If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

READ: Gallery — Stars

Stars, their sizes, and their unique cycles of life and death.

The Red Supergiant Betelgeuse

The Red Supergiant Betelgeuse. Source: ESO/L. Calcada
This is an artist's impression of the red supergiant Betelgeuse in Orion, a prominent constellation throughout the world. Betelgeuse, the 8th brightest star in the night sky, can be easily identified as one of Orion's armpits. Betelgeuse's exact size is hard to calculate but if the star were at the center of our Solar System it would entirely engulf Earth, Venus, and Mars.

A Black Hole in Centaurus A

A Black Hole in Centaurus A. Source: X-ray: NASA/CXC/CFA/R.Kraft et al.; Submillimeter: MPIfR/ESO/APEX/A.Weiss et al.; Optical: ESO/WFI
This image of the galaxy Centaurus A demonstrates the incredible size and power of the supermassive black hole at its center. The X-ray jet in the upper left side of this image is powered by the central black hole and extends outwards for about 13,000 light years from the event horizon.

The Basic Structure of a Star

The Basic Structure of a Star. Source: ESA/NASA/SOHO and the Big History Project
This diagram shows the basic structure of a star like our Sun. Hydrogen is fused in the star's core, forming helium and sometimes heavier elements as the fusion process continues. Incredible amounts of energy are released in the process. Source: ESA/NASA/SOHO and the Big History Project

Our Sun and VY Canis Majoris

Our Sun and VY Canis Majoris.
This is an approximate comparison of the size difference between our Sun and the largest known star, VY Canis Majoris, in the constellation Canis Major. The diameter of VY Canis Majoris is more than 1,800 times that of the Sun. Bear in mind that these two stars are at different stages in their lives, further contributing to the size difference.

The Hertzsprung-Russell Diagram

The Hertzsprung-Russell Diagram. Source: ESO
In the Hertzsprung-Russell Diagram, the luminosities (brightnesses) of stars are plotted against their temperatures. The position of a star in the diagram demonstrates its present stage and its mass. Stars that fuse hydrogen into helium lie on the central diagonal branch, the so-called "main sequence." Red dwarfs like AB Doradus C lie in the cool and faint corner.  When a star exhausts all if its hydrogen, it leaves the main sequence and becomes a red giant or a supergiant, depending on its mass. When medium-sized stars with masses similar to our Sun age, they will swell in size and become red giants. Without enough mass to cause a supernova, they will burn all of their fuel and eventually shrink into white dwarfs (seen in the lower left).

An Unstable, Dying Star Called Eta Carinae

An Unstable, Dying Star Called Eta Carinae. Source: X-ray: NASA/CXC/GSFC/M. Corcoran et al: Optical: NASA/STScl
Eta Carinae is a massive (100-150 solar masses) and unstable star that astronomers expect will end in a supernova. In the 1840s Eta Carinae erupted, ejecting material 10 times the mass of the Sun and briefly becoming the second brightest star in the sky - an early indication of the massive explosion expected to come.

The Dying Star Eta Carinae

The Dying Star Eta Carinae. Source: Jon Morse (University of Colorado) and NASA
In this image of Eta Carinae, the dying star resembles a cancerous tumor or an infected organ. Eta Carinae's final demise is likely to be a supernova that will look as bright as the full Moon.

Tycho's Supernova Remnant

Tycho's Supernova Remnant. Source: X-ray: NASA/CXC/SAO; Infrared: NASA/JPL-Caltech; Optical: MPIA, Calar Alto, O. Krause et al.
This blazing hot cloud of gas and debris in the constellation Cassiopeia, SN 1572 or B Cas, is the remnant of the supernova that Tycho Brahe and other astronomers and stargazers witnessed in November 1572. This bright explosion deep in space demonstrated to astronomers like Brahe that the Universe was alive and in constant motion.

Want to join the conversation?