaxies as some of the largest in the universe. These galaxies are the result of galaxy mergers and are located in the centers of galaxy clusters. The paragraph also discusses the concept of 'galaxy cannibalism' and the role of supermassive black holes in powering radio lobes, which are immense structures that emit radio waves. The largest known radio lobe is found in the galaxy 3C 236, with jets spanning 40 million light years. The paragraph concludes by pondering the lifespan of these radio lobes and the role of black holes in their formation.

This paragraph focuses on supermassive black holes, which are millions to billions of times the mass of the Sun and are found at the centers of galaxies. It describes the immense gravitational pull of these black holes and their effects on surrounding matter. The paragraph introduces the current record holder for the largest black hole, located in the quasar HS 1946+7658, which is estimated to be 10 billion times the mass of the Sun. The discussion also includes the various ways black holes can be observed, such as through their interaction with nearby stars or the accretion of matter. The paragraph concludes with a look at the broader implications of these massive objects in the universe.

The sixth paragraph shifts the focus to stars, which are luminous balls of plasma that vary greatly in size and power. It discusses the range of stars from red dwarfs to blue-white supergiants and highlights the Sun's role in our solar system. The paragraph introduces red hypergiants as the largest and most powerful stars, with VY Canis Majoris being the largest known star by diameter. It also touches on the methods astronomers use to measure the size and luminosity of stars, as well as the short but intense lifespan of massive stars and their importance in creating elements essential for life.

The seventh paragraph explores the largest objects within our solar system, starting with planets and moving on to asteroids. It highlights Jupiter as the largest planet and TrES-4 as the largest known extrasolar planet by radius, which is unusually large for its mass. The paragraph also discusses the challenges of determining the size of such large planets and the factors that may contribute to their size, such as their proximity to their parent stars. Additionally, it introduces Ceres as the largest asteroid in our solar system and its dual title as a dwarf planet due to its round shape. The paragraph concludes with a look at the potential for discovering even larger asteroids in other solar systems.

The final paragraph discusses the Oort cloud, a vast and diffuse cloud of comets that marks the outermost boundary of our solar system. It is described as being so distant that it would take hundreds of thousands of years for a spacecraft to traverse its outer edge. The Oort cloud is believed to be composed of icy remnants from the early solar system, making it an archaeological treasure trove of our cosmic origins. The paragraph concludes with a reflection on the importance of large structures in the universe and the ongoing quest to discover even larger objects as our understanding and technology advance.