Sizes of Stars and Sub-Stellar Objects: From Brown Dwarf to Red Hypergiant

Professor Dave Explains
12 Jun 202008:54
EducationalLearning
32 Likes 10 Comments

TLDRThis script delves into the fascinating world of stellar sizes, comparing our Sun's immense scale to other stars. It explores the limits of stellar mass, from the smallest red dwarfs at around 80 Jupiter masses to the proposed upper limit of 150 solar masses. Through vivid visual comparisons, the script unveils the astonishing sizes of hypergiant stars like Canis Majoris and UY Scuti, which dwarf our Sun to an almost invisible speck. The script invites viewers to ponder the existence of even larger stars and the fundamental principles governing their formation, leaving an awe-inspiring impression of the universe's grandeur.

Takeaways
  • ๐ŸŒŸ The Sun is not considered a very large star in comparison to other stars in the universe.
  • ๐Ÿ”ด The smallest type of star capable of sustaining nuclear fusion is a red dwarf, starting at around 80 Jupiter masses (0.08 solar masses).
  • ๐ŸŸค Brown dwarfs are substellar objects with masses between 13 and 80 Jupiter masses, unable to sustain hydrogen fusion like stars.
  • ๐ŸŒ  There is no definitive upper limit to the mass and size of stars, but a mathematical model suggests an upper bound of around 150 solar masses.
  • ๐Ÿ”ญ The largest known stars, like Canis Majoris and UY Scuti, are red hypergiants with diameters that would engulf multiple planets in our solar system.
  • ๐ŸŒ€ The formation processes behind these hypergiant stars are not fully understood, and there may be even larger stars yet to be discovered.
  • ๐ŸŒŽ Visualizing the scale of massive stars in comparison to Earth and the Sun helps illustrate their astounding size.
  • โญ The mass of a star is the primary factor determining its life cycle, behavior, and the type of remnant it leaves behind.
  • ๐ŸŒŒ The range of stellar masses observed in our galaxy provides a glimpse into the diversity of star sizes across the universe.
  • ๐Ÿ” Studying the extremes of stellar masses, both small and large, can potentially lead to new insights and fundamental principles in astrophysics.
Q & A

  • What is the minimum mass required for a gas cloud to trigger nuclear fusion and become a star?

    -The minimum mass required for a gas cloud to trigger nuclear fusion and become a star is around 80 Jupiter masses, or about 8% of the mass of our Sun. This is the mass range where objects are classified as red dwarf stars.

  • What are brown dwarfs, and how do they differ from stars?

    -Brown dwarfs are substellar objects with masses between 13 and 80 Jupiter masses. They are not massive enough to sustain nuclear fusion of ordinary hydrogen in their cores like stars do. However, some may be able to fuse heavier elements like deuterium or lithium if their mass is on the upper end of this range. They do not glow like stars but have been observed with planetary systems.

  • Is there an upper limit to the mass and size of stars?

    -There is no definitive upper limit to the mass and size of stars. However, it has been proposed, with mathematical basis, that there may be an upper limit around 150 solar masses. Stars approaching and even exceeding this limit have been observed, but it is not considered a firm value.

  • How do the largest known stars compare in size to our Sun?

    -The largest known stars, such as Canis Majoris and UY Scuti, are so massive that if one were to replace our Sun, it would engulf the entire solar system up to Saturn. These stars are so large that our Sun becomes invisible in comparison when shown to scale.

  • Why are larger and larger stars statistically less probable?

    -Larger and larger stars become more and more statistically improbable because it requires a larger mass of gas and dust to accumulate during the star formation process. While there is no definitive upper limit, the higher the mass, the rarer the occurrence.

  • What fundamental principles or processes might govern the formation of hypergiant stars?

    -The script does not explicitly address the fundamental principles or processes that govern the formation of hypergiant stars. It suggests that further research and understanding may be needed to elucidate the formation of these extremely massive stars.

  • How do astronomers determine the mass and size of distant stars?

