Researchers aren't 100 percent certain what formed the so-called Local Bubble, but it's looking more like a nearby supernova-of the violent Type-II variety-excavated the hole. The Local Bubble is a vast "hole" that was opened in the interstellar medium that surrounds our Sun; it extends for over 1,000 light-years in at least one direction.
The resulting blast punched through the interstellar dust and gas that originally surrounded our local region of space. Think of a fireball of a thermonuclear nuclear device but on a vast interstellar scale. As the shockwave front of a Type-II fireball spreads out into deep space, it blows away everything in its path.
Ironically, astronomers have benefited from the Local Bubble. Because our local region of space has been swept clear of much of its dust and gas, deep-sky telescopic observing has offered a "clearer" view in the direction of the bubble's point of origin; we'd never have known this fact if we didn't, first, have the understanding of looking out from inside this Local Bubble. Also, if we didn't have astronomical instruments capable of observing space in the extreme ultraviolet (UV) region of the electromagnetic spectrum, we probably wouldn't have been able to discover the Local Bubble in the first place.
Back in 1975, astronomers first noticed that, in wavelengths ranging from 10 to 100 nm, short-wavelength photons were ionizing neutral hydrogen atoms. This evidence suggested that some kind of a monster "hole" or bubble existed in the space around our solar system.
The Local Bubble extends 1,000 light-years (300 parsecs) in the direction of the star Beta Canis Majoris in the constellation Canis Major. In 1992, NASA's Extreme Ultraviolet Explorer spacecraft was the first to map the Local Bubble. At the same time, the European ROSAT spacecraft detected a pulsating beam of X-rays that strongly suggested a possible point of origin for the bubble in space.
Energetic x-rays are almost always the fingerprints left behind at a dramatic cosmic "crime" scene-an enormous uncontrolled thermonuclear explosion, sending out high energy subatomic particles from "ground zero", must have blown through our region of space like a tsunami. This cosmic tsunami, the shockwave of the immense stellar explosion, opened up our Local Bubble. It has not been clearly identified if there were extinctions on Earth associated with the event that created the Local Bubble; much research remains to be done with the fossil record.
The X-ray source detected by ROSAT in 1992 is located 300 light-years (100 parsecs) or more away in the constellation Gemini. It was quickly dubbed "Geminga" by Italian astronomer Giovanni Bignami who was involved in analyzing the ROSAT x-ray data.
Geminga, as Bignami tells it, is an Italian word that means "I'm not there!"-an appropriate name since at the time of detection, no object could be resolved at the focal point of the pulsed x-ray beams. Later, Bignami and his team of astronomers were credited with discovering a pulsar object at the location of the Gemini X-rays. In 1997, it was suggested by astronomer John Mattox that a planetary system, obviously formed after the supernova event, exists around Geminga.
A pulsar, short for pulsating star, is a rapidly rotating, very dense, neutron star that forms after a supernova explosion. The cores of these pulsars are composed of super dense matter, made purely of neutrons, popularly called neutronium. (A teaspoon size of neutronium would pass of its own weight completely through the Earth!)
Bignami estimates that Geminga may have exploded 300,000 or more years ago. This estimate is based on the pulsar's lengthening pulse period. Geminga appears to have been left over from the Type-II supernova-the original stellar heavyweight that delivered the massive one, two punch that created our Local Bubble.
What's in the Sky: On Friday, April 30, look for the Moon rising in the S.E. at midnight. The giant star Antares, in Scorpius, is to the right of Luna.
Lou Varricchio, M.Sc., was a senior science writer at the NASA Ames Research Center. He is currently involved with NASA's JPL Solar System Ambassador program in Vermont and is a senior member of the Civil Air Patrol, an auxiliary of the U.S. Air Force, in Rutland, Vt. He is a recipient of the Maj. Gen. Chuck Yeager Aerospace Education Achievement Award.