Making the first stars

Nov 18, 2013
Making the first stars
A simulation of the formation of the first stars. A new computer code can track to very small scales the process of star formation in the early Universe, when stars were made from hydrogen gas. The image shows the distribution of gas density (red is high density) over a region only 200 astronomical units in size. (The legend refers to the simulation number.) Credit: Greif et al. 2013

(Phys.org) —The first stars in the Universe are believed to have formed only a few hundred million years after the big bang, about 13.7 billion years ago. They heated and ionized the pristine intergalactic medium, and their supernova explosions enriched the primordial gas with the first heavy elements (the Universe was born with only hydrogen and a dash of helium). These stars thus altered in a fundamental way the chemical and thermal state of the gas from which the first galaxies then formed, in turn triggering the first self-sustaining cycle of star formation, feedback, and chemical enrichment. Understanding the formation and properties of the first stars is thus an important step towards a comprehensive picture of structure formation in the early Universe.

The first stars have yet to be directly observed. They are faint, although future space missions and giant telescopes hope to spot them. Meanwhile, theorists thinking about them have for several decades relied on basic physical concepts and computational simulations. In the current model, hydrogen and dark matter, coupled by gravity, form large structures at the centers of which gas forms. Molecular hydrogen can then radiate and cool the structures, allowing them to collapse further and heat up until stars are born. The final stages of the process occur rapidly and inside tiny volumes compared to the whole structure; both of these issues make it very difficult for the computations to track what's going on. As a result, there are major uncertainties, for example: how fragmentation at the final scale affects the birth weight of the stars produced.

CfA astronomer Thomas Greif and two colleagues have developed a new computational algorithm that can follow the process down to the very small scales. With it, they are able to track the development of filamentary substructures and secondary clumps as wide as only a few tens of astronomical units (one astronomical unit is the average distance of the Earth from the Sun), and to follow whether they form their own stars or recombine; they can also estimate when such fragmentation tends to occur. The new results suggest that not all structures do fragment in the initial stages of collapse. They can stabilize for an interim period but then collapse later, implying that the previously estimated time scale for making some first could be longer than previously expected.

Explore further: Old young stars

More information: "On the Operation of the Chemothermal Instability in Primordial Star-Forming Clouds," Thomas H. Greif, Volker Springel, and Volker Bromm, MNRAS 434, 3408, 2013. arxiv.org/abs/1305.0823

Related Stories

Old young stars

Nov 11, 2013

(Phys.org) —The early stages of a star's life are critical both for the star and for any future planets that might develop around it. The process of star formation, once thought to involve just the simple ...

Astronomers gain new knowledge about early galaxies

Jul 03, 2013

The early galaxies of the universe were very different from today's galaxies. Using new detailed studies carried out with the ESO Very Large Telescope and the Hubble Space Telescope, researchers, including ...

Making stars in early galaxies

Dec 10, 2012

(Phys.org)—Ten billion years ago or so, at least according to the current picture, the youthful universe began to produce an abundance of new stars. The very first ones appeared in the young cosmos after ...

A burst of stars 13 billion years ago

Jun 03, 2013

(Phys.org) —The universe immediately following the big bang contained mostly hydrogen and some helium. All the other elements needed to make galaxies, planets, and life were formed in stellar interiors ...

Recommended for you

Mystery of rare five-hour space explosion explained

8 hours ago

Next week in St. Petersburg, Russia, scientists on an international team that includes Penn State University astronomers will present a paper that provides a simple explanation for mysterious ultra-long gamma-ray ...

Glowing galaxies in telescopic timelapse

8 hours ago

We often speak of the discoveries and data flowing from astronomical observatories, which makes it easy to forget the cool factor. Think of it—huge telescopes are probing the universe under crystal-clear ...

Violent origins of disc galaxies probed by ALMA

15 hours ago

For decades scientists have believed that galaxy mergers usually result in the formation of elliptical galaxies. Now, for the the first time, researchers using the Atacama Large Millimeter/sub-millimeter ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Tuxford
1 / 5 (3) Nov 18, 2013
'...implying that the previously estimated time scale for making some first stars could be longer than previously expected.'

Oh my....Ending on the cliffhanger....
Fleetfoot
5 / 5 (1) Nov 19, 2013
"The first stars in the Universe are believed to have formed only a few hundred million years after the big bang .."


The expected range has been earlier than that, around 30 million years taking DM proper motion effects into account.