常速英语:Scientists discover Milky Way's youngest exploding star

Scientists have announced the discovery of the youngest known exploding star, or supernova, in our Milky Way galaxy. Astronomers say the remnant of the most recent supernova could provide clues to a long-standing mystery about why so few supernovae seem to explode in our galaxy, compared to other galaxies. VOA Correspondent Cindy Saine reports from Washington.

Astronomers using NASA's Chandra X-ray Observatory and the Very Large Array radio telescope in New Mexico have discovered the remains of a supernova, known as "G1.9", which must have lit up our galaxy with a bright flash of light about 140 years ago.

At a NASA news conference Wednesday, scientists said they were able to estimate the age of the supernova by tracking its remnant's rate of expansion over the last 20 years. They say it expanded by 16 percent - a surprisingly large amount - indicating it is much younger than previously thought.

The scientist who led the study, Stephen Reynolds of North Carolina State University, said radio and X-ray technology allowed scientists to track the dying star through a dense field of gas and dust that had previously obscured the view.

The second most recent supernova is believed to have occurred around 1680. Ever since astronomers discovered that supernova more than 50 years ago, they have been searching for more "missing" supernovae and their remnants. Reynolds explains that scientists have measured the rates of exploding stars in other galaxies, and found out that our own Milky Way galaxy seems to be lagging behind in the number of supernovae per century.

"Large spiral galaxies like the Milky Way seem to have two or three per century," he said. "But it is clear we have not been getting our share. A half dozen or so have been reported over the last millennium, but there should be 20 or 30. Now the galaxy is full of gas and dust, which could hide a distant supernova optically, but the remnant would still produce detectable radio waves and X-rays. This lack is a significant puzzle."

The discovery of the young remnant does not immediately provide an answer to the puzzle, but scientists say it will be a "goldmine" to study, since it is still so recent and energetic. They say it is an important finding for understanding the life cycles of stars in the Milky Way galaxy.

Bob Kirshner, of Harvard University, explains why supernovae are important for all of us.

"The supernovae make the chemical elements through real alchemy, transforming one element, the light elements into the heavy ones," he said. "So the calcium that is in your bones and the iron that is in your blood probably came from supernovae that exploded before the sun formed. So, we are all stardust, and it seems reasonable for us to want to know how these elements get formed when stars explode."(Www.hxen.com)

Supernovae and their remnants create and distribute the majority of the elements in the universe, spreading everything from cobalt to gold.

supernova:超新星