Finding the Ashes of the First Stars

Recent observations with the Hubble Space Telescope
suggest that the first stars formed as little as 200 million years
after the Big Bang. This is much earlier than previously thought.
Astronomers have observed large amounts of iron in the ultraluminous
light from very distant, ancient quasars. This iron is the “ashes”
left from supernova explosions in the very first generation of stars.

We do not know exactly how and when galaxies, stars, and eventually
planets formed in the early Universe. Astronomers look back in time
to these early years by observing objects so remote that their light
needs thousands of millions of years to travel to Earth. These
objects provide clues about conditions in the early Universe.

Stars are nuclear factories that process lighter elements such as
hydrogen and helium to successively heavier elements such as
nitrogen, carbon, and finally iron. New observations with the
NASA/ESA Hubble Space Telescope show massive amounts of iron in very
distant and ancient quasars. This pushes the era of the very first
stars in the Universe back to as early as 200 million years after the
Big Bang (corresponding to a redshift of around 20). This is much
earlier than previously thought and is in agreement with recent
results from the Wilkinson Microwave Anisotropy Probe.

In October 2002, a team led by Wolfram Freudling used Hubble’s
infrared instrument, NICMOS (Near Infrared Camera and Multi-Object
Spectrograph), to observe three of the most distant quasars known
(redshifts 5.78-6.28). The light from these three quasars had
travelled for 12.8 thousand million years before reaching Hubble’s
spectrograph. It had left the quasars 900 million years after the Big
Bang. The spectra show clear signs of the large amounts of iron. This
is the first time that elements created in the first generation of
stars are found.

Wolfram Freudling comments “Iron is a good indicator of the
evolutionary state of a quasar. This element is not created during
the Big Bang but in stars later on. These stars have to form, burn
their fuel and explode before iron can be detected. This process
takes times, up to 500 or 800 million years. This is the reason why
we believe that the iron we detected with Hubble was created in the
very first generation of stars which formed soon after the Big
Bang.”

Hubble’s position above the atmosphere allows it to detect the
infrared region of the spectrum that includes iron’s signature at
about 1.6-1.7 microns. This range is normally absorbed by the
Earth’s atmosphere and unavailable to Earth-bound telescopes.

The detection of iron so early in the Universe’s history has profound
implications. “The presence of iron, and, by implication, all other
lighter elements, shows that basic ingredients for planets and life
were present, at least in some places, very early in the history of
the Universe. This is much earlier than the formation of the Earth
itself 4.6 thousand million years ago,” says team member Michael
Corbin.

These results also suggest that the first stars formed before the
super-massive black holes that power the quasar engines in the
centres of galaxies. Other observations have shown that the first
quasar engines started slightly before 900 million years after Big
Bang. The first stars would therefore appear to precede them by
several hundred million years. The creation of the black holes
themselves still remains a mystery, although the birth date of the
first stars may prove to be a very valuable clue.

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Notes for editors

This is the first major scientific result to emerge from the NICMOS
instrument that was revived during the Hubble Servicing Mission 3B in
2002. Servicing Mission 3B was the last successful mission of the
Space Shuttle Columbia that was lost on 1 February. The authors would
like to respectfully dedicate this paper and the discoveries therein
to the memory of the crew of the Space Shuttle Columbia.

The team is composed of W. Freudling (ST-ECF/ESO, Germany), M. R.
Corbin (CSC/STScI, United States), and K. T. Korista (Western
Michigan University, United States).

The team announced their discovery in the 20 April 2003 issue of
Astrophysical Journal Letters.

For broadcasters, animations of the discovery, interviews and general
Hubble Space Telescope background footage are available from the ESA
Television Service, see http://television.esa.int, and from
telescope.org/video/releases.html”>http://www.spacetelescope.org/video/releases.html

Image credit: European Space Agency and Wolfram Freudling (Space
Telescope-European Coordinating Facility/European Southern
Observatory, Germany)

For more information, please contact:

Wolfram Freudling

Space Telescope-European Coordinating Facility/European Southern

Observatory, Germany

Tel: +49-89-3200-6425 (089 within Germany)

Cellular: +49-179-541-8920

E-mail: wfreudli@eso.org

Lars Lindberg Christensen

Hubble European Space Agency Information Centre, Garching, Germany

Tel: +49-89-3200-6306 (089 within Germany)

Cellular (24 hr): +49-173-3872-621 (0173 within Germany)

E-mail: lars@eso.org