The First Star: Things Heated Up Quickly, Scientists Say

There arecurrently more stars in the cosmos than any one person could ever count. Ourgalaxy alone contains about 400 billion. But it wasn't always this way.

For manymillions of years after our universe first formed no stars existed, and thenthere was one. That primordialstar was likely a massive blazing behemoth that burned brighter and fasterthan any star around today.

A newcomputer model now suggests that it also formed much earlier than previouslythought.

Otherstudies have estimated that the first star sparked into existence some 155million years after our universe exploded into life in the Big Bang13.7 billion years ago.

The newsimulation indicates that this event occurred much earlier, when the universewas only 30 million years old. It also suggests that it took about another 370million years for the first galaxy as massive as our own MilkyWay to form.

The modelis detailed in an upcoming issue of the Monthly Notices for the RoyalAstronomical Society.

Whenexactly?

Usingdetailed computer simulations, astronomers reconstructed the conditions underwhich the first star was born and even the precise sequence of steps thatoccurred soon after to allow other stars, and eventually galaxies, to form.

Astronomerssuspect, for example, that the first starformed in a dense cloud of dark matter and gas. They also think that manypresent-day galaxies are the products of mergersbetween much smaller galaxies during the early days of our universe.

Estimating whenthe first star formed, however, has been difficult. That's because even themost powerful supercomputers can only simulate small portions of the universeat a time.

"Toestimate when the first stars formed, we must remember that the first 100,000solar mass clumps collapsed in regions that happened to have particularly highdensities early on," said study leader Rennan Barkana, an astrophysicistat the University of Tel Aviv in Israel.

"Therewere initially only a few such regions in the entire universe, so a simulationthat is limited to a small volume is unlikely to find such [regions] until muchlater," he said.

The modelcreated by Barkana and his colleagues gets around this problem by approximatinghow many darkmatter clumps large enough to host the first star were present at differenttimes of the universe.

"Weintegrated this over time to find the total expected number of observablestars," Barkana said. The researchers then crosschecked their predictionswith simulations.

Primalstars

Even bystellar standards, the primordial star was a monster. It likely had a mass ofabout 100 times that of our Sun and it would have spewed out vast amounts ofenergetic radiation, especially in the ultraviolet range. Had human eyes beenaround to see it, it would have appeared blue-violet in color.

The firststar shone brighter than most stars in existence today and it zipped throughits stellar life in only 2 million to 3 million years, compared to theseveral-billion-year lifetimes that some of today's stars have. Our Sun ismiddle-aged now and has been around for 4.6 billion years.

Scientiststhink that when it spent its fuel, the first star exploded in a titanic stellarcataclysm called a supernova,flinging heavy elements forged during the star's lifetime into space, settingthe stage for the next generation of stars.

"Aftera short time, stars began appearing in greater abundance throughout theuniverse," Barkana told SPACE.com.

The secondgeneration stars likely formed within about a million years after the first,Barkana said. Within five million years, there were about 100 stars; within tenmillion years, 10,000 celestial orbs of fire were lighting up the heavens.

Unlike thatfirst star, which was made up mostly of hydrogen and helium, the stars thatcame after contained heavier elements, such as carbon and iron.

Stilldetectable

Light onceemitted by the first star might still be detectable, Barkana said.

In space,the older an object is, the farther away it is. It would require a telescopeabout 100 million times more sensitive than the Hubble Space Telescope toobserve light from the first star, but it's not impossible.

"If thefirst star was indeed massive and produced in its death a huge supernovaexplosion or gamma ray burst, then we might have a chance to see the explosionwith the instruments planned for the coming decade," Barkana said.

Relatedstories

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  • Our Tangled Universe: How the First Galaxies Were Born
  • Studies Pins Down Quantity, Size of Dark Matter in Universe
  • Hubble Lifts Fog on Early Universe

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