With computers, astronomers show predicted present day distribution of elusive first stars

Dec 12, 2006
Distribution of the oldest stars
Distribution of the oldest stars in our galaxy (upper panel) compared with the full population of primordial stars (lower panel). While the oldest stars are all located near the center, where they are very difficult to detect, later forming stars made of gas without heavy elements should be located throughout the galaxy. The fact that no such stars have ever been detected places important scientific constraints on the properties and formation of these stars. Background image from DIRBE data, (c) Edward L. Wright

With the help of enormous computer simulations, astronomers have now shown that the first generation of stars –– which have never been observed by scientists –– should be distributed evenly throughout our galaxy, deepening the long-standing mystery about these missing stellar ancestors. The results are published in this week's issue of the Astrophysical Journal.

The problem is that despite years of looking, no one has ever found any of these stars. "Many astronomers thought this was because the stars without heavy elements were hidden from us," said Evan Scannapieco, first author and a postdoctoral fellow at the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara. "Because our galaxy formed from the inside out, the idea was that these very old stars would all be near the center. But the center of Milky Way is extremely crowded with dust and newer stars, making it very hard to detect individual old stars in this environment."

This earliest generation of stars should look very different from later-forming stars like the Sun; yet so far, no one has detected a survivor from this primordial population. One of the long-standing explanations for this discrepancy was that these stars might all be contained in regions near the center of the Milky Way, where they are very hard to observe. The results of the new study make that explanation unlikely.

Oxygen, carbon, and most of the elements we encounter every day on Earth were
made in stars, rather than during the Big Bang. "But these heavy elements are made in the centers of stars and remain buried under the gas at the surface until the stars die and explode, so what you see when you look at a star are the elements that were present when it was born," said Brad K. Gibson, co-author and chair of the Department of Theoretical Astrophysics at the University of Central Lancashire in Britain. "This means that the stars still living from this first generation should continue to show no heavy elements."

Carrying out a detailed simulation of the formation of the Milky Way, the research group constructed not only the history of where stars formed over time, but the chemical composition of the gas out of which these stars formed. "We found that while the very oldest stars all end up near the center of the Milky Way, it takes a long time for heavy elements to enrich the gas that is further out," said co-author Daisuke Kawata, a scientist with the Carnegie Observatories in Pasadena, California. "This means that while the oldest stars all end up near the center of the galaxy, plenty of stars that contain only primordial elements are formed at later times throughout the galaxy. These primordial stars should be everywhere."

Because the stars forming in the Milky Way suburbs are easily detectable with present day telescopes, there must be some other reason that the remnants of this primordial generation didn't survive. "It could be that they were all high-mass stars, which would not have lived long enough to still be around, or there could be another twist to the story that we haven't yet figured out," said co-investigator Chris Brook, a scientist with the University of Washington. "Whatever the answer, it's clear that studies of the outskirts of our galaxy will have lots more to tell us about this remarkable, missing generation."

Source: University of California - Santa Barbara

Explore further: Is the universe finite or infinite?

add to favorites email to friend print save as pdf

Related Stories

Far from home: Wayward cluster is both tiny and distant

Mar 03, 2015

Like the lost little puppy that wanders too far from home, astronomers have found an unusually small and distant group of stars that seems oddly out of place. The cluster, made of only a handful of stars, ...

What is Mars made of?

Feb 26, 2015

For thousands of years, human beings have stared up at the sky and wondered about the Red Planet. Easily seen from Earth with the naked eye, ancient astronomers have charted its course across the heavens ...

Getting a grip on exotic atomic nuclei

Feb 18, 2015

A new model describing atomic nuclei, proposed by a physicist from the University of Warsaw Faculty of Physics, more accurately predicts the properties of various exotic isotopes that are created in supernova explosions or ...

Exploded star blooms like a cosmic flower

Feb 12, 2015

Because the debris fields of exploded stars, known as supernova remnants, are very hot, energetic, and glow brightly in X-ray light, NASA's Chandra X-ray Observatory has proven to be a valuable tool in studying ...

Recommended for you

Is the universe finite or infinite?

6 hours ago

Two possiblities exist: either the Universe is finite and has a size, or it's infinite and goes on forever. Both possibilities have mind-bending implications.

'Teapot' nova begins to wane

8 hours ago

A star, or nova, has appeared in the constellation of Sagittarius and, even though it is now waning, it is still bright enough to be visible in the sky over Perth through binoculars or a telescope.

Dark matter is darker than once thought

10 hours ago

This panel of images represents a study of 72 colliding galaxy clusters conducted by a team of astronomers using NASA's Chandra X-ray Observatory and Hubble Space Telescope. The research sets new limits on ...

Galaxy clusters collide—dark matter still a mystery

Mar 26, 2015

When galaxy clusters collide, their dark matters pass through each other, with very little interaction. Deepening the mystery, a study by scientists at EPFL and the University of Edinburgh challenges the ...

Using 19th century technology to time travel to the stars

Mar 26, 2015

In the late 19th century, astronomers developed the technique of capturing telescopic images of stars and galaxies on glass photographic plates. This allowed them to study the night sky in detail. Over 500,000 ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.