First for astronomers: Observed birth of supernova

William Atkins
Thursday, 22 May 2008 20:22

Science - Space

On January 9th, Soderberg and Berger were looking at the afterglow of Supernova 2007uy within the spiral galaxy NGC 2770—they had missed its beginning. This supernova was approximately 90 million light-years away in the constellation Lynx.

Much to their surprise, they observed a bright x-ray explosion in another portion of NGC 2770. They stated that it burst into brightness but faded within several minutes.

The two astronomers contacted astronomers from all around the world, who were using one of eight different ground-based or space-based telescopes, to observe this very important event.

It was designated Supernova 2008D, being the fourth (D) supernova to be discovered in the year (2008).

Supernova 2008D was classified as a Type Ibc supernova. A “Type Ibc” supernova is one where “the dense iron core of a hydrogen-depleted, massive but compact blue-giant star (a Wolf-Rayet star) collapses in on itself to form a tiny neutron star or black hole.” [Sky and Telescope: “Supernove Caught at its Very Start”]

In addition, a Type Ibc is “the rarest and most luminous of the explosions caused by the collapse of the cores of massive stars.” [The New York Times: “Scientists See Supernova in Action”]

The explosion was found to be off centered, with gas moving faster from one side of the explosion than on the other side.

The Wolf-Rayet (WR) star that died and produced Supernova 2008D was probably over twenty times as massive as the Sun. It was a very hot star with a surface temperature of between 25,000 and 50,000 Kelvin (44,540 and 89,540 degrees Fahrenheit, or 27,430 and 49,730 degrees Celsius), which contained strong, violent solar winds that expelled large amounts of mass from the star.

In their paper, forty two astronomers taking part in the discovery, stated, “Massive stars end their short lives in spectacular explosions, supernovae, that synthesize new elements and drive galaxy evolution. Throughout history supernovae were discovered chiefly through their delayed optical light, preventing observations in the first moments (hours to days) following the explosion.”

They continue, “As a result, the progenitors of some supernovae and the events leading up to their violent demise remain intensely debated. Here we report the serendipitous discovery of a supernova at the time of explosion, marked by an extremely luminous X-ray outburst. We attribute the outburst to the break-out of the supernova shock-wave from the progenitor, and show that the inferred rate of such events agrees with that of all core-collapse supernovae.”

And, in conclusion, “We forecast that future wide-field X-ray surveys will catch hundreds of supernovae each year in the act of explosion, and thereby enable crucial neutrino and gravitational wave detections that may ultimately unravel the explosion mechanism.”

Supernova 2004D was the first supernova to be observed with x-ray emissions at the beginning of its violent birth (from the death of a star). Soderberg stated, "The next generation of [wide-field] X-ray satellites will find hundreds of supernovae every year exactly when they explode." [Sky and Telescope]

NatureNews tells about the experiences with Supernova 2008D in the article “Stellar blast watched in real time.”