Beaches. And Deserts and Sandboxes.

Perhaps you’ve heard this before: There are more stars in the universe than all the grains of sand in all the beaches, desserts and sandboxes on Earth.

There are a lot of sand grains on Earth. Sand constitutes a major fraction of the makeup of Earth. Scientists estimate the number by measuring the average size of a sand grains, then calculating how many sand grains it would take to fill, say, a gallon jug. Using the latest geological studies, they calculate the total volume of sand on Earth. Scientists estimate that Earth contains 7.5 sextillion sand grains. That is 75 followed by 17 zeros. That’s a lot of sand.

Astronomers calculate the total number of stars in the universe by studying nearby galaxies, ones in which we can count the stars, to see how many it takes to make a galaxy shine. Then, based on detailed counts of galaxies we can see, and making conservative estimates of how many we can’t see, they estimate the total number of stars in the universe. Our universe contains at least 70 septillion stars, 7 followed by 23 zeros.

Astronomers estimate there exist roughly 10,000 stars for each grain of sand on Earth. That’s a lot of stars.

Credit NASA-ESA

Astronomers recently discovered the origin of sand grains. For years, they believed that only sun-like stars created lots of carbon and silicon dust, and the silicon dust is the source of sand. That meant that the universe had to evolve to the point where there were lots of sun-like stars before lots of sand could accumulate. Recently, astronomers discovered the galaxies that formed very early in the universe, before many sun-like stars could form, contained a lot of dust. Long before stars like our sun were common, planets like Earth may have formed.

There may be a huge number of planets in our universe capable of supporting life.

On the first Tuesday of each month, I write an astronomy-related column piece for the Oklahoman newspaper. On the following day, I post that same column to my blog page.

This is reprinted by permission form the Oklahoman and www.newsok.com.

First Generation Stars

When the universe began 13.7 billion years ago, the only hydrogen and helium plus a tiny smattering of lithium existed. All other elements, like carbon, nitrogen, oxygen, gold, platinum, all the stuff we and our planet are made of, was created in the nuclear furnaces that power stars.

A star forms when gravity causes a cloud of gas to collapse until the central region is dense enough to support that nuclear fusion which converts hydrogen and helium into other elements. To do that, the cloud must shed heat or the thermal pressure halts the collapse. Hydrogen and helium can’t lose heat very efficiently, so the very first stars had to be huge, with a gravitational pull strong to overpower the thermal pressure. Those first stars were 200 to 400 times the size of our sun.

Huge stars live very short lives, and after only a few million years at best, these stars explode in supernova explosions more powerful than anything this side of the Big Bang. The heavier elements created then blast into space to help form the second generation of stars. Heavier elements shed thermal heat at a higher efficiency, so second generation can be small, even smaller than our sun.

Astronomers have looked for stars as close as possible to that first generation of giant stars. They judge closeness to first generation by the amount of elements heavier than helium, “metals” to astronomers.

A team of astronomers from Johns Hopkins University recently announced the discovery of a star with the lowest known amount of heavy elements of any known star. The star is 13.5 billion years old, and may well be a second generation star. Lead author, Dr. Kevin Schlaufman, commented “The discovery of this star means more stars with very low mass and very low metal content are likely out there – perhaps even the universe’s very first stars.”

The next big step would be discovering a star containing nothing but hydrogen and helium, a first generation star.

On the first Tuesday of each month, I write an astronomy-related column piece for the Oklahoman newspaper. On the following day, I post that same column to my blog page.

This is reprinted by permission form the Oklahoman and www.newsok.com.