Supernova Lights Up The Galactic Scene
August 31, 2012

Stellar Explosion Helps Astronomers Understand Far-Off Galaxy

April Flowers for - Your Universe Online

A recent study, led by Edo Berger of Harvard University, made the most of a dying star's fury to probe a distant galaxy some 9.5 billion light years away. The most distant stellar explosion of its kind ever studied, that dying star lit up the galactic scene.

“It´s like someone turned on a flashlight in a dark room and suddenly allowed us to see, for a short time, what this far-off galaxy looks like, what it is composed of," said Berger.

Published in The Astrophysical Journal, the study describes how this international team of researchers used the exploding star's light (called an ultra-luminous core-collapse supernova) as a probe to study the gas conditions in the space between the host galaxy's stars.

The findings reveal that the distant galaxy's interstellar conditions appear "reassuringly normal" when compared to those seen in the galaxies of our local universe.

“This shows the enormous potential of using the most luminous supernovae to study the early universe,” Berger says. “Ultimately it will help us understand how galaxies like our Milky Way came to be.”

The discovery of the dying star in this distant galaxy was made using images from the Pan-STARRS1 survey telescope on Haleakala in Maui, Hawaii. Pan-STARRS, or the Panoramic Survey Telescope & Rapid Response System, is an innovative design for a wide-field imaging facility at the University of Hawaii's Institute for Astronomy situated on Mount Haleakala. Pan-STARRS major goal is to discover and characterize Earth-approaching objects that might pose a danger to our planet.

“These are the types of exciting and unexpected applications that appear when a new capability comes on line,” said John Tonry, one of the study's co-authors and supernovae researcher at the University of Hawai℠i at Manoa's Institute for Astronomy. Tonry adds, “Pan-STARRS is pioneering a new era in deep, wide-field, time-critical astronomy — and this is just the beginning.”

After the Pan-STARRS discovery, spectroscopic follow-up studies using the Multiple Mirror Telescope in Arizona and the 8-meter Gemini North Telescope on Mauna Kea, Hawaii provided the data used by the team to probe the gas of the distant galaxy´s interstellar environment.

The signatures of a distant ultra-luminous supernova were revealed by the spectra. Equally important, the unique fingerprints of iron and magnesium were detected within the distant galaxy that hosted the explosion. This galaxy contains a very young selections of stars (15 to 45 million years old) with a mass totaling some 2 billion Suns.

The ultra-luminous supernova explosion is a recently-identified and special breed of exploding star. It is 10 — 100 times more luminous than an ordinary less-energetic supernova and usually blue in color. While the process leading to the demise of such a star is still being explored, evidence points to the central core-collapse of a star having as much as 100 times the mass of our Sun. An enormous explosion that blasts prodigious amounts of heavier elements through the star's huge outer layers before expanding into space is triggered by the collapse.

Astronomers have used two methods to study distant galaxies, traditionally. The first involves looking directly for chemical elements leaving bright imprints on the galaxy's spectrum of light, while the second is to search indirectly for dark signatures in the spectrum of an even more distant quasar. This second method reveals chemical elements in an intervening system that have absorbed light along our line of sight.

Recently, a new method has come into vogue; seeking dark absorption imprints in the afterglows of "gamma-ray bursts" (GRBs). These brief flashes are the brightest and most energetic explosions in the Universe, but they fade away within hours. The need for expensive Earth-orbiting satellites to first detect and pinpoint a burst's location with precision before astronomers can make ground-based studies is another limit of this method.

“The beauty of studying distant galaxies using ultra-luminous supernovae as a tool is that it eliminates the need for satellites and offers more time for study,” says Alicia Soderberg of Harvard University. “A typical ultra-luminous supernova can take several weeks to fade away.”

The study by Berger and his team provides the first direct demonstration that ultra-luminous supernovae can serve as probes of distant galaxies. Their results suggest that with the future combination of large survey and spectroscopic telescopes, ultra-luminous supernovae could be used to probe galaxies 90 percent of the way back to the Big Bang.