Suzaku Spies Treasure Trove of Intergalactic Metal
Watch video on Suzaku’s search for chemical elements. Click the “YouTube” link on the player to see a larger version of this video. Credit: NASA/GSFC
Every cook knows the ingredients for making bread: flour, water, yeast, and time. But what chemical elements are in the recipe of our universe?
Most of the ingredients are hydrogen and helium. These cosmic lightweights fill the first two spots on the famous periodic table of the elements.
Less abundant but more familiar to us are the heavier elements, meaning everything listed on the periodic table after hydrogen and helium. These building blocks, such as iron and other metals, can be found in many of the objects in our daily lives, from teddy bears to teapots.
Recently astronomers used the Suzaku orbiting X-ray observatory, operated jointly by NASA and the Japanese space agency, to discover the largest known reservoir of rare metals in the universe.
Suzaku Snaps First Complete X-ray View of a Galaxy Cluster
This Suzaku image shows X-ray emission from hot gas throughout the galaxy cluster PKS 0745-191. Brighter colors indicate greater X-ray emission. The circle is 11.2 million light-years across and marks the region where cold gas is now entering the cluster. Inset: A Hubble optical image of the cluster’s central galaxies is shown at the correct scale. Credit: NASA/ISAS/Suzaku/M. George, et al.The massive radio galaxy PKS 0745-191, for which the cluster is named, appears at the center of this Hubble Space Telescope image. The picture forms the inset in the Suzaku image above. Credit: NASA/STScI/Fabian, et al.
The joint Japan-U.S. Suzaku mission is providing new insight into how assemblages of thousands of galaxies pull themselves together. For the first time, Suzaku has detected X-ray-emitting gas at a cluster’s outskirts, where a billion-year plunge to the center begins.
“These Suzaku observations are exciting because we can finally see how these structures, the largest bound objects in the universe, grow even more massive,” said Matt George, the study’s lead author at the University of California, Berkeley.
The team trained Suzaku’s X-ray telescopes on the cluster PKS 0745-191, which lies 1.3 billion light-years away in the southern constellation Puppis. Between May 11 and 14, 2007, Suzaku acquired five images of the million-degree gas that permeates the cluster.
By looking at a cluster in X-rays, astronomers can measure the temperature and density of the gas, which provides clues about the gas pressure and total mass of the cluster. Astronomers expect that the gas in the inner part of a galaxy cluster has settled into a “relaxed” state in equilibrium with the cluster’s gravity. This means that the hottest, densest gas lies near the cluster’s center, and temperatures and densities steadily decline at greater distances.
In the cluster’s outer regions, though, the gas is no longer in an orderly state because matter is still falling inward. “Clusters are the most massive, relaxed objects in the universe, and they are continuing to form now,” said team member Andy Fabian at the Cambridge Institute of Astronomy in the UK. The distance where order turns to chaos is referred to as the cluster’s “virial radius.”
New observations from Suzaku, a joint Japanese Aerospace Exploration Agency (JAXA) and NASA X-ray observatory, have challenged scientists' conventional understanding of white dwarfs. Observers had believed white dwarfs were inert stellar corpses that slowly cool and fade away, but the new data tell a completely different story.
At least one white dwarf, known as AE Aquarii, emits pulses of high-energy (hard) X-rays as it whirls around on its axis. “We're seeing behavior like the pulsar in the Crab Nebula, but we're seeing it in a white dwarf,” says Koji Mukai of NASA Goddard Space Flight Center in Greenbelt, Md. The Crab Nebula is the shattered remnant of a massive star that ended its life in a supernova explosion. “This is the first time such pulsar-like behavior has ever been observed in a white dwarf.” Mukai is co-author of a paper presented at a Suzaku science conference in San Diego, Calif., in December.
The white dwarf in the AE Aquarii system is the first star of its type known to give off pulsar-like pulsations that are powered by its rotation and particle acceleration. Credit: Casey Reed
White dwarfs and pulsars represent distinct classes of compact objects that are born in the wake of stellar death. A white dwarf forms when a star similar in mass to our sun runs out of nuclear fuel. As the outer layers puff off into space, the core gravitationally contracts into a sphere about the size of Earth, but with roughly the mass of our sun. The white dwarf starts off scorching hot from the star's residual heat. But with nothing to sustain nuclear reactions, it slowly cools over billions of years, eventually fading to near invisibility as a black dwarf.
A pulsar is a type of neutron star, a collapsed core of an extremely massive star that exploded in a supernova. Whereas white dwarfs have incredibly high densities by earthly standards, neutron stars are even denser, cramming roughly 1.3 solar masses into a city-sized sphere. Pulsars give off radio and X-ray pulsations in lighthouse-like beams.
