This visible light view shows the central part of
the Virgo Cluster. The brightest object is the giant elliptical galaxy
M87 (left of center). The image spans approximately 1.2 degrees, or
about 2.4 times the apparent diameter of a full moon. Credits: NOAO/AURA/NSF. Download the image in HD at NASA's Scientific Visualization Studio
Suzaku mapped iron, magnesium, silicon and sulfur
in four directions all across the Virgo galaxy cluster for the first
time. The northern arm of the survey (top) extends 5 million light-years
from M87 (center), the massive galaxy at the cluster's heart. Ratios of
these elements are constant throughout the cluster, which means they
were mixed well early in cosmic history. The dashed circle shows what
astronomers call the virial radius, the boundary where gas clouds are
just entering the cluster. Some prominent members of the cluster are
labeled as well. The background image is part of the all-sky X-ray
survey acquired by the German ROSAT satellite. The blue box at center
indicates the area shown in the visible light image. Credits: A. Simionescu (JAXA) and Hans Boehringer (MPE). Download the graphic in HD at NASA's Scientific Visualization Studio
A new survey of hot, X-ray-emitting gas in the Virgo galaxy cluster
shows that the elements needed to make stars, planets and people were
evenly distributed across millions of light-years early in cosmic
history, more than 10 billion years ago.
The Virgo cluster, located about 54 million light-years away, is the
nearest galaxy cluster and the second brightest in X-rays. The cluster
is home to more than 2,000 galaxies, and the space between them is
filled with a diffuse gas so hot it glows in X-rays.
Using Japan's Suzaku X-ray satellite, a team led by Aurora
Simionescu, an astrophysicist at the Japan Aerospace Exploration Agency
(JAXA) in Sagamihara, acquired observations of the cluster along four
arms extending up to 5 million light-years from its center.
"Heavier chemical elements from carbon on up are produced and
distributed into interstellar space by stars that explode as supernovae
at the ends of their lifetimes," Simionescu said. This chemical
dispersal continues at progressively larger scales through other
mechanisms, such as galactic outflows, interactions and mergers with
neighboring galaxies, and stripping caused by a galaxy's motion through
the hot gas filling galaxy clusters.
Supernovae fall into two broad classes. Stars born with more than
about eight times the sun's mass collapse under their own weight and
explode as core-collapse supernovae. White dwarf stars may become
unstable due to interactions with a nearby star and explode as so-called
Type Ia supernovae.
These different classes of supernovae produce different chemical
compositions. Core-collapse supernovae mostly scatter elements ranging
from oxygen to silicon, while white dwarf explosions release
predominantly heavier elements, such as iron and nickel. Surveying the
distribution of these elements over a vast volume of space, such as a
galaxy cluster, helps astronomers reconstruct how, when, and where they
were produced. Once the chemical elements made by supernovae are
scattered and mixed into interstellar space, they become incorporated
into later generations of stars.
The overall composition of a large volume of space depends on the mix
of supernova types contributing to it. For example, accounting for the
overall chemical makeup of the sun and solar system requires a mix of
roughly one Type Ia supernova for every five core-collapse explosions.
"One way to think about this is that we're looking for the supernova
recipe that produced the chemical makeup we see on much larger scales,
and comparing it with the recipe for our own sun," said co-author
Norbert Werner, a researcher at the Kavli Institute for Particle
Astrophysics and Cosmology (KIPAC) at Stanford University in California.
In an earlier study
led by Werner, Suzaku data showed that iron was distributed uniformly
throughout the Perseus Galaxy Cluster, but information about lighter
elements mainly produced by core-collapse supernovae was unavailable.
The Virgo Cluster observations supply the missing ingredients. Reporting their findings
in the Oct. 1 issue of The Astrophysical Journal, Simionescu and her
colleagues show they detect iron, magnesium, silicon and sulfur all the
way across a galaxy cluster for the first time. The elemental ratios are
constant throughout the entire volume of the cluster and roughly
consistent with the composition of the sun and most of the stars in our
own galaxy.
Because galaxy clusters cover enormous volumes of space, astronomers
can use one example to extrapolate the average chemical content of the
universe. The study shows that the chemical elements in the cosmos are
well mixed, showing little variation on the largest scales. The same
ratio of supernova types -- the same recipe -- thought to be responsible
for the solar system's makeup was at work throughout the universe. This
likely happened when the universe was between 2 and 4 billion years
old, a period when stars were being formed at the fastest rate in cosmic
history.
"This means that elements so important to life on Earth are
available, on average, in similar relative proportions throughout the
bulk of the universe," explained Simionescu. "In other words, the
chemical requirements for life are common throughout the cosmos."
Launched on July 10, 2005, Suzaku was developed at the Institute of
Space and Astronautical Science (ISAS) in Japan, which is part of JAXA,
in collaboration with NASA and other Japanese and U.S. institutions.
NASA's Goddard Space Flight Center in Greenbelt, Maryland, supplied
Suzaku's X-ray telescopes and data-processing software, and operated a
facility supporting U.S. astronomers who used the satellite.
Suzaku operated for 10 years -- five times its target lifespan -- to
become the longest-functioning Japanese X-ray observatory. On Aug. 26,
JAXA announced the end of the mission due to the deteriorating health of the spacecraft.
"Suzaku provided us with a decade of revolutionary measurements,"
said Robert Petre, chief of Goddard's X-ray Astrophysics Laboratory.
"We're building on that legacy right now with its successor, ASTRO-H, Japan's sixth X-ray astronomy satellite, and we're working toward its launch in 2016."