    -The script does not provide details on the methods astronomers use to determine the mass and size of distant stars. However, techniques such as spectroscopy, parallax measurements, and analyzing the star's brightness and color can provide insights into a star's properties.

  • Are there any known stars larger than UY Scuti, currently the largest known star?

    -The script does not mention any stars larger than UY Scuti, which is currently the largest known star. However, it raises the question of whether even larger stars might exist in the entire universe and suggests that more discoveries may be made in the future.

  • How do the masses and sizes of stars impact their life cycles and eventual fates?

    -The script mentions that the mass of a star is the primary variable in determining its behavior and the remnant it leaves behind. It references how low-mass stars like our Sun eventually become white dwarfs, while high-mass stars can become neutron stars or even black holes above a certain mass threshold.

  • What other factors, aside from mass, might influence the size and behavior of stars?

    -The script focuses primarily on the mass as the determining factor for a star's size and behavior. However, other factors such as the star's composition, rotation, and interaction with external forces (e.g., companion stars, gas clouds) could also play a role in shaping its characteristics.

Outlines
00:00
๐ŸŒŸ Exploring the Vast Range of Stellar Sizes

This paragraph delves into the diverse sizes of stars, from our relatively small sun to the largest known stars. It highlights that while our sun appears massive from our perspective, it is actually quite small compared to many other stars. The paragraph introduces the concept of stellar mass as a primary factor determining a star's behavior and eventual fate. It then explores the lower mass limit for stars, discussing red dwarfs (starting around 80 Jupiter masses) and brown dwarfs (sub-stellar objects with masses between 13 and 80 Jupiter masses). The paragraph also touches upon the upper mass limit for stars, mentioning a proposed limit of 150 solar masses, but acknowledging the existence of even larger stars, hinting at the immense size some stars can attain.

05:05
๐Ÿ”ญ Visualizing the Astonishing Size of Hypergiant Stars

This paragraph focuses on providing a visual comparison of the sizes of various stars, starting from the Earth and zooming out to reveal the truly astounding scale of some of the largest known stars. It emphasizes the awe-inspiring magnitude of red hypergiant stars like Canis Majoris, which would engulf the planets of our solar system up to Saturn if it replaced our sun. The paragraph further notes that even larger stars, like UY Scuti, have been discovered, with a radius 20% larger than Canis Majoris. It concludes by pondering the potential existence of even more massive stars in the universe and the fundamental principles that govern the formation of these hypergiant stars, leaving the reader to contemplate the mysteries and vastness of the cosmos.

