Press Release

Massive Old Star Reveals Secrets on Deathbed

By SpaceRef Editor
January 26, 2004
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Massive Old Star Reveals Secrets on Deathbed
m74_int_after.jpg

Like a doctor trying to understand an elderly patient’s sudden
demise, astronomers have obtained the first-ever detailed
observations of an old but otherwise normal massive star just before
and after its life ended in a spectacular supernova explosion.

The star was imaged by the Gemini Observatory and Hubble Space
Telescope (HST) less than a year prior to the gigantic explosion, and
is located in the nearby galaxy M-74 in the constellation of
Pisces. These observations allowed a team of European astronomers
led by Dr. Stephen Smartt of the University of Cambridge, England
to verify theoretical models showing how a star like this can meet
such a violent fate.

The results were published in the January 23, 2004 issue of the
journal Science. This work provides the first confirmation of the
long-held theory that some of the most massive (yet normal) old
stars in the Universe end their lives in violent supernova explosions.

“It might be argued that a certain amount of luck or serendipity was
involved in this finding,” said Dr. Smartt. “However, we’ve been
searching for this sort of normal progenitor star on its deathbed for
some time. I like to think that finding the superb Gemini and HST
data for this star is a vindication of our prediction that one day we
had to find one of these stars in the immense data archives that now
exist.” For more details on Dr. Smartt’s ongoing supernova
program to:
http://hubble.esa.int/science-e/www/object/index.cfm?fobjectid=3D33858

During the last few years, Smartt’s research team has been using the
most powerful telescopes, both in space and on the ground, to image
hundreds of galaxies in the hope that one of the millions of stars in
these galaxies will some day explode as a supernova (see URL in
previous paragraph). In this case, the renowned Australian amateur
supernova hunter, Reverend Robert Evans, made the initial discovery
of the explosion (identified as SN203gd) while scanning galaxies
with a 12-inch (31cm) backyard telescope from his home in New
South Wales, Australia in June, 2003.

Following Evans’ discovery, Dr. Smartt’s team quickly followed up
with detailed observations using the Hubble Space Telescope. These
observations verified the exact position of the original or
“progenitor” star. Using this positional data, Smartt and his team
dug through data archives and discovered that observations by the
Gemini Observatory and HST contained the combination of data
necessary to reveal the nature of the progenitor.

The Gemini data was obtained during the commissioning of the
Gemini Multi-Object Spectrograph (GMOS) on Mauna Kea, Hawai=A1=AEi
in 2001. These data were also used to produce a stunning high-
resolution image of the galaxy that clearly shows the red progenitor
star. The full resolution Gemini image can be found at:
http://www.gemini.edu/media/images_2004-2.html

Armed with the earlier Gemini and HST observations Smartt’s team
was able to demonstrate that the progenitor star was what
astronomers classify as a normal red supergiant. Prior to exploding,
this star appeared to have a mass about 10 times greater, and a
diameter about 500 times greater than that of our Sun. If our sun
were the size of the progenitor it would engulf the entire inner solar
system out to about the planet Mars.

Red supergiant stars are quite common in the universe and an
excellent example can be easily spotted during January from almost
anywhere on the Earth by looking at Betelgeuse, the bright red
shoulder star in the constellation of Orion (see finder chart on web
release indicated above.) Like SN2003gd, it is believed that
Betelgeuse could meet the same explosive fate at any time from next
week to thousands of years from now.

After SN2003gd exploded, the team observed its gradually fading
light for several months using the Isaac Newton Group of telescopes
on La Palma. These observations demonstrated that this was a
normal type II supernova, which means that the ejected material from
the explosion is rich in hydrogen. Computer models developed by
astronomers have long predicted that red supergiants with extended,
thick atmospheres of hydrogen would produce these type II
supernovae but until now have not had the observational evidence to
back up their theories. However, the fantastic resolution and depth
of the Gemini and Hubble images allowed the Smartt team to
estimate the temperature, luminosity, radius and mass of this
progenitor star and reveal that it was a normal large, old star. “The
bottom-line is that these observations provide a strong confirmation
that the theories for both stellar evolution and the origins of these
cosmic explosions are correct,” said co-author Seppo Mattila of
Stockholm Observatory.

This is only the third time astronomers have actually seen the
progenitor of a confirmed supernova explosion. The others were
peculiar type II supernovae: SN 1987A, which had a blue supergiant
progenitor, and SN 1993J, which emerged from a massive interacting
binary star system. See more details at:
http://hubble.esa.int/science-e/www/object/index.cfm?fobjectid=3D34455

Dr. Smartt concludes, “Supernova explosions produce and
distribute the chemical elements that make up everything in the
visible Universe — especially life. It is critical that we know what
type of stars produce these building blocks if we are to understand
our origins.”

