Astronomers have discovered that a nearby dwarf galaxy
is spewing oxygen and other “heavy” elements into
intergalactic space. This observation from NASA’s Chandra X-
ray Observatory supports the idea that dwarf galaxies might
be responsible for most of the heavy elements between the
galaxies.
Despite comprising only a very small fraction of the mass of
the universe, so-called heavy elements — everything other
than hydrogen and helium — are essential for the formation
of planets and can greatly influence astronomical phenomena,
including the rate at which galaxies form.
A team led by Crystal Martin of the University of California,
Santa Barbara, observed the dwarf galaxy NGC 1569 using
Chandra. As reported in an article to be published in The
Astrophysical Journal, the group found that huge quantities
of oxygen and other heavy elements are escaping from the
galaxy in bubbles of multimillion-degree gases thousands of
light-years in diameter.
“Dwarf galaxies are much smaller than ordinary galaxies like
our Milky Way and much more common,” said Martin. “Because of
their small mass, they have relatively low gravity and matter
can escape more easily from dwarfs than from normal galaxies.
This makes them very important in understanding how the
universe was seeded with various elements.”
Scientists have speculated that heavy elements escaping from
dwarf galaxies in the early universe could play a dominant
role in enriching the intergalactic gas from which other
galaxies form. Enriched gas cools more quickly, so the rate
and manner of formation of new galaxies in the early universe
would have been strongly affected by this process.
“With Chandra it was possible to test these ideas,” said
Henry Kobulnicky of the University of Wisconsin, Madison, a
member of the research team. “We could trace the distribution
of oxygen and other elements in the galaxy and determine how
much of this matter is escaping from the galaxy.”
NGC 1569 is a good case study because it is only about seven
million light-years from Earth, and for the last 10 million
to 20 million years has been undergoing a burst of star
formation and supernova explosions, perhaps triggered by a
collision with a massive gas cloud. The supernovae eject
oxygen and other heavy elements at high velocity into the gas
in the galaxy, heating it to millions of degrees. Hot gas
boils off the gaseous disk of the galaxy and expands outward
at speeds of hundreds of thousands of miles per hour.
The team found large hot bubbles extending above and below a
disk of gas along the equator of the galaxy. The measured
concentration of oxygen, neon, magnesium and silicon showed
that the elements from thousands of supernovas are
evaporating out of the galaxy, carrying much of the
surrounding gas with them. The astronomers estimate the
bubbles are carrying away an amount of oxygen equivalent to
that found in about three million Suns.
In addition to Martin and Kobulnicky, Timothy Heckman of The
John Hopkins University in Baltimore, was part of the team
that observed NGC 1569 for 27.4 hours using the Advanced CCD
Imaging Spectrometer (ACIS) on April 11, 2001. ACIS was built
for NASA by Penn State, University Park, and the
Massachusetts Institute of Technology, Cambridge. NASA’s
Marshall Space Flight Center, Huntsville, Ala., manages the
Chandra program for the Office of Space Science, Washington.
TRW, Inc., Redondo Beach, Calif., is the prime contractor for
the spacecraft. The Smithsonian’s Chandra X-ray Center
controls science and flight operations from Cambridge, Mass.
Images and additional information about this result are
available at:
and