Mindmap
Keywords
๐Ÿ’กStellar Mass
Stellar mass refers to the amount of matter contained within a star, usually measured in units of the Sun's mass (solar masses). The video emphasizes that stellar mass is the primary variable determining a star's behavior and the type of remnant it leaves behind. For example, low-mass stars like the Sun eventually become white dwarfs, while high-mass stars become neutron stars or black holes.
๐Ÿ’กRed Dwarf Star
A red dwarf star is the smallest type of star that is massive enough to sustain nuclear fusion. According to the video, red dwarfs begin at around 80 times the mass of Jupiter, or about 8% of the Sun's mass. Despite their greater mass, they are only slightly larger than Jupiter due to their high densities. Proxima Centauri, discussed in the context of the Alpha Centauri system, is an example of a red dwarf star.
๐Ÿ’กBrown Dwarf
Brown dwarfs are substellar objects that are less massive than stars, ranging from around 13 to 80 Jupiter masses. Unlike stars, they lack sufficient gravitational pressure to sustain fusion of ordinary hydrogen in their cores. However, they may fuse heavy hydrogen (deuterium) or lithium if their mass is on the higher end of this range. The video mentions that hundreds of brown dwarfs, some with planetary systems, have been identified in our galaxy.
๐Ÿ’กHypergiant Star
Hypergiant stars are some of the most massive and largest stars known. The video proposes a theoretical upper limit of around 150 solar masses for stars, but acknowledges that even larger stars, exceeding this limit, have been discovered. To illustrate the immense size of these objects, the video provides a visual comparison showing that a hypergiant star like Canis Majoris would engulf every planet in our solar system up to Saturn if it replaced the Sun.
๐Ÿ’กNuclear Fusion
Nuclear fusion is the process that defines stars and is the source of their energy output. The video explains that there is a minimum mass required for a gas cloud (around 80 Jupiter masses for a red dwarf) such that the inward gravitational pressure is sufficient to trigger nuclear fusion of hydrogen in the core. Stars that cannot sustain this process, like brown dwarfs, are not considered true stars.
๐Ÿ’กStellar Remnant
A stellar remnant is the dense core or object that remains after a star has exhausted its nuclear fuel and shed its outer layers. The video discusses various types of stellar remnants, such as white dwarfs (resulting from low-mass stars like the Sun), neutron stars, and black holes (both resulting from high-mass stars). The type of remnant formed depends primarily on the star's initial mass.
๐Ÿ’กGravitational Pressure
Gravitational pressure refers to the inward force exerted by the star's own gravity, which counteracts the outward pressure generated by nuclear fusion in the core. The video explains that the mass of a star determines whether the gravitational pressure is sufficient to trigger and sustain nuclear fusion, which is the defining characteristic of a star. For example, brown dwarfs lack the necessary mass to sustain fusion of ordinary hydrogen.
๐Ÿ’กSolar Mass
Solar mass is a unit used to measure the mass of stars, expressed as a multiple of the Sun's mass. The video initially describes the Sun as being about a million times the mass of the Earth, but later transitions to using Jupiter masses for smaller objects like red dwarfs and brown dwarfs, as these are significantly less massive than the Sun.
๐Ÿ’กStellar Life Cycle
The stellar life cycle refers to the various stages that a star goes through, from its formation to its eventual demise as a stellar remnant. The video briefly mentions that previous episodes covered the life cycles of low-mass stars like the Sun (which become white dwarfs) and high-mass stars (which become neutron stars or black holes), emphasizing the importance of a star's mass in determining its life cycle.
๐Ÿ’กGalactic Distribution
The video touches on the distribution of stars within our galaxy and the vastness of the cosmos by mentioning that there are so many stars observable even in our own galaxy, let alone the billions of other galaxies. This highlights the diversity of stellar properties and the importance of studying the range of masses and sizes that stars can exhibit across the universe.
Highlights

The sun is not very large as far as stars go, despite being about a million times larger than Earth.

The mass of a star is the primary variable in determining its behavior and the remnant it leaves behind.

The smallest type of star is a red dwarf, which begins at around 80 times the mass of Jupiter (8% of the sun's mass).

Brown dwarfs are sub-stellar objects with masses between 13 and 80 Jupiter masses, unable to sustain fusion of ordinary hydrogen.

There is no definitive upper limit to how big a star can be, but it has been proposed that there is a limit around 150 solar masses.

The largest known stars, such as Canis Majoris and UY Scuti, are so massive that they would engulf all planets in our solar system up to Saturn if placed at the center.

A visual comparison demonstrates the astonishing size difference between the largest stars and our sun, which becomes invisible at the same scale.

The formation of these hypergiant stars is not yet fully understood, and there may be even larger stars in the universe.

The transcript explores the extreme range of stellar masses and sizes, from the smallest red dwarfs to the largest known hypergiants.

The mass of a star determines its behavior and fate, such as becoming a white dwarf, neutron star, or black hole.

The minimum mass required for a gas cloud to trigger nuclear fusion and become a star is around 80 Jupiter masses.

Red dwarfs are compact stars, only slightly larger than Jupiter despite their higher mass.

Brown dwarfs may be able to fuse heavy hydrogen or lithium if their mass is on the upper end of the sub-stellar range.

There is a range of masses commonly seen in stars around the galaxy, but particularly enormous stars can form occasionally.

The visual comparison aims to astonish the viewer with the immense size difference between the largest stars and our sun.

Transcripts

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