Archived Gemini and HST data was critical to the success of this
project. “This discovery is a perfect example of archival data=A8Vs
immense value to new scientific projects,” said Dr. Colin Aspin who
is the Gemini Scientist responsible for the development of the
Gemini Science Archive (GSA). He continued, “this discovery
demonstrates the spectacular results that can be realized by using
archival data and stresses the importance of developing the GSA for
future generations of astronomers.”

The Gemini Multi-Object Spectrograph used to make the Gemini
observations is one of two twin instruments built as a joint partnership
between Gemini, the Dominion Astrophysical Observatory, Canada, the UK
Astronomy Technology Centre and Durham University, UK.
Separately, the U.S. National Optical Astronomy Observatory
provided the detector subsystem and related software. GMOS is
primarily designed for spectroscopic studies where several hundred
simultaneous spectra are required, such as when observing star and
galaxy clusters. GMOS also has the ability to focus astronomical
images on its array of over 28 million pixels.

The Gemini Observatory is an international collaboration that has
built two identical 8-meter telescopes. The Frederick C. Gillett
Gemini Telescope is located on Mauna Kea, Hawai=A1=AEi (Gemini
North) and the Gemini South telescope is located on Cerro Pach=A8=AEn
in central Chile (Gemini South), and hence provide full coverage of
both hemispheres of the sky. Both telescopes incorporate new
technologies that allow large, relatively thin mirrors under active
control to collect and focus both optical and infrared radiation from
space.

The Gemini Observatory provides the astronomical
communities in each partner country with state-of-the-art
astronomical facilities that allocate observing time in
proportion to each country’s contribution. In addition to
financial support, each country also contributes significant
scientific and technical resources. The national research
agencies that form the Gemini partnership include: the US
National Science Foundation (NSF), the UK Particle
Physics and Astronomy Research Council (PPARC), the
Canadian National Research Council (NRC), the Chilean
Comisiin Nacional de Investigacon Cientifica y
Tecnol=A8=AEgica (CONICYT), the Australian Research Council
(ARC), the Argentinean Consejo Nacional de
Investigaciones Cientoficas y T=A8=A6cnicas (CONICET) and the
Brazilian Conselho Nacional de Desenvolvimento
Cientofico e Tecnologico (CNPq). The Observatory is
managed by the Association of Universities for Research in
Astronomy, Inc. (AURA) under a cooperative agreement
with the NSF. The NSF also serves as the executive agency
for the international partnership.

The Space Telescope Science Institute (STScI) is operated by the
Association of Universities for Research in Astronomy, Inc.
(AURA), for NASA, under contract with the Goddard Space Flight
Center, Greenbelt, MD. The Hubble Space Telescope is a project of
international cooperation between NASA and the European Space
Agency (ESA).

The Isaac Newton Group of Telescopes (ING) is an establishment
of the Particle Physics and Astronomy Research Council (PPARC)
of the United Kingdom, the Nederlandse Organisatie voor
Wetenschappelijk Onderzoek (NWO) of the Netherlands and the
Instituto de Astrofisica de Canarias (IAC) in Spain. The ING
operates the 4.2 metre William Herschel Telescope, the 2.5 metre
Isaac Newton Telescope, and the 1.0 metre Jacobus Kapteyn
Telescope. The telescopes are located in the Spanish Roque de Los
Muchachos Observatory on La Palma which is operated by the
Instituto de Astrofisica de Canarias (IAC).

Background and Notes for Editors:

Supernovae are among the most energetic phenomena observed in
the entire Universe. When a star of more than about eight times the
mass of our Sun reaches the end of its nuclear fuel reserve, its core is
no longer stable from collapsing under its own immense weight. As
the core of the star collapses, the outer layers are ejected in a fast-
moving shock wave. This huge energy release results in a supernova
that is about one billion times brighter than our Sun, and is
comparable to the brightness of an entire galaxy. After destroying
itself, the core of the star becomes either a neutron star or a black
hole.

The team is composed of Stephen J. Smartt, Justyn R. Maund,
Margaret A. Hendry, Christopher A. Tout, and Gerald F. Gilmore
(University of Cambridge, UK), Seppo Mattila (Stockholm
Observatory, Sweden), and Chris R. Benn (Isaac Newton Group of
Telescopes, Spain).

SpaceRef staff editor.