Space telescope spots new supernova

The latest image from NASA's Hubble Space Telescope highlights a stellar blast that was first discovered by an amateur astronomer a little more than a month ago.

In the Hubble image, an arrow points to the supernova explosion, which is blazing with the light of 200 million suns.

"The supernova is so bright in this image that it easily could be mistaken for a foreground star in our Milky Way Galaxy," the Baltimore-based Space Telescope Science Institute said in its commentary on the picture. "And yet, this supernova, called SN 2004dj, resides far beyond our galaxy. Its home is in the outskirts of NGC 2403, a galaxy located 11 million light-years from Earth. Although the supernova is far from Earth, it is the closest stellar explosion discovered in more than a decade."

Astronomers say the star that became SN 2004dj may have been about 15 times as massive as the sun, with an age of only about 14 million years. In comparison, our sun is thought to be about 5 billion years old. Massive stars tend to live much shorter lives than the sun; they have more fuel to "burn" through nuclear fusion, but they use it up at a disproportionately faster rate.

Japanese amateur astronomer Koichi Itagaki discovered the supernova on July 31 with a small telescope. Hubble scientists followed up on Aug. 17 with observations by the Wide Field Camera on the telescope's Advanced Camera for Surveys.

The observations showed that SN 2004dj was a "Type II supernova," resulting from the explosion of a massive, hydrogen-rich star at the end of its life.

A team of astronomers led by Jesus Maiz of the Space Telescope Science Institute found that the supernova was part of a compact cluster of stars known as Sandage 96, whose total mass is about 24,000 times the mass of the sun. The image shows many such clusters — the blue regions — as well as looser associations of massive stars. The large number of massive stars in the galaxy leads to a high supernova rate. Two other supernovas have been seen in this galaxy during the past half-century.

The heart of galaxy NGC 2403 is the glowing region at lower left in the image. Sprinkled across the region are pink areas of starbirth. The myriad of faint stars visible in the Hubble image belong to NGC 2403, but the handful of very bright stars in the image belong to our own Milky Way galaxy and are only a few hundred to a few thousand light-years away.

SN 2004dj is ejecting heavy chemical elements, generated by nuclear reactions inside the star, into the cosmos. Like other Type II supernovae, this exploding star is providing the raw material for future generations of stars and planets. Elements on Earth such as oxygen, calcium, iron, and gold came long ago from exploding stars such as this one.

In addition to the visible-light image shown here, ultraviolet images and spectra are being obtained with the Advanced Camera for Surveys. Astronomers are also using ground-based telescopes to study the supernova.

They will continue to study SN 2004dj over the next few years, as it slowly fades from view, in order to gain a better understanding of how certain types of stars explode and what kinds of chemical elements they eject into space.

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