Supernova Remnant Is Young and Quick

About a century ago, the light from the explosion of a star within our galaxy swept past Earth. No one noticed. Such explosions, called supernovas, can shine brightly in the night sky. But this dying star was close to the center of the galaxy, where thick dust and gas blocked most of the light, and astronomers of the era saw nothing. Now radio telescopes on Earth and the Chandra X-ray Observatory in orbit have taken pictures of the stellar debris, revealing it to be the youngest supernova remnant known in the Milky Way galaxy. The observations, reported in a telephone news conference Wednesday, show that it is still expanding outward at an unexpectedly quick pace of perhaps 30 million miles an hour, or about 5 percent of the speed of light. The rapid expansion means the interstellar gas around the star was thin and did not slow the remnant as much as usual. In addition to that quick expansion, the remnant is growing brighter at radio frequencies: being so young, it is still getting warmer. “It’s doing things we have never seen before,” said Stephen P. Reynolds, a professor of physics at North Carolina State University, who led the Chandra study. While the dust and gas at the galactic core block visible light, other frequencies of light can make it through. David A. Green of the University of Cambridge in England originally identified the supernova remnant in 1985 using the Very Large Array, a Y-shaped configuration of 27 radio telescopes in New Mexico. At the time, he estimated the age at 400 to 1,000 years. Last year Dr. Reynolds pointed Chandra at the same remnant, known as G1.9+0.3. The new X-ray image indicated that G1.9+0.3 had become considerably larger since Dr. Green first looked at it. Dr. Green then took another radio image of the remnant with the Very Large Array and found that the remnant was now about 16 percent wider than in 1985. “We can extrapolate backwards for the age of the object,” Dr. Green said. The star was about 26,000 light-years away. So the actual explosion occurred about 26,000 years ago, and the light from the blast traveled that long to arrive at Earth no more than 150 years ago. The findings will appear in two scientific articles, one in The Astrophysical Journal and one in Monthly Notices of the Royal Astronomical Society. The G1.9+0.3 remnant is still mostly debris from the exploded star. In older remnants, the glow comes from interstellar gases heated by the shock waves rather than pieces of the dead star. “You are actually getting to see the rock that made the splash, not the wave that’s going out into the pond,” said Robert P. Kirshner, a professor of astronomy at Harvard who was not connected with the research. “This is a stellar death, and the corpse is still warm.” The discovery helps fill in the deficit of supernovas for the Milky Way, where the rate of explosions appears much lower than in similar spiral galaxies. “This lack is a significant puzzle,” Dr. Reynolds said. Either astronomers have not been able to identify the remnants, or the Milky Way is somehow different. “Either way,” he said, “is very interesting.”