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More star births than astronomers have calculated
October 02, 2008Bonn study in Nature' explains the discrepancy
The "birth rate" for stars is certainly not easy to determine. Distances in the universe are far too great for astronomers to be able to count all the newly formed celestial bodies with the aid of a telescope. So it is fortunate that the emerging stars give themselves away by a characteristic signal known as "H-alpha" emissions. The larger the number of stars being formed in a particular region of the firmament, the more H-alpha rays are emitted from that region.
However, new observations make this theory untenable. On the edges of "disc galaxies" (like the Milky Way) the H-alpha radiation ceases abruptly. For a long time astronomers concluded from this finding that no stars are being born in this region. "The explanation offered is simply that too little gaseous matter exists for it to collapse into balls and form stars," says Jan Pflamm-Altenburg. "These theories largely inform our understanding of how galaxies developed from the Big Bang to the present."
Satellite mission baffles astronomers
A satellite mission has recently revealed that stars are in fact being formed beyond the H-alpha perimeter. These stars are, without exception, so light that no H-alpha radiation is emitted. Consequently, the numerical ratio of 230 light stars to one heavy star does not apply to the edges of galaxies. "This observation presented the astronomy community with quite a conundrum," says Professor Dr. Pavel Kroupa of the Argelander Institute.
Kroupa and Pflamm-Altenburg have come up with a solution which, they say, is basically very simple. They note that star births are not evenly distributed across galaxies but are focused on the star clusters - well known examples being the Seven Sisters and the Orion Nebula. And only large, high-mass clusters produce heavy stars, i.e. the newborn stars that can create the H-alpha emission. "But these heavy star clusters primarily occur in the core regions of disc galaxies," says Jan Pflamm-Altenburg. "Towards the edges they become increasingly rare. The outer regions tend to contain smaller clusters in which the formation of lighter stars is more frequent."
The conclusion is that a numerical ratio of 230 to 1 is only valid for the centres of galaxies. On the edges of galaxies each "H-alpha baby" might be accompanied by a thousand or more light stars. Those astronomers who always use the same factor when calculating total star formations from their H-alpha readings therefore underestimate the number of newborn stars.
The theoretical work of the two Bonn-based astrophysicists supports affirms that the mass of new stars depends linearly on the mass of the gas in their vicinity. Their conclusions open up completely new perspectives for research into the development of galaxies.
University of Bonn
Galaxy Clusters Current Events and Galaxy Clusters News RSSShedding light on the cosmic skeleton
"Matter is not distributed uniformly in the Universe," says Masayuki Tanaka from ESO, who led the new study. "In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called 'cosmic web', in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure."
Galaxy cluster smashes distance record
The most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes.
Turbulence responsible for black holes' balancing act
We live in a hierarchical Universe where small structures join into larger ones. Earth is a planet in our Solar System, the Solar System resides in the Milky Way Galaxy, and galaxies combine into groups and clusters.
Largest ever survey of very distant galaxy clusters completed
An international team of researchers led by a UC Riverside astronomer has completed the largest ever survey designed to find very distant clusters of galaxies.
Suzaku Snaps First Complete X-ray View of a Galaxy Cluster
The joint Japan-U.S. Suzaku mission is providing new insight into how assemblages of thousands of galaxies pull themselves together.
The NASA/ESA Hubble Space Telescope provides new evidence for dark matter around small galaxies
The NASA/ESA Hubble Space Telescope has uncovered a strong new line of evidence that galaxies are embedded in halos of dark matter.
Ghostly glow reveals galaxy clusters in collision
A team of scientists, including astronomers from the Naval Research Laboratory (NRL), have detected long wavelength radio emission from a colliding, massive galaxy cluster which, surprisingly, is not detected at the shorter wavelengths typically seen in these objects.
Scientists Detect Cosmic 'Dark Flow' Across Billions of Light Years
Using data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), scientists have identified an unexpected motion in distant galaxy clusters. The cause, they suggest, is the gravitational attraction of matter that lies beyond the observable universe.
Yale Astronomer Discovers Upper Mass Limit for Black Holes
here appears to be an upper limit to how big the universe's most massive black holes can get, according to new research led by a Yale University astrophysicist.
Clash of clusters provides new dark matter clue
A powerful collision between galaxy clusters has been captured by the NASA/ESA Hubble Space Telescope and NASA's Chandra X-ray Observatory. This clash of clusters provides striking evidence for dark matter and insight into its properties.
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