Betelgeuse – A Red Giant with a Really Bright Future

GellerAtRotaryTalk3by Prof. Harold A. Geller of GMU

As we approach summer, one constellation you won’t be seeing in the night sky, is the well known Orion. The brightest star in the constellation Orion is commonly known as Betelgeuse. Actually, all stars are so far away that they are observed by our telescopes as points of light, not an object with height or breadth. However, in 1998, the Hubble Space Telescope, above the atmospheric jitter and fuzziness, captured a picture of Betelgeuse for the first time by an individual telescope.

Now when I say that a star is very far away, I am talking in terms of how long it would take light to reach us if it left the star today. In the specific instance of Betelgeuse, it takes light about 643 years to reach the Earth once it leaves the surface of Betelgeuse. Actually, Betelgeuse, like all stars doesn’t really have a surface, it is a ball of hot gas, called a plasma, because its temperature is so high, all of its atoms have shed their electrons and so all you have is a bunch of charged atoms called ions and a sea of electrons.

Betelgeuse comparison chartNow suppose you wanted to build a scale model of the universe so you can get a handle around the idea of the distance to Betelgeuse. You see, most people don’t really realize how big space really is. One scale that I have used in my classes is one inch to a million miles. Although not precise, that would make the Sun about 1 inch in diameter. On this scale, the Earth would be about 9 feet away from our model Sun. The planet Jupiter would be about 46 feet away from our Sun, and a single light year would be represented by over 100 miles (a single light year is actually almost 6 trillion miles). The nearest star next to our Sun is about 4.3 light years distant. On this scale, that star, Proxima Centauri, would be almost 460 miles away. You see, space is really large and mostly devoid of matter, that is it is empty.

Using this same scale model of space, Betelgeuse would be a little less than 300,000 miles away, more than the distance to the Moon. Now that is certainly far away, but Betelgeuse is a really big star. Remember when I said that on this scale, Jupiter would be about 46 feet away? Well, as it turns out, Betelgeuse is a really giant star, called a red supergiant. If you happened to plop Jupiter right in the location that our Sun is today, the outer edge of Betelgeuse would be just about where Jupiter orbits the Sun today.

position of Betelgeuse in OrionBut that’s not the only interesting thing about Betelgeuse. You see, Betelgeuse is in the last years of life as a star whose energy is derived from thermonuclear fusion. Like Hollywood stars on Earth, they eventually die. Betelgeuse is in the final stages of its life cycle. It’s a more massive star than our Sun, and so it actually won’t live to be as old as our Sun is now. Betelgeuse is not going to end its life like our Sun, because it is so massive. It is estimated that Betelgeuse is about 20 times the mass of our Sun. Thus, Betelgeuse will end its life in a supernova explosion. This will cause the brightness of Betelgeuse to increase about 100 million times.

Another way to look at this is to realize that Betelgeuse will be shining more than 10 billion times the brightness of our Sun when it does explode. Now we really don’t know when exactly Betelgeuse will blow as a supernova. Some believe it may be as soon as a few years, others as much as 100,000 years. Whenever it happens it will truly be a really big show. It will be so bright in the night time sky from Earth, that if anyone is left on Earth, they will see it as bright as the full Moon for a couple of weeks.

So what will remain after the explosion of Betelgeuse as a supernova? It actually depends upon how much material remains in the central region. If there remains anything less than 2-3 times the mass of the Sun in the central region, then Betelgeuse will become a neutron star. If the Earth is in the correct position, Betelgeuse will appear to us as a pulsar, a rapidly rotating neutron star whose magnetic field lines whip out charged particles in two beams of radiation.

Star map of OrionAfter the supernova explosion, if there remains more than ~3 solar masses of material, then Betelgeuse will end its life as a black hole. Black holes get their name from the fact that nothing, not even light, can escape from a region surrounding the black hole called the event horizon. A common misconception about black holes is that they will appear to be literally a black hole in space. But just like the development of a pulsar (rapidly spinning neutron star), black holes are spinning within a strong magnetic field which accelerate charged particles causing radiation. In fact, the best evidence for a black hole is the presence of x-ray radiation from the point in space within which the black hole resides. It is also believed to be surrounded by a donut shaped region of material orbiting at high velocity leading to a bright donut of radiation, similar to Earth’s own Van Allen radiation belts.

So you see, while Betelgeuse is already one of the brightest stars in the night sky, it has an even brighter future in store for itself